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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 are hepatic encephalopathy and impaired protein synthesis (as measured by the levels of serum albumin and the prothrombin time in the blood). The 1993 classification defines hyperacute as within 1 week, acute as 8-28 days and subacute as 4-12 weeks. It reflects the fact that the pace of disease evolution strongly influence prognosis. Underlying aetiology is the other significant determinant of outcome.
Additional recommended knowledge
Common causes for acute liver failure are paracetamol (acetaminophen) overdose, idiosyncratic reaction to medication (e.g. tetracycline, troglitazone), excessive alcohol intake (severe alcoholic hepatitis), viral hepatitis (hepatitis A or B - it is extremely uncommon in hepatitis 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 that aspirin use may play a significant role. Wilson's disease (hereditary copper accumulation) may infrequently present with acute liver failure.
In the majority of acute liver failure (ALF) there is widespread hepatocellular necrosis beginning in the centrizonal distribution and progressing towards portal tracts. The degree of parenchymal inflammation is variable and is proportional to duration of disease.
Cerebral oedema and encephalopathy
In ALF, cerebral oedema leads to hepatic encephalopathy, coma, brain herniation and eventually death. Detection of encephalopathy is central to the diagnosis of ALF. It may vary from subtle defecit in higher 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. The pathogenesis remains unclear but is likely to be a consequence of several phenomenon. There is a build up of toxic substances like ammonia, mercaptan, endogenous benzodiazepines and serotonin/tryptophan in the brain. This affects neurotransmitter level and neuroreceptor activation. Autoregulation of cerebral blood flow is impaired and is associated with anaerobic glycolysis and oxidative stress. Neuronal cell astrocytes are susceptible to these changes and they swell up, resulting in increased intracranial pressure. Inflammatory mediators also play important role.
Unfortunately, signs of elevated intracranial pressure such as papilloedema and loss of pupillary 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 possible benefit (1% fatal haemorrhage). The aim is to maintain intracranial pressures below 25 mmHg, cerebral perfusion pressures above 50 mm Hg.
Coagulopathy is another cardinal feature of ALF. Liver has central role in synthesis of almost all coagulation factors and some inhibitors of coagulation and fibrinolysis. Hepatocellular necrosis leads to impaired synthesis of many coagulation factors and their inhibitors. the former produces a prolongation in Prothrombin time which is widely used to monitor severity of hepatic injury.There is significant platelet dysfunction (with both quantitative and qualitative platelet defects). Progressive thrombocytopenia with loss of larger and more active platelet is almost universal. Thrombocytopenia with or without DIC increases risk of intracerebral bleeding.
Renal failure is common, present in more than 50% of ALF patients, either due to original insult such as paracetamol resulting in acute tubular necrosis or from hyperdynamic circulation leading to hepatorenal syndrome or functional 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. 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 to gram positive organisms and fungal sepsis are observed in up to 80% and 30% patients respectively.
Hyponatraemia is almost universal finding due to water retention and shift in intracellular sodium transport from inhibition of Na/K ATPase. Hypoglycaemia (due to depleted hepatic glycogen store and hyperinsulinaemia), hypokalaemia, hypophosphataemia and Metabolic 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 low systemic vascular resistance leads to hypotension. There is a compensatory increase in cardiac output. Adrenal insufficiency has been documented in 60% of ALF and is likely to contribute in haemodynamic compromise. There is also abnormal oxygen 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.
Pulmonary complications occur in up to 50% patients. Severe lung injury and hypoxemia result in high mortality. Most cases of severe lung injury is due to ARDS with or without sepsis. Pulmonary haemorrhage, pleural effusions, atelectasis, and intrapulmonary shunts also contribute to respiratory difficulty.
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. Initial laboratory examination must be extensive in order to evaluate both the aetiology and severity.
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 of coagulopathy 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 involves admission to hospital; often intensive care unit admission or very close observation are required. Supportive treatment is with adequate nutrition, optimalisation of the fluid balance, mechanical ventilation and intracranial pressure monitoring (in severe encephalopathy), and treatment aimed at removing the underlying cause (such as acetylcysteine for paracetamol poisoning). Other supportive measures may include the drainage of ascites.
While many people who develop acute liver failure recover with supportive treatment, liver transplantation 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.
Historically mortality has been unacceptably high, being in excess of 80%. 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%.
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 and Clichy criteria.
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". 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. 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.
Categories: Organ failure | Hepatology
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Acute_liver_failure". A list of authors is available in Wikipedia.|