Accidental Hypothermia: An Evidence-Based Approach

Transcription

Three physicians, 3 cities, 3 patients, 1 theme – and many questions:
Oakland, California: Change of shift on a busy, rainy Friday in
January. A John Doe appearing to be in his 50’s is brought in by EMS after
being “found down” with obvious ethanol alcohol (ETOH) on board. He is
intubated, pulseless, cold to touch, and CPR is in progress. While the ET
tube placement is confirmed, the nurse places a Foley catheter and reports
that his temperature is 25°C (77°F). When CPR is paused, the monitor
shows ventricular fibrillation. A forced air warming device is requested
STAT while the physician begins to think about the next steps. The hospital
does not have cardiopulmonary bypass and the physician wonders, “Should
ACLS guidelines be followed? Should the patient be transferred to a higher
level facility? Is there a role for hemodialysis? Does this patient even have a
chance of surviving?”
Jackson Hole, Wyoming: EMS calls in that they have a hypothermic,
30-year-old female who had probably gotten lost while backcountry skiing,
though fortunately made it to a roadside before collapsing. It was unclear
how long she had been down before she was found by a passing motorist.
The medics report she is breathing and has a pulse but is unconscious; they
have an estimated time of arrival (ETA) of 15 minutes. The paramedics
request permission to intubate the patient. As the physician considers the
wisdom of securing the airway in this patient, he quickly begins to think
through the resources available to resuscitate such a critical patient . . . and
what to do if this patient goes into cardiac arrest . . .
Jacksonville, Florida: An 80-year-old man is brought in from a skilled
nursing facility with altered mental status. The core temperature measured
via the Foley catheter is 32°C (89.6°F). Unsure of the patient’s baseline or
Editor-in-Chief
Andy Jagoda, MD, FACEP
Professor and Vice-Chair of
Academic Affairs, Department
of Emergency Medicine, Mount
Sinai School of Medicine; Medical
Director, Mount Sinai Hospital, New
York, NY
Editorial Board
William J. Brady, MD
Professor of Emergency Medicine
and Medicine Vice Chair of
Emergency Medicine, University
of Virginia School of Medicine,
Charlottesville, VA
Peter DeBlieux, MD Professor of Clinical Medicine,
LSU Health Science Center;
Director of Emergency Medicine
Services, University Hospital, New
Orleans, LA
Wyatt W. Decker, MD
Chair and Associate Professor of
Emergency Medicine, Mayo Clinic
College of Medicine, Rochester, MN
Francis M. Fesmire, MD, FACEP
Director, Heart-Stroke Center,
Erlanger Medical Center; Assistant
Professor, UT College of Medicine,
Chattanooga, TN
Michael A. Gibbs, MD, FACEP
Chief, Department of Emergency
Medicine, Maine Medical Center,
Portland, ME
Steven A. Godwin, MD, FACEP
Assistant Professor and Emergency
Medicine Residency Director,
University of Florida HSC,
Jacksonville, FL
Gregory L. Henry, MD, FACEP
CEO, Medical Practice Risk
Assessment, Inc.; Clinical Professor
of Emergency Medicine, University
of Michigan, Ann Arbor, MI
John M. Howell, MD, FACEP
Clinical Professor of Emergency
Medicine, George Washington
University, Washington, DC;Director
of Academic Affairs, Best Practices,
Inc, Inova Fairfax Hospital, Falls
Church, VA
Charles V. Pollack, Jr., MA, MD,
FACEP
Chairman, Department of
Emergency Medicine, Pennsylvania
Hospital, University of Pennsylvania
Health System, Philadelphia, PA
Michael S. Radeos, MD, MPH
Research Director, Department of
Emergency Medicine, New York
Hospital Queens, Flushing, NY;
Assistant Professor of Emergency
Medicine, Weill Medical College of
Cornell University, New York, NY.
Robert L. Rogers, MD, FACEP,
FAAEM, FACP
Medicine and Medicine Director of
Undergraduate Medical Education,
Department of Emergency
Medicine, The University of
Maryland School of Medicine,
Baltimore, MD
January 2009
Volume 11, Number 1
Authors
Allison R. Mulcahy, MD
Alameda County Medical Center/Highland Hospital, Oakland, CA
Melanie R. Watts, MD
Alameda County Medical Center/Highland Hospital, Oakland, CA
Special Guest Editor
Scott Weingart, MD
Assistant Professor of Emergency Medicine, Elmhurst Hospital
Center, Mount Sinai School of Medicine, New York, NY
Peer Reviewers
Andy Jagoda, MD, FACEP
Professor and Vice-Chair of Academic Affairs, Department of
Emergency Medicine, Mount Sinai School of Medicine; Medical
Director, Mount Sinai Hospital, New York, NY
CME Objectives
Upon completion of this article, you should be able to:
1. Demonstrate the ways in which cold exposure impacts human
physiology.
2. Identify ways in which hypothermic patients must be treated
differently than normothermic patients with similar findings on
initial presentation, with special regard to the medical code
situation.
3. Be able to rapidly identify and work up underlying
abnormalities contributing to or complicating the case in the
hypothermic patient.
4. Create a systematic strategy for treating and rewarming the
hypothermic patient based on core temperature and degree of
physical abnormalities.
Prior to reading this activity, see “Physician CME Information” on
the back page.
Emergency Medicine, Mayo Clinic,
Jacksonville, FL
Corey M. Slovis, MD, FACP, FACEP
Professor and Chair, Department
of Emergency Medicine, Vanderbilt
University Medical Center,
Nashville, TN
Jenny Walker, MD, MPH, MSW
Assistant Professor; Division Chief,
Family Medicine, Department
of Community and Preventive
Medicine, Mount Sinai Medical
Center, New York, NY
Ron M. Walls, MD
Professor and Chair, Department
of Emergency Medicine, Brigham
and Women’s Hospital,Harvard
Medical School, Boston, MA
Scott Weingart, MD
Medicine, Elmhurst Hospital
Center, Mount Sinai School of
Medicine, New York, NY
Alfred Sacchetti, MD, FACEP
Assistant Clinical Professor,
Keith A. Marill, MD
Department of Emergency Medicine, Research Editors
Assistant Professor, Department of
Thomas Jefferson University,
Nicholas Genes, MD, PhD
Emergency Medicine, Massachusetts Philadelphia, PA
Chief Resident, Mount Sinai
General Hospital, Harvard Medical
Emergency Medicine Residency,
Scott Silvers, MD, FACEP
School, Boston, MA
New York, NY
Medical Director, Department of
Lisa Jacobson, MD
Mount Sinai School of Medicine,
Emergency Medicine Residency,
New York, NY
International Editors
Valerio Gai, MD
Senior Editor, Professor and Chair,
Department of Emergency Medicine,
University of Turin, Turin, Italy
Peter Cameron, MD
Chair, Emergency Medicine,
Monash University; Alfred Hospital,
Melbourne, Australia
Amin Antoine Kazzi, MD, FAAEM
Associate Professor and Vice
Chair, Department of Emergency
Medicine, University of California,
Irvine; American University, Beirut,
Lebanon
Hugo Peralta, MD
Chair of Emergency Services,
Hospital Italiano, Buenos Aires,
Argentina
Maarten Simons, MD, PhD
Emergency Medicine Residency
Director, OLVG Hospital,
Amsterdam, The Netherlands
Accreditation: This activity has been planned and implemented in accordance with the Essentials and Standards of the Accreditation Council for Continuing Medical Education
(ACCME) through the sponsorship of EB Medicine. EB Medicine is accredited by the ACCME to provide continuing medical education for physicians. Faculty Disclosure: Dr.
Mulcahy, Dr. Watts, Dr. Weingart, Dr. Jagoda, and their related parties report no significant financial interest or other relationship with the manufacturer(s) of any commercial
product(s) discussed in this educational presentation. Commercial Support: Emergency Medicine Practice does not accept any commercial support.
etiology of the hypothermia, the physician places a forced
air rewarming device on the patient, administers warm
humidified oxygen, and reflects, “Should I give the patient
broad spectrum antibiotics or wait to see if his mental
status improves? Should I give him steroids? How aggressively should I warm him? “
for the treatment of accidental hypothermia.6 Without strong outcomes, research, or evidence to show
clear survival benefit, it is not possible to provide a
high-level recommendation for the best approach to
rewarm the hypothermic patient.
Searches of numerous evidence-based medicine
data banks were performed, including the National
Guideline Clearinghouse, Cochrane Database of
Systematic Reviews, Evidence Based Medicine Reviews: Best Evidence (ACP), Database of Abstracts
of Reviews of Effectiveness (DARE), and Evidence
Based Medicine Reviews Multifile (EBMZ). Only
the National Guideline Clearinghouse provided any
results for accidental hypothermia.
There were only 2 published protocols identified
for the treatment of hypothermia: The State of Alaska
Cold Injuries and Cold Water Near Drowning Guidelines
(last revised 1/2005) and the American Heart Association Guidelines from 2005.7, 8 The AHA also has
specific hypothermia guidelines within the larger
context of its BLS and ACLS protocols.9 A search
on guidelines.gov also yielded guidelines on hypothermia treatment in the first aid and advanced life
support sections from the 2005 International Consensus Conference on cardiopulmonary resuscitation and
emergency cardiovascular care science with treatment
recommendations and the 2005 European Resuscitation Council’s recommendations on cardiopulmonary arrest in special circumstances.10, 11 All of these
guidelines are derived from a few prospective studies
that look at the various warming techniques for treating moderate to severe hypothermia, numerous case
series and case reports, and studies on intra-operative
hypothermia and experimental hypothermia.12-25
Within the past 10 years, several authors have
attempted to develop management recommendations based on a systematic review of the literature;
however, the diversity in study and reporting design
has undermined their success.18, 24, 26-32 Although the
evidence is weak, the volume of information on this
topic does make it possible to construct a rational
treatment plan specific to the patient and the resources available to the treating physician.
F
rom Florida to Alaska, hypothermia is prevalent in every emergency department (ED)
regardless of location or time of year. In the
United States, there are more than 650 deaths per
year from primary hypothermia with 66% of the
deaths occurring in men. Beyond that, there are an
unknown number of deaths where hypothermia is
a secondary or contributing cause.1
Hypothermia occurs in a wide variety of environmental settings and is complicated by multiple patient co-morbidities. It does not have to be a subzero
night in Wyoming to encounter severely hypothermic
patients. The homeless, intoxicated patient in Miami
is also at risk for accidental hypothermia. The states
with the highest hypothermia-related death rates
are those with milder climates that experience rapid
temperature changes (eg, North Carolina and South
Carolina) and western states that have high elevations
and considerable changes in nighttime temperatures.2
The best strategy to manage the hypothermic
patient must be individually tailored and varies
depending on the resources available. However,
there are basic principles that apply to all hypothermic patients. Some hypothermic patients can
make seemingly miraculous recoveries and must
be treated very differently than their normothermic
counterparts. The adage that “a person is not dead
until he is warm and dead” is corroborated by the
fact that the lowest initial temperature recorded in
a child who survived from hypothermia was 14.2°C
(57.6°F),3 and the lowest recorded temperature in an
adult was 13.7°C (56.7°F).4
This issue of Emergency Medicine Practice reviews the evidence and current understanding of
the pathophysiology, clinical assessment, and treatment options for maximizing outcomes in accidental hypothermia.
Etiology And Pathophysiology
Critical Appraisal Of The Literature
Hypothermia is defined as a core temperature less
than 35º C (95ºF)6 and it is classified by severity. (See
Table 1.)6
These distinctions have marked clinical relevance. In mild hypothermia, all of the body’s
normal adaptations to counter heat loss continue
to function. The mild hypothermic state is akin
to a sympathetic adrenergic surge with increased
oxygen consumption, increased minute ventilation,
tachycardia, significant vasoconstriction, as well as
tremulousness and shivering.
