Arterial and mixed venous acid-base status in patients with cirrhosis. Influence of liver failure

Acid-Base Balance during Continuous Veno-Venous Hemofiltration: The Impact of Severe Hepatic Failure

Background

Continuous renal replacement therapy (CRRT) affects acid-base balance but the influence of severe hepatic failure (SHF) on this effect is unknown.

Aim

To assess the effect of SHF on acid-base balance in patients receiving CVVH.

Design

Retrospective laboratory investigation.

Subjects

Forty patients with SHF and acute renal failure (ARF) treated with CVVH and 42 critically ill patients with severe ARF but no liver disease also treated with CVVH (controls).

Intervention

Retrieval of clinical and laboratory data from prospective unit and laboratory databases.

Methods

Quantitative acid-base status assessment using the Stewart-Figge methodology. Comparison of findings between the two groups.

Results

Although CVVH had a major effect on acid base balance in both groups, patients with SHF had a higher mean lactate concentrations (4.8 vs. 3.1 mmol/L; p<0.0005), a greater base deficit compared to controls (-1 vs. 4.1 mEq/L; p<0.0001) and a lower PaCO2 tension (36.8 vs. 42.5 mmHg; p<0.0001), despite the use of bicarbonate replacement fluid. The acidifying effect of hyperlactatemia was slightly worsened by an increased strong ion gap (9.3 vs. 4.9 mEq/L; p<0.0001). It was, however, attenuated by an increased strong ion difference apparent (SIDa) (43.6 vs. 41.9 mEq/L; p<0.05) secondary to hypochloremia (96 vs. 100 mmol/L; p<0.0001) and by hypoalbuminemia, although hypoalbuminemia in SHF patients (26 vs. 23; p<0.005) was less pronounced than in controls.

Conclusion

The use of CVVH does not fully correct the independent acidifying effect of liver failure on acid-base status. Increased lactate and strong ion gap values maintain a persistent base deficit despite the alkalinizing effects of hypoalbuminemia and hypochloremia. The correction of acidosis in SHF patients may require more intensive CVVH.

Acid-base Balance in Combined Severe Hepatic and Renal Failure: A Quantitative Analysis

Background

Severe hepatic failure (SHF) commonly leads to major changes in acid-base balance status. However, the direct effects of liver failure per se on acid base balance are poorly understood because this condition is usually associated with acute renal failure (ARF).

Aim

To assess the effect of SHF on acid-base balance.

Design

Retrospective laboratory investigation.

Subjects

Thirty-seven critically ill patients with SHF complicated by ARF, and 42 patients with severe ARF without liver failure prior to renal replacement therapy.

Intervention

Retrieval of clinical and laboratory data from prospective unit and laboratory databases.

Methods

Quantitative acid-base assessment using Stewart-Figge methodology. Comparison of findings between the two groups. Comparison of demographic and clinical features.

Results

Patients with combined SHF and ARF were younger and had significantly higher mean bilirubin, ALT and INR levels (p<0.0001). Their mean lactate concentration was higher (6.4 vs. 2.1 mmol/L; p<0.0001) leading to a greater anion gap (25.8 vs. 16.1 mmol/L; p<0.0001). The ionized calcium concentration (1.00 vs. 1.15 mmol/L; p<0.0001) was lower but the strong ion difference apparent (SIDa) was greater (42.0 vs. 38.0 mEq/L; p<0.005) due to hypochloremia. The albumin concentration was low but higher than in control patients (28 vs. 24 g/L; p<0.01) and the calculated strong ion gap (SIG) was greater (12.6 vs. 9.3 mEq/L; p<0.01). The base excess was similar to controls and the pH was preserved in the near normal range by marked hypocapnea.

Conclusions

Combined SHF and ARF is a syndrome with unique acid-base changes due mostly to lactic metabolic acidosis and, in smaller part, to the accumulation of unmeasured anions. This acidosis, like that of ARF, is attenuated by hypoalbuminemia, by a unique preservation of the SIDa due to hypochloremia, and by marked hypocapnea.

