Acute Liver Failure in Children
Transcription
Acute Liver Failure in Children
Review Article Acute Liver Failure in Children Joel B. Cochran, DO and Joseph D. Losek, MD Objective: To review the incidence, etiologies, pathophysiology, and treatment of acute liver failure (ALF) in children. Emphasis will be placed on the initial management of the multiple organ system involvement of ALF. Method: MEDLINE search from 1970 to March 2005 was performed. Search headings were as follows: acute liver failure, fulminant liver failure, pediatric liver failure, hepatic encephalopathy, and liver transplantation. Studies written in English were selected. Pediatric studies were emphasized. Adult studies were referenced if there were no pediatric studies available in regard to a specific aspect of liver failure. Conclusions: Pediatric acute liver failure is a rare but lifethreatening disease. The common etiologies differ for given age groups. Management includes treating specific causes and supporting multiple organ system failure. Commonly associated disorders that require initial recognition and treatment include energy production deficiencies (hypoglycemia), coagulation abnormalities, immune system dysfunctions, encephalopathy, and cerebral edema. Criteria used to determine the need for liver transplant are reviewed as well as the difficulties associated with predicting which patients will meet these criteria and how rapidly liver transplant will become the only option. Finally, experimental procedures that may provide additional time for the liver to recover are briefly reported. Key Words: acute liver failure, multiple organ system A cute liver failure (ALF) is classically described as severe liver injury in a patient without a previous history of liver disease who develops encephalopathy within 8 weeks of the initial symptoms.1 This definition can be problematic in children who may or may not develop encephalopathy in the course of their ALF. Therefore, a more applicable definition of ALF in children is a multisystem disease process in a patient with severe liver dysfunction who had not had a previous history of liver disease.2 The true incidence of ALF in children is not known. Approximately 675 pediatric liver transplants are done in the United States each year, of which 10% to 13% are done secondary to ALF.3,4 However, these numbers do not account for most children who recover without liver transplant. Pediatric Department, Medical University of South Carolina, Charleston, SC. Address correspondence and reprint requests to Joseph D. Losek, MD, Division of Emergency/Critical Care, Pediatric Department, Medical University of South Carolina, 135 Rutledge Ave, PO Box 250566, Charleston, SC 29425. E-mail: losek@musc.edu. Copyright n 2007 by Lippincott Williams & Wilkins ISSN: 0749-5161/07/2302-0129 The etiology of ALF varies with age (Table 1). The most common causes in neonates are metabolic abnormalities, neonatal hemochromotosis, acute viral hepatitis, and unknown causes.5 In children older than 1 year viral hepatitis, drugs and unknown causes are the most common etiologies.6,7 The diagnosis of ALF can be difficult if obvious signs of jaundice have not developed. There is usually a prodrome of malaise, nausea, emesis, and anorexia. Progressive jaundice develops and encephalopathy can occur hours to weeks later. The classic adult symptoms of asterixis, tremors, and fetor hepaticus (the peculiar breath odor of patients with severe liver disease) are often absent in children. Because both ALF and sepsis are associated with multiple organ system failure, differentiating between the two can be difficult. The purpose of this report is to review the management of the multiple organ system dysfunctions associated with ALF in children. These will include energy production deficiencies, coagulation abnormalities, immune deficiencies, encephalopathy and cerebral edema. Emphasis will be give to the initial medical treatment, and the difficulties determining when liver transplant becomes the only option. ENERGY PRODUCTION DEFICIENCIES The liver is the key organ in the production and the distribution of nutrients in fasting and fed states.8,9 The liver uses 20% to 25% of the body’s energy requirements.10 In ALF, there can be an 80% to 85% loss of hepatocyte mass, but hepatic energy requirements are not decreased. This is likely due to the systemic inflammatory response to ALF even in the absence of sepsis.11 Liver failure often results in impaired glycogen storage and a diminished ability for gluconeogenesis.12 Fat and protein stores are