The human body has a circadian temperature
Accidental hypothermia may be one of the oldest human afflictions; it is tied to the most basic of human
needs for warmth and shelter. Medical literature is replete with miraculous survival stories, and there is an
abundance of case reports and retrospective reviews
of plausible hypothermia treatment and rewarming
techniques. Unfortunately, there is a striking absence
of large scale prospective or randomized clinical
investigations within this body of literature. Even the
experts in the field admit that it has not been possible
to derive a strong evidence-based practice guideline
Emergency Medicine Practice © 2008
2
EBMedicine.net • January 2009
variation of only 1ºC (33.8ºF). The body’s regulatory
mechanisms are much more adept at cooling than
warming, making humans especially susceptible to
hypothermia.29, 33 Cooling of the human body, as it
occurs in accidental hypothermia, causes a spectrum
of physiologic effects on each organ system based
on the magnitude of temperature change. As hypothermia progresses past the mild stage into moderate
and severe, the adaptations to counter heat loss begin
to disappear, including the cessation of shivering.
Systemic metabolic demands diminish, functionally
shutting down and decreasing oxygen consumption.
The physiologic effects of hypothermia are most easily understood if broken down by organ system and
severity, as summarized in Table 2.
are at increased risk of aspiration and pulmonary
infections. Finally, as with many other severe systemic insults, severely hypothermic patients have
an increased incidence of acute respiratory distress
syndrome (ARDS).31, 39, 40
Cardiovascular System
Renal System
Neurologic System
The overarching theme of initial stimulation followed by subsequent profound decreased metabolism also holds true for brain function in hypothermia. Early in hypothermia, neurons are stimulated
by the first 1º drop in core temperature. However,
below 35ºC (95ºF), the cerebral metabolism and thus
oxygen requirement decreases by about 10% for
every 1º drop.31
Exposure to a cold environment and the subsequent
initial attempt to maintain temperature homeostasis
causes a sympathetic surge and increased level of
circulating catecholamine. This leads to tachycardia
and vasoconstriction, initially resulting in an increased cardiac output. As hypothermia progresses,
there is a decrease in cardiac pacemaker depolarization with resultant bradycardia and decreased cardiac output; bradycardia occurs in a linear relationship to decreasing core temperature.36, 37
There are numerous cardiac arrhythmias, including
atrial and ventricular fibrillation, that occur in the setting
of hypothermia. The His-Purkinje fibers, as well as the
myocardium, are sensitized and increasingly irritable
in the cold patient, most significantly below 30ºC (86ºF).
This irritability, as well as the electrolyte derangements
that occur with hypothermia, likely contributes to the
etiology of these common cardiac arrhythmias.31, 38
Even those of us who have never experienced significant hypothermia have likely experienced the
Table 2. Physiologic Effects Of Hypothermia
By Organ System And Severity
Mild
32° C to 35°
C (89.6° F to
95° F)
Moderate
28° C to 32°C
(82.4° F to 89.6°
F)
Severe
<28°C (82.4
° F)
Cardiovascular
d HR
d CO
f HR, f BP, f CO
Vfib g
32
asystole
Hypotension
Respiratory
d RR g
d VO2; f RR g
f VO2
Neurologic
Ataxia g
Apathy g
amnesia,
dysarthria
Pupils dilate, f
Areflexia, f
pupillary reflex,
EEG activity;
paradoxical unf Corneal,
dressing, stupor,
OC reflex,
f LOC
f CBF; no
movement/
pain re34
sponse
Renal
Cold diuresis
Cold diuresis, f
GFR, metabolic
acidosis
Oliguria
Metabolic
f Insulin
f Shivering
No shivering
Respiratory System
Much like the initial response in the cardiovascular system, the respiratory system is stimulated
by exposure to the cold, prompting an increase in
respiratory drive. However, with further cooling
and subsequent impaired metabolism, the respiratory rate slows significantly. If the hypothermia is
profound enough to impair brainstem functioning,
the patient may become apneic.31, 39
Other noted effects of cold exposure and subsequent hypothermia on the respiratory system
include increased secretions and decreased ciliary
motility which can lead to impaired ability to clear
secretions. In the context of decreased mental status
and impaired cough reflex, hypothermic patients
Table 1. Classification Of Hypothermia
Mild
32°C to 35°C (90°F to 95°F)
Moderate
28°C to 32°C (82°F to 90°F)
Severe
less than 28°C (82°F)
January 2009 • EBMedicine.net
Respiratory
alkalosis
release/uptake g
hyperglyce35
mia
Prolonged
cardiac conduction intervals,
Osborn wave,
Afib
Respiratory
Acidosis, d
brochorrhea, f
cough reflex,
f ciliary fxn
Pulmonary
33, 34
Edema
31
Afib: Atrial Fibrillation; BP: Blood Pressure; CO: Cardiac Output; CBF:
Cerebral Blood Flow; GFR: Glomerular Filtration Rate; HR: Heart
Rate; OC: Oculocephalic; RR: Respiratory Rate; Vfib: Ventricular
Fibrillation; VO2: Oxygen Consumption
3
phenomenon of cold diuresis after spending a few
minutes outside in cold weather. The mechanism of
this phenomenon is unclear, but the most commonly
purported theory is that initial peripheral vasoconstriction occurring in cold temperatures leads to a
central functional hypervolemia. This in turn stimulates a compensatory diuresis.29-31 Derangements
in ADH and impaired sodium pump dysfunction
may also play a role.36, 41 A concomitant effect of the
sodium-potassium pump derangement is impaired
potassium secretion; this may result in hyperkalemia,
which is often reported in patients with severe hypothermia.36
The hypothermic patient is at risk for significant
mixed acid-base problems. In a retrospective review
of 135 patients, 25% were alkalotic and 30% were
acidotic.42 Early in hypothermia, a patient may have
a respiratory alkalosis from increased respiratory
drive. As hypothermia progresses this often gives
way to a mixed respiratory and metabolic acidosis
from both the decreased respiratory drive as well as
a lactic acidosis from shivering and impaired oxygenation.31, 36, 43
ments leading to decreased heat production – as in
the case of hypoglycemia or hypothyroidism; or c)
increased heat losses from intrinsic dermal dysfunction – such as in burns and erythrodermas.36
Accidental Hypothermia
Accidental hypothermia is primarily an extrinsic
problem in patients with no intrinsic thermoregulatory, metabolic, or dermal dysfunction.46 Common
mechanisms involved in increased heat loss leading
to accidental hypothermia include:
l Convection – direct transfer of heat from skin to
ambient air.
l Conduction – direct transfer of heat by direct
contact with cooler object.
l Radiation – heat loss to surrounding objects via
infrared electromagnetic energy.
l Evaporation – vaporization of water from sweat
and other insensible losses.47
Of these mechanisms, the most significant
is radiation, accounting for up to 60% of normal
heat loss. However, this amount is dependent on
the amount of body surface area exposed to the
cold environment and the temperature differential
between the patient and the ambient environment.
Conduction typically accounts for as little as 2% of
heat losses, although this can increase to 50% when
submersion is involved.26
There are several noted risk factors, both behavioral and physiologic, that can predispose a patient
to hypothermia.
l Ethanol - The most common contributory factor to hypothermia seen in urban emergency
departments, ethanol interacts with thermoregulatory mechanisms by causing increased periph-
Core Temperature Afterdrop
A physiologic phenomenon frequently noted in both
hypothermia and water immersion literature is that of
core temperature afterdrop. This term refers to a continued decrease in the hypothermic patient’s core temperature even after they have been removed from the
cold environment and rewarming has been initiated.31
The specific mechanisms contributing to afterdrop as
well as the extent to which various rewarming strategies can either potentiate or minimize afterdrop are
highly debated topics. For more information, see the
“Controversies/Cutting Edge” section.
Differential Diagnosis
Table 3. Differential Diagnosis For
Hypothermia
The differential diagnosis for patients with hypothermia can be divided into 3 broad categories based
on etiology: increased heat loss, decreased heat
production, and impaired thermoregulation. (See
Table 3.)
From a functional standpoint, hypothermia can
be subdivided by etiology into 3 broad categories:
controlled hypothermia, endogenous hypothermia,
and accidental hypothermia.44
Controlled Hypothermia
Controlled hypothermia is the active cooling of
patients; it has been shown to improve neurologic
outcomes after cardiac arrest patients.17, 45
Endogenous Hypothermia
Endogenous hypothermia is an intrinsic dysfunction
in either: a) thermoregulation – such as in CNS trauma
or neurodegenerative disorders; b) metabolic derangeEmergency Medicine Practice © 2008
Increased Heat Loss Decreased Heat
Production
Impaired Thermoregulation
Cold exposure
Iatrogenic (eg, cold
fluid infusions,
exposure)
Induced vasodilation
Pharmacologic/toxins
Dermatologic (eg,
erythrodermas,
dermatitis, burns)
Peripheral failure
Neuropathies/spinal
injury
Diabetes
Central or neurologic
failure
CNS trauma
CVA
Age Extremes
Hypoglycemia
Malnutrition
Marasmus
Kwashiork or extreme
exertion
Endocrinologic failure
l Hypopituitaryism
l Hypoadrenalism
l Hypothyroidism
DKA/AKA
Fatigue/exhaustion/
trauma
Adapted with permission from Giesbrecht, GG, Wilkerson, JA. Hypothermia Frostbite and other Cold Injuries. P. 38 Copyright ©2006 The
Mountaineers
4
eral vasodilation which leads to convective heat
loss.42 Chronic alcohol consumption impairs the
shivering and thermogenesis through hypothalamic degeneration.48 In addition, hepatic clearance of ethanol and other hepatically metabolized drugs is reduced in hypothermia as hepatic
conjugation and detoxification is depressed.
Alcohol toxicity can result in hypothermia by a
combination of the above plus loss of consciousness and consequent failure to seek shelter.49, 50
l Malnutrition - Malnutrition increases heat loss
due to diminished insulation in the form of
subcutaneous adipose tissue and alters thermoregulation.31
l Age - There is a decline in ability to thermoregulate that occurs with age. The elderly population
often has altered thermal perception and autonomic dysfunction that can lead to decreased
peripheral blood flow. All of these intrinsic
factors are coupled with the fact that the aging
population is more prone to concomitant illness
and immobility.51, 52
Standard thermometers do not typically measure below 34°C (93.2°F), thus the EMS provider
cannot know the exact temperature in a hypothermic
patient unless they are equipped with thermometers designed to measure lower temperatures. The
International Commission for Mountain Emergency
Medicine recommends tympanic or esophageal field
measurements to maximize accuracy.12
Watts et al performed a prospective study on
prehospital rewarming of 174 trauma patients to assess techniques for maintaining euthermia. The study
had 5 arms comparing no intervention, hot packs,
reflective blankets, warmed intravenous fluids, and
warmed IV fluids plus reflective blankets. Patients
who received hot pack rewarming showed a mean
increase in body temperature during transport, while
all other groups showed a mean decrease in temperature during transport. 53 Winter storms and rural
locations can contribute to long transport times, making the interventions to prevent further heat loss and
initiating rewarming all the more crucial.
Hypothermia has been shown to be neuroprotective in post-cardiac arrest patients.54, 55 As a result,
guidelines recommend that most patients be transported for further evaluation and resuscitation in
the hospital as opposed to being declared deceased
in the field.54, 56 Recall that the lowest temperature
recorded in a child who survived from hypothermia
was 14.2°C (57.6°F)3, and in an adult was 13.7°C
(56.7°F).4 Resuscitation should be continued until
the patient is at least 32°C (89.6°F) unless the patient is completely frozen or the mouth and nose are
blocked with ice, thus making chest compressions
and artificial respirations impossible.57
Prehospital Care
Although it is intuitive that a hypothermic patient
should be rewarmed, there is little data to guide
prehospital care of hypothermic patients. The goal
of prehospital care is to rescue the patient, provide
modified BLS or ACLS, provide insulation with
whatever means available to prevent further heat
loss, and rapidly transport the patient to the nearest
hospital. The 2005 International Consensus Conference recommends that, “The first aid provider
should provide passive warming (using blankets) as
feasible for victims of hypothermia.” Victims should
be transported to a facility where active rewarming
can be initiated. If the victim is in a remote location
far from medical help, the first aid rescuer may initiate active rewarming.” 10 The State of Alaska Cold
Injuries Guidelines (most recent edition 2005) is the
only guideline available for care of hypothermic
patients in the field. It states that BLS/ACLS procedures should not be initiated in the field if:7
l core temperature is less than 15°C (59° F)
l chest is frozen/non-compliant
l victim has been submersed in water more than 1
hour
l obvious lethal injury is present
l these procedures significantly delay evacuation
to controlled rewarming
l these procedures put rescuers at risk BLS Treatment
BLS treatment of the hypothermic patient focuses
on airway, breathing and circulation just as in their
normothermic counterparts. Some modifications are
necessary as pulse and respirations are slow and can
be difficult to detect. Alongside the ABCs, the initial
focus in a very cold patient is to prevent additional
heat loss by removing wet clothing and insulating
the patient from further exposure.
