Liver disease

Liver disease is classified by time course and severity.

1. Parenchymal
   1. Acute hepatocellular injury has many etiologies, including viral infection (hepatitis A, B, C, D, and E; Epstein-Barr virus; cytomegalovirus; herpes simplex virus; ECHO virus; and coxsackievirus), drugs, chemicals and poisons (including alcohol, halothane, phenytoin, propylthiouracil, isoniazid, tetracycline, and acetaminophen), and inborn errors of metabolism (e.g., Wilson disease and α₁-antitrypsin deficiency).
   2. Chronic parenchymal disease may be associated with varying degrees of functional impairment. Cirrhosis may result from many insults, including chronic active hepatitis, alcoholism, hemochromatosis, primary biliary cirrhosis, and congenital disorders. End-stage hepatic fibrosis causes significant resistance to portal blood flow, leading to portal hypertension and esophageal varices. Further complications from the combination of portal hypertension and decreased hepatic function include ascites, coagulopathy, gastrointestinal bleeding, and encephalopathy.
2. Cholestasis occurs most frequently in cholelithiasis and acute or chronic cholecystitis. Primary biliary cirrhosis and primary sclerosing cholangitis also begin as cholestatic diseases, ultimately leading to parenchymal damage and liver failure. Hyperbilirubinemia is an important marker for hepatobiliary disease. Unconjugated hyperbilirubinemia is due to excess bilirubin production (e.g., massive transfusion, absorption of large hematomas, or hemolysis) or impaired uptake of unconjugated bilirubin by the hepatocyte (e.g., Gilbert syndrome). Conjugated hyperbilirubinemia generally occurs with hepatocellular disease (e.g., alcoholic or viral hepatitis and cirrhosis), disease of the small bile ducts (e.g., primary biliary cirrhosis and Dubin-Johnson syndrome), or obstruction of the extrahepatic bile ducts (e.g., pancreatic carcinoma, cholangiocarcinoma, and gallstones).

