Cerebral oedema and increased intracranial pressure in chronic liver disease

Acute changes in cerebral blood flow and metabolism during portasystemic shunting

This report describes the instantaneous changes in cerebral blood flow (CBF), determined by intravascular ultrasound and Doppler, in a patient with cirrhosis undergoing placement of a transjugular intrahepatic stent-shunt for uncontrolled variceal bleeding. Acute changes in CBF were observed during and after portasystemic shunting, which culminated in cerebral edema and cerebral herniation.

Diagnosis and treatment of hepatic encephalopathy

Hepatic encephalopathy arises from the combination of hepatocellular dysfunction and portal-systemic shunting. Encephalopathy is more prominent in advanced stages of liver cirrhosis and signals the presence of fulminant hepatic failure in patients with acute liver injury. As important as the extent of shunting is the presence of large spontaneous collaterals. Ammonia continues to be a leading toxin influencing brain function. Endogenous benzodiazepines and cytokines may contribute to one of ammonia's key effects in the brain: astrocyte swelling. The diagnosis of hepatic encephalopathy is a diagnosis of exclusion; the search for a precipitating factor should be started immediately in all cases of encephalopathy. The treatment of hepatic encephalopathy has three aims: decrease the nitrogenous load from the gut, improve the extra-intestinal elimination of ammonia and counteract central abnormalities of neurotransmission. The mainstay of treatment is directed at the colon. Newer approaches targeting the brain, such as flumazenil, have become available.

Detection and monitoring of intracranial pressure dysregulation in liver failure by ultrasound

BACKGROUND

Development of elevated intracranial pressure (ICP) in hepatic failure indicates poor prognosis. Its detection by invasive methods poses methodological problems. We applied ultrasound studies of the optic nerves to noninvasively estimated ICP status.

METHODS

A total of 22 pediatric patients with hepatic failure were examined by serial B scan ultrasound and followed up clinically. Outcome was scored as survival or death due to multiorgan failure (MOF) or raised ICP. In 18 patients, transplantations were performed.

RESULTS

Four patients died before transplantation was possible (raised ICP: n=3, MOF: n=1). After OLT there were 10 survivors and 8 patients died (MOF: n=3, raised ICP: n=5). In 10 patients we found optic nerve sheath diameter (ONSD) above normal limits. Eight patients died, mostly because of raised ICP (n=7). Only 2 of the 10 survivors experienced a transient ONSD increase, steadily normalized after transplantation. Preoperatively, normal ONSD was detected in four of seven patients. The outcome of these four cases was clearly superior (three survivors and one MOF) compared with abnormal pre-OLT ultrasound findings (raised ICP: n=3).

CONCLUSION

Patients with poor prognosis related to raised ICP in pediatric liver failure can be identified by ultrasound measurement of ONSD without the disadvantages of invasive procedures. Although the exact intracranial pressure level cannot be deduced from single examinations, ONSD trends can reflect the evolution of ICP in hepatic encephalopathy.

Cerebral perfusion, cardiac output, and arterial pressure in patients with fulminant hepatic failure

OBJECTIVE

To evaluate whether changes in cardiac output influence cerebral perfusion directly. In fulminant hepatic failure, the circulation is characterized by wide variations in cardiac output and cerebral blood flow (CBF).

DESIGN

A retrospective, interindividual analysis of CBF and cardiac output (part 1) and a prospective evaluation of cerebral perfusion, cardiac output, and arterial pressure during norepinephrine infusion (part 2).

SETTING

A four-bed specialist liver failure unit.