Providers should assess for breathing and pulses
for 30 to 45 seconds to confirm arrest before beginning rescue breathing or CPR.8 If the patient is not
breathing, warm humidified oxygen (from 42°C- 46°C
or 107.6°F-114.8°F) administered during bag-mask
ventilation is recommended if available. Before beginning CPR, providers should assess whether the patient has an organized electrical rhythm (not fibrillation) by placing the patient on a monitor or attaching
defibrillation pads. The provider should assume that
any organized rhythm is sufficient to provide circulation in the setting of severely reduced metabolism.
There is controversy surrounding CPR and other
BLS interventions in the severely hypothermic patient.
While these guidelines are helpful and come
from a highly experienced group, they have obvious
limitations: often times it is impossible to measure
core temperatures in the field and the time of submersion is unknown.
5
Some case reports indicate that CPR may convert the
rhythm into fibrillation under these circumstances.32
Physiologically it is clear that severe hypothermia
results in cardiac irritability. It is generally believed that
severely hypothermic patients are prone to ventricular
fibrillation with movement and therefore should be
transported carefully.22 However, this has not been
supported by animal or human studies.58
If the patient does convert into fibrillation, the
patient should continue to be rewarmed and resuscitated. In a case report published in 2008, a 29-yearold was resuscitated after being rescued from an
avalanche with a core body temperature of 21.7°C
(71.1°F). The patient was initially breathing spontaneously, and then went into cardiac arrest with
ventricular fibrillation during the helicopter evacuation; CPR was not initiated for 15 minutes. The
patient was in arrest for a total of 150 minutes, yet
ultimately had a complete recovery after rewarming
with femoral venoarterial bypass. Follow-up 2 years
later showed no deficits from the accident.59 Despite
a lack of large scale prospective studies, cases such
as this one provide evidence for the continued treatment in the field in the absence of any signs of life
when circumstances reasonably allow.
defibrillation attempts or medication boluses should
be deferred until the core temperature is above 30°C
(86°F).8,61 In 1 case study, a patient’s cardiac activity
was re-established with CPR and rewarming from
20°C (68° F).62
Active rewarming, either externally or internally,
using fluids, air, and/or blankets is often difficult
in the field due to environmental or equipment
constraints. One non-human study did show novel
potential techniques of active rewarming in the field
as may be the case if a long extraction and transport
is necessary: Platts-Mills et al compared 4 techniques of warming IV fluids: with camp stoves, with
military MRE heat packs, and with 2 commercially
available chemical heat packs. Only heating with the
camp stove or MRE pack was successful in achieving
the ideal infusion temperature of 35ºC to 42ºC (95ºF
to 107.6ºF) for rewarming.63 The main treatment
goal for cardiac arrest secondary to hypothermia is
aggressive active core rewarming which is generally
reserved for in-hospital resuscitation.
ACLS
When a hypothermic patient arrives into the ED, it is
important to obtain a focused but thorough history.
This information assists in not only diagnosing the
hypothermia itself but also in determining any other
factors contributing to or complicating the hypothermia. It is important to identify patients with underlying
medical conditions predisposing them to hypothermia
before attributing the hypothermia to exposure alone.
Table 3, page 4 illustrates the many factors that can
complicate accidental hypothermia that must be considered while obtaining a patient’s history.
In cold environments, attributing hypothermia
solely to exposure may result in potentially missing underlying etiologies. For example, a homeless
man who is “found down” presents additional
treatment considerations, such as potential metabolic or infectious comorbidities. In the unconscious patient, the only information available may
be that from family, friends, rescuers, medical alert
bracelets, or patient medical records. It is important
to try to determine how long the patient has been
down and if there were any other insults prior to
the hypothermia such as trauma, hypoxia, alcohol,
or drug intoxication.
ED Evaluation
History
Airway and Breathing
Patients should be intubated in the field as soon as
possible when clinically indicated. Excessive movement should be avoided but not at the expense of securing the airway. In a multicenter survey, endotracheal intubation was performed on 117 hypothermic
patients without induction of any dysrythmias.57
Intubation enables administration of warm humidified air and reduces the risk of aspiration.
Circulation
If the patient does not have a pulse, the provider
should check the rhythm before initiating CPR. If
the patient has any sort of organized rhythm, the
assumption is that there is adequate perfusion. For
more information, see the “Controversies” section.29
There is also some concern (with no strong evidence)
that CPR may convert the rhythm into ventricular
fibrillation.147 Doppler ultrasound is emerging as a
valuable tool to assess pulses and cardiac activity
and its role in the prehospital arena is an active area
of investigation. If there is obvious fibrillation on
the monitor or ultrasound, 1 defibrillation attempt
is appropriate. Although uncommon, patients have
been successfully defibrillated below 30°C (86°F)
as confirmed by a recent case report of a successful
defibrillation of a patient who was 26.5°C (79.7°F).60
One round of ACLS vasoactive drugs is also appropriate. If the patient does not respond, it is possible
that the electricity is not conducting and / or vasoactive drugs are not circulating; in these cases further
Physical
Hypothermic patients will have varied presentations
depending on the degree of hypothermia. There are
no studies that have looked specifically at physical findings in hypothermic patients. The clinical
picture does not always correlate with the degree of
hypothermia; therefore, the grade of hypothermia
must be determined by recording the core body
6
Heart Rate: In uncomplicated accidental hypothermia, the patient will be tachycardic until the
temperature drops below 29°C (84.2°F) at which
point, bradycardia often ensues.32, 71, 72
temperature, and the physical examination should
be focused initially to direct management.
The physical examination focuses on mental
status, vital signs and physical signs of trauma, illness or poisoning. In mild hypothermia, patients
will have vigorous shivering, and cold white skin.
Patients in moderate hypothermia may have mental
status changes (amnesia, confusion, apathy) plus
reduced shivering, slurred speech, hyporeflexia, loss
of fine motor skills and / or ataxia. Severely hypothermic patients will have clinical presentations that
include combinations of no shivering, cold edematous skin, hallucinations, areflexia, oliguria, fixed dilated pupils, bradycardia, hypotension, pulmonary
edema, and sometimes cardiac arrest.6, 28, 64-66
Blood Pressure: Animal studies suggest that blood
pressure rises with progressive hypothermia down to
27°C (80.6°F).73 This is secondary to catecholamine release causing increased vasoconstriction and increased
cardiac output. Severely hypothermic patients are often hypotensive secondary to fluid shifts, cold diuresis,
and dehydration.6 However, this is not uniform across
all patients, as uncomplicated hypothermic patients
have been shown in case studies to maintain a normal blood pressure with temperatures down to 25°C
(77°F).74 It is crucial to continuously monitor blood
pressure for potential hemodynamic collapse that can
occur during the rewarming process.6, 32, 75
Mental Status
Mental status depression is seen in patients with
a core temperature less than 31.7°C (89.1°F). If the
patient is above this temperature and mentally
depressed, the clinician should consider head injury,
infection, toxins, or a metabolic abnormality.67
Respirations: Tachypnea is noted only in mild, early
hypothermia during the adrenergic surge while the
patient is severely shivering. As the temperature
drops below 33°C (91.4°F), respiratory drive diminishes and the respiratory rate drops. Other possible
respiratory effects include bronchorrhea and noncardiogenic pulmonary edema.6, 76
Vital Signs
In accidental hypothermia without other confounding factors such as toxins or infection, patients
should be able to maintain relative hemodynamic
stability down to temperatures of 27°C (80.6°F).
Below this temperature shivering stops, initially
elevated catecholamine levels decrease, the patients’
cardiac output and blood pressure decrease, and
severe organ dysfunction begins. This has been demonstrated in a cross-over study with baboons who
are cooled to severe hypothermia.68
Pulse Oximetry: Pulse oximetry may be difficult to
measure in severely hypothermic patients secondary to vasoconstriction. Arterial blood gases (ABGs)
may be the only way to assess oxygen perfusion.
There have been no direct studies on pulse oximetry
in accidental hypothermia. However, some guidance
comes from the anesthesiology literature: a study of
10 healthy subjects found a statistically significant
lag time in pulse oximetry, noting a hypoxic desaturation when the subjects were mildly hypothermic
versus when they were normothermic. In addition,
there was decreased failure of forehead pulse oximetry versus standard fingertip reading devices.77
Temperature: Most standard clinical thermometers
do not record temperatures below 34°C (93.2°F). Rectal, esophageal, or bladder thermometers with the
ability to measure low temperatures must be used
to accurately assess the patient. Rectal and bladder temperature may lag behind actual core body
temperature; esophageal thermometers may be more
accurate.7,32 One study of 25 hypothermic patients in
the OR reported that non-invasive recording (tympanic, oral and axillary) did not accurately indicate
core temperature when compared to pulmonary
artery, bladder, and esophageal temperatures.69
Another study of 160 patients found tympanic
thermometers to be inaccurate compared with core
temperature from a pulmonary artery catheter.70 It
is clear that some sort of semi-invasive or invasive
temperature measuring is necessary to accurately assess the core temperature of a hypothermic patient.
In the absence of a pulmonary artery catheter, the
authors recommend using esophageal temperature
monitoring as it is closest to the core, although there
are no studies directly proving its efficacy over rectal
or bladder temperature.
Other Physical Examination Findings
Pupils will often be dilated in moderate and severe
hypothermia.6 Consequently, dilated pupils alone,
in the absence of decerebrate posturing or lateralizing signs, should not drive hyperventilation or
use of mannitol in the hypothermic patient. It is also
important to examine the patient carefully for other
exposure injuries such as frostbite.
Diagnostic Studies
Laboratory Testing
White Blood Cell Count
The white blood cell (WBC) count may be increased or
decreased in hypothermia. An elevated WBC count in
hypothermia may be due to leukocyte demargination
associated with shivering. It is also possible to see a
7
Blood Gases
decreased WBC count as a result of splenic sequestration during the physiologic stress of hypothermia.78
The hemoglobin / hematocrit may be elevated due to
hemoconcentration secondary to cold diuresis.36,67
Blood gas values are notoriously difficult to interpret
in the hypothermic patient and provide a source of
controversy. Blood gas analyzers warm the blood
sample to 37°C (98.6°F); this increases the partial
pressure of the gases thereby increasing the hydrogen ion concentration of the sample.83 The result is
a corrected value which falsely elevates the CO2 and
lowers the pH.27 Therefore, it is our preference to use
an uncorrected ABG to guide clinical management.84
Correcting a patient’s acid-base balance using the
lab-corrected ABG could result in exacerbating an
acidosis and worsen outcomes by hindering cerebral
blood flow, hindering coronary blood flow, and potentiating arrhythmogenicity.85 Practically speaking,
this can be accomplished by omitting the patient’s
temperature from the blood gas lab requisition.
The reality is that hypothermic patients can have
many types of acid-base disturbances: metabolic acidosis due to lactate, a respiratory alkalosis from the cold
blood, a respiratory acidosis from the hypoventilation,
or any combination of those. Therefore, it is best to simply treat the actual uncorrected ABG, with a goal of an
uncorrected pH of 7.35 and a pCO2 of 40 mm Hg while
looking for underlying contributing factors.
