Blood ammonia and lactate levels on hospital arrival as a predictive biomarker in patients with out-of-hospital cardiac arrest.

INTRODUCTION: No reliable predictor for the prognosis of out-of-hospital cardiac arrest (OHCA) on arrival at hospital has been identified so far. We speculate that ammonia and lactate may predict patient outcome.
METHODS: This is a prospective observational study. Non-traumatic OHCA patients who gained sustained return of spontaneous circulation and were admitted to acute care unit were included. Blood ammonia and lactate levels were measured on arrival at hospital. The patients were classified into two groups: 'favourable outcome' group (Cerebral Performance Category CPC1-2 at 6-months' follow-up) and 'poor outcome' group (CPC3-5). Basal characteristics obtained from the Utstein template and biomarker levels were compared between these two outcome groups. Independent predictors were selected from all candidates using logistic regression analysis.
RESULTS: A total of 98 patients were included. Ammonia and lactate levels in the favourable outcome group (n=10) were significantly lower than those in poor outcome group (n=88) (p<0.05, respectively). On receiver operating characteristic analysis, the optimal cut-off value for predicting favourable outcome was determined as 170 μg dl(-1) of ammonia and 12.0 mmol l(-1) of lactate (area under the curve; 0.714 and 0.735, respectively). Logistic regression analysis identified ammonia (≤170 μg dl(-1)), therapeutic hypothermia and witnessed by emergency medical service personnel as independent predictors of favourable outcome. When both these biomarker levels were over threshold, positive predictive value (PPV) for poor outcome was calculated as 100%.
CONCLUSIONS: Blood ammonia and lactate levels on arrival are independent prognostic factors for OHCA. PPV with the combination of these biomarkers predicting poor outcome is high enough to be useful in clinical settings.