Acid-base disorders in liver disease

Alongside the kidneys and lungs, the liver has been recognised as an important regulator of acid-base homeostasis. While respiratory alkalosis is the most common acid-base disorder in chronic liver disease, various complex metabolic acid-base disorders may occur with liver dysfunction. While the standard variables of acid-base equilibrium, such as pH and overall base excess, often fail to unmask the underlying cause of acid-base disorders, the physical-chemical acid-base model provides a more in-depth pathophysiological assessment for clinical judgement of acid-base disorders, in patients with liver diseases. Patients with stable chronic liver disease have several offsetting acidifying and alkalinising metabolic acid-base disorders. Hypoalbuminaemic alkalosis is counteracted by hyperchloraemic and dilutional acidosis, resulting in a normal overall base excess. When patients with liver cirrhosis become critically ill (e.g., because of sepsis or bleeding), this fragile equilibrium often tilts towards metabolic acidosis, which is attributed to lactic acidosis and acidosis due to a rise in unmeasured anions. Interestingly, even though patients with acute liver failure show significantly elevated lactate levels, often, no overt acid-base disorder can be found because of the offsetting hypoalbuminaemic alkalosis. In conclusion, patients with liver diseases may have multiple co-existing metabolic acid-base abnormalities. Thus, knowledge of the pathophysiological and diagnostic concepts of acid-base disturbances in patients with liver disease is critical for therapeutic decision making.

Acid-base disturbance in patients with cirrhosis: relation to hemodynamic dysfunction

PURPOSE

Acid-base disturbances were investigated in patients with cirrhosis in relation to hemodynamic derangement to analyze the hyperventilatory effects and the metabolic compensation.

METHODS

A total of 66 patients with cirrhosis and 44 controls were investigated during a hemodynamic study.

RESULTS

Hyperventilatory hypocapnia was present in all patients with cirrhosis and progressed from Child class A to C (P<0.01). Arterial pH increased significantly from class A to C (P<0.001) and was correlated inversely to the mean arterial blood pressure (r=-0.30, P<0.02), systemic vascular resistance (r=-0.25, P<0.05), indocyanine green clearance (r=-0.37, P<0.005), and serum sodium (r=-0.38, P<0.002). Metabolic compensation was shown by a reduced standard base excess in all patients (P<0.001). Standard base excess contained elements related to changes in serum albumin, water dilution, and effects of unidentified ions (all P<0.001). A significant hepatic component in the acid-base disturbances could not be identified.

CONCLUSION

Hypocapnic alkalosis is related to disease severity and hyperdynamic systemic circulation in patients with cirrhosis. The metabolic compensation includes alterations in serum albumin and water retention that may result in a delicate acid-base balance in these patients.

Perioperative monitoring in liver transplant patients

Liver transplant (LT) is a major surgical undertaking involving major fluid shifts, hemodynamic instability and metabolic derangements in a patient with preexisting liver failure and multisystemic derangements. Monitoring and organ support initiated in the preoperative phase is continued intraoperatively and into the postoperative phase to ensure an optimal outcome. As cardiovascular events are the leading cause of non-graft related death among LT recipients, major emphasis is placed on cardiovascular monitoring. The other essential monitoring are the continuous assessment of coagulapathy, extent of metabolic derangements, dyselectrolytemis and intracranial pressure monitoring in patients with fulminant hepatic failure. The type and extent of monitoring differs with need according to preexisting child status of the patient and the extent of systemic derangements. It also varies among transplant centers and is mainly determined by individual or institutional practices.

Das Säure-Basen-Modell nach Stewart

In addition to paCO(2), Stewart's acid base model takes into account the influence of albumin, inorganic phosphate, electrolytes and lactate on acid-base equilibrium. It allows a comprehensive and quantitative analysis of acid-base disorders. Particularly simultaneous and mixed metabolic acid-base disorders, which are common in critically ill patients, can be assessed. Stewart's approach is therefore a valuable tool in addition to the customary acid-base approach based on bicarbonate or base excess. However, some chemical aspects of Stewart's approach remain controversial.

Acid-Base and Potassium Disorders in Liver Disease

Acid-base and potassium disorders occur frequently in the setting of liver disease. As the liver's metabolic function worsens, particularly in the setting of renal dysfunction, hemodynamic compromise, and hepatic encephalopathy, acid-base disorders ensue. The most common acid-base disorder is respiratory alkalosis. Metabolic acidosis alone or in combination with respiratory alkalosis also is common. Acid-base disorders in patients with liver disease are complex. The urine anion gap may help to distinguish between chronic respiratory alkalosis and hyperchloremic metabolic acidosis when a blood gas is not available. A negative urine anion gap helps to rule out chronic respiratory alkalosis. In this disorder a positive urine anion gap is expected owing to suppressed urinary acidification. Distal renal tubular acidosis occurs in autoimmune liver disease such as primary biliary cirrhosis, but often is a functional defect from impaired distal sodium delivery. Potassium disorders are often the result of the therapies used to treat advanced liver disease.

