Hepatic encephalopathy
Hepatic encephalopathy: Excerpt from Professional Guide to Diseases (Eighth Edition)
Hepatic encephalopathy, also known as portosystemic encephalopathy or hepatic coma, is a neurologic syndrome that develops as a complication of chronic liver disease. Most common in patients with cirrhosis, this syndrome is due primarily to ammonia intoxication of the brain. It may be acute and self-limiting or chronic and progressive. Treatment requires correction of the precipitating cause and reduction of blood ammonia levels. In advanced stages, the prognosis is extremely poor despite vigorous treatment.
Causes
Hepatic encephalopathy follows rising blood ammonia levels. Normally, the ammonia produced by protein breakdown in the bowel is metabolized to urea in the liver. When portal blood shunts past the liver, ammonia directly enters the systemic circulation and is carried to the brain. Such shunting may result from the collateral venous circulation that develops in portal hypertension or from surgically created portosystemic shunts. Cirrhosis further compounds this problem because impaired hepatocellular function prevents conversion of ammonia that reaches the liver.
Other factors that predispose rising ammonia levels include excessive protein intake, sepsis, excessive accumulation of nitrogenous body wastes (from constipation or GI hemorrhage), and bacterial action on protein and urea to form ammonia. Certain other factors heighten the brain’s sensitivity to ammonia intoxication: hypoxia, azotemia, impaired glucose metabolism, infection, and administration of sedatives, narcotics, and general anesthetics. Depletion of the intravascular volume, from bleeding or diuresis, reduces hepatic and renal perfusion and leads to contraction alkalosis. In turn, hypokalemia and alkalosis increase ammonia production and impair its excretion.
Signs and symptoms
Clinical manifestations of hepatic encephalopathy vary (depending on the severity of neurologic involvement) and develop in four stages:
❑ In the prodromal stage, early signs and symptoms are commonly overlooked because they’re so subtle: slight personality changes (disorientation, forgetfulness, and slurred speech) and a slight tremor.
❑ During the impending stage, tremor progresses into asterixis (liver flap and flapping tremor), the hallmark of hepatic encephalopathy. Asterixis is characterized by quick, irregular extensions and flexions of the wrists and fingers, when the wrists are held out straight and the hands flexed upward. Lethargy, aberrant behavior, and apraxia also occur.
❑ At the stuporous stage, hyperventilation occurs; the patient is typically stuporous, but becomes noisy and abusive when aroused.
❑ In the comatose stage, the patient has hyperactive reflexes, a positive Babinski’s sign, fetor hepaticus (musty, sweet odor to the breath), and coma.
Diagnosis
CONFIRMING DIAGNOSIS Clinical features, a history of liver disease, and elevated serum ammonia levels in venous and arterial samples confirm hepatic encephalopathy.
Other supportive laboratory values include an EEG that slows as the disease progresses, an increase in spinal fluid glutamine, elevated bilirubin, and prolonged prothrombin time. Recently, evoked potential testing has been advocated as a more specific indicator of encephalopathy, but its benefit over an EEG isn’t yet clear.
Treatment
Effective treatment stops progression of encephalopathy by reducing blood ammonia levels. Treatment includes eliminating ammonia-producing substances from the GI tract by administering neomycin to suppress bacterial flora (preventing them from converting amino acids into ammonia), performing sorbitol-induced catharsis to produce osmotic diarrhea and continuous aspiration of blood from the stomach, and reducing dietary protein intake.
Lactulose, which traps ammonia in the bowel and promotes its excretion, is administered to reduce blood ammonia levels. Bacterial enzymes change lactulose to lactic acid, thereby rendering the colon too acidic for bacterial growth. At the same time, the resulting increase in free hydrogen ions prevents diffusion of ammonia through the mucosa; lactulose promotes conversion of systemically absorbable ammonia to ammonium, which is poorly absorbed and can be excreted. It’s usually given orally. However, if the patient is in a coma, it may be administered by retention enema.
Treatment may also include potassium supplements to correct alkalosis due to increased ammonia levels, especially if the patient is taking diuretics. Hemodialysis may sometimes be used to clear toxic blood temporarily. Salt-poor albumin may be used to maintain fluid and electrolyte balance, replace depleted albumin levels, and restore plasma. Sedatives, tranquilizers, and other medications metabolized or excreted by the liver should be avoided if possible. Medications containing ammonium (including certain antacids) should also be avoided.
Special considerations
Patient care includes monitoring symptoms and support.
❑ Assess and record the patient’s level of consciousness frequently. Continually orient him to place and time. Keep a daily record of his handwriting to monitor the progression of neurologic involvement.
❑ Monitor the patient’s intake, output, and fluid and electrolyte balance. Check daily weight and measure abdominal girth. Watch for, and immediately report, signs of anemia (decreased hemoglobin level), infection, alkalosis (increased serum bicarbonate), and GI bleeding (melena and hematemesis).
❑ If the encephalopathy is acute, ask the dietary department to provide the specified low-protein diet, with carbohydrates supplying most of the calories.
❑ Promote rest, comfort, and a quiet atmosphere. Discourage stressful exercise.
❑ Use restraints, if necessary, but avoid sedatives. Protect the comatose patient’s eyes from corneal injury by using artificial tears or eye patches.
❑ Provide emotional support for the patient’s family in the terminal stage of encephalopathy.
Book Source Details
- Book Title: Professional Guide to Diseases (Eighth Edition)
- Author(s): Springhouse
- Year of Publication: 2005
- Copyright Details: Professional Guide to Diseases (Eighth Edition), Copyright © 2005 Lippincott Williams & Wilkins.
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Copyright notice for book excerpts: Copyright © 2008 Lippincott Williams & Wilkins. All rights reserved.
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