used, and this can lead to breakdown of muscle and adipose tissue. Insulin, glucagon, and growth hormone levels are increased which further leads the catabolic drive for gluconeogenesis.8 Hypoglycemia becomes a persistent problem and causes increased pancreatic glucagon synthesis and subsequent muscle protein catabolism and release of amino acids. Therefore, ALF needs to be considered in children who are found to be hypoglycemic and, likewise, children who are diagnosed with ALF need to be closely monitored for hypoglycemia. It has been shown that energy expenditure in ALF is still increased despite sedation, analgesia, muscle paralysis, and mechanical ventilation.13 COAGULATION ABNORMALITIES Coagulation abnormalities can be significant in patients with ALF. The production of multiple clotting factors Pediatric Emergency Care Volume 23, Number 2, February 2007 Copyr ight © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited. 129 Pediatric Emergency Care Volume 23, Number 2, February 2007 Cochran and Losek TABLE 1. Etiology of ALF in Children Younger than 1 yr (80) Etiology 1 yr and older (146) Percentage Metabolic Type I tyrosinemia Mitochondrial Urea cycle disorder Galactosemia Fructose intolerance Neonatal hemochromatosis Undetermined Viral hepatitis Other 42 16 16 15 10 Etiology Percentage Unknown Viral hepatitis Hepatitis non-A and non-B Hepatitis A Hepatitis B Drug induced Other 47 27 10 4 10 2 IMMUNE DEFICIENCIES remaining contraindications to liver transplant.28,29 Levels and function of complement are reduced in children with ALF.18,30 Neutrophil adherence and killing function are also reduced.18,31 Kupffer cells are dysfunctional in ALF.32 These cells help clear gut derived endotoxins from the portal circulation and prevent the release of cytokines into the portal circulation. In a study of children with ALF, 43% had bacteremia.33 The etiology for most infections is Staphylococcus aureus, but in 1 study,34 nearly one third of the infections were fungal. Patients with acute liver failure and serious infections often do not show the classic signs of fever and laboratory results of leukocytosis. This is likely secondary to the altered immune response that increases the risk of infection in acute liver failure patients. Because ALF and sepsis are associated with multiple organ system failure and sepsis is a complication of ALF, it may be difficult to differentiate one from the other. Several studies have looked at methods of prophylaxis against bacterial infections in ALF. In a combined adult and pediatric study, 58% of the patients who did not receive prophylactic antibiotics developed bacterial infections compared with 35% who did receive prophylactic antibiotics.34 In a study of 101 adult patients with ALF, patients were divided into groups that did or did not receive prophylactic antibiotics at the time of admission.29 The patients randomized to receive prophylactic intravenous antibiotics, or a combination of intravenous and oral antibiotics, had statistically less infections than those given antibiotics at the time of clinical suspicion. Those patients who received prophylactic antibiotics had a significantly better chance of receiving a liver transplant when they met transplant criteria versus those who did not receive prophylactic antibiotics. Antibiotics used for prophylaxis in these studies were either intravenous cefuroxime alone or with amphotericin B. After blood cultures, the initiation of cefuroxime should be considered in children with ALF. Infection is a major cause of morbidity and mortality in patients with ALF.26 Infection has been found to be the primary cause of death in 11% to 20% of patients with ALF.26,27 Also extrahepatic sepsis is one of the few There are multiple potential mechanisms that lead to the encephalopathy and cerebral edema seen in ALF. A key important in hemostasis is reduced. There is also the consumption of clotting factors and platelets secondary to disseminated intravascular coagulation. Qualitative platelet abnormalities are also seen in acute liver failure.14,15 Correcting the coagulopathy in ALF has historically involved the transfusion of fresh frozen plasma (FFP), platelets, cryoprecipitate, and packed red blood cells. However, the use of these products often does not correct the coagulopathy.16 Supplemental doses of vitamin K also do not improve the coagulopathy in acute liver failure.17 Vitamin K is a cofactor, and the underlying problem in ALF is decreased synthesis of clotting factors, not vitamin K deficiency. Fresh frozen plasma is of limited benefit