Influence of cardiac function and failure on sleep-disordered breathing: evidence for a causative role

Heart failure is an increasingly common public health problem that is strongly linked to both central and obstructive sleep apnea, collectively referred to as sleep-disordered breathing. Much attention has been given to the deleterious effects of sleep-disordered breathing on the failing heart and potential mechanisms by which treatment of sleep-disordered breathing may result in improved cardiac performance and long-term outcomes. However, there is compelling evidence that cardiac dysfunction may contribute to sleep-disordered breathing. Although there is recognized overlap between pathophysiological mechanisms in central sleep apnea and obstructive sleep apnea, data supporting the role of cardiac function are certain forms of central sleep apnea are well established, whereas investigation into the relationship with obstructive sleep apnea is less mature but continues to evolve. This review will examine experimental and observational data that explore possible pathophysiological mechanisms and potential targets for therapy in heart failure and sleep-disordered breathing.

Renal replacement therapy in patients with chronic liver disease

As the prevalence of chronic liver disease and chronic kidney disease (CKD) increase, clinicians are likely to be increasingly faced with difficult diagnostic, treatment, and ethical challenges when facing both of these diseases in a single patient. Alterations in creatinine formation and elimination in cirrhotic patients render creatinine-based estimates of glomerular filtration rate and dialysis adequacy less accurate in this population. Furthermore, differentiating signs and symptoms of uremia from hepatic disease may be difficult and clear indications for renal replacement therapy (RRT) in these patients have not been defined. Hemodialysis is associated with a high rate of complications and has not been shown to prolong life in cirrhotic patients with acute renal failure (ARF), but has not been carefully examined in those with CKD. Peritoneal dialysis is, similarly, unhelpful in chronic liver disease complicated by ARF, but has been found to be a viable option in some cirrhotic patients with CKD. Continuous RRT is generally tolerated by patients with decompensated cirrhosis and either acute or chronic renal failure and may act to bridge patients to liver transplantation. Given the poor underlying survival of cirrhotic patients with renal failure, clinicians should carefully consider the utility of RRT in each patient.

Equilibrium of acidifying and alkalinizing metabolic acid-base disorders in cirrhosis

BACKGROUND AND AIMS

Conflicting results exist with regard to metabolic acid-base status in liver cirrhosis, when the classic concept of acid-base analysis is applied. The influence of the common disturbances of water, electrolytes and albumin on acid-base status in cirrhosis has not been studied. The aim of this study was to clarify acid-base status in cirrhotic patients by analyzing all parameters with possible impact on acid-base equilibrium.

PATIENTS AND METHODS

Fifty stable cirrhotic patients admitted to a university hospital. Arterial acid-base status was analyzed using the principles of physical chemistry and compared with 10 healthy controls.

RESULTS

Apart from mild hypoalbuminemic alkalosis, acid-base state was normal in Child-Pugh A cirrhosis. Respiratory alkalosis was the net acid-base disorder in Child-Pugh B and C cirrhosis with a normal overall metabolic acid-base state (Base excess-1.0 (-3.6 to 1.6) vs 1.1 (-0.2 to 1.1) mmol/l, P = 0.136, compared with healthy controls, median (interquartile range)). Absence of an apparent metabolic acid-base disorder was based on an equilibrium of hypoalbuminemic alkalosis and of dilutional acidosis and hyperchloremic acidosis.

CONCLUSION

A balance of offsetting acidifying and alkalinizing metabolic acid-base disorders leaves the net metabolic acid-base status unchanged in cirrhosis.

Extracellular cAMP inhibits proximal reabsorption: are plasma membrane cAMP receptors involved?

Glucagon binding to hepatocytes has been known for a long time to not only stimulate intracellular cAMP accumulation but also, intriguingly, induce a significant release of liver-borne cAMP in the blood. Recent experiments have shown that the well-documented but ill-understood natriuretic and phosphaturic actions of glucagon are actually mediated by this extracellular cAMP, which inhibits the reabsorption of sodium and phosphate in the renal proximal tubule. The existence of this "pancreato-hepatorenal cascade" indicates that proximal tubular reabsorption is permanently influenced by extracellular cAMP, the concentration of which is most probably largely dependent on the insulin-to-glucagon ratio. The possibility that renal cAMP receptors may be involved in this process is supported by the fact that cAMP has been shown to bind to brush-border membrane vesicles. In other cell types (i.e., adipocytes, erythrocytes, glial cells, cardiomyocytes), cAMP eggress and/or cAMP binding have also been shown to occur, suggesting additional paracrine effects of this nucleotide. Although not yet identified in mammals, cAMP receptors (cARs) are already well characterized in lower eukaryotes. The amoeba Dictyostelium discoideum expresses four different cARs during its development into a multicellular organism. cARs belong to the superfamily of seven transmembrane domain G protein-coupled receptors and exhibit a modest homology with the secretin receptor family (which includes PTH receptors). However, the existence of specific cAMP receptors in mammals remains to be demonstrated. Disturbances in the pancreato-hepatorenal cascade provide an adequate pathophysiological understanding of several unexplained observations, including the association of hyperinsulinemia and hypertension, the hepatorenal syndrome, and the hyperfiltration of diabetes mellitus. The observations reviewed in this paper show that cAMP should no longer be regarded only as an intracellular second messenger but also as a first messenger responsible for coordinated hepatorenal functions, and possibly for paracrine regulations in several other tissues.

