Haemodialysis for hyperammonaemic encephalopathy

Extracorporeal Ammonia Clearance for Hyperammonemia in Critically Ill Patients: A Scoping Review

INTRODUCTION

Hyperammonemia is a life-threatening condition. However, clearance of ammonia via extracorporeal treatment has not been systematically evaluated.

METHODS

We searched EMBASE and MEDLINE databases. We included all publications reporting ammonia clearance by extracorporeal treatment in adult and pediatric patients with clearance estimated by direct dialysate ammonia measurement or calculated by formula. Two reviewers screened and extracted data independently.

RESULTS

We found 1,770 articles with 312 appropriate for assessment and 28 studies meeting eligibility criteria. Most of the studies were case reports. Hyperammonemia was typically secondary to inborn errors of metabolisms in children and to liver failure in adult patients. Ammonia clearance was most commonly reported during continuous renal replacement therapy (CRRT) and appeared to vary markedly from <5 mL/min/m2 to >250 mL/min/m2. When measured during intermittent hemodialysis (IHD), clearance was highest and correlated with blood flow rate (R2 = 0.853; p < 0.001). When measured during CRRT, ammonia clearance could be substantial and correlated with effluent flow rate (EFR; R2 = 0.584; p < 0.001). Neither correlated with ammonia reduction. Peritoneal dialysis (PD) achieved minimal clearance, and other extracorporeal techniques were rarely studied.

CONCLUSIONS

Extracorporeal ammonia clearance varies widely with sometimes implausible values. Treatment modality, blood flow, and EFR, however, appear to affect such clearance with IHD achieving the highest values, PD achieving minimal values, and CRRT achieving substantial values especially at high EFRs. The role of other techniques remains unclear. These findings can help inform practice and future studies.

[Fulminant coma: think hyperammonemia and urea cycle disorders]

The authors report the case of 14-year-old boy admitted for acute coma without neurological focal symptom. The only relevant finding was the death of one uncle after a coma in the year 1992. This coma was associated with an ammonia blood level of 344 mumol l-1 and it rapidly lead to cerebral death despite a symptomatic treatment. The diagnosis of hereditary ornithine transcarbamylase deficiency was confirmed by liver biopsy in the immediate post-mortem period. The authors recommend the measurement of blood ammonia in every coma without diagnosis, whatever patient's age.