in correcting the coagulopathy in ALF. The use of FFP should be discouraged unless there is active hemorrhage, or the patient is hemodynamically unstable.18 Problems associated with the use of FFP include the volume overload to the patient, risk of transmission of infectious agents, short duration of action, and the unknown composition of this pooled product.19 Factor VII is the primary initiator of the hemostatic process.19 It has the shortest half-life of the vitamin K dependent factors, therefore is the first factor depleted in ALF.8,20,21 Recombinant factor VII (rFVIIa) helps form a stable clot by establishing complexes with exposed tissue factor, and it also enhances platelet activation.22 The rFVIIa has several advantages over FFP and other blood products. It is a recombinant product, therefore it does not pose an infectious disease transmission risk. It is given in very small volumes, and its duration is dose dependent. Dosage recommendations vary from 5 to 110 mg/kg. A dose of 80 mg/kg can normalize the prothrombin time up to 12 hours.20 The rFVIIa should be considered in pediatric ALF patients with hemorrhagic shock or before invasive procedures such as liver biopsies.23 – 25 130 HEPATIC ENCEPHALOPATHY n 2007 Lippincott Williams & Wilkins Copyr ight © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited. Pediatric Emergency Care Volume 23, Number 2, February 2007 factor is ammonia.35 The liver’s ability to metabolize ammonia is reduced during acute failure. This results in hyperammonemia which is associated with the development of encephalopathy and cerebral edema. Nearly half the ammonia in the gut is produced by colonic bacteria.36 Bowel cleansing may be helpful in decreasing the amount of ammonia in the gut by decreasing the colonic bacterial counts.35 Agents used for bowel cleansing include poorly absorbed enteral disaccharides and antibiotics. Most of the studies have used lactulose and neomycin, but other disaccharides and antibiotics have been studied as well.37,38 Virtually, all the studies have looked at these compounds in the setting of chronic liver failure. The treatment in ALF should be similar but is only minimally effective.37 The role of naturally occurring benzodiazepines may be involved in the development of hepatic encephalopathy.39 Endogenous benzodiazepinelike substances and receptors have been found in patients with ALF.40 However, benzodiazepine antagonists have been shown to only have intermittent and short-lived benefits in hepatic encephalopathy.36 Two additional measures to decrease the production of ammonia include dietary protein restriction36 and urea cycle activation agents.37 In ALF, unlike chronic liver failure, protein restriction is possible because patients are less likely to be malnourished, at least initially. Activation of the urea cycle may also decrease the ammonia load. Ornithine aspartate provides substrates for ureagenesis and glutamine, both of which can help remove ammonia from the portal blood.37 Hepatic encephalopathy of ALF has been classified into grades 1 to 4B (Table 2). Children with grades 3, 4A, and 4B are likely candidates for liver transplantation.6 Therefore, prearranged transfer agreements to pediatric liver transplant centers are recommended for medical centers which do not provide a liver transplant service. Such agreements are likely to reduce the risk of treatment delays during the initial management of the child with ALF. CEREBRAL EDEMA Increased intracranial pressure (ICP) is common in ALF and is the major cause of death.41,42 Cerebral edema has been found in up to 80% of patients dying from ALF.43 The mechanism of cerebral edema in ALF is unknown. Cerebral edema is not the direct result of hepatic encephalopathy.44 Two basic theories have been proposed to help understand the development of cerebral edema: the glutamine hypothesis and the cerebral vasodilatation hypothesis.41 TABLE 2. Classification of Hepatic Encephalopathy Adapted to Infants/Children Grade 1: confused, mood changes Grade 2: drowsy, inappropriate behavior Grade 3: stuporous but obeys simple commands or sleepy but arousable Grade 4A: comatose but arousable with painful stimuli Grade 4B: deep coma, not arousable with any stimuli Acute Liver Failure in Children In ALF, the liver is unable to metabolize ammonia, and it enters the brain circulation. In the brain, ammonia is detoxified by the conversion of glutamate to glutamine by glutamine synthetase. This conversion is located near the astrocyte cells.45 If significant amounts of glutamine are produced, it can act as an