Compulsory hyperventilation and hypocapnia of patients with Leigh syndrome associated with SURF1 gene mutations as a cause of low serum bicarbonates

Experimental data show that elevation of intracellular pH leads to severe lesions of brain cells. Acidification of intracellular fluid by accumulation of lactate may compensate the effect of respiratory alkalosis. Increased serum pH, and low PCO2, associated with hyperlactataemia (sometimes incorrectly called 'acidosis') have been reported in children with Leigh syndrome (LS). The aim of the study was to determine whether respiratory alkalosis is characteristic of patients with LS due to SURF1 mutations. All venous blood gas data (88 samples) of 18 spontaneously breathing LS patients with recently established SURF1 mutations, hospitalized during 1986-2000, were retrospectively reviewed. The data of an affected boy who survived on a respirator for more than 3 months (79 daily samples) were analysed separately. In spontaneously breathing patients, the data indicated that the patients had compensated or partially compensated respiratory alkalosis (pH 7.388+/-0.060, Pco2 29.2+/-5.7 mmHg, HCO3- 17.4+/-3.0 mmol/L, BE -6.7+/-3.2 mmol/L). Bicarbonate excretion was detected in urine of two examined LS cases in spite of decreased serum HCO3-. In the affected child maintained on a respirator, simple manipulation of the inspired CO2 tension to establish a normal pressure of 35-45 mmHg automatically caused an increase of serum HCO3- concentration to a normal value of 26.3+/-2.9 mmol/L (and BE to +2.2+/-3.1 mmol/L), in spite of cytochrome oxidase (COX) deficiency due to a confirmed SURF1 mutation. We suggest that respiratory alkalosis (hypocapnia) of Leigh syndrome patients with SURF1 mutations results from compulsory hyperventilation and speculate that hypocapnia may contribute to Leigh-like brain damage in the SURF1-deficient patients as well as in other patients presenting with Leigh-like syndrome. The supposition that accumulation of lactate may protect the brain of LS patients from alkalosis-related damage requires further study. Avoidance of any factors stimulating hyperventilation of LS patients and caution when attempting to correct low plasma bicarbonate are suggested.

Relationships between haemodynamic alterations and the development of ascites or refractory ascites in patients with cirrhosis

OBJECTIVE

In patients with cirrhosis, the relationships between haemodynamic alterations and the development of ascites or the occurrence of refractory ascites are unknown. The aim of the present study was to compare haemodynamic measurements obtained in patients with non-refractory ascites to haemodynamic measurements obtained in patients without ascites and in patients with refractory ascites.

METHODS

A cohort of 121 patients was prospectively studied, of whom 29 patients did not have ascites, 45 had non-refractory ascites and 47 had refractory ascites. Splanchnic, renal and systemic haemodynamics were measured in all patients.

RESULTS

The hepatic venous pressure gradient was significantly higher in patients with non-refractory ascites than in patients without ascites (18.5 +/- 0.8 mmHg versus 15.8 +/- 0.7 mmHg). Renal and systemic haemodynamics did not significantly differ between patients with non-refractory ascites and patients without ascites. The glomerular filtration rate and renal blood flow were significantly lower in patients with refractory ascites than in patients with non-refractory ascites (77 +/- 4 versus 107 +/- 5 ml/min and 867 +/- 62 versus 1,008 +/- 68 ml/min, respectively). Splanchnic and systemic haemodynamics did not significantly differ between patients with refractory ascites and patients with non-refractory ascites.

CONCLUSIONS

In patients with cirrhosis, an increase in portal hypertension was the sole haemodynamic alteration related to the development of ascites. Renal vasoconstriction (and subsequent renal hypoperfusion and hypofiltration) was the only haemodynamic alteration related to the occurrence of refractory ascites. The development of ascites or refractory ascites was not associated with any alteration in systemic haemodynamics.