Chemistry Panel
Electrolyte levels may change frequently during
rewarming. In particular, potassium levels will
fluctuate as the acid-base balance changes.57 Sodium, calcium, magnesium, and chloride concentrations do not change significantly, although sodium
is often elevated secondary to dehydration. Serum
osmolality is also elevated for the same reason. Mild
hypothermia is associated with hypokalemia, and
severe hypothermia is associated with hyperkalemia
from cell death and renal failure. Renal function is
abnormal in over 40% of hypothermic patients who
require ICU admission.28
As the history is often not clear in a patient
found down and hypothermic, creatine kinase (CK)
should be checked, and the clinician should have a
high suspicion of potential renal failure secondary to
rhabdomyolysis or acute tubular necrosis. Hypothermic patients may have abnormal liver function tests
and reduced clearance of lactic acid due to decreased
cardiac output. 32
Ethyl Alcohol Level
Coagulation Studies
Generally, patients with altered mental status have
their blood alcohol level tested, especially if they are
hypothermic since alcohol or drug intoxication is a
frequent cause of, or contributor to, hypothermia.
Severely hypothermic patients are usually coagulopathic due to the temperature dependence of
various enzymes in the coagulation cascade. Rohrer
et al demonstrated that both prothrombin time (PT)
and partial thromboplastin time (PTT) increase with
decrease in temperature. Fifteen samples of pooled
plasma were tested at 37°C (98.6°F), 34°C (93.2°F),
31°C (87.8°F), and 28°C (82.4°F) demonstrating a
statistically significant increase in both the PT and
PTT (p< 0.001) as temperature declined. The mean
PT at 37°C (98.6°F) was 11.8 seconds compared to a
mean of 16.6 seconds at 28°C (82.4°F).80 In a similar
study, Felfernig and colleagues examined the PTT
of in vitro plasma and found a 10% increase in PTT
between plasma below 35°C (95°F) as compared to
plasma at 37°C (98.6°F) (p < 0.05).81 The reported
lab values are often normal as the blood is heated to
37°C (98.6°F) prior to analysis. This is an important
consideration in trauma patients where the patient
may be exsanguinating despite coagulation studies
that appear normal. The coagulopathy is self limiting and resolves with rewarming.80, 81
A meta-analysis of 24 published randomized
trials comparing blood loss/transfusion requirements in normothermic patients versus hypothermic
patients corroborates the significance of coagulopathy with hypothermia. Even mild hypothermia (<
1°C or 33.8°F) significantly increases blood loss by
approximately 16% and increases the relative risk for
transfusion by approximately 22% (3%–37%).82
Urine Toxicology
As with alcohol, patients with altered mental status
should be considered for urine toxicologic screening.
Depending on the hospital, the panel may be limited
but may help in a patient with altered mental status
of undetermined etiology. The clinician must consider the fact that urine toxicologies are often positive
long after the intoxication is resolved.
Other
If the hypothermic patient fails to respond to rewarming techniques or there is no clear source of
cold exposure, the emergency physician should consider testing for other possible underlying etiologies
(eg, hypothyroidism or adrenal insufficiency).
Diagnostic Imaging
Radiography
Hypothermic patients with altered mental status
are inherently at risk for aspiration pneumonia and
should have a screening chest radiograph (CXR).
Ultrasound
There are no studies specifically looking at the use
of ED ultrasound in hypothermic patients. However,
ED bedside ultrasound has an established role in
8
evaluating for contributing causes of altered mental status: A FAST examination evaluates for free
fluid indicating trauma or eroding intra-abdominal
processes. If any of these examinations are positive,
further studies and consults can be expedited. The
heart can also be examined for pericardial effusion,
contractility, and wall motion abnormalities.
dial impulse conduction; all of which result in abnormal repolarization.28 These changes are manifest in
the numerous ECG changes observed in hypothermic
patients, including but not limited to: prolonged
intervals (PR, QRS, and QT), premature beats, atrioventricular blocks, ST depressions and elevations,
bradycardia, and atrial and ventricular arrhythmias.32
The most common ECG finding is the Osborn
wave, seen in approximately 80% of hypothermic patients. 86 (See Figure 1.) Also known as the J-wave, the
Osborn wave is a positive deflection at the QRS-ST
junction.87, 88 In a retrospective review of 59 patients
with hypothermia, 51 of these patients, or 86%, were
noted to have an Osborn wave on initial ECG.89 In 1
of the few prospective trials in the accidental hypothermia literature, Vassallo et al looked at 43 patients
with hypothermia over 2 years; 37 patients had evidence of the Osborn wave on their initial ECG.90
The evidence is not clear on what exactly
prompts the electrocardiographic formation of a
J-wave. One hypothesis is that hypothermia-induced
ion fluxes result in delayed depolarization or early
repolarization of the left ventricle. Another theory is
that there may be an unidentified hypothalamic or
neurogenic factor.31
The Osborn wave can be seen at any degree of
hypothermia, from mild to severe. There is some evidence that the absolute size of the J-wave is correlated
to the temperature, and it tends to resolve as the patient is rewarmed.90 While this unusual ECG change is
sometimes considered pathognomic for hypothermia,
it can be seen in normothermic patients, often in the
context of cardiac arrest and hypercalcemia.91
CT Scan
CT imaging is not clearly indicated for the hypothermic patient. However, it can be considered, especially in the patient who continues to have altered
mental status after they are warmed above 32°C.
Once the severely hypothermic patient is stabilized,
directed CT scan, based on patient signs and symptoms, can be considered and can help reveal underlying infection or trauma.
Other Diagnostic Studies
Electrocardiography (ECG)
The heart of a hypothermic patient will have decreased spontaneous depolarization of pacemaker
cells, prolonged action potential, and slowed myocar-
Figure 1. ECG Of J-Wave (Osborn Wave)
Treatment
Once the diagnosis of hypothermia is made, the
physician must decide how to resuscitate the patient
based on the severity of hypothermia and the resources available. The physician should also be on the
lookout for underlying illnesses or toxins and treat
them early and aggressively. The clinical pathway on
page 10 provides a treatment algorithm based on the
best available evidence.
Rewarming
There are 4 general types of rewarming with numerous modalities within each category. (See Table 4,
page 11.)
Passive Rewarming
In a mildly hypothermic patient with a core temperature greater than 32°C (89.6°F), passive rewarming is recommended. The goal of passive
rewarming is reducing convective, conductive, and
radiant heat loss. Complicating factors must be
considered since passive rewarming requires intact
thermoregulatory mechanisms, normal endocrine
Image is courtesy of William Brady, MD, University of Virginia.
9
Hypothermia Clinical Pathway
The evidence for recommendations is graded using
the following scale. For complete definitions, see back
page. Class I: Definitely recommended. Definitive,
excellent evidence provides support. Class II: Acceptable and useful. Good evidence provides support.
Class III: May be acceptable, possibly useful. Fairto-good evidence provides support. Indeterminate:
Continuing area of research.
This clinical pathway is intended to supplement, rather than substitute for, professional judgment and may
be changed depending upon a patient’s individual
needs. Failure to comply with this pathway does not
represent a breach of the standard of care.
Copyright © 2008 EB Practice, LLC. 1-800-249-5770.
No part of this publication may be reproduced in any
format without written consent of EB Practice, LLC.
Cold Patient
Check core temp
Remove cold clothing
l Insulate to prevent further loss
l Minimize patient jostling
l Keep horizontal
l Treat disorders
Unresponsive
l
l
Patient frozen solid
Ice in nose/mouth
l Core temperature < 10°C (50°F)
l Submerged >1 hour
l Obvious lethal injury
l
l
Temperature < 35°C (95°F) =
Hypothermic
Check responsiveness
NO
Yes
Intubate gently
(Class I)
Hold
resuscitation
Check pulse
Pulseless
Responsive
Handle gently
l Cardiac monitor
Check for organized rhythm
or sign of life.*
Pulse present?
l
Yes
Check temperature
Mild
32°C to 35°C
(89.6°C to
95°C )
Passive
rewarming
Moderate
28°C to 32°C
(82.4°C to
89.6°C)
• Active internal
rewarming
• Passive
rewarming
•Active external
rewarming
PEA
Check
temperature
> 30°C(86°F)
ACLS drugs
but given
at longer
intervals
• Extracorporeal
blood warming
(CAVR)
(Class II)
Bradycardia
VFib
Asystole
Consider
pacing. (Indeterminant)
Shock
x1
ALCS
drugs x 1
<30°C(86°F)
*Signs of Life
Spontaneous Ventilation
l Spontaneous movement/sound
l Audible beat on auscultation
Yes
Pulse
No Pulse
Aggressive rewarming/active internal warming (Class
III) until 30°C (86°F) then
re-evaluate.
l
10
Check pulse
ALCS
drugs x 1
Defer drugs
Start CPR
(Class III)
Consider holding CPR
(Class III)
Severe
<28°C
(82.4°C)
• Active external
rewarming
NO
Organized
NO
Check rhythm
Vfib/Asystole
Aggressive rewarming/active internal warming (Class
III) until 30°C(86°F) then
re-evaluate.
function, and adequate energy stores to create endogenous heat.76
Passive rewarming begins by removing wet
clothing, insulating the patient, and protecting them
from the environment. Ideally, the patient should be
in an ambient temperature of at least 21°C (69.8°F) to
prevent further cooling. Warmed and humidified air
is preferable to reduce heat loss during respiration. In-
sulation may consist of blankets, foil insulators (“space
blankets”), or any other type of insulation available.
Assuming shivering is intact, this method should
warm the core body temperature 0.5°C (41°F)/h to
2°C (35.6°F)/h which is significantly lower than active
rewarming techniques. If shivering is not intact, the
patient must be actively re-warmed.92, 93
Table 4. Rewarming Methods
Category
Methods
Rewarming Rate (°C/h)
Rewarming Rate (°F/h)
Comments
Passive external
Blankets
0.5
32.9
Insulation. Only effective if shivering intact.
Space blanket
0.5
32.9
Only effective if shivering intact. In 1 study
75
half as effective as a heating pad.
Forced air rewarming
device
1-2.5
33.8-36.5
Warm blankets, heating
pads
Variable
Variable
Radiant heat
Variable
Variable
Hot water bottles
Variable
Variable
Negative-pressure
rewarming
Variable
Variable
Not readily available.
Hands and feet in warm
water
Variable
Variable
Easy to do, not sufficiently studied.
Warm water immersion
2-4
35.6-39.2
Difficult to monitor patient, risk of
temperature after-drop and rewarming
hypotension.
Warm (42°C or 107.6°F)
and/or humidified air
0.5-1.2
32.9-34.2
Low heat transport capacity, minimizes afterdrop when used with active external methods.
Warm (42°C or 107.6°F)
intravenous fluids
Variable
Variable
More effective with large volumes, fluid
overload possible, central venous IVF’s
effective in dogs up to 65°C (149°F).
Mediastinal, gastric,
colonic, thoracic,
peritoneal or
bladder lavage
Variable
Variable
Limited data, risk of mucosal injury,
Invasive, risk of aspiration with gastric
lavage.
Peritoneal dialysis
1-3
33.8-37.4
Combine with heated oxygen, 6 to
10 L/hour heated to 45°F (113°F).
Open thoracotomy lavage
up to 8 (median 2.95)
Hemodialysis and
hemofiltration
2-3
35.6-33.8
Available in most facilities, requires
adequate blood pressure, trained dialysis
nurse needed.
Continuous arteriovenous
rewarming (CAVR)
3-4
33.8-39.2
Rapid initiation, trained perfusionist not
required, less available, requires ad
equate blood pressure.
Cardiopulmonary
bypass
7-10
44.6-50
Provides full circulatory support, allows
oxygenation, less available, requires
trained perfusionist, delays in initiation. Fastest overall rapid warming
method: 3 to 4 times faster than other
active core rewarming methods.
Active external
Active internal
Extracorporeal
23
up to 8 (median 2.95)
11
Risks of burns, temperature after-drop, and
rewarming hypotension.
23
Highly invasive, 71% survival in 1 study.