idiogenic osmol and lead to swelling of the astrocyte and resultant cerebral edema.46 This cytotoxic edema, rather then vasogenic edema, has been demonstrated in histological samples to be a mechanism of cerebral edema in patients with ALF.47 A second mechanism of cerebral edema is changes that occur in the cerebral vasculature. Cerebral arterioles are dilated in patients with ALF. Patients with acute liver failure and cerebral edema have higher cerebral blood flow than patients who have not developed cerebral edema.41 The autoregulation of cerebral blood flow is absent in acute liver failure.47,48 Both systemically mediated factors and local (brain) factors have been postulated, but the causes of these changes in the cerebral vasculature are unknown. Monitoring ICP in patients with ALF is important because clinical signs and computed tomography scans are insensitive diagnostic methods of determining significant ICP in these patients.49,50 The placement of ICP monitors in patients with acute liver failure can be risky secondary to their severe coagulopathy. Plasmapheresis has been used to correct the coagulopathy before ICP monitor placement. Neurosurgery consultation is indicated for all children with ALF. Children who present with signs of pending cerebral herniation obviously require treatment to lower the ICP and maintain cerebral perfusion. TREATMENT OF ACUTE LIVER FAILURE The treatment of the failing liver itself can be simplified to 2 arms: medical treatment and surgical treatment (ie, transplantation). The medical treatments attempt to improve the physiological functions of the liver, giving the liver time to recover. The surgical options, for the most part, are taken once it is clear that the liver has failed. The medical treatments include plasmapheresis,51 prostaglandin E1,52 and N-acetylcysteine (NAC). Of these, only NAC is likely to be initially indicated in the patient who presents with ALF. The use of NAC in the treatment of acute acetaminophen hepatotoxicity is well documented.53 – 55 The NAC administered within 8 hours of an acute ingestion of acetaminophen is totally effective in preventing hepatotoxicity. The mechanism of action is the replenishment of depleted glutathione stores in the liver. Initial medical evaluation (as opposed to home management) is recommended for prior healthy children who have ingested 200 mg/kg or greater of a single dose immediate-release acetaminophen preparation.56 Initiating NAC treatment is determined by plotting serum acetaminophen levels measured between 4 to 24 hours after an acute ingestion on the Rumack-Matthews nomogram.53 The duration (20 to 72 hours), the total dose and the route (oral versus intravenous) of NAC are dependent on the risk of hepatotoxicity.57 Oral NAC is 140 mg/kg loading dose followed by 17 maintenance n 2007 Lippincott Williams & Wilkins Copyr ight © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited. 131 Cochran and Losek Pediatric Emergency Care Volume 23, Number 2, February 2007 doses of 70 mg/kg every 4 hours. Intravenous NAC is 150 mg/kg in 200 mL of D5W over 15 minutes, 50 mg/kg in 500 mL of D5W over 4 hours, and then 100 mg/kg in 1000 mL of D5W over 15 hours.58 Intravenous NAC is approved for children 20 kg or greater in weight. If intravenous NAC is used in children less than 20 kg, a more concentrated solution (3%) is recommended to prevent hyponatremia from excess delivery of free water.59 The efficacy and adverse events of oral versus intravenous NAC are not significantly different in children.60,61 Recent evidence has shown that NAC may be beneficial even when initiated at greater than 24 hours after acetaminophen ingestion.62 The NAC has also shown to be beneficial in non– acetaminophen-induced liver failure.63 In non– acetaminophen-induced acute liver failure NAC increases hepatic oxygen delivery, consumption, and extraction; improves coagulation parameters; and decreases the progression of encephalopathy.63,64 There has only been 1 pediatric study examining the effects of NAC in non – acetaminophen-induced acute liver failure.65 This study was done in combination with prostaglandin E1 at the time of reperfusion of the grafted liver and included 25 children. It was a pilot, open-labeled study to examine the safety of this combination in pediatrics. No significant adverse effects occurred. Secondary results showed a significant decrease in severity of rejection in the treated group. The results further demonstrated a trend toward decreasing liver enzymes and the length of hospital stay in the treated group. TRANSPLANTATION