Prognostic value of venous blood ammonia in patients with out-of-hospital cardiac arrest

Background: Although studies have shown there is a correlation between increased blood ammonia level and hepatic encephalopathy, little information is available for patients with out-of-hospital cardiac arrest. Methods and Results: We did a prospective study of 357 adult patients with out-of-hospital cardiac arrest whose venous blood ammonia levels were measured on arrival at the emergency room. The primary endpoint was favorable of neurological outcome to hospital discharge. Of the 357 patients, 25 (7%) had a favorable neurological outcome. The venous ammonia levels were lower in the favorable neurological outcome group than in the unfavorable neurological outcome group (median, 50μg/dl vs. 210μg/dl, P<0.0001). The adjusted odds ratio of ammonia levels for favorable neurological outcome was 0.98 (95% confidence interval, 0.96-0.99; P<0.0001). The ammonia cutoff value of 93.0μg/dl for the identification of favorable neurological outcome had the highest combined sensitivity and specificity, and higher ammonia levels were associated with more accurate negative predictive values (for ammonia levels of 192.5μg/dl, the negative predictive value was 100%). Hyperammonemia was significantly related to patient variables that had a poor outcome (R=0.439, P<0.001). In addition, there was a significant correlation between venous ammonia level and arterial pH on emergency room arrival (R=0.633, P<0.0001). Conclusions: The measurement of ammonia was found to provide valuable information regarding neurological outcome to hospital discharge in adult patients with out-of-hospital cardiac arrest.