Active External Rewarming
fluids and warm humidified air. It is important to
assure adequate volume resuscitation to minimize
rewarming complications.29 The exception to the
core rewarming first rule is with rewarming of arteriovenous anastamosis, the next section.100
In patients with mild hypothermia who are not
responding to passive rewarming or patients with
moderate hypothermia, active external rewarming
is indicated. Active external rewarming involves
applying heat directly to the skin; it assumes circulation is intact to return warmed blood to the core. In a
crossover study of 8 healthy patients, active external
rewarming was shown to be twice as fast as passive
rewarming.95 Forced warm air devices are a very
effective method of active external rewarming and
allow the provider to continually monitor the patient.
Forced air rewarming devices warm the patient 1°C
(33.8°F)/h to 2.5°C (36.5°F)/h and when placed only
over the patient’s trunk can minimize the risk core
afterdrop.92, 93 One prospective, randomized trial
looked at 16 patients re-warmed from temperatures
below 30°C (86°F) using cotton blankets compared
with forced air rewarming devices. The study found
that patients re-warmed using the forced air rewarming device rewarmed 1°C (33.8°F)/h faster than
patients warmed with cotton blankets only.92 Another
study compared rewarming of 8 patients using forced
air rewarming compared with inhalation rewarming and spontaneous rewarming. The patients were
cooled on 3 separate occasions and meperidine was
administered to prevent shivering. Forced air rewarming warmed patients 2°C (35.6°F)/h faster than
either of the other methods.93 The American Society
of Anesthesiologists recommends the use of forced air
rewarming devices to treat hypothermia and maintain normothermia in post-operative patients during
emergence and recovery.96 One prospective study
by anesthesiologists compared forced air rewarming to no intervention intra-operatively and found
that forced air rewarming effectively maintained
normothermia.97 Another meta-analysis showed that
intraoperative normothermia is maintained most effectively with forced air-rewarming.98 One 1999 retrospective study showed that 15 severely hypothermic
patients were successfully re-warmed to 35°C (95°F)
using forced air rewarming.99
Water blankets, warm blankets, warm water
bottles, heating pads, and warm water immersion are other effective methods of active external
rewarming. Care must always be taken to prevent
dermal heat injury from these techniques. External
heating should be done with temperatures between
40°C (104°F) to 45°C (113°F) to be effective and
prevent burning.100 With all of these methods, the
patient should ideally have their trunk warmed first
and extremities warmed later in order to prevent
core-afterdrop and rewarming acidosis. For more
information, see the “Controversies/Cutting Edge”
section. Both of these phenomena have been anecdotally related to poor outcomes.31, 75 For these
reasons, it is recommended that the core be warmed
first, and that active external rewarming be combined with internal rewarming using warmed IV
Active Internal Rewarming
In patients with severe hypothermia or patients with
cardiovascular instability, active internal rewarming is the recommended modality. Active internal rewarming consists of warm IV fluids, warm
humidified inhaled air, and warm fluid lavage of
body cavities. Extracorporeal warming, which is the
most effective type of active internal rewarming, is
discussed separately in the following section.
There are no studies comparing the active internal rewarming modalities. Warm humidified air and
warm IV fluids are 2 effective rewarming methods
with little side effects that should be used on all hypothermic patients when available. Warm humidified
oxygen (to 42°C or 107.6°F) increases core body temperature by 0.5°C (32.9°F)/h to 1.2°C (34.2°F)/h and
decreases evaporative heat loss from respiration.101
Warm IV fluids (preferably 40°C or 104°F) will
rewarm a patient with minimal complications. The
rate of warming depends on the rate of infusion.
Studies on beagles have shown warm IV fluids, up to
60°C (140°F), to be effective in warming hypothermic
patients if administered centrally but comparative
studies have not been done on humans.102 The concern in fluids warmed to 60°C (140°F) is endovascular
damage. Peripherally, fluids should be no warmer
than 40°C (104°F). The authors believe that centrally
administered fluids at warmer temperatures would
be an effective technique for rewarming patients, but
this needs to be further investigated to minimize risk
of complications. IV fluids are best heated using a
blood warmer, given that microwave warming can
create dangerous temperature differentials within
the fluid bag.103 It is important to monitor the patient
for fluid overload and most importantly pulmonary
edema during rapid infusions.
In the absence of extracorporeal rewarming,
active internal rewarming can also be accomplished
via lavage of body cavities. Closed thoracic lavage
involves placement of 2 thoracostomy tubes. The
first is placed in the midaxillary line at the second
to third intracostal space for warm saline infusion
and the second is placed lower in the traditional mid
clavicular line to allow continuous outflow. (See
Figure 2.) A literature review looked at 14 patients
treated with open thoracotomy or thoracostomy
tubes for active re-warming in severely hypothermic
patients with cardiac arrest. All of the patients were
successfully restored to normal sinus rhythm after a
median time of 120 minutes. Eight patients survived
without sequelae, 1 patient survived with neurologic
deficit, and 5 patients died.23 Another case series of
5 mildly hypothermic patients reported that all 5
12
were successfully warmed via pleural lavage and
discharged to their homes without sequelae. 107
Open thoracic lavage, has been shown to raise
the core body temperature up to 8°C (46.4°F)/h. 106A
retrospective review of 11 patients in hypothermic
cardiac arrest reported a 71% (7 patients) survival
rate in patients who received a thoracotomy in the
ED (5 of these patients later underwent cardiopulmonary bypass); four patients went straight to the
OR for cardiopulmonary bypass and none of these
patients survived.106 This does not imply that open
thoracotomy is superior to cardiopulmonary bypass
as the study was non-matched and not randomized.
It does, however, provide evidence to the potential
efficacy of open thoracotomy lavage. It is a highly
invasive procedure with risk for further morbidity
or mortality. The authors cannot advocate the use
of this procedure, given there is no clear evidence
that it is a superior warming technique to other less
invasive methods.
pressure are continuous arteriovenous rewarming (CAVR) or continuous venovenous rewarming
(CVVR). (See Figure 3). CAVR is relatively simple, requiring minimal equipment and set-up, and uses the
patients’ blood pressure to drive the blood through
a small counter current heat exchanging device.19
CAVR warms the core temperature 3°C (37.4°F)/h to
4°C (39.2°F)/h.32 CVVR, which is technically easier
for the emergency physician to set up and is less
invasive, has also been shown to effectively resuscitate severely hypothermic patients in studies.108,111 A
randomized controlled trial using swine found CAVR
to offer a more rapid rate of rewarming than CVVR,
but both methods were superior to less invasive
methods.113 In patients who are bradycardic and
hypotensive, 1 case report on 2 patients demonstrated
the efficacy of transcutaneous pacing to maintain the
patient’s blood pressure during CAVR.114
In patients who are hypotensive, another method which has been shown to be efficacious in canine
models is high-flow venovenous rewarming (HFVR)
using bypass. This needs to be studied in humans
before it can be implemented but may prove to be
useful as it would be easier to set up than cardiopulmonary bypass.20
Cardiopulmonary bypass raises the core body
temperature 7°C (44.6°F)/h to 10°C (50°F)/h, supports the circulation, and avoids cardiac trauma
through CPR or open thoracotomy massage. (See Figure 4, page 15)115,116 There have been no prospective
randomized controlled trials looking at the efficacy
of cardiopulmonary bypass versus other rewarming
methods, but there are several published case reports
that show positive outcomes after cardiac arrest.
A Finnish study showed a 61% survival rate in
Extracorporeal Rewarming
The most effective method of rapidly rewarming
patients is extracorporeal blood warming. In light of
the more recent literature supporting the benefit of
hypothermia post arrest, it remains to be seen if it is
better to slowly correct the temperature of hypothermic patients post arrest. Regardless of the long-term
morbidity question, extracorporeal blood warming
is definitively the fastest way to re-warm a patient.
Hemodialysis is probably the most readily
available extracorporeal rewarming technique and
will raise the core temperature 2°C (35.6°F)/h to 3°C
(37.4°F)/h.108-111 Hemodialysis requires adequate
blood pressure. Other methods that require blood
Figure 2. Thoracic Lavage
Figure 3. Continuous Arteriovenous
Rewarming
This image is used with permission from Auerbach, Paul S. Auerbach:
Wilderness Medicine 5th Edition, Figure 5-11. Copyright ©2007 Mosby
Elsevier
Wilderness Medicine 5th Edition, Figure 5-14. Copyright ©2007
Mosby Elsevier
13
23 patients after a mean arrest time of 70 minutes
using cardiopulmonary bypass. All 23 patients had
completely arrested and required cardiovascular
support as well as rewarming.117 Another study had
a survival of 15 of 32 patients with a mean temperature of 21.8°C (71.2°F) and a mean down time before
cardiopulmonary bypass was initiated of 141 minutes. In a 7 year follow-up of these patients, none
had significant sequelae.119 A study of Mount Hood
hypothermia survivors showed similar success with
cardiopulmonary bypass.120 In patients who have
cardiac arrest from hypothermia and can no longer
circulate their own blood, cardiopulmonary bypass
effectively circulates and rewarms the blood.
There are many case reports attesting to the
efficacy of cardiopulmonary bypass.121 One case
report published in 2007 demonstrated complete
recovery of an asystolic hypothermic (to 23.8°C or
74.8°F) 2-year-old after cardiopulmonary bypass.122
Cardiopulmonary bypass is 3 to 4 times faster at
rewarming than other active internal warming methods and maintains oxygenation and blood flow for
the patient who has arrested.123 Thus, in severely
hypothermic patients with cardiac arrest, this is an
effective method of resuscitating the patient. Pleural
lavage also provides effective treatment under these
circumstances. There have been no studies comparing the 2 modalities directly.
A review of multiple studies supports therapeutic hypothermia to 32°C (89.6°F) to 34°C (93.2°F)
for 12 to 24 hours post cardiac arrest.118 There is
no definitive evidence to advise only rewarming
hypothermic patients to this range post-arrest as
the patients have had the neuroprotective effects of
hypothermia during the time they were pulseless.
It is unclear whether this should be extrapolated to
recommend maintaining patients who have arrested
secondary to hypothermia at 32°C (89.6°F) to 34°C
(93.2°F) for 12 to 24 hours post cardiac arrest.
Although cardiopulmonary bypass is the fastest
method of rewarming, there is evidence to indicate
that this invasive type of treatment may be unnecessary in patients with a pulse. One study in Vienna
published in 2002 suggested a conservative approach
is successful in achieving normothermia in patients
with deep hypothermia with or without stable hemodynamics. The study looked at rewarming 36 patients
with a median temperature of 25.6°C (78.4°F) using
Cost-Effective Strategies
internal rewarming should be initiated. It should
also be noted that although studies have shown
urban patients can be successfully rewarmed with
non-invasive methods, the influence of the rewarming strategy on late in-hospital mortality remains
unclear.
1. Extracorporeal rewarming methods such as
cardiopulmonary bypass and continuous
arteriovenous devices are expensive and only
available in limited facilities. More readily
available and less expensive treatments must
often be implemented.
Warmed humidified air, warmed IV fluids and
a forced air rewarming devices are all readily available with little overhead cost. Invasive
rewarming including thoracic lavage, peritoneal
lavage, and gastric lavage are relatively accessible but time- and resource-consuming. In a patient with severe hypothermia with full cardiac
arrest, the patient is unlikely to regain cardiac
function until they are warmed to at least 30°C
(86°F). In this circumstance, thoracic lavage or
cardiopulmonary bypass is necessary.
3. The most effective way to minimize the time
and cost involved in hypothermia treatment is
education and prevention.
Elderly people need to be educated about keeping
warm in the winter. Many cities have resources that
help keep at-risk populations warm in the setting
of cold and wet weather. Homeless people are particularly at risk, and substance abuse can not only
pre-dispose a person to hypothermia but will also
cause a person to be kicked out of a shelter. This is
clearly a national problem that contributes enormously to healthcare dollars spent treating hypothermic patients. Another population that is at risk
is those who recreate outdoors. As the prevalence
of outdoor recreation increases, people need to be
educated about layering clothing with insulative,
wind-proof, and waterproof layers. Education about
survival and mountaineering skills will also reduce
incidence. There are many outdoor schools and
programs that teach this, but it is also easy to give a
quick reminder to patients in the ED.
