Hepatic disease may affect the hepatocytes and/or the biliary tract. The former include hepatitis (most commonly viral, alcoholic, or autoimmune) and hepatocellular carcinoma. The latter includes choledocholithiasis, primary biliary cirrhosis, primary sclerosing cholangitis, and tumors of the bile ducts. Drug-induced liver disease tends to overlap both categories.
Hepatic disease adds a number of challenges to the risks of surgery and anesthesia. One must account for both preexisting liver disease as well as asymptomatic undiagnosed liver disease. Metabolism and excretion of anesthetics and other medications may be impaired. Medication distribution may also be affected due to the decrease in albumin and alterations in protein binding. Certain medications may affect liver blood flow or cause direct hepatotoxicity. End-stage liver disease adds additional considerations including esophageal varices, ascites, and decreased inotropic and chronotropic response to stress.
ASSESSING SEVERITY OF HEPATIC DISEASE
There are two primary methods for grading the severity of hepatobiliary disease:
Child–Turcotte–Pugh (CTP) Score—The CTP score was the first grading system for liver disease (Table 83-1). Scores fall under Class A (mild, 5–6 points), Class B (moderate, 7–9 points), and Class C (severe, 10–15 points). Although this system has not been prospectively validated, CTP scores have been widely used for assessing the severity of liver disease and predicting morbidity and mortality from surgery. However, the subjective nature of the clinical parameters and arbitrary laboratory value cutoffs limit the accuracy of the CTP score in predicting surgical risk.
Model for End-Stage Liver Disease (MELD)—The MELD score has been prospectively validated as a prognostic marker for mortality in patients with cirrhosis, acute variceal bleeding, or acute alcoholic hepatitis. Scores range from <10 (low risk), 10–15 (intermediate risk), to >15 (high risk). The equation to calculate the MELD score uses three major variables:
++ Table Graphic Jump Location TABLE 83-1Child–Turcotte–Pugh Scoring System for Liver Disease ||Download (.pdf) TABLE 83-1 Child–Turcotte–Pugh Scoring System for Liver Disease
|Clinical Trait ||1 Point ||2 Points ||3 Points |
|Ascites ||None ||Present ||Moderate/severe |
|Encephalopathy ||None ||Grade 1–2 ||Grade 3–4 |
|Bilirubin (mg/dL) ||<2 ||2–3 ||>3 |
|Albumin (g/dL) ||>3.5 ||2.8–3.5 ||<2.8 |
|INR ||<1.7 ||1.7–2.3 ||>2.3 |
Severity of hepatic disease may also be assessed via liver scintigraphy (99mTc-galactosyl-labeled human serum albumin), indocyanine-green retention test, aminopyrine breath test, and measurement of lidocaine metabolite monoethylglycinexylidide. These approaches are rarely used other than for assessing hepatic reserve for potential liver resection.
Both the CTP and MELD scores are helpful in predicting surgical mortality in patients with liver disease (Table 83-2). The most severe categories of the CTP and MELD scores indicate high risk. Patients with the highest risk for any type of surgery have CTP Class C, MELD > 15, acute liver failure, acute alcoholic hepatitis, or high serum bilirubin (>11 m/dL).