- Acute liver failure
Acute liver failure is the appearance of severe complications rapidly after the first signs of liver disease (such as
jaundice ), and indicates that the liver has sustained severe damage (loss of function of 80-90% of liver cells). The complications arehepatic encephalopathy and impairedprotein synthesis (as measured by the levels ofserum albumin and theprothrombin time in the blood). The 1993 classification defines "hyperacute" as within 1 week, "acute" as 8-28 days and "subacute" as 4-12 weeks. [cite journal |author=O'Grady JG, Schalm SW, Williams R |title=Acute liver failure: redefining the syndromes |journal=Lancet |volume=342 |issue=8866 |pages=273–5 |year=1993 |pmid=8101303 |doi= |url=http://linkinghub.elsevier.com/retrieve/pii/0140-6736(93)91818-7] It reflects the fact that the pace of disease evolution strongly influences prognosis. Underlyingaetiology is the other significant determinant of outcome.cite journal |author=O'Grady JG |title=Acute liver failure |journal=Postgraduate medical journal |volume=81 |issue=953 |pages=148–54 |year=2005 |pmid=15749789 |doi=10.1136/pgmj.2004.026005]Causes
Common causes for acute liver failure are
paracetamol (acetaminophen) overdose, idiosyncratic reaction to medication (e.g.tetracycline ,troglitazone ), excessive alcohol intake (severealcoholic hepatitis ), viral hepatitis (hepatitis A or B - it is extremely uncommon inhepatitis C ),acute fatty liver of pregnancy , and idiopathic (without an obvious cause).Reye syndrome is acute liver failure in a child with a viral infection (e.g.chickenpox ); it appears thataspirin use may play a significant role.Wilson's disease (hereditary copper accumulation) may infrequently present with acute liver failure.Pathology
In the majority of acute liver failure (ALF) there is widespread hepatocellular necrosis beginning in the centrizonal distribution and progressing towards
portal tract s. The degree ofparenchymal inflammation is variable and is proportional to duration ofdisease . [cite journal |author=Boyer JL, Klatskin G |title=Pattern of necrosis in acute viral hepatitis. Prognostic value of bridging (subacute hepatic necrosis) |journal=N. Engl. J. Med. |volume=283 |issue=20 |pages=1063–71 |year=1970 |pmid=4319402 |doi=]Clinical consequence
Cerebral oedema and encephalopathy
In ALF,
cerebral oedema leads tohepatic encephalopathy ,coma ,brain herniation and eventually death. Detection of encephalopathy is central to the diagnosis of ALF. It may vary from subtle deficit inhigher brain function (e.g. mood, concentration in grade I) to deep coma (grade IV). Patients presenting as acute and hyperacute liver failure are at greater risk of developing cerebral oedema and grade IV encephalopathy. Thepathogenesis remains unclear but is likely to be a consequence of several phenomena. There is a build up of toxic substances likeammonia ,mercaptan , endogenousbenzodiazepines andserotonin /tryptophan in the brain. This affectsneurotransmitter level andneuroreceptor activation. Autoregulation of cerebral blood flow is impaired and is associated withanaerobic glycolysis andoxidative stress . Neuronal cellastrocyte s are susceptible to these changes and they swell up, resulting in increased intracranial pressure. Inflammatory mediators also play important role. [cite journal |author=Hazell, Alan S.; Butterworth, Roger F. |title=Hepatic encephalopathy: An update of pathophysiologic mechanisms |journal=Proc. Soc. Exp. Biol. Med. |volume=222 |issue=2 |pages=99–112 |year=1999 |pmid=10564534 |doi=10.1046/j.1525-1373.1999.d01-120.x] [cite journal |author=Larsen FS, Wendon J |title=Brain edema in liver failure: basic physiologic principles and management |journal=Liver Transpl. |volume=8 |issue=11 |pages=983–9 |year=2002 |pmid=12424710 |doi=10.1053/jlts.2002.35779]Unfortunately, signs of elevated
intracranial pressure such aspapilloedema and loss ofpupillary reflexes are not reliable and occur late in the disease process. CT imaging of the brain is also unhelpful in detecting early cerebral oedema but is often performed to rule out intra-cerebral bleeding. Invasive intracranial pressure monitoring via subdural route is often recommended, however the risk of complications must be weighed against the possiblebenefit (1% fatal haemorrhage). [cite journal |author=Armstrong IR, Pollok A, Lee A |title=Complications of intracranial pressure monitoring in fulminant hepatic failure |journal=Lancet |volume=341 |issue=8846 |pages=690–1 |year=1993 |pmid=8095592 |doi=10.1016/0140-6736(93)90458-S] The aim is to maintain intracranial pressures below 25 mmHg, cerebral perfusion pressures above 50 mm Hg.Coagulopathy
Coagulopathy is another cardinal feature of ALF. Liver has central role in synthesis of almost all coagulation factors and some inhibitors ofcoagulation andfibrinolysis .Hepatocellular necrosis leads to impairedsynthesis of manycoagulation factors and their inhibitors. the former produces a prolongation inProthrombin time which is widely used to monitor severity ofhepatic injury.There is significant platelet dysfunction (with both quantitative and qualitative platelet defects). Progressivethrombocytopenia with loss of larger and more activeplatelet is almost universal. Thrombocytopenia with or without DIC increases risk of intracerebral bleeding.Renal failure
