Renal sodium retention complicating alcoholic liver disease: relation to portosystemic shunting and liver function

Arterial ammonia levels in cirrhosis are determined by systemic and hepatic hemodynamics, and by organ function: a quantitative modelling study

BACKGROUND & AIMS

Hyperammonaemia is a common complication of chronic liver failure. Two main factors are thought to underlie this complication: a loss of hepatic detoxification function and the development of portosystemic shunting. However, few studies have tried to quantify the importance of portosystemic shunting. Here, we used a theoretical approach to test the hypothesis that the development of portosystemic shunting is sufficient to cause hyperammonaemia in cirrhosis.

METHODS

Two mathematical models are developed. The first one describes the main vascular resistances of the circulation and is used to provide scenarios for the distributions of organ blood flow in cirrhosis, which are necessary to run the second model. The second model predicts arterial ammonia levels resulting from ammonia metabolism in gut, liver, kidney, muscle and brain, and the distribution of organ blood flow.

RESULTS

The fraction of gastrointestinal blood flow shunted through collaterals was estimated to be 41% in mild cirrhosis, 69% in moderate and 85% in severe cases. In the second model, the redistribution of organ blood flow associated with severe cirrhosis was sufficient to cause hyperammonaemia, even when the hepatic detoxification function and the ammonia production were set to normal.

CONCLUSIONS

The model indicates that the development of portosystemic shunting in cirrhosis is sufficient to cause hyperammonaemia. Interventions that reduce the fraction of shunting may be future targets of therapy to control severity of hyperammonaemia.

Noninvasive evaluation of liver disease severity

In assessing the severity of chronic liver disease, one measures either the fibrotic structure of the liver or liver function. This article reviews the methods for evaluating the severity of liver disease noninvasively by estimating function or structure.

Pathogenesis of ascites and predictors of resistance to therapy

Ascites is one of the most frequent complications of cirrhosis. Its appearance is considered as the marker of the transition from the compensated to the decompensated stage of the disease. Appearance of ascites also has prognostic significance, as it causes a sharp drop in the expected survival rate. Portal hypertension is a sine qua-non for the development of ascites. Although no precise portal pressure threshold has been defined for the development of ascites, the latter rarely develops with portal pressures below 12 mmHg. In addition, in patients treated with interventions that markedly decrease portal pressure, such as surgical porta-caval shunts or transjugular intrahepatic portalsystemic shunts, a disappearance or a marked reduction of ascites can be observed. The currently most accepted theory of ascites formation is the so-called 'forward' theory. According to this theory, the development of ascites is related to the presence of severe sinusoidal portal hypertension, which causes marked splanchnic arterial vasodilation and a forward increase in the splanchnic production of lymph. Splanchnic arterial vasodilation also causes a significant reduction of the effective blood volume, leading to activation of sodium and water-retaining mechanisms. The retained sodium and water, however, while increasing total plasma volume, are unable to compensate for the reduced effective blood volume, initiating a vicious cycle. In the advanced stages of cirrhosis, the extreme underfilling of the arterial circulation leads to a maximal stimulation of the vasoconstrictor mechanisms which override the protective effect of renal vasodilator factors and cause renal vasoconstriction, further aggravating ascites and leading to functional renal insufficiency. Renal insufficiency is also one of the main causes of resistance to diuretic therapy. While several studies have investigated the predictors of survival in cirrhotic patients with ascites, this has not been done for the occurrence of resistance to therapy. However, as the mechanisms of refractoriness are associated with advanced disease and short survival, the models developed for predicting survival should be employed also to verify if they can exert such additional prediction.

The pathophysiologic basis for the treatment of cirrhotic ascites

Advances in the understanding of the pathophysiology of sodium retention and ascites formation in cirrhosis has helped improve the treatment of ascites in these patients. It is likely that further unraveling of these pathophysiologic changes will lead to the development of novel and better treatment options. For example, the development of aquaretic agents for the management of hyponatremia in cirrhosis may allow more effective use of diuretic therapy. The ultimate challenge is to use the understanding of the pathophysiology to develop new strategies to prevent the development of ascites in cirrhosis.

[Indications and role of albumin, plasma volume expansion excluded, in the preoperative or postoperative management of portal hypertension]

Low serum albumin levels are common in patients with cirrhosis and liver failure. Decreased synthesis is the main but not the only mechanism leading to decreased serum levels. The consequences of low albumin concentrations are a decreased plasma colloid osmotic pressure and a decreased binding of liposoluble xenobiotics and endogenous substances. Besides the fluid accumulation in pleura and peritoneum, the complications directly related to low serum albumin levels have been only poorly assessed. An increase in serum albumin levels (by a few g.L-1) for a few days can be achieved by the infusion of large amounts of human albumin (approximately 120 g over 3 days). The efficacy of this treatment has been only tested in association with large paracentesis: albumin infusion, which induces volume expansion, reduced the incidence of hyponatremia and functional renal failure. No significant effect on ascites production rate or survival has been observed. Similar results were achieved through polygelin or dextran-70 infusions. No well-conducted controlled study on the value of albumin infusion in other circumstances apart from cirrhotic patients is available. In conclusion, albumin infusion should be reserved to the treatment of hyponatraemia or functional renal failure complicating cirrhosis with severe liver failure and marked hypoalbuminaemia, when the infusion of colloids failed to correct these anomalies.