2. Invasive rewarming methods may not always
be necessary in select populations.
At times, some groups of patients with significant
comorbidities may be best treated with less aggressive rewarming methods. In-hospital mortality
of severe accidental hypothermia in patients with
comorbidities is high, and these patients may be
best served by correcting the underlying conditions.124, 125 If the patient does not respond to empiric treatment with non-invasive rewarming, active
14
warmed infusions, inhalation rewarming, and forced
air rewarming. Although 92% of the patients were
successfully rewarmed to normothermia, in-hospital
mortality was 42% but was largely related to comorbidities. Thus, it appears patients can be adequately
rewarmed with conservative methods but unfortunately the influence of the rewarming strategy on late
in-hospital mortality remains unclear.124
ED with hypothermia, rewarming rates were found
to reflect a patient’s intrinsic capacity for thermogenesis. Patients who were also infected responded
poorly to rewarming.125 In a retrospective study of
59 adults admitted to Bellevue Hospital, New York,
between 1968 and 1979 because of hypothermia due
to exposure, 24 (41%) had 32 serious infections. Nine
of these infections were not diagnosed at the time of
admission and had increased morbidity and mortality.79 Peripheral blood cultures should be drawn
prior to consideration of empiric antibiotic therapy.
While treating the patient, it is important to observe the patient’s response to the therapy. Whichever rewarming method is chosen, the patient should
be monitored during and after rewarming. Possible
complications of rewarming are listed in Table 5.
One placebo controlled study of 20 patients showed
that desmopressin partially reverses hypothermiainduced impairment of primary hemostasis in vitro
and may be potentially useful in improving hemostasis in hypothermic patients with bleeding where
immediate rewarming is difficult or undesirable.
Whole blood from the 20 patients was cooled to 32°
C (89.6°F) and clotting time was measured compared to the same blood at 37° C (98.6°F). Clotting
time was then measured after administration of various amounts of desmopressin compared to saline
placebo, and researchers found that desmopressin
improved clotting time. This needs to be looked at in
vivo but provides a potentially life-saving therapy in
bleeding hypothermic patients where rapid rewarming is not immediately available.25
Other Treatment Considerations
Patients with uncomplicated hypothermia should
have a rapid rate of rewarming. Patients with
poisoning or infection often rewarm slowly due to
decreased intrinsic capacity for thermogenesis (<
1°C or 33.8°F/hour). Achievement of normothermia
in these patients does not necessarily prevent death.
Thus, in addition to rewarming the patient, other
general treatment principles must be considered
with a focus on detecting and treating underlying
illness.125 If a bedside glucometer is not available,
the patient should be administered dextrose. Hypothermic patients will mask signs and symptoms of
hypoglycemia and may also have depleted glycogen
stores. Thiamine may also be given empirically.
Alcohol or drug intoxication is often associated
with or is the cause of hypothermia and must be
addressed.23, 108 The presence of an elevated alcohol level in an altered hypothermic patient should
raise the suspicion of aspiration. In the absence of
additional history, a high alcohol level will alert the
physician to the potential for withdrawal.
Most patients are severely dehydrated from cold
diuresis and events leading up to their presentation,
and they will have elevated serum sodium and osmolality. Patients who have been hypothermic for over
45 minutes will often require fluid administration
because the vascular space expands due to vasodilatation.76 There is no evidence to support the use of
empiric steroids unless there is a history of adrenal insufficiency or the patient fails to re-warm adequately
despite aggressive rewarming techniques.
High-risk groups such as the homeless, neonates, and the elderly should be empirically treated
with broad spectrum antibiotics. In a prospective
observational study of 96 patients presenting to the
Special Circumstances
Anoxic Injuries
Evidence has shown that patients who have sustained asphyxia prior to hypothermia (ie, from
Figure 4. Cardiopulmomary Bypass
Table 5. Potential Complications From
Rewarming The Severely Hypothermic Patient
l
l
l
l
l
l
l
l
l
l
Core temperature after-drop
Rewarming related hypotension
Hypoglycemia, paralytic ileus
Bladder atony
Bleeding diathesis
Rhabdomyolysis
Acid-base balance
Ventricular fibrillation
Changes in electrolytes
Hyperkalemia and hypophosphatemia
Wilderness Medicine 5th Edition, Figure 5-15. Copyright ©2007 Mosby
Elsevier
15
submersion in water or avalanches) have a poorer
prognosis. One retrospective study published in
2001 looked at 26 patients with accidental hypothermia combined with circulatory arrest or severe
circulatory failure who were rewarmed to normothermia by use of extracorporeal circulation (ECC).
Based on the reports from the site of the accidents,
15 of the patients were identified as having asphyxia prior to hypothermia. Of these, only 1 survived
to discharge, and this patient had severe neuro-
logic deficit. Seven of the 11 non-asphyxia patients
survived without deficit.18 Patients with nonasphyxiation hypothermia have a better prognosis
than asphyxiation hypothermia.4, 18, 99, 108, 126 One
proposed etiology for the difference in outcome is
that patients who have sustained an anoxic event
while normothermic will often have hyperkalemia
and, thus, a poorer prognosis.127, 128
The Alaska guidelines state that a patient should
not be resuscitated if they have been submerged for
Risk Management Pitfalls For Management Of Hypothermia (Cont. on page 17)
measurement without interference from rewarming techniques. Intubation allows for safe
and successful active external rewarming via
warmed humidified air running through the
ventilatory circuit.
1. “The nurse wasn’t able to obtain/didn’t record
a temperature.”
Temperature is a vital sign and should be given
almost the same weight as blood pressure or respirations. However, in a medical code or trauma,
this vital sign can be easily overlooked in the
hustle and bustle of ABC’s, ACLS, or ATLS. Temperature can slip through the cracks all the more
easily in a hypothermic patient whose temperature cannot be established with a standard clinical
thermometer, which does not read below 34°C
(93.2°F). Ensure that a low-reading rectal, bladder,
or esophageal thermometer is readily available
to accurately assess temperature. Finding a low
temperature in a trauma or cardiac arrest patient
changes the appropriate course of action.
4. “The patient was in PEA arrest and didn’t
respond to 4 rounds of ACLS drugs, so I called
the code.”
If the patient’s core temperature is less than 32°C
(89.6°F), it is not appropriate to stop resuscitation. Continue resuscitation until the hypothermic patient has been rewarmed to above 30°C
(86°F) to 32°C (93.2°F). This may result in a
prolonged resuscitation times; however, heed
the adage that ‘the patient is not dead until he is
are warm and dead’. The severely hypothermic
patient will often be refractory to defibrillation
and vasoactive medications due to poor circulation and vasoconstriction. If the first round of
defibrillation or medications is not successful in
converting the rhythm or re-establishing a pulse,
it is appropriate to deviate from standard ACLS,
holding further rounds until after the patient has
been adequately rewarmed.
2. “The patient didn’t have a pulse, so we initiated CPR.”
Beware of falling into a routine ACLS protocol with
a patient who feels cold to the touch. Even if the
patient does not have a pulse, CPR may not be
warranted. Check the temperature and assess the
cardiac rhythm first. While there is still controversy
surrounding this issue, there is some evidence that
starting CPR in the severely hypothermic patient
with an organized rhythm may precipitate fatal ventricular dysrhythmias. Given the decreased metabolic demands of the hypothermic patient, any
organized rhythm, (even if severely bradycardic)
may be a perfusing rhythm.
5. “The patient was warming up well, but all of
a sudden became hypotensive and crashed. I
don’t know what happened.”
The exact mechanism of ‘core afterdrop’ is controversial; however, it is a well documented phenomenon that patients may transiently deteriorate in
the midst of rewarming, either from a decrease in
core temperature, a decrease in blood pH or from
hypotension and shock. While the exact mechanism
is still unclear, the expert consensus recommends
preferential core rewarming, with active techniques
in the case of moderate to severe hypothermia. In
addition, it is important to ensure that the patient
has been sufficiently volume resuscitated to maintain adequate blood pressure.
3. “The patient seemed to be protecting his airway,
so we decided to hold off on intubating him.”
Avoid delays in intubating the unresponsive
hypothermic patient. Hypothermic patients
with altered mental status are at high risk for
aspiration and developing subsequent aspiration pneumonia. While esophageal temperature
probe placement does not require concomitant
intubation, it can be easily facilitated in the
intubated patient for continuous temperature
16
submersion injuries. Cardiopulmonary bypass is the
best method of resuscitation, where available.129 In
adults, further studies are needed to establish treatment guidelines following asphyxiation events.
over 1 hour.7 The pediatric population is particularly
susceptible to drowning accidents. In a retrospective review of 12 pediatric patients with cold water
submersion and hypothermia with cardiac arrest,
the outcome was better with lower core temperatures at the beginning of extracorporeal circulation.
Nine out of the 12 survived with the lowest temperature survived 16°C (60.8°F). The time in the water
was unknown. In children, resuscitation should be
continued until the patients are rewarmed even in
Trauma
Studies have shown the protective aspects of hypothermia on head injured patients, cardiac patients,
and patients in shock.33 Therefore, it would seem
that hypothermia would be protective in a trauma
Risk Management Pitfalls For Management Of Hypothermia (Cont. from page 16)
climate, or weather. Hypothermia should remain on
the differential for every medical code and trauma
patient and every patient with altered mental status. While the absolute death rate from hypothermia is highest in traditionally colder climates such
as Alaska, Montana, and Wyoming, and 83% occur
from October to March, there are still significant
deaths in traditionally mild climates such as Arizona
and South Carolina.2
6. “I tried everything and the temperature
wouldn’t budge.”
If the patient is not responsive to passive rewarming techniques, it is likely that they have
lost the capacity for thermogenesis, and active
rewarming must be initiated. However, when
the patient fails to respond to active external
or internal methods of rewarming (ie, raising
their core temperature by less than 1°C [33.8°F]/
hr), it is important to consider other underlying
contributing factors, including hypothyroidism,
adrenal insufficiency, or infection. Prospective
studies have indicated that hypothermic patients
who are slower to rewarm, both passively and
actively, are more likely to have an underlying
infection, which also gives them a higher mortality rate.125 In addition, hypothermia appears
to impair neutrophil function, predisposing
patients to infection.24
9.
7. “The patient was rewarmed to 36°C (96.8°F) but
remained unresponsive.”
If a hypothermic, unresponsive patient continues to have significantly altered mental status
after his core temperature has been rewarmed to
above 32°C (89.6°F), it is crucial to explore other
possible etiologies for the altered mental status.
Hypothermic patients seen in the emergency department are often trauma victims, hypoglycemic, acutely intoxicated, or septic. Diabetic and
alcoholic patients frequently remain comatose at
higher temperatures than patients without these
comorbidities.143 Do not wait until the patient
has been fully rewarmed to reassess and consider other underlying issues.
10. “I just assumed that the ABG values were
accurate. I didn’t know what to do with the corrected values.”
Most hospital labs correct ABG samples based
on the patient’s temperature. While this is a
highly debated topic, expert consensus recommends using the uncorrected values to guide
clinical decision making for acid-base disturbances in hypothermic patients. Hence, when
sending a blood gas to the laboratory, do not
record the hypothermic patient’s temperature.83
8. “I just moved to Arizona and started practicing
at the local city hospital, so I didn’t even think
that the patient found down on the street corner
could have been hypothermic; I just assumed he
was a drunk, needing to metabolize.”
Accidental hypothermia can occur in any season,
“Bypass isn’t available in the middle of the
night at my hospital, so we transferred the
patient to a tertiary care center. I found out
the next day that he went into v-fib arrest on
transport”
Transporting the hypothermic patient great
distances often involves significant movement;
this puts the patient at risk for precipitating ventricular arrhythmias (which are often refractory to
conventional treatment) until rewarming has been
completed.47, 101, 144 If the patient has a cardiac
rhythm that will allow for adequate perfusion, or an
adequate blood pressure, it is reasonable to begin
other active internal rewarming methods, such as
CAVR, instead of putting the patient at risk from
transport. However, if the patient is in full cardiac
arrest or ventricular fibrillation, some evidence indicates that even delayed cardiopulmonary bypass
may have good survival outcomes.141, 144, 145
17
patient. Although this is still a controversial subject,
evidence actually shows that hypothermia is associated with poor outcomes in trauma patients with
bleeding. Hypothermia in the trauma patient is a
type of secondary, unintentional hypothermia; it is
both a marker of and a contributor to poor outcome.