Renal failure is common, present in more than 50% of ALF patients, either due to original insult such as paracetamol resulting inacute tubular necrosis or fromhyperdynamic circulation leading tohepatorenal syndrome orfunctional renal failure . Because of impaired production of urea, blood urea do not represent degree of renal impairment.Inflammation and infection
About 60% of all ALF patients fulfil the criteria for systemic inflammatory syndrome irrespective of presence or absence of infection. [cite journal |author=Schmidt LE, Larsen FS |title=Prognostic implications of hyperlactatemia, multiple organ failure, and systemic inflammatory response syndrome in patients with acetaminophen-induced acute liver failure |journal=Crit. Care Med. |volume=34 |issue=2 |pages=337–43 |year=2006 |pmid=16424712 |doi=10.1097/01.CCM.0000194724.70031.B6] This often contributes towards multi organ failure. Impaired host defence mechanism due to impaired
opsonisation ,chemotaxis and intracellular killing substantially increase risk of sepsis. Bacterial sepsis mostly due togram positive organisms and fungal sepsis are observed in up to 80% and 30% patients respectively.cite journal |author=Gimson AE |title=Fulminant and late onset hepatic failure |journal=British journal of anaesthesia |volume=77 |issue=1 |pages=90–8 |year=1996 |pmid=8703634 |doi=]Metabolic derangements
Hyponatraemia is almost universal finding due to water retention and shift inintracellular sodium transport from inhibition ofNa/K ATPase Fact|date=June 2008.Hypoglycaemia (due to depleted hepaticglycogen store and hyperinsulinaemia),hypokalaemia ,hypophosphataemia andMetabolic alkalosis are often present independent of renal function.Lactic acidosis occurs predominantly in paracetamol overdose.Haemodynamic and cardio-respiratory compromise
Hyperdynamic circulation with peripheral vasodilatation from lowsystemic vascular resistance leads tohypotension . There is a compensatory increase incardiac output .Adrenal insufficiency has been documented in 60% of ALF and is likely to contribute in haemodynamic compromise. [cite journal |author=Harry R, Auzinger G, Wendon J |title=The clinical importance of adrenal insufficiency in acute hepatic dysfunction |journal=Hepatology |volume=36 |issue=2 |pages=395–402 |year=2002 |pmid=12143048 |doi=10.1053/jhep.2002.34514] There is also abnormaloxygen transport and utilization. Although delivery of oxygen to the tissues is adequate, there is a decrease in tissue oxygen uptake, resulting in tissue hypoxia and lactic acidosis. [cite journal |author=Bihari D, Gimson AE, Waterson M, Williams R |title=Tissue hypoxia during fulminant hepatic failure |journal=Crit. Care Med. |volume=13 |issue=12 |pages=1034–9 |year=1985 |pmid=3933911 |doi=10.1097/00003246-198512000-00010]Pulmonary complications occur in up to 50% patients. [cite journal |author=Trewby PN, Warren R, Contini S, "et al" |title=Incidence and pathophysiology of pulmonary edema in fulminant hepatic failure |journal=Gastroenterology |volume=74 |issue=5 Pt 1 |pages=859–65 |year=1978 |pmid=346431 |doi=] Severe lung injury andhypoxemia result in high mortality. Most cases of severe lung injury is due toARDS with or withoutsepsis . Pulmonaryhaemorrhage ,pleural effusion s,atelectasis , andintrapulmonary shunt s also contribute to respiratory difficulty.Evaluation
All patients with clinical or laboratory evidence of moderate to severe acute hepatitis should have immediate measurement of prothrombin time and careful evaluation of mental status. If the prothrombin time is prolonged by ≈ 4-6 seconds or more (INR ≥1.5)and there is any evidence of altered
sensorium , the diagnosis of ALF should be strongly suspected and hospital admission is mandatory.cite journal |author=Polson J, Lee WM |title=AASLD position paper: the management of acute liver failure |journal=Hepatology |volume=41 |issue=5 |pages=1179–97 |year=2005 |pmid=15841455 |doi=10.1002/hep.20703] Initial laboratory examination must be extensive in order to evaluate both the aetiology and severity.;Initial laboratory analysis
*Prothrombin time /INR
*Complete blood count
*Chemistries
**Liver function test: AST, ALT,alkaline phosphatase ,GGT , totalbilirubin ,albumin
**Creatinine , urea/blood urea nitrogen , sodium, potassium, chloride, bicarbonate, calcium, magnesium, phosphate
**glucose
**Amylase andlipase
*Arterial blood gas , lactate
*Blood type and screen
*Paracetamol (Acetaminophen) level, Toxicology screen
*Viral hepatitis serologies: anti-HAV IgM, HBSAg, anti-HBc IgM, anti-HEV
*Autoimmune markers: ANA, ASMA, LKMA, Immunoglobulin levels
*Ceruloplasmin Level ( when Wilson's disease suspected)
*Pregnancy test (females)
*Ammonia (arterial if possible)
*HIV status (has implication for transplantation)History taking should include careful review of possible exposures to viral infection and drugs or other toxins. From history and clinical examination possibility of underlying chronic disease should be ruled out as it may have different management.
