21. Eran Segal - Critical Care Symposium

Using High Frequency Jet Ventilation in patients with ARDS
Eran Segal, MD
Director
Department of Anesthesia, Intensive Care and Pain Medicine
Assuta Medical Centers
Israel
Why HFJV?
In recent years, the damage incurred by the lungs from mechanical ventilation
has received increasing attention. The mechanism of VILI – ventilator induced
lung injury is multifactorial, and significant components leading to damage are
volutrauma – ventilating with large tidal volumes, atelectrauma – allowing for
de-recruitment during the ventilator cycle, in addition to barotrauma, and toxic
and humoral effects.
It has been demonstrated that patients are still being ventilated with higher than
optimal tidal volumes, and that the acceptance of low tidal volumes as a critically
important part of ventilating the patient with ARDS, is still not universal.
Thus, the concept of rapid, high rate and very low tidal volume as delivered with
high frequency ventilation is very attractive as an approach directed at
prevention of lung injury due to the mechanical ventilation. It could theoretically
be expected that there would be less stress due to recruitment-derecruitment of
alveoli, and patient outcome may be improved.
What is HFJV?
HFJV is one of a group of mechanical ventilation modes which utilize high rates
at low tidal volumes. HFV has been classified to a number of modalities: HFPPV,
HFJV, HFO. HFPPV is essentially increasing respiratory rates, while decreasing
the tidal volumes to the low end of that prescribed for conventional mechanical
ventilation. HFO is a technique in which a continuous gas flow at the patients
ETT, is “oscillated” that is a positive and negative pressure is applied at the
proximal end of the tube, leading to a ventilator mode with very low tidal
volumes, very high rates and a unique element which is that in this ventilator
mode both inspiration and exhalation are active.
HFJV is a mode in which a high speed (jet) stream of gas is delivered at rapid
rates – often in the hundreds per minute. The velocity of the gas flow leads to the
venture effect with entrainment of ambient gas, or from a circuit with continuous
flow to which the jet is connected. This means that the tidal volume delivered is
comprised of two components – the jet volume and the entrained volume, which
can be equivalent in size. Various conditions, such as the location at which the
jet is delivered, the size of the injector, and the pressure differences, may lead to
a change in the ratio of the entrained volume size versus the jet volume,
therefore the assessment of tidal volume during HFJV can be challenging and the
“true” tidal volume is usuallyunknown. In contrast to HFO and similarly to
conventional ventilation the expiratory phase of ventilation in HFJV is passive.
But due to the high rate and short expiratory time, there is an element of air
trapping when ventilating with HFJV, and this is a major component of the
improved oxygenation seen with HFJV.
HFJV has been shown in experimental models to improve gas exchange in lung
failure. Quan et al showed improved lung function in an ARDs model induced by
lung lavage in rabbits.[1] Johnson and Lachman used HFJV in a dog model of
ARDS, and showed that gas exchange could be well controlled, and that
oxygenation could be improved by use of external PEEP and increased VE, and
frequency had a significant effect of CO2 removal with the lower rate leading to
hypocapnea.[2]
Is HFJV of value in patients with ARDS?
As mentioned before, using HFJV makes great physiological sense. Unfortunately,
data proving this potential are extremely weak if at all. A few studies have shown
that patients ventilated with HFJV have an improved oxygenation. However, this
has not been translated into a better survival rate.
Holzapfel showed that using HFJV could achieve the same gas exchange as
conventional ventilation but that the patients ventilated with HFJV were more
hemodynamically unstable, thus leading to the conclusion that this may not be
an appropriate mode for patients with severe lung injury.[3]
Simes described a case of a patient with severe ARDS and bronchopleural fistula
[4]in which the use of HFJV was very beneficial.
Series of patients ventilated with HFJV are few. In 1987 Hurst et al described the
use of HFJV in a group of 45 patients with post-traumatic ARDS. The patients
showed improved gas exchange but no impact on survival could be
demonstrated. [5]
Abel et al showed a reduced mortality from ARDS between 2 time periods. They
ascribe this improved outcome to organizational change in ICU care between the
two time periods. They do note, however that the use of different ventilatory
modes including HFV may have contributed to this improved outcome.[6]
Still, the data for effectiveness of HFJV or HFV in general in ARDS is not there.
Wunsch and colleagues searched for evidence and found only 2 randomized
trials looking at GFV in either children or adults. [7] Although there was a trend
towards improved outcome, the bottom line is that there is not enough data at
this time to support use of HFV in ARDS. Further studies are needed to either
prove or disprove the utility of this interesting and potentially useful modality.
1.
2.
3.
4.
5.
6.
7.
Quan, S.F., et al., Comparison of high-frequency jet ventilation with
conventional mechanical ventilation in saline-lavaged rabbits. Crit Care
Med, 1984. 12(9): p. 759-63.
Jonson, B. and B. Lachmann, Setting and monitoring of high-frequency jet
ventilation in severe respiratory distress syndrome. Crit Care Med, 1989.
17(10): p. 1020-4.
Holzapfel, L., et al., Comparison of high-frequency jet ventilation to
conventional ventilation in adults with respiratory distress syndrome.
Intensive Care Med, 1987. 13(2): p. 100-5.
Simes, D.C., Supplemental jet ventilation in a case of ARDS complicated by
bronchopleural fistulae. Crit Care Resusc, 2005. 7(2): p. 111-5.
Hurst, J.M., R.D. Branson, and C.B. DeHaven, The role of high-frequency
ventilation in post-traumatic respiratory insufficiency. J Trauma, 1987.
27(3): p. 236-42.
Abel, S.J., et al., Reduced mortality in association with the acute respiratory
distress syndrome (ARDS). Thorax, 1998. 53(4): p. 292-4.
Wunsch, H. and J. Mapstone, High-frequency ventilation versus
conventional ventilation for the treatment of acute lung injury and acute
respiratory distress syndrome: a systematic review and cochrane analysis.
Anesth Analg, 2005. 100(6): p. 1765-72.