Determinants of ammonia clearance by hemodialysis

Role of the molecular adsorbent recycling system (MARS) in the treatment of patients with acute exacerbation of chronic liver failure

OBJECTIVE

To test the efficacy of the molecular adsorbent recycling system (MARS) in patients with acute exacerbation of chronic liver disease.

DESIGN

A prospective case analysis.

SETTING

A university-affiliated tertiary medical center.

PATIENTS AND METHODS

We applied MARS to treat a consecutive series of eight patients with acute exacerbation of chronic liver disease.

RESULTS

The overall survival rate was 62.5%. All patients demonstrated improvement with regard to their degree of encephalopathy. In three patients, intracranial pressure and jugular bulb oxygen saturation decreased and cerebral perfusion pressure increased after treatment institution. Patients' hyperdynamic state was attenuated, as demonstrated by elevation of systemic vascular resistance, mean arterial pressure, and parallel reduction in cardiac index. A prompt reduction in serum ammonia, bilirubin, and lactate levels was observed. There were no complications during the treatment period.

CONCLUSIONS

Applying MARS treatments to patients with acute exacerbation of chronic liver disease can detoxify blood, improve cerebral circulation, and reduce brain edema, as reflected by the reduction in intracranial pressure and jugular bulb oxygen saturation values in our patients. A partial reversal of the characteristic hyperdynamic circulation was also achieved. Despite our encouraging results, further testing is needed to determine the reliability of the system.

Hyperammonemia in urea cycle disorders: role of the nephrologist

Hyperammonemia associated with inherited disorders of amino acid and organic acid metabolism is usually manifested by irritability, somnolence, vomiting, seizures, and coma. Although the majority of these patients present in the newborn period, they may also present in childhood, adolescence, and adulthood with failure to thrive, persistent vomiting, developmental delay, or behavioral changes. Persistent hyperammonemia, if not treated rapidly, may cause irreversible neuronal damage. After the diagnosis of hyperammonemia is established in an acutely ill patient, certain diagnostic tests should be performed to differentiate between urea cycle defects and other causes of hyperammonemic encephalopathy. In a patient with a presumed inherited metabolic disorder, the aim of therapy should be to normalize blood ammonia levels. Recent experience has provided treatment guidelines that include minimizing endogenous ammonia production and protein catabolism, restricting nitrogen intake, administering substrates of the urea cycle, administering compounds that facilitate the removal of ammonia through alternative pathways, and, in severe cases, dialysis therapy. Initiation of dialysis in the encephalopathic patient with hyperammonemia is indicated if the ammonia blood level is greater than three to four times the upper limit of normal. Hemodialysis is the most effective treatment for rapidly reducing blood ammonia levels. Continuous hemofiltration and peritoneal dialysis are also effective modalities for reducing blood ammonia levels. An improved understanding of the metabolism of ammonia and neurological consequences of hyperammonemia will assist the nephrologist in providing optimal care for this high-risk patient population.

Continuous arteriovenous hemodiafiltration in the acute treatment of hyperammonaemia due to ornithine transcarbamylase deficiency

BACKGROUND

Acute hyperammonemia caused by urea cycle disorder is a medical emergency for which immediate managements should be taken to minimize permanent brain damage. Among different enzyme defects, ornithine transcarbamylase deficiency (OTC) is one of the most common enzyme defect in urea cycle disorders. We utilized continuous renal replacement therapy techniques in the acute treatment of hyperammonemia due to ornithine transcarbamylase deficiency.

PATIENTS AND METHODS

Three male neonates with elevated serum ammonia levels were shown, based on urine organic acid analysis and serum amino acid studies, to have OTC deficiency. Administration of sodium benzoate and sodium phenylacetate for activating alternative nitrogen waste pathway were used associated with protein restriction. Other modalities, including blood exchange transfusion, peritoneal dialysis, continuous renal replacement therapy were utilized in an attempt to lower serum ammonia concentration.