A
liver biopsy done via the transjugular route because ofcoagulopathy is not usually necessary other than in occasional malignancies. As the evaluation continues, several important decisions have to be made such as whether to admit the patient to an ICU, or whether to transfer the patient to a transplant facility. Consultation with the transplant centre as early as possible is critical due to possibility of rapid progression of ALF.Treatment
Treatment involves admission to hospital; often
intensive care unit admission or very close observation are required. Supportive treatment is with adequatenutrition , optimalisation of thefluid balance ,mechanical ventilation andintracranial pressure monitoring (in severe encephalopathy), and treatment aimed at removing the underlying cause (such asacetylcysteine for paracetamol poisoning). Other supportive measures may include the drainage ofascites .While many people who develop acute liver failure recover with supportive treatment,
liver transplant ation is often required in people who continue to deteriorate or have adverse prognostic factors."
Liver dialysis " (various measures to replace normal liver function) is evolving as a treatment modality and is gradually being introduced in the care of patients with liver failure.Prognosis
Historically mortality has been unacceptably high, being in excess of 80%. [cite journal |author=Rakela J, Lange SM, Ludwig J, Baldus WP |title=Fulminant hepatitis: Mayo Clinic experience with 34 cases |journal=Mayo Clin. Proc. |volume=60 |issue=5 |pages=289–92 |year=1985 |pmid=3921780 |doi=] In recent years the advent of liver transplantation and multidisciplinary intensive care support have improved survival significantly. At present overall short term survival with transplant is more than 65%. [cite journal |author=Ostapowicz G, Fontana RJ, Schiødt FV, "et al" |title=Results of a prospective study of acute liver failure at 17 tertiary care centers in the United States |journal=Ann. Intern. Med. |volume=137 |issue=12 |pages=947–54 |year=2002 |pmid=12484709 |doi=]
Several prognostic scoring systems have been devised to predict mortality and to identify who will require early liver transplant. These include kings college hospital criteria, MELD score,
APACHE II andClichy criteria .Terminology
To date no universally accepted nomenclature has been adopted. Trey and Davidson introduced the term "fulminant hepatic failure" in 1970 to describe "potentially reversible condition, the consequence of severe liver injury, with an onset of encephalopathy within 8 weeks of the appearance of the first symptoms and in the absence of pre-existing liver disease". [cite journal |author=Trey C, Davidson CS |title=The management of fulminant hepatic failure |journal=Progress in liver diseases |volume=3 |issue= |pages=282–98 |year=1970 |pmid=4908702 |doi=] Later it was suggested that the term "fulminant" should be confined to patients who develop jaundice to encephalopathy within 2 weeks. Terms "subfulminant" hepatic failure and "late onset" hepatic failure were coined for onset between 2 weeks to 3 months and for 8 weeks to 24 weeks respectively. [cite journal |author=Bernuau J, Goudeau A, Poynard T, "et al" |title=Multivariate analysis of prognostic factors in fulminant hepatitis B |journal=Hepatology |volume=6 |issue=4 |pages=648–51 |year=1986 |pmid=3732998 |doi=10.1002/hep.1840060417] [cite journal |author=Gimson AE, O'Grady J, Ede RJ, Portmann B, Williams R |title=Late onset hepatic failure: clinical, serological and histological features |journal=Hepatology |volume=6 |issue=2 |pages=288–94 |year=1986 |pmid=3082735 |doi=10.1002/hep.1840060222] The umbrella term of "acute liver failure" was proposed by Kings college group which has been adopted in this article. Paradoxically in this classification the best prognosis is in the "hyperacute" group. [cite journal |author=Sass DA, Shakil AO |title=Fulminant hepatic failure |journal=Liver Transpl. |volume=11 |issue=6 |pages=594–605 |year=2005 |pmid=15915484 |doi=10.1002/lt.20435]
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References
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