Renal response to a saline load in well-compensated alcoholic cirrhosis

A total of 29 patients with well-compensated alcoholic cirrhosis and 9 healthy control subjects of similar age and sex were studied to assess their response to a challenge of 2 L of normal saline infused over a 1 hr period. Patients with cirrhosis had an adequate effective arterial blood volume in the basal state as assessed by neurohumoral markers of vascular filling. They also had a lower renal vascular resistance (p = 0.048) and a higher glomerular filtration rate (p = 0.014) than the controls, indicating the presence of renal vasodilation. Both groups were in sodium balance, but the patients with cirrhosis had a higher filtered load of sodium, an increased proximal tubular reabsorption of sodium (p = 0.015) and a decreased fractional excretion of sodium (p < 0.001). The administration of a saline load was not accompanied by any significant changes in the renal circulation in the patients with cirrhosis. They were unable to suppress their proximal tubular reabsorption of sodium to the same extent as the controls (p = 0.012), so by the fourth hour a significant difference in the rate of urinary excretion of sodium was evident. In the patients with cirrhosis, glomerular filtration rate before and after the saline load correlated significantly with indocyanine green extraction (r = 0.65; p = 0.002), whereas the tubular handling of sodium was dependent on antipyrine clearance (r = 0.80; p < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Arteriovenous shunting, hemodynamic changes, and renal sodium retention in liver cirrhosis

BACKGROUND

Arterial vasodilation has been postulated to initiate sodium retention in cirrhosis. This work was designed to analyze whether arteriovenous shunting underlies vasodilation and influences renal function in cirrhosis.

METHODS

The femoral arteriovenous difference in oxygen content (Ca-VO2) was measured in 10 healthy subjects (control group) and 31 cirrhotic patients: 9 without ascites (group 1), 10 with ascites and a urinary sodium excretion rate (UNaV) of > 10 mEq/24 h (group 2), and 12 with ascites and UNaV of < or = 10 mEq/24 h (group 3). In 8 subjects from each group, femoral blood flow and the cardiac output were determined by duplex-Doppler ultrasonography. In 9 cases arteriovenous shunting in the femoral territory was estimated using 30 +/- 5-microns radiolabeled microspheres.

RESULTS

Ca-VO2 was lower in group 3 than in controls or group 1. Ca-VO2 correlated inversely with femoral blood flow, plasma renin activity, plasma aldosterone concentration, and degree of shunting measured by microspheres. Ca-VO2 correlated directly with systemic vascular resistance and prothrombin index.

CONCLUSIONS

In decompensated cirrhotic patients, there is an increased arteriovenous shunt for oxygen in the lower extremities that is associated with increased arterial blood flow, decreased systemic vascular resistance, and worsening of liver function. This shunt is due partly to opening of arteriovenous precapillary connections.

Arterial vasodilation is not the cause of increased cardiac output in cirrhosis

A pathological state of arterial vasodilation has been postulated to cause the increased cardiac output commonly observed in cirrhosis. Further, subsequent arterial underfilling has been proposed as the stimulus to sodium retention and ascites formation. Left ventricular size during the cycle of a cardiac contraction is predictably altered by a decrease in afterload. Specifically, increased systolic emptying should be observed. The relationship of left ventricular size during the cardiac cycle to systemic hemodynamic indices and urinary sodium retention was investigated in patients with alcoholic cirrhosis to test these hypotheses. Echocardiographic studies were performed on 24 male patients with alcoholic cirrhosis and compared with the results obtained in 10 age-matched male controls. Patients with cirrhosis had increased cardiac output and heart rate and decreased arterial pressure compared with normal subjects, confirming the presence of a hyperdynamic circulation. Patients with cirrhosis had enlarged left ventricular diameter at both end diastole (0.08 +/- 0.01 vs. 0.07 +/- 0.007 cm/kg dry body wt; P less than 0.001) and end systole (0.06 +/- 0.01 vs. 0.05 +/- 0.005 cm/kg; P less than 0.05). Left ventricular end-diastolic diameter was directly related to blood volume (r = 0.56, P less than 0.005). No significant differences in cardiac output, arterial pressure, or systemic resistance were found between patients with and patients without ascites. Increased cardiac output in cirrhosis occurs in conjunction with an enlarged ventricle throughout the cardiac cycle. The increase in left ventricular end-systolic diameter indicates that diminished afterload is not responsible for the increase in cardiac output. As the diameter of the ventricle during diastolic filling correlates with vascular volume, cardiac output in cirrhosis may be primarily determined by an increase in vascular volume.