Trauma patients whose core temperatures drop
below 32°C (89.6°F) have a 39% mortality based on
a retrospective analysis of the 2004 national trauma
data bank.131 Trauma patients become hypothermic
from many different reasons including cold ED and
OR temperatures, cold fluid resuscitation, open body
cavities, and lack of thermogenesis due to tissue
hypoxia. The proposed etiologies for increased morbidity and mortality include dysfunction in platelets,
induction of coagulopathy, and the worsening of
acidosis. Every effort should be made to minimize
temperature drop and initiate rewarming when
dealing with the bleeding trauma patient in the ED.
It may therefore seem counter-intuitive that a
new area of trauma resuscitation research is focusing
on the induction of severe hypothermia in the trauma patient. Critical and arresting trauma patients
are now being placed on bypass upon their arrival in
the ED and cooled down to profoundly hypothermic
temperatures.146 While this work is still in its nascent
stages, it may allow salvage of otherwise unrecoverable injuries.
vals in between.8 Bretylium tosylate 5 mg/kg has
been anecdotally shown to be useful in the treatment
of hypothermia induced ventricular fibrillation in a
case study but it has never been validated.134
Core Afterdrop
An often stated phenomenon and possible risk of
active external rewarming is that of core temperature
afterdrop. This term refers to systemic vascular collapse and recurrent further temperature drop during
the rewarming process. There are 2 potential physiologic explanations for this occurrence, the first of
which illuminates a potential risk in active external
warming. Some experts believe that peripheral extremity rewarming causes the return of cold acidemic
blood to the core causing further temperature drop
and worsening acidosis. In addition, the peripheral
vasodilatation can lead to circulatory collapse.75 This
may contribute to hypothermia patients’ propensity
toward potentially fatal ventricular dysrhythmias.135
However, another explanation exonerates active
external rewarming, focusing instead on inadequate
fluid resuscitation coupled with volume contraction
causing circulatory collapse. The cold exposure can
cause vasoconstriction, cold diuresis, and cellular
swelling, all of which can cause volume depletion
that could lead to severe hypotension and shock.
Proponents of this explanation point to the fact that
core afterdrop and circulatory collapse have been
seen in animal models even in the context of complete
circulatory arrest – hence they are not impacted by
the return of cold, acidemic blood.29
Controversies/Cutting Edge
Controversies
CPR In Hypothermic Patients
Cutting Edge
The American Heart Association Recommendations
from 2005 state that if there is any doubt whether a
pulse is present, compressions should be started.8
However, all experts agree that palpating a pulse in
the cold, stiff hypothermic patient is extremely difficult. In addition, given the profoundly decreased
metabolic demands of the hypothermic patient,
there is growing evidence that any organized
rhythm is probably a perfusing rhythm. It is likely
that the organized pulseless electrical activity (PEA)
or severe bradycardia provides enough cardiac
squeeze to perfuse the hypothermic body. An organized rhythm can be taken as a sign of life.29
There are very mixed opinions on the degree
to which movement, such as CPR, can precipitate
ventricular fibrillation. However, it is well documented that ventricular fibrillation in the setting
of hypothermia can be refractory to defibrillation
attempts.32 The hypothermic heart is often unresponsive to cardioactive drugs. Additionally, drug
metabolism is reduced and levels in peripheral
circulation can become toxic. For this reason, the
American Heart Association advises that cardiac
drugs be withheld until the core body temperature is
at least 30°C (86°F) and be given with longer interEmergency Medicine Practice © 2008
Warming Fluids In A Conventional Microwave
Microwaves certainly are not cutting edge and are
not regularly used to rewarm IV fluids when resuscitating patients. However, some facilities do not
have IV fluid warmers and others may not have
sufficient numbers if multiple patients are being
resuscitated. Thus, warming fluids in a microwave
offers an inexpensive solution. Several studies have
demonstrated the efficacy of warming IV fluids in a
conventional microwave before administering them
to the patient.103, 136, 137 One study cautioned about
the danger of warming the fluids too much if the
microwave is not adequately calibrated.138 The fluids
should not be warmed above 40°C (104°F) as there is
a risk of endovascular damage.136 Leaman et al studied warming PRBC in a conventional microwave
and found it caused hemolysis.103 The bottom line
is that it appears conventional microwaves offer an
inexpensive and easy way to warm IV fluids before
administering them, but there is potential danger if
they are not used carefully. Microwaves do not provide uniform heating, thus it is imperative that the
fluids are shaken and their temperature measured
prior to infusing to prevent endovascular damage.
18
Arteriovenous Anastomoses Rewarming
the resuscitation of the patient. The study identified
several prognostic factors for the 18 patients who
died compared with those who survived including age, systolic blood pressure, blood bicarbonate
level, SAPS II score, the use of mechanical ventilation, the use of vasopressor agents, rewarming
time, the discovery of the patient at home, and the
initial temperature. The initial temperature did not
influence vital outcome. Only the use of vasoactive
drugs (odds ratio, 9; 95% confidence interval, 1.6
to 50.1) was identified as a prognostic factor in the
multivariate analysis. Put simply — shock, requiring vasoactive drugs, is an independent factor for
mortality while initial temperature is not, according
to this retrospective analysis.141
The select group of patients stable for discharge
home after rewarming are the mildly hypothermic
patients, with an initial temperature above 32°C
(89.6°F). Even these patients should not be discharged
if they were resistant to passive external rewarming,
do not have a clear cause for their hypothermia (such
as excessive cold exposure, intoxication, etc), or there
is any indication of an underlying complication, such
as infection or thyroid abnormalities.
All other hypothermic patients, falling into
the moderate to severe categories, are automatic
hospital admissions, usually to the intensive care
unit given their need for continuous monitoring. Rewarming is typically a lengthy process,
often not completed prior to their transfer out of
the emergency department. Even the most rapid
invasive methods such as CAVR or cardiopulmonary bypass only rewarm a patient 4°C (39.2°F)/h
to 7 °C (44.6°F)/hr.32 In addition, hypothermic
patients need close monitoring for the myriad of
complications that may occur during or following rewarming. Some of the most common include
delayed hypotension, arrhythmias, hypoglycemia,
hyperkalemia, bleeding diathesis, rhabdomyolysis,
extremity injuries, and infection/sepsis.
A patient who is slow to respond to rewarming
techniques should be tested and treated empirically
for other contributory causes for their hypothermia.
The most common of these includes myxedema
coma, adrenal insufficiency, and infection. The most
pressing issue with regards to the disposition of the
hypothermic patient is often the length of resuscitation. Because of the pathophysiology of hypothermia, it is possible to successfully resuscitate a patient
who initially has no pulse and minimal cardiac
activity. As a result, a hypothermic patient should be
fully resuscitated, even if they do not have any clear
signs of life, until their core temperature has been elevated to > 30°C.76, 142 The exceptions, as previously
noted, include other obvious lethal injuries, a clear
do not resuscitate order, or a severely frozen patient
for whom resuscitation is not possible.31
A newly described method of active external
rewarming is recruiting the arteriovenous anastomoses by submerging the hands and feet in water
heated to 45°C (113°F). This allows warmed venous
blood to return to the core.139 One study looked at
rewarming patients from 34.3°C (93.7°F) comparing
shivering vs. submersion of the distal extremities in
42°C (107.6°F) or 45°C (113°F) water. The rewarming rate in the 45°C (113°F) was 9.9°C (49.8°F) /h
versus 6.1°C (42.9°F) /h in the 42°C (107.6°F) group
and 3.4°C (38.1°F) /h in the shivering cohort. The
rectal temperature, however, lagged considerably
behind the esophageal and aural canal so large
temperature gradients may still exist. 100 There is
also a warmed negative pressure device that can
be applied to the forearm that accomplishes the
same thing. This is an application that is still being
investigated.139 This method would also seem to
exacerbate the core afterdrop phenomena, although
adequate fluid resuscitation may be the solution to
preventing this rather than initial core rewarming,
as previously discussed.
A promising rewarming method recently reported for the first time in a case report is using an
endovascular warming device to warm a severely
hypothermic patient. The endovascular temperature
control systems are the same systems that are used
to induce resuscitative hypothermia for comatose
survivors or cardiac arrest. The system successfully
rewarmed the patient by 2.8°C (37°F) /h and was
ultimately removed once the patient’s temperature
reached 37°C (98.6°F). The patient had good hemodynamic recovery although care was ultimately
withdrawn secondary to poor neurologic prognosis.
Endovascular rewarming devices are being placed
in increasing numbers of EDs for therapeutic cooling
and offer a less invasive, more effective alternative to pleural lavage in facilities that do not have
extracorporeal rewarming methods available. The
systems will be familiar to more and more emergency physicians as they become more widespread
for therapeutic cooling and will not require a team to
run the machine. The only clear drawback compared
with cardiopulmonary bypass is the patient must
have a pulse.140
Disposition
Hypothermia is a severe illness, with numerous
possible complications as a result of the cascade
of physiologic abnormalities that occur. The vast
majority of hypothermic patients will require hospital admission, often to the intensive care unit. In
a retrospective analysis of 47 patients admitted to
the ICU with a diagnosis of accidental hypothermia, the only variable that was correlated with an
increase in mortality was the use of vasopressors in
19
Summary
and a temperature of 32°C (89.6°F).Underlying comorbidities were suspected and broad-spectrum antibiotics
were initiated while warming was started with a forced
air rewarming device and warm humidified oxygen. A
positive urinalysis for nitrites and leukocytes suggested
a diagnosis of urosepsis which prompted the early goal
directed therapy protocol. The patient warmed to the point
of being febrile but recovered and was discharged back to
the nursing facility the following week.
Hypothermia can affect anyone, anywhere, at any
time of year. While the weak and compromised
are certainly at greater risk, the powerful forces of
weather can easily take the life of even the youngest and healthiest of patients. From biblical times to
modern popular television shows, hypothermic patients are depicted as miraculously ‘returning from
the dead’ in the hands of the physician. While this
outcome is possible, it requires thoughtful diagnosis
and proper treatment.
Unfortunately, despite significant interest in
hypothermia, there is limited evidence to support
clinical decision making. The majority of patients
can be rewarmed using warmed IV fluids and
forced warm air. Those who do not respond must
be further explored for the overlooked underlying
causes. In patients who deteriorate, evidence points
to potential great success with even delayed cardiopulmonary bypass. Finally, the old adage continues
to be backed up by the best evidence available. “The
hypothermic patient is not dead until he is warm
and dead.” This may place large demands on the
physician and department for resuscitation time
and resources; however, the seemingly miraculous
successful resuscitation not only makes this demand
worthwhile, but also keeps hypothermia a captivating topic in emergency medicine practice.
References
Evidence-based medicine requires a critical appraisal of the literature based upon study methodology and number of subjects. Not all references are
equally robust. The findings of a large, prospective,
randomized, and blinded trial should carry more
weight than a case report.
To help the reader judge the strength of each
reference, pertinent information about the study,
such as the type of study and the number of patients
in the study, will be included in bold type following
the reference, where available.
1.
2.
3.
4.
Case Conclusions
5.
Remembering that a patient is not dead until he is warm
and dead, the 50-year-old “John Doe” who was 25°C
(77°F) was defibrillated once and given epinephrine once
without return of pulses or an organized cardiac rhythm.
CPR was continued; transferring the patient for cardiopulmonary bypass was not possible and it would take at
least two hours to initiate dialysis. A decision was made
to place chest tubes for closed pleural lavage in addition
to using warmed IV fluids. The patient was rapidly rewarmed to 30°C and regained pulses. Aggressive pleural
lavage was continued, broad-spectrum antibiotics were
initiated as the patient was high risk, and the patient
was transferred to the ICU for close monitoring. Unfortunately, due to his myriad of comorbidities, the patient
ultimately expired 4 days later.