RESULTS

We report the successful use of continuous arteriovenous hemofiltration (CAVH), continuous arteriovenous hemodialysis (CAVHD), continuous arteriovenous hemodiafiltration (CAVHDF) in the acute management of hyperammonemia due to OTC deficiency. We also compared the ammonia clearance between peritoneal dialysis, exchange transfusion, CAVH, CAVHD and CAVHDF. It demonstrated the evidence that CAVHDF provides the best ammonia clearance.

CONCLUSION

Continuous renal replacement therapy including CAVH, CAVHD, and CAVHDF may be the alternative techniques for acute management of hyperammonemia in inborn error of metabolism when dialysis machine is not available. Our data suggests CAVHDF provides the best ammonia clearance.

Current status of liver support systems

The search for a support system for liver failure has been intensified. Methods currently being tested include those based on artificial support, on biological approaches (including extracorporeal liver perfusion and transplanted hepatocytes) as well as hybrid devices that combine artificial aspects with biological systems. Each of these three areas is undergoing fast technological and conceptual development. Controlled clinical trials are also under way.

Hyperbaric oxygenation, plasma exchange, and hemodialysis for treatment of acute liver failure in a 3-year-old child

A girl aged 3 years and 4 months weighing 16 kg was treated with plasma exchange (PE), hemodialysis (HD), and hyperbaric oxygenation (HBO) for acute hepatic failure and coma. She was given a total of 13 PEs, 13 HD sessions, and 9 HBO treatments over a period of 1 month. The initial 4 PEs were followed by HD sessions while the other 8 PE treatments were given simultaneously with HD. There was no renal failure; HD was instituted to improve ammonia elimination. In 1 HD session, 20% human albumin (370 ml) was used as the dialysate to enhance bilirubin elimination. Three volumes of plasma (2,000 ml) per PE were exchanged and replaced with fresh frozen plasma (FFP). The Bellco BL 791 plasmapheresis monitor and Gambro PF1000 and PF2000 plasma filters were used. Heparin was added to prevent clotting. A dual lumen pediatric HD catheter (7 Fr) placed percutaneously into the femoral vein was used as a blood access. The Fresenius 2008 C HD monitor and the Filtral 10 dialyzer were used for HD. PE and HD were instituted simultaneously to prevent the tetanic (hypocalcemic) cramps observed with 2 previous PEs due to citrate in the FFP. The extracorporeal circuit was primed with a mixture of concentrated red cells, human albumin, and saline solution and was discarded at the end of the procedure. The average blood flow rate in PE and/or HD circuits was 80 ml/min. During HBO, the girl breathed 100% oxygen at 2.5 atm for 90 min. Throughout the treatment, the patient was in good clinical, physical, and mental condition, but she was dependent on blood purification procedures. She was referred to a liver transplant center and successfully transplanted. The etiology of liver failure has not been clarified.

Arteriovenous difference of blood ammonia in uremic patients under hemodialysis

In this study the ammonia concentration was determined in arterial and venous blood samples pre- and posthemodialysis (HD) in 18 uremic patients and in 18 health subjects (controls). The mean values (+/- SD) of ammonia in the arterial blood of uremic patients pre-HD were 98.32 +/- 26.55; post-HD, 63.18 +/- 17.09; and in control group patients, 72.37 +/- 10.09 micrograms/dl. In venous blood they were pre-HD, 71.70 +/- 20.68; post-HD, 58.05 +/- 16.73; and in control patients, 74.46 +/- 12.0 micrograms/dl. According to our findings, the ammonia concentration in the arterial blood of uremic patients pre-HD exceeds the normal limits and is significantly higher (p < 0.001) than that post-HD and that of control patients. The ammonia contents of venous blood pre- and post-HD ranges were within normal values, but the post-HD range was significantly lower than the pre-HD range (p < 0.05) and the control range (p < 0.01). Comparison between ammonia levels from arterial and venous blood showed significant and positive arteriovenous differences pre-HD (p < 0.001), which disappeared post-HD and were not observed in the control patients. In conclusion, uremic patients under HD present pre-HD high levels of ammonia in arterial blood with a significantly positive arteriovenous difference. In contrast, the post-HD ammonia levels in arterial and venous blood are decreased, and the arteriovenous difference is not significant.