EVALUATION OF THE LIVER
Clinical Assessment
Detecting liver disease often requires special attention to detail.
The only manifestations may be mild, nonspecific symptoms, such as loss of appetite,
easy fatigability, malaise, altered sleep patterns, or subtle changes in personality.
Even long-standing, severe hepatic disorders may elude detection until peripheral
edema, overt ascites, or encephalopathy develops. The history should probe for causes
of liver disease, including alcoholism, illicit drug use, sexual promiscuity, exposure
to harmful chemicals or toxins, and blood transfusions. It should also seek to identify
clinical features of hepatobiliary disease, including pruritus, abdominal pain, indigestion,
changes in color of the stool or urine, and prior bouts of jaundice (particularly
after anesthesia). Occasionally, it is
TABLE 19-2 -- Flow-dependent versus capacity-limited elimination of drugs by the liver
|
Type of Hepatic Elimination |
Extraction Ratio (ER) |
Rate of Hepatic Drug Metabolism |
|
Flow-dependent elimination |
High ER: At clinically relevant
concentrations, most of the drug in the afferent hepatic blood is eliminated on first
pass through the liver. |
Rapid: Because drugs with a
high ER are metabolized so rapidly, their hepatic clearances roughly equal their
rates of transport to the liver (i.e., hepatic blood flow). |
|
Capacity-limited elimination (also referred to as dose-dependent,
nonlinear, saturable, or zero-order elimination) |
Low ER: The hepatic elimination
of these drugs is determined by their plasma concentration. |
Slow: When the capacity of the
liver to eliminate a drug is less than the dosing rate, a steady state is unachievable;
plasma levels of drug will continue to rise unless the dosing rate is decreased.
Drug clearance has no real meaning in such settings. |
useful to inquire about heritable diseases such as hemochromatosis, α1
-antitrypsin
deficiency, and Wilson's disease. The physical examination should focus on stigmata
of advanced liver disease, including icterus, jaundice, ascites, collateral portal
circulation, spider angiomata, palmar erythema, xanthelasma, encephalopathy, and
fetor hepaticus.
