Table 22.21 Child’s Classification of Liver Dysfunction was originally designed to predict mortality following portosystemic shunt surgery. It divides patients into three classes of severity based on five easily assessed clinical parameters. Measurement of prothrombin time may be helpful in patients with significant histories of liver disease. If a history of hepatitis is ascertained, the patient should be tested for serum aminotransferase, alkaline phosphatase, bilirubin, albumin levels, and prothrombin time. Serologic documentation of hepatitis is important. If a patient has a known malignancy, biochemical testing of the liver may be of some benefit as a screen for metastatic disease, although this was not proven conclusively.
Anesthesia With few exceptions, most anesthetic agents, including those administered by epidural or spinal routes, reduce hepatic blood ﬂow and decrease oxygenation of the liver. Other perioperative factors—hemorrhage, intraoperative hypotension, hypercarbia, congestive heart failure, and intermittent positive pressure ventilation, especially in critically ill patients—lead to decreased hepatic perfusion and hypoxia (268).
Drug Metabolism Patients with altered liver function should be carefully monitored because of the prolonged action of many medications used during surgery. In addition to impaired metabolism, hypoalbuminemia decreases drug binding, which alters serum levels and biliary clearance rates. The degree of hepatic metabolism varies greatly, depending on the type of medication considered. For inhalation anesthetics, isoﬂurane is preferred because it undergoes minimal hepatic metabolism in comparison with halothane or enﬂurane. Narcotics, induction agents, sedatives, and neuromuscular blocking agents all undergo abnormal metabolism in patients with decompensated liver disease. Diazepam, meperidine, and phenobarbital cause prolonged depression of consciousness and may precipitate hepatic encephalopathy because of their altered rates of clearance. Sufentanil and fentanyl are the preferred narcotics. Oxazepam, a benzodiazepine that does not undergo hepatic metabolism, is considered safe. Muscle relaxants, such as D-tubocurarine, pancuronium, and vecuronium, cause prolonged neuromuscular blockade in patients with impaired liver function and are not ideal drugs to use in this situation. Atracurium is not metabolized by the liver and is the preferred muscle relaxant for patients with abnormal hepatic function. Succinylcholine metabolism is prolonged in patients with hepatic dysfunction and must be used with great caution (269).
Determination of Operative Risk