12. LIVER DISEASE

Hepatic failure may be acute or chonic. Causes of acute hepatic failure include viral hepatitis, shock, drugs (e.g. paracetamol, halothane, chloroform, chlorpromazine, phenytoin) and poisons. Causes of chonic hepatic failure include autoimmune hepatitis, viral hepatitis, drugs (e.g. methyldopa, alcohol), metabolic diseases (e.g. haemochomatosis), biliary disease and cardiac failure.

When a patient has liver failure he or she will have many changes in their health, which will affect anaesthesia.

Preoperative Assessment

The liver has many functions including the production of plasma proteins, clotting factors and plasma cholinesterase. The liver is a site of gluconeogenesis, bilirubin metabolism, drug metabolism and detoxification. Depending on the severity of the liver failure other organs may be affected.

Reduced detoxification of toxic waste products will cause neurological impairment. This may range from mild to marked confusion or coma. As liver failure patients also have an increased sensitivity to sedatives due to reduced liver metabolism, the dosages of sedative drugs must be reduced. The patients with impaired consciousness are also at risk of gastric aspiration especially if they also have ascites. They may need treatment to prevent aspiration and undergo rapid sequence intubation of the trachea.

Patients with liver failure have decreased levels of albumin, increased levels of aldosterone and antidiuretic hormone which all lead to increased total body water (e.g. ascites, oedema, pleural effusion) but they usually have a reduced intravascular volume. Their cardiac output is usually increased as a result of decreased systemic vascular resistance. They are usually hyponatraemic, hypokalaemic and have a metabolic acidosis. There may be poor gas exchange (ventilation/perfusion mismatch) in the lungs resulting in low levels of oxygen in the blood. Patients with liver failure may also have renal failure (hepatorenal syndrome). Coagulation defects occur for several reasons. There is decreased production of clotting factors, decreased absorption of vitamin K (which is an important factor in the production of factors II, VII, IX, and X) and thombocytopenia. Hypoglycaemia may occur in liver failure.

The risk of complications and death depends on the severity of the liver disease and the type of surgery. The severity of the liver disease can be estimated by a modified Child’s classification.

Child’s Classification

Anaesthetic Management

Patients undergoing emergency surgery, or with a prothombin time greater than 2.5 times normal despite treatment, or hepatorenal syndrome or severe liver failure, are at a greater risk of death. Patients at high risk should not have elective surgery.

The anaesthetist must take a full history and examination. Appropriate investigations include liver function tests, renal function test, sodium, potassium, clotting profile, chest X-ray, electrocardiogram, blood glucose and blood gases if available. They should aim to correct any complications of liver failure. In particular they should correct hypovolaemia and coagulation and electrolyte abnormalities. Care must be taken to prevent aspiration. Regional anaesthesia may be contraindicated if coagulation changes cannot be corrected. In general the effects of all drugs will be greater and prolonged, so the anaesthetist may need to reduce drug dosages.