PATIENTS AND INTERVENTIONS

Twenty patients with fulminant hepatic failure (median age, 43 yrs; range, 17-54; 13 women) maintained on mechanical ventilation (Paco2, 33 torr [4.40 kPa]; range, 26-36 torr [3.47-4.80 kPa) after development of hepatic encephalopathy, stages 3 to 4, had mean arterial pressure (MAP) and cardiac output determined by radial and pulmonary artery catheters. Cerebral perfusion was measured by the 133Xenon clearance technique (n = 8) and by transcranial Doppler sonography, which was used to measure mean flow velocity (Vmean). CBF and Vmean in patients with high cardiac output (>9 L/min) were compared with those with normal or low cardiac output. In the second part of the study, cerebral autoregulation was evaluated by concomitant measurement of Vmean, cardiac output, and MAP during norepinephrine infusion in nine patients.

MEASUREMENTS AND MAIN RESULTS

Median cardiac output was 8.5 L/min (range, 3.2-17.3), CBF was 33 mL/100 g/min (12-77 g/min), and Vmean was 45 cm/sec (22-65 cm/sec). In patients with elevated cardiac output, MAP, Vmean, and CBF were similar compared with patients with normal cardiac output. Neither CBF nor Vmean correlated to cardiac output. During norepinephrine infusion, Vmean increased from 49 cm/sec (34-69 cm/sec) to 63 cm/sec (58-90 cm/sec; p < .05), as MAP increased from 75 mm Hg (54-105 mm Hg) to 97 mm Hg (90-128 mm Hg). On average, cardiac output remained unchanged at 5.7 L/min (range, 3.2-17.3), as it increased in five patients and decreased in four patients. The change in Vmean was related to MAP (r2 = .76; p < .01) but not to cardiac output (r2 = .01).

CONCLUSION

This study shows that CBF correlates to arterial pressure rather than to cardiac output in patients with fulminant hepatic failure. The presence of pressure-passive cerebral circulation stresses the importance of strict cardiovascular control in securing continuous and sufficient cerebral oxygenation and in avoiding the development of cerebral hyperemia and cerebral edema.

Partial pressure of ammonia versus ammonia in hepatic encephalopathy

Ammonia is considered the major pathogenetic factor of cerebral dysfunction in hepatic failure. The correlation between total plasma ammonia and the severity of hepatic encephalopathy (HE), however, is variable. Because ammonia that is present in gaseous form readily enters the brain, the correlation with the grade of HE of the pH-dependent partial pressure of gaseous ammonia (pNH(3)) could be better than that of total arterial ammonia levels. To test this hypothesis, 56 cirrhotic patients with acute episodes of clinical HE (median age, 54 years; range, 21-75) were studied by clinical examination and by long-latency median-nerve sensory-evoked potentials (SEPs) N70 peak, an objective and sensitive electrophysiological measure of HE. pNH(3) was calculated from arterial blood according to published methods. The clinical grade of HE correlated (P <.001) with both pNH(3) and total ammonia, but correlation was stronger with pNH(3) (r =.79 vs.69, P =.01). A similar correlation was found for N70 peak latency (r =.71 with pNH(3) vs.64 with total ammonia, respectively, P =.08). In summary, arterial pNH(3) correlates more closely than total ammonia with the degree of clinical and electrophysiological abnormalities in HE. These findings support the ammonia hypothesis of HE and suggest that pNH(3) might be superior to total ammonia in the pathophysiological evaluation of HE.

Portal hypertension

Cirrhosis represents the end stage of any chronic liver disease. Two major syndromes result from cirrhosis: portal hypertension and hepatic insufficiency. Additionally, vasodilatation and the hyperdynamic circulation are hemodynamic abnormalities typical of cirrhosis and portal hypertension. Complications of cirrhosis occur as a consequence of a combination of these factors. Gastroesophageal varices result almost solely from portal hypertension, although the hyperdynamic circulation contributes to variceal growth and hemorrhage. Ascites results from sinusoidal hypertension and sodium retention, which is, in turn, secondary to vasodilatation and activation of neurohumoral systems. Hyponatremia and the hepatorenal syndrome result from water retention and renal vasoconstriction, respectively, both of which are also consequences of peripheral vasodilatation. Vasodilatation that occurs in the pulmonary circulation leads to the hepatopulmonary syndrome. Another complication of cirrhosis, portosystemic encephalopathy, is a consequence of both portal hypertension (shunting of blood through portosystemic collaterals) and hepatic insufficiency. This paper reviews the recent advances in the pathophysiology and management of the complications of cirrhosis and portal hypertension.