Manifestations of Liver Disease

Manifestations of Liver Disease

1. Central nervous system. Hepatic dysfunction can lead to encephalopathy. Although the exact pathogenesis is unclear, impaired neurotransmission, presence of intrinsic γ-aminobutyric acid–ergic substances, and altered cerebral metabolism may be involved in its pathogenesis. Ammonia levels are often elevated in encephalopathic patients but do not correlate with the severity or outcome of encephalopathy. Signs may vary from sleep disturbances to the presence of asterixis or coma. Patients with severe acute liver failure often present with a rapidly progressive encephalopathy complicated by cerebral edema. Elevated intracranial pressure must be aggressively managed to prevent cerebral ischemia. Extreme hyponatremia or its overly aggressive treatment may lead to fatal central pontine myelinolysis. Changes in mental status and increased sensitivity to sedatives mandate caution in dosing premedications.
2. Cardiovascular system
   1. Patients with advanced liver disease exhibit a hyperdynamic circulatory state with an elevated cardiac output, resting tachycardia, and decreased systemic vascular resistance. Elevated levels of nitric oxide, glucagon, and prostaglandins are thought to be responsible for the arteriolar vasodilation. Arteriovenous shunts, such as spider angiomata in the skin, can be present in almost all vascular beds.
   2. Patients with advanced liver failure also have a reduced effective intravascular volume due to vasodilation and portosystemic shunting. In addition, hypoalbuminemia, increased levels of aldosterone, and inappropriate secretion of antidiuretic hormone all lead to increased total body fluid volume that worsen ascites and edema/anasarca.
   3. Alcoholic cardiomyopathy (ACM) should always be considered in patients with a history of alcohol abuse. ACM is characterized by an increase in myocardial mass, dilation of the ventricles, and wall thinning. Changes in ventricular function may depend on the stage of the disease, in that asymptomatic ACM is associated with diastolic dysfunction, whereas systolic dysfunction is a common finding in symptomatic ACM patients characterized by a dilated left ventricle, normal or reduced left ventricular wall thickness, and increased left ventricular mass.
3. Respiratory system
   1. Airway protection is a major concern in patients with liver disease. Patients with the typical stigmata of advanced disease have ascites (increased abdominal pressure—causing a reduction in functional residual capacity [FRC]) and encephalopathy (altered mental status) which can affect their ability to protect their airway and should be considered at increased risk for aspiration. Definitive airway protection with rapid sequence induction and intubation is frequently advisable when general anesthesia is required.
   2. Chronic hypoxemia results from many causes. Massive ascites and pleural effusions lead to atelectasis and restrictive lung physiology. Diminished hypoxic pulmonary vasoconstriction results in ventilation perfusion mismatch; intrapulmonary shunting can be significant (10% to 40%). Pulmonary hypertension can coexist with portal hypertension and can produce right heart failure. The hepatopulmonary syndrome is a triad of liver disease, increased alveolar–arterial oxygen gradient, and intrapulmonary vascular dilatations. The syndrome of platypnea–orthodeoxia may be seen (postural hypoxemia and dyspnea induced by upright posture) as the presence of a hyperdynamic circulation, and low pulmonary resistance results in the rapid transit of blood through the lungs and potentiates the transit of deoxygenated blood to the systemic circulation. Because of gravity, shifting of blood to the dilated precapillary beds of the lung bases results in an increased hypoxemic dyspnea when the patient is in the upright position.
4. Gastrointestinal system
   1. The increased pressure in the portal system due to increased volume of blood through these vessels or increased resistance (scarring, fibrosis) to portal blood flow results in portal hypertension, splenomegaly, and splanchnic venous congestion. This increases collateral circulation, which is manifested as hemorrhoids, esophageal varices, and dilated abdominal wall veins (caput medusae). Ascites is due to splanchnic venous congestions coupled with hypoalbuminemia and decreased oncotic pressure. Ascites may increase the risk of abdominal wound dehiscence, abdominal wall herniation, and respiratory compromise. Ascites can be managed with diuretics, with careful attention to electrolytes and renal function. If a large volume of ascites is uncontrolled prior to surgery, paracentesis may be advisable. Replacement of ascites with albumin, colloids, or blood products is advisable to reduce the risk of hepatorenal syndrome (HRS).
   2. Variceal bleeding can progress rapidly to hemorrhagic shock. After volume resuscitation, treatment consists of vasopressin, somatostatin, β-adrenergic blockade, sclerotherapy, or endoscopic ligation.
5. Renal system
   1. Intravascular volume depletion may produce prerenal azotemia. The blood urea nitrogen level may be deceptively low because of the liver's inability to synthesize urea from ammonia.
   2. Water and electrolyte balance is complicated by frequent use of diuretics. Metabolic alkalosis, hypokalemia, and hyponatremia (despite total body sodium overload) are common in patients with hepatic disease. Hyponatremia may lead to seizures and worsening of hepatic encephalopathy; caution should be used when treating hyponatremia as rapid correction may lead to central pontine myelinosis. Correction of hyponatremia is typically done with fluid restriction and discontinuation of diuretics.
   3. Hepatorenal syndrome is characterized by increased renal vascular resistance, oliguria, and renal failure in the presence of hepatic failure. The sequelae include decreased renal blood flow, sodium retention, and increased sensitivity to nonsteroidal anti-inflammatory medications. Normal renal function returns after liver transplantation or if liver failure resolves.
6. Coagulopathy is caused by several factors.
   1. Synthesis of clotting factors (II, VII, IX, and X) as well as that of endogenous anticoagulants (proteins C, S, and Z) is impaired in liver failure.
   2. Cholestasis causes impaired absorption of fat and fat-soluble vitamins (A, D, E, and K). Vitamin K, produced in the intestinal mucosa, is an important cofactor in the synthesis of clotting factors II, VII, IX, and X.
   3. Thrombocytopenia secondary to hypersplenism, alcohol-induced bone marrow failure, and consumption is frequently seen.
   4. Preoperative correction of clotting abnormalities with fresh frozen plasma (FFP) or vitamin K should be performed as necessary. In emergency situations, vitamin K should be avoided due to its prolonged time of onset (approximately 8 hours). In these situations, FFP can be administered, and cryoprecipitate, DDAVP, factor VIIa, and platelets should be considered for refractory situations. Regional anesthesia may not be appropriate in the setting of liver failure or anticipated liver failure. The potential for postoperative coagulopathy should be taken into account before placing an epidural. Invasive monitoring can help evaluate and guide volume status. The importance of adequate venous access for intraoperative infusion of crystalloid, colloid, blood products, and vasoactive drugs should not be underestimated.
7. Nutritional deficiency, as manifested by the forms of protein–energy malnutrition marasmus and kwashiorkor, can be part of liver disease, especially in alcoholics. Nutritional deficiency is a risk factor for increased morbidity and mortality postoperatively and should be treated with supplementation high in carbohydrate/lipid content and low in amino acid content to prevent worsening of hepatic encephalopathy. Nutritional supplementation is especially important in alcoholics and should include vitamin B₁ supplementation. If surgery is not urgent, nutritional status should be optimized preoperatively.
8. Glycemic control depends heavily on the liver. Hypoglycemia may occur in end-stage hepatic insufficiency, during the anhepatic phase of liver transplantation, or in liver failure that may accompany an episode of severe circulatory shock. Close monitoring of blood glucose levels should be performed frequently, and glucose-containing solutions should be administered as necessary. Severe hepatic insufficiency leads to diminished glycogen stores, requiring gluconeogenesis to maintain normoglycemia. Gluconeogenesis is also impaired in severe liver disease and alcoholism.

Outline

• Hepatic Anatomy
• Hepatic Function
• Metabolism of Anesthetics
• Liver Disease
• Surgical Risk in Patients with Liver Disease
• Anesthesia in Patients with Liver Disease
• Postoperative Liver Dysfunction
• Suggested Readings