A compelling question in pediatric patients with ALF is which child will get better and which child will have irreversible liver failure and be a candidate for liver transplantation.66 Acute liver failure in children can progress rapidly. The progression from grade 0 encephalopathy to grade 3 or 4 (Table 2) may be as short as 3 days.6 Rapid referral to a pediatric liver transplant center is recommended because nearly half the children who have grade 3 or 4 encephalopathy may die if transplant is not performed.67 In addition, more than half of patients with grade 4 encephalopathy at the time of transplant do not recover neurologically.6,68 The largest study attempting to predict recovery from ALF was done by O’Grady et al69 on 588 adult and pediatric patients. Important variables were the etiology, the age of the patient, and the grade of encephalopathy. Survival rates were variable depending on the etiology of the liver failure. Hepatitis A and acetaminophen toxicity had improved survival rates (45% and 34%) compared with hepatitis B and drug reactions (24% and 14%). Second, the age of the patient was predictive. Patients younger than 11 or older than 40 years had worse survival rates. Lastly, the higher grades of encephalopathy were associated with poorer survival rates. Other predictive variables were found for acetaminophenand non – acetaminophen-related liver failure. In acetaminophen toxicity, predictors of poor survival rates were pH less than 7.3 or a prothrombin time (PT) greater than 100 seconds combined with a creatinine greater than 3.5 mg/dL and grade 3 or 4 encephalopathy. In non –acetaminophen-related ALF, poor survival rates were seen if the PT was greater than 100 132 seconds or if any three of the following were found: PT greater than 50 seconds, bilirubin greater than 17.5 mg%, younger than 11 years or older than 40 years, cryptogenic or drug-induced, or jaundice appearing longer than 7 days before encephalopathy. Most liver transplant centers still use the O’Grady criteria.70 Although the study by O’Grady et al69 did include pediatric patients, the specific number and age of these patients were not made available. The question of whether these criteria are applicable to pediatric patients was recently raised.71 Four other studies that have looked at prognostic factors of ALF in pediatrics were all retrospective. The first study looked at pediatric patients with hepatitis A.72 Patients at risk for mortality without liver transplantation were those with a PT less than 21% of normal combined with a serum bilirubin greater than 400 mmol/L independent of the grade of encephalopathy. The second study is from the Pediatric Acute Liver Study Group and included 82 patients who presented with ALF.73 Using logistic regression analysis, encephalopathy was the only factor which predicted death, or a need for transplant in these patients. The third study looked at pediatric risk of mortality scores.74 There were significantly lower pediatric risk of mortality scores (8.8 ± 5.0) in patients with ALF who recovered versus those who required emergency liver transplantation (14.9 ± 7.7). The fourth study of 36 children with ALF concluded that elevated international normalized ratio, bilirubin, and white blood cell counts were predictors of poor outcome in ALF without transplantation.75 Currently, pediatric liver transplants have the highest graft survival rate of a solid organ at any age.76 Approximately 10% to 15% of pediatric liver transplants are done secondary to ALF. The largest published series of pediatric liver transplants included 569 transplants over a 13-year period.4 Approximately 10% were done secondary to ALF. The survival rate for all the patients was dependent on 3 factors: the age of the patient, the era of the transplant, and the number of transplants required. Patients younger than 1 year of age had a survival rate of 65% compared with 79% for older children at 10 years posttransplant. Patients transplanted after 1993 had increased survival rates versus those transplanted before 1993. Survival rates were inversely proportional to the number of transplants needed per patient. The pretransplant diagnosis did not change the postoperative survival rate. The introduction of split liver transplants improved survival rates versus caderveric transplants, but the difference was not significant. The success of split liver transplants is important in pediatrics because it has increased the availability of donors for the pediatric population.77,78 This allows transplantation to occur before multiple organ dysfunction and irreversible hepatic encephalopathy develop. The use of split liver grafts and living related donors has made a favorable impact in decreasing pretransplant mortality in pediatric patients. Another key in the treatment of ALF is supporting the functions of the damaged liver until it is clear whether the damage will be irreversible. Auxiliary liver transplants involve the transplantation of a small piece of a living n 2007 Lippincott Williams & Wilkins Copyr ight © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited. Pediatric Emergency Care Volume 23, Number 2, February 2007 Acute Liver Failure in Children TABLE 3. Treatment Options in ALF Dysfunction Treatment Hypermetabolic status Coagulation abnormalities Immune deficiency Encephalopathy (hyperammonemia) Cerebral edema Hepatic failure Comments IV glucose Hyperalimentation FFP Platelet transfusion Cryoprecipitate rFVIIa Plasmapheresis Cefuroxime and consider amphotericin B Bowel cleansing, lactulose/neomycin Benzodiazepine antagonist (flumazenil) Urea cycle activation agent ornithine aspartate Intraventricular monitoring Medical Plasmapheresis N-acetylcysteine Prostaglandins Surgical Transplantation Extracorporeal systems Close monitoring of serum glucose Low-protein diet Active bleeding with shock Active bleeding with platelet count < 20,000 mm3 Bleeding risk per PT and INR Invasive procedure Bleeding risk per PT and INR Prophylactic antimicrobials Short-lived benefit Maintain intracranial perfusion pressure > 40 mm Hg Coagulopathy/encephalopathy Acetaminophen and non– acetaminophen-induced acute liver failure Coagulopathy/encephalopathy improve transplant outcome IV indicates intravenous; INR, international normalized ratio. related donor liver.79 The native liver can be removed or left intact mostly depending on the disease process. In ALF, the hope is to transplant adequate liver mass to allow the patient’s native liver enough time to recover. EXTRACORPOREAL SYSTEMS Extracorporeal systems, which temporarily take over the function of the liver, include 2 main categories, bioartificial and artificial. Bioartificial devices include the extracorporeal liver assist device (ELAD) and the bioartificial liver (BAL). The artificial device most thoroughly studied is the molecular adsorbent recycling system (MARS). The ELAD and BAL systems use a dialysislike cartridge which house hepatocytes from a porcine (BAL) or a human hepatoblastoma cell line (ELAD). The patient’s plasma traverses through the cartridge for a variable period. The MARS dialyzes blood against an albumin-coated membrane and then a charcoal column and an ion-exchange resin. Of these extracorporeal systems, both the BAL and ELAD have improved the level of encephalopathy and survival of children with ALF.80 – 82 MARS has had similar effectiveness in adult patients, but its use in children has not been reported.83 CONCLUSIONS Acute liver failure in children is a rare but potentially devastating process. Metabolic disorders are the most common cause in children younger than 1 year, whereas viral hepatitis is the most common cause in children 1 year of age and older. Acute liver failure is associated with the dysfunction of multiple organ systems. Options for treating these organ dysfunctions as well as treating liver failure itself are summarized in Table 3. Because of the difficulties in predicting the children who will require liver transplant, consultation with or transfer to a pediatric liver transplant service is strongly recommended early in the management of children with acute liver failure. Liver transplantation is a viable option in these patients with 1-year survival rates now approaching 90%. REFERENCES 1. Trey C, Davidson C. The management of fulminant hepatic failure. In: Popper H, Schaffner F, eds. Progress in Liver Diseases, vol 111. New York, NY: Grun and Stratten; 1970:282–298. 2. Bhanduri B, Mieli-Vergani G. Fulminant hepatic failure: pediatric aspects. Semin Liver Dis. 1996;16:349–355. 3. Detre K. The NIDDK liver transplantation database. In: Terasaki P, ed. Clinical Transplants 1986. Los Angeles, CA: UCLA Tissue Typing Laboratory; 1986:29–33. 4. Goss J, Shackleton C, McDiarmid S, et al. Long-term results of pediatric liver transplantation. An analysis of 569 transplants. Ann Surg. 1998;228: 411–420. 5. Durand P, Debray D, Mandel R, et al. Acute liver failure in infancy: a 14-year experience of a pediatric liver transplantation center. J Pediatr. 2001;139:871–876. 6. Devictor D, Desplanques L, Debray D, et al. 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