Effect of liver disease and transplantation on urea synthesis in humans: relationship to acid-base status

It has been suggested that hepatic urea synthesis, which consumes HCO-3, plays an important role in acid-base homeostasis. This study measured urea synthesis rate (Ra urea) directly to assess its role in determining the acid-base status in patients with end-stage cirrhosis and after orthotopic liver transplantation (OLT). Cirrhotic patients were studied before surgery (n = 7) and on the second postoperative day (n = 11), using a 5-h primed-constant infusion of [15N2]urea. Six healthy volunteers served as controls. Ra urea was 5.05 +/- 0.40 (SE) and 3.11 +/- 0.51 micromol. kg-1. min-1, respectively, in controls and patients with cirrhosis (P < 0. 05). Arterial base excess was 0.6 +/- 0.3 meq/l in controls and -1.1 +/- 1.3 meq/l in cirrhotic patients (not different). After OLT, Ra urea was 15.05 +/- 1.73 micromol. kg-1. min-1, which accompanied an arterial base excess of 7.0 +/- 0.3 meq/l (P < 0.001). We conclude that impaired Ra urea in cirrhotic patients does not produce metabolic alkalosis. Concurrent postoperative metabolic alkalosis and increased Ra urea indicate that the alkalosis is not caused by impaired Ra urea. It is consistent with, but does not prove, the concept that the graft liver responds to metabolic alkalosis by augmenting Ra urea, thus increasing HCO-3 consumption and moderating the severity of metabolic alkalosis produced elsewhere.

Hemodynamic and metabolic effects of terlipressin in patients with cirrhosis receiving a nonselective beta-blocker

Terlipressin (Glypressin), a vasopressin analog, may be administered to patients with cirrhosis receiving a beta-adrenergic antagonist. Since terlipressin alone and beta-blockers alone both decrease portal pressure, a combination of these substances may have additional portal hypotensive effects. However, the negative side effects of terlipressin may be accentuated by long-term beta-blockade. Thus, the present study examined hemodynamic and metabolic responses to terlipressin in 12 patients receiving nonselective beta-blockers (propranolol or nadolol). Hemodynamics and oxygen (O2) -derived variables were measured prior to and 30 min after the administration (intravenous bolus) of terlipressin (1 to 2 mg, according to body weight). The hepatic venous pressure gradient and azygos blood flow significantly decreased (from 15.3 +/- 1.1 to 12.5 +/- 1.1 mm Hg, and from 0.6 +/- 0.1 to 0.5 +/- 0.1 liters/min, respectively). Arterial and pulmonary wedged pressures significantly increased. Heart rate, cardiac index, and O2 consumption were not significantly affected by terlipressin. In conclusion, in patients with cirrhosis being treated with a nonselective beta-blocker, terlipressin administration decreased portal pressure. Moreover, terlipressin induced only mild systemic hemodynamic effects in these patients. These results suggest that terlipressin can be administered in patients receiving a beta-adrenergic blocker.

Altered control of vascular tone by adenosine triphosphate-sensitive potassium channels in rats with cirrhosis

BACKGROUND/AIMS

Because the activation of arterial adenosine triphosphate (ATP)-sensitive potassium (KATP) channels is known to induce vasodilation, these channels may contribute to baseline vasodilator tone in cirrhosis. This study aimed to examine hemodynamic responses to glibenclamide, a KATP channel blocker, and to aprikalim, a vasodilator activating KATP channels, in normal and cirrhotic rats.

METHODS

Splanchnic and systemic hemodynamic responses to glibenclamide (2.5, 5, 20, 30 mg/kg, intravenously) were studied. The arterial pressure response to aprikalim (200 mu/kg, intravenously) was studied with and without glibenclamide pretreatment (20 mg/kg).

RESULTS

In cirrhotic rats, glibenclamide (5, 20, 30 mg/kg but not 2.5 mg/kg) significantly increased vascular resistance in portal and systemic territories. In normal rats, the latter effects occurred with 20 and 30 mg/kg of glibenclamide only. Aprikalim-induced arterial hypotension was significantly less marked in cirrhotic than in normal rats. Following glibenclamide, aprikalim-induced arterial hypotension was significantly less marked in cirrhotic than in normal animals.

CONCLUSIONS

In rats with cirrhosis, the glibenclamide-induced vasoconstriction indicates that a vasodilator tone due to KATP channel opening existed under baseline conditions. Moreover, this study suggests that the control of vascular tone by KATP channels is altered in cirrhosis.