PORTOSYSTEMIC Medical Assignment Help

ENCEPHALOPATHY

The term portosystemic encephalopathy refers to a chronic neuropsychiatric syndrome secondary to chronic liver disease. This condition occurs with cirrhosis, but a similar acute encephalopathy can occur in acute FHF. PSE is seen in patients with portal hypertension due to spontaneous ‘shunting’ or in patients following a portocaval shunt operation. Encephalopathy is potentially reversible. The mechanism is unknown but several factors are thought to playa part. In cirrhosis, the blood bypasses the liver via the collaterals and the ‘toxic’ metabolites pass directly to the brain to produce the encephalopathy. Many ‘toxic’ substances have been suggested as the causative factor, including ammonia, free fatty acids, mercaptans and accumulation of false neurotransmitters (octopamine) or activation of the y-aminobutyric acid (GABA) inhibitory neurotransmitter system. Increased blood levels of aromatic amino acids (tyrosine and phenylalanine) and reduced branched-chain amino acids (valine, leucine and isoleucine) also occur. Nevertheless, ammonia seems to playa major role. Ammonia is produced by the breakdown of protein by intestinal bacteria and a high blood ammonia is seen in most patients. It may alter the blood-brain barrier and allow ‘toxins’ to interfere with cerebral metabolism. The factors that can precipitate PSE are shown.

CLINICAL FEATURES

An acute onset often has a precipitating factor . The patient becomes increasingly drowsy and comatose.
Chronically, there is a disorder of personality, mood and intellect, with a reversal of normal sleep rhythm. These changes may be fluctuating and a history from a relative must be obtained. The patient is irritable, confused, disorientated and has slow slurred speech. General features include nausea, vomiting and weakness. Convulsions and coma occur as the encephalopathy becomes more marked. Hyperventilation and pyrexia are seen. Signs include fetor hepaticus (a sweet smell to the breath) and a coarse flapping tremor seen when the hands are outstretched and the wrists hyperextended (asterixis). There is a constructional apraxia and the patient cannot write or draw, for example a five-pointed star. Mental function can be assessed by using the serial-sevens test (see p. 960). A trail-making test (the ability to join numbers and letters with a pen within a certain time-a standard psychological test for brain dysfunction) is prolonged and is a useful bedside test to assess encephalopathy.
Diagnosis is clinical and routine liver biochemistry merely confirms the presence of liver disease, not the presence of encephalopathy.
Additional investigations include:

ELECTROENCEPHALOGRAM (EEG). This shows a decrease in the frequency of the normal ex waves (8- 13 Hz) to S waves (1.5-3 Hz). These changes occur before coma supervenes.
VISUAL EVOKED RESPONSES also detect subclinical encephalopathy.
ARTERIAL BLOOD AMMONIA. This is occasionally useful in the differential diagnosis of the cause of the coma and to follow the course of the PSE, but is not readily available.

Factors precipitating portosystemic epha lopathy.

Factors precipitating portosystemic epha lopathy.

ELECTROENCEPHALOGRAM (EEG). This shows a decrease in the frequency of the normal ex waves (8- 13 Hz) to S waves (1.5-3 Hz). These changes occur before coma supervenes.
VISUAL EVOKED RESPONSES  also detect subclinical encephalopathy.
ARTERIAL BLOOD AMMONIA. This is occasionally useful in the differential diagnosis of the cause of the coma and to follow the course of the PSE, but is not readily available.

MANAGEMENT

Management consists of restricting protein intake and sterilizing the bowel. Immediate IDENTIFY AND REMOVE THE POSSIBLE PRECIPITATING CAUSE, e.g. drugs with cerebral depressant properties. GIVE PURGATION AND ENEMAS to empty the bowels of nitrogenous substances. Lactulose (10-30 ml three times daily) is an osmotic purgative that reduces the colonic pH and limits ammonia absorption. Lactilol (J3-galactoside sorbitol 30 g daily) is metabolized by colonic bacteria and is comparable in efficacy to lactulose. Hypernatraemia can result from water loss.
INSTITUTE A PROTEIN-FREE DIET, with adequate calories, given if necessary via a fine-bore nasogastric tube.
ANTIBIOTICS. Oral neomycin 1 g 6-hourly can be used if lactulose fails. Neomycin can also be used in retention enemas. It is mainly unabsorbed, but in the long term it can produce deafness. Metronidazole (200 mg four times daily) is also effective in the acute situation.
STOP OR REDUCE DIURETIC THERAPY.
CORRECT ANY ELECTROLYTE IMBALANCE.
GIVE INTRAVENOUS FLUIDS as necessary (beware of too much sodium).

TREAT ANY INFECTION.

FLUMAZENIL, a benzodiazepine receptor antagonist, can induce a transient improvement; controlled trials are in progress.
Long term.
INCREASE PROTEIN IN THE DIET to the limit of tolerance (20-50 g) as the encephalopathy improves. AVOID CONSTIPATION.
GIVE LACTULOSE 10-30 ml three times daily.
AVOID PRECIPITATING FACTORS, e.g. narcotic drugs,
which depress cerebral function, overdiuresis producing electrolyte imbalance.

COURSE AND PROGNOSIS

Acute encephalopathy, often seen after FHF, has a very poor prognosis as the disease itself has a high mortality. In cirrhosis, chronic PSE is very variable and the prognosis is that of the underlying liver disease. Renal failure (hepatorenal syndrome).
The hepatorenal syndrome occurs typically in a patient with advanced cirrhosis with jaundice and ascites. The urine output is low with a low urinary sodium concentration, a residual capacity to concentrate urine (i.e. tubular function is intact) and an almost normal renal histology. The renal failure here is described as ‘functional’. This is often precipitated by overvigorous diuretic therapy, diarrhoea or paracentesis, but often no precipitating factor is found. Advanced cases may progress beyond the ‘functional’ stage to produce an acute tubular necrosis. The mechanism is similar to that producing ascites. The initiating factor is thought to be extreme peripheral vasodilation possibly due to nitric oxide, leading to an extreme decrease in the arterial blood volume and hypotension. This activates the homeostatic mechanisms causing a rise in plasma renin, aldosterone, noradrenaline and vasopressin leading to vasoconstriction of the renal vasculature. There is an increased preglomerular vascular resistance causing the blood flow to be directed away from the renal cortex. This leads to a reduced glomerular filtration rate and plasma renin remains high. Salt and water retention occur with reabsorption of sodium from the renal tubules. A number of other mediators have been incriminated in the pathogenesis of the hepatorenal syndrome, in particular the eicosanoids. This has been supported by the precipitation of the syndrome by inhibitors of prostaglandin synthetase such as non-steroidal antiinflammatory agents.
The patient should be treated for prerenal failure and diuretic therapy should be stopped. The prognosis is poor.

Posted by: brianna

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