The patient in Wyoming was intubated gently to protect her airway and ventilated with warm humidified air.
Before arrival to the ED, the physician set up to use the
forced air rewarmer and warm IV fluids; a recently purchased arteriovenous extracorporeal blood warming device
was also prepared. Upon arrival, the patient’s esophageal
temperature was 28°C (82.4°F); she still had pulses so the
continuous arteriovenous rewarming was initiated. The
patient warmed rapidly, was extubated the next morning,
and was discharged after 24-hour observation.
The patient in Jacksonville had altered mental status
6.
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13.
14.
15.
16.
20
Hypothermia-related deaths — United States, 1999-2002 and 2005.
MMWR Morb Mortal Wkly Rep. Mar 17 2006;55(10):282-284.(Retrospective review)
Hypothermia-related deaths--United States, 2003-2004. MMWR Morb
Mortal Wkly Rep. Feb 25 2005;54(7):173-175. (Retrospective review)
Dobson JA, Burgess JJ. Resuscitation of severe hypothermia by extracorporeal rewarming in a child. J Trauma. Mar 1996;40(3):483-485.
(Case report; 1 case)
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135. Sterba JA. Efficacy and safety of prehospital rewarming techniques to
treat accidental hypothermia. Ann Emerg Med. Aug 1991;20(8):896-901
(Prospective, cross-over study; 8 subjects)
136. Lindhoff GA, Mac GPJH. An assessment of the thermal safety
of microwave warming of crystalloid fluids. Anaesthesia. Mar
2000;55(3):251-254. (In vitro study)
137. Aldrete JA. Preventing hypothermia in trauma patients by microwave warming of i.v. fluids. J Emerg Med. 1985;3(6):435-442. (Prospective; 19 subjects)
138. Delaney A. Reliability of modern microwave ovens to safely heat
intravenous fluids for resuscitation. Emerg Med (Fremantle). Jun
2001;13(2):181-185. (Prospective study; 185 bags of saline)
139. Soreide E, Grahn DA, Brock-Utne JG, Rosen L. A non-invasive means
to effectively restore normothermia in cold stressed individuals: a
preliminary report. J Emerg Med. Jul-Aug 1999;17(4):725-730. (Case
report; 4 cases)
140. Laniewicz M, Lyn-Kew K, Silbergleit R. Rapid endovascular warming
for profound hypothermia. Ann Emerg Med. Feb 2008;51(2):160-163.
141. Vassal T, Benoit-Gonin B, Carrat F, Guidet B, Maury E, Offenstadt G.
Severe accidental hypothermia treated in an ICU: prognosis and outcome. Chest. Dec 2001;120(6):1998-2003. (Prospective observational;
1947 patients)
142. Steinman A. Cardiopulmonary resucitation and hypothermia. Circulation. 1986;74 part 2:IV29-IV32 (Review article)
143. Thomas DR. Accidental hypothermia in the sunbelt. J Gen Intern Med.
Nov-Dec 1988;3(6):552-554 (Retrospective case review; 24 cases)
144. Mulpur AK, Mirsadraee S, Hassan TB, McKeague H, Kaul P. Refractory ventricular fibrillation in accidental hypothermia: salvage with
cardiopulmonary bypass. Perfusion. 2004;19(5):311-314. (Case review;
1 case)
145. Vretenar DF, Urschel JD, Parrott JC, Unruh HW. Cardiopulmonary
bypass resuscitation for accidental hypothermia. Ann Thorac Surg. Sep
146. Safar P, Tisherman SA, Behringer W, Capone A, Prueckner S,
Radovsky A, et al.Crit Care Med. 2000; Nov;28(11 Suppl):N214-8
(Canine Model)
147. Breitkreutz R, Walcher F, Seeger FH. Focused echocardiographic
evaluation in resuscitation management: concept of an advanced life
support-conformed algorithm. Critical Care Med. May 2007; 35(5):
S150-161.
CME Questions
1. Mild hypothermia (32-35°C or 89.6°F-95°F)
should be treated with:
a. Active internal rewarming
b. Passive rewarming if shivering intact
c. Active external rewarming
d. Extracorporeal rewarming
2. Resuscitation should be continued in a hypothermic patient even if the patient:
a. Is frozen
b. Was submerged for over an hour
c. Has been receiving CPR for over an hour
d. Has sustained lethal injuries
3. A patient should have a normal mental status
above what temperature?
a. 25°C (77°F)
b. 28°C (82.4°F)
c. 32°C (89.6°F) d. 34°C (93.2°F)
4. Which type of extracorporeal rewarming does
not require that the patient have a perfusing
blood pressure?
a. Continuous arteriovenous rewarming
b. Hemodialysis
c. Continuous venovenous rewarming
d. Cardiopulmonary bypass
5. All undifferentiated hypothermic patients
should be given which of the following?
a. Stress dose steroids
b. Thiamine
c. Dextrose
d. Antibiotics
6. Core afterdrop is a problem with which of the
following types of rewarming?
a. Continuous arteriovenous rewarming
b. Warm IV fluids
c. Warm humidified air
d. Forced air rewarming device (forced heated air)
7. The most common ECG finding in hypothermia is which of the following?
a. Peaked T waves b. J-wave (Osborn wave)
c. Prolonged QT d. AV block
8. If a patient is rewarming at a rate less than 1°/
hour, which of the following is the most common etiology?
a. Intoxication
b. Infection
c. Hypothyroidism d. Adrenal insufficiency
23
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24
EVIDENCE-BASED CLINICAL RECOMMENDATIONS FOR PRACTICE
Mulcahy, A, Watts, M. January 2009, Volume 11; Number 1
This issue of Emergency Medicine Practice reviews the evidence and current understanding of the pathophysiology, clinical assessment, and treatment options for maximizing outcomes in accidental hypothermia.
Key Points
Accidental hypothermia can occur in mild climates, and even indoors, especially among high risk populations such as the elderly,
the homeless, or in the setting of acute intoxication or trauma.
Standard thermometers do not read below 34°C (93.2°F). Diagnosis of hypothermia (temperature < 35°C (95°F) taken with a rectal,
bladder, or esophageal probe) requires a low-reading thermometer.
The initial focus in a very cold patient is to prevent additional
heat loss by removing wet clothing and insulating the patient from
further exposure.
Active external rewarming, such as a forced air rewarming device,
warmed humidified air, and warm IV fluids is sufficient for most
hypothermic patients.
References* 1,2
12
8
96
Comments
Hypothermia occurs in a wide variety of environmental settings and is complicated by multiple patient comorbidities.
The International Commission for Mountain Emergency
Medicine recommends tympanic or esophageal field measurements to maximize accuracy.
Generally, BLS and ACLS protocols should be followed, although there is some controversy surrounding BLS interventions in the severely hypothermic patient.
The American Society of Anesthesiologists recommends the
use of forced air rewarming devices to treat hypothermia
and maintain normothermia in post-operative patients during
emergence and recovery.
If a hypothermic patient has been rewarmed to > 32°C (89.6°F)
but continues to have an altered mental status, look for other
underlying etiologies such as infection or toxic ingestion.
Do not wait until the patient has been fully rewarmed to reassess and consider other underlying illnesses.
If a patient is resistant to rewarming techniques, consider other
causes such as hypoglycemia, infection, myxedema coma, or
adrenal insufficiency.
In addition to rewarming the patient, other general treatment
principles must be considered, with a focus on detecting and
treating underlying illness.
125
“A patient is not dead until they are warm and dead.” Continue
resuscitation until the patient is rewarmed to 30°C (86°F) to 32°C
(89.6°F).
3,4
Resuscitation may be withheld only if the patient is frozen solid,
there is an ice-occluded airway, there is a clear “Do Not Resuscitate” order, there are other obvious lethal injuries, or the patient
was documented to be submerged for over an hour.
31, 76, 142
Even if an unresponsive patient does not have a pulse, consider
holding CPR if the patient has an organized rhythm on cardiac
monitor.
32
If a patient in asystole or ventricular fibrillation does not respond
to initial vasoactive medication or defibrillation, respectively,
hold further rounds and actively rewarm the patient, considering
more invasive active rewarming such as cardiopulmonary bypass.
32
The lowest initial temperature recorded in a child who survived from hypothermia was 14.2°C (57.6°F),and the lowest
recorded temperature in an adult was 13.7°C (56.7°F).
Except in these instances, a hypothermic patient should be
fully resuscitated, even if they do not have any clear signs of
life, until their core temperature has been elevated to > 30°C.
There is controversy surrounding CPR and other BLS interventions in the severely hypothermic patient. Some case reports
indicate that CPR may convert the rhythm into fibrillation under
these circumstances.
It is well documented that ventricular fibrillation in the
setting of hypothermia can be refractory to defibrillation
attempts.
* See reverse side for reference citations.
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REFERENCES
These
references are
excerpted from
the original
manuscript.
For additional
references and
information
on this topic,
see the full text
article at
ebmedicine.net.
1. Hypothermia-related deaths — United States, 1999-2002 and 2005. MMWR Morb Mortal Wkly Rep. Mar 17 2006;55(10):282-284. (Retrospective review)
2. Hypothermia-related deaths--United States, 2003-2004. MMWR Morb Mortal Wkly Rep. Feb 25
2005;54(7):173-175. (Retrospective review)
3. Dobson JA, Burgess JJ. Resuscitation of severe hypothermia by extracorporeal rewarming in a child. J Trauma. Mar 1996;40(3):483-485. (Case report; 1 case)
4. Gilbert M, Busund R, Skagseth A, Nilsen PA, Solbo JP. Resuscitation from accidental hypothermia of 13.7 degrees C with circulatory arrest. Lancet. Jan 29 2000;355(9201):375-376. (Case report; 1 case)
8. AHA. Hypothermia. Circulation: Journal of the American Heart Association. 2005;Part 10.4(112):IV-136 - IV -138. (Guideline; Consensus Paper)
12. Samuelson T. Experience with standardized protocols in hypothermia, boom or bane? The Alaska experience. Arctic Med Res. 1991;50 Suppl 6:28-31. (Review)
31. Auerbach PS. Wilderness medicine. 5th ed. Philadelphia: Mosby Elsevier; 2007. (Textbook)
32. Aslam AF, Aslam AK, Vasavada BC, Khan IA. Hypothermia: evaluation, electrocardiographic manifesta
-tions, and management. Am J Med. Apr 2006;119(4):297-301. (Review article)
76. McCullough L, Arora S. Diagnosis and treatment of hypothermia. Am Fam Physician. Dec 15 2004;70(12):2325-2332. (Review article)
96. Practice guidelines for postanesthetic care: a report by the American Society of Anesthesiologists Task Force on Postanesthetic Care. Anesthesiology. Mar 2002;96(3):742-752. (Guideline)
125. Delaney KA, Vassallo SU, Larkin GL, Goldfrank LR. Rewarming rates in urban patients with hypo
-thermia: prediction of underlying infection. Acad Emerg Med. Sep 2006;13(9):913-921. (Prospective
observtional study; 96 patients)
142. Steinman A. Cardiopulmonary resucitation and hypothermia. Circulation. 1986;74 part 2:IV29-IV32 (Review article)
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and is intended to supplement, rather than substitute, professional judgment. It covers a highly technical and complex subject and should not be used for making specific medical decisions.
The materials contained herein are not intended to establish policy, procedure, or standard of care. Emergency Medicine Practice is a trademark of EB Practice, LLC. Copyright © 2008 EB
Practice, LLC. All rights reserved. No part of this publication may be reproduced in any format without written consent of EB Practice, LLC. This publication is intended for the use of the individual
subscriber only and may not be copied in whole or part or redistributed in any way without the publisher’s prior written permission — including reproduction for educational purposes or for
internal distribution within a hospital, library, group practice, or other entity.

Accidental Hypothermia: An Evidence-Based Approach

Transcription

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