Mild hypothermia modifies ammonia-induced brain edema in rats after portacaval anastomosis

BACKGROUND & AIMS

The pathogenesis of brain edema in fulminant hepatic failure is still unresolved. Mild hypothermia (33 degrees-35 degreesC) can ameliorate brain edema after traumatic brain injury. We evaluated mild hypothermia in a model of ammonia-induced brain edema in which accumulation of brain glutamine has been proposed as a key pathogenic factor.

METHODS

After portacaval anastomosis, anesthetized rats were infused with ammonium acetate at 33 degrees, 35 degrees, and 37 degreesC or vehicle at 37 degreesC. Water and glutamine levels in the brain, cardiac output, and regional and cerebral hemodynamics were measured when intracranial pressure increased 3-4-fold (ammonia infusion at 37 degrees) and matched times (other groups).

RESULTS

Mild hypothermia reduced ammonia-induced brain swelling and increased intracranial pressure. Brain glutamine level was not decreased by hypothermia. Brain edema was accompanied by a specific increase in cerebral blood flow and oxygen consumption, which were normal in both hypothermic groups. When the ammonia infusion was continued in hypothermic rats, plasma ammonia levels continued to increase and brain swelling eventually developed.

CONCLUSIONS

Mild hypothermia delays ammonia-induced brain edema. In this model, an increase in cerebral perfusion is required for brain edema to become manifest. Mild hypothermia could be tested for treatment of intracranial hypertension in fulminant hepatic failure.

Early complications after orthotopic liver transplantation

The cost and impact of early post-transplant complications continue to be high. Diagnosis and management involves a high index of suspicion, rapid diagnostic and therapeutic interventions, and elimination of technical problems. Preoperative assessment of the donor and recipient medical condition and meticulous attention to detail during the technical performance of OLTx are the mainstays in achieving a good outcome.

Chronic hyponatremia exacerbates ammonia-induced brain edema in rats after portacaval anastomosis

BACKGROUND/AIM

Abnormalities in brain organic osmolytes are associated with hepatic encephalopathy and with chronic hyponatremia. In spite of the high frequency of hyponatremia in acute and chronic hepatic failure, its role in the development of neurological complications in liver disease is poorly understood. We aimed to study the effect of prior hyponatremia on the development of ammonia-induced brain edema in rats after portacaval anastomosis. In this model, brain swelling is mediated in part through an increase in brain glutamine, an organic osmolyte.

METHODS

Hyponatremia was induced in rats with 1-desamino-8-D-arginine vasopressin (DDAVP) administered through an osmotic minipump for 1 week. This was followed by performance of a portacaval anastomosis and ammonia infusion. At the end of the infusion, brain water (density gradient) and key brain organic osmolytes (HPLC) were measured.

RESULTS

Rats with hyponatremia showed a decrease in all three brain organic osmolytes measured: glutamine, myo-inositol and taurine. Hyperammonemia resulted in the expected rise in glutamine, with a reduction of myo-inositol and taurine. In the combined group (hyponatremia plus hyperammonemia), the rise in brain glutamine induced by ammonia infusion was attenuated (10.6+/-0.9 mM/kg vs. 15.5+/-0.8 mM/kg hyperammonemia alone; p<0.05). In spite of this limited rise in brain glutamine, ammonia infusion to hyponatremic rats exacerbated brain swelling (82.3+/-0.3% vs. 80.6+/-0.1%; p<0.05).

CONCLUSIONS

Hyponatremia worsens brain swelling in a model of ammonia-induced brain edema. The decrease in the concentration of brain organic osmolytes induced by hyponatremia does not protect the brain from the development of ammonia-induced brain edema.