Abstract 9: Ammonia as a Marker of Neurological Outcomes in Patients with Out-of-Hospital Cardiac Arrest
BACKGROUND Excessive accumulation of ammonia (NH3) induces neuronal metabolic derangements, promotes astrocyte swelling and perturbs cerebral nitric oxide metabolism which can mediate some of the pathophysiologic changes. Although studies have shown that there was a correlation between increase in blood NH3 level and hepatic encephalopathy, few studies were available for patients with out-of-hospital cardiac arrest. We therefore evaluated NH3 as a biochemical marker of neurological outcome.
METHODS We conducted a prospective clinical study of patients with out-of-hospital cardiac arrest that followed Utstein style reporting guidelines. Blood samples to measure the NH3 concentration were taken from a vein before drug administration in the emergency room (normal range of NH3; 12 to 66μg/dl). The primary endpoint was a favorable neurological outcome at the time of hospital discharge.
RESULTS Of the 461 patients with out-of-hospital cardiac arrest, 291 adult patients were eligible. The NH3 level ranged from 10 to 400μg/dl, with a mean (±SD) of 208± 133μg/dl, and a median of 186μg/dl, and 25th and 75th percentile values of 79 and 337μg/dl, respectively. Of those, 20 (7%) had a favorable neurological outcome at the time of hospital discharge, and the NH3 level was lower among such patients than among those with unfavorable neurological outcomes (a median, 48μg/dl vs. 205μg/dl, p<0.0001). The adjusted odds ratio for a favorable neurological outcome after NH3 level was 0.98 (95% CI, 0.97– 0.99; p=0.0005), and the NH3 level was more accurate than any components of the chain of survival. The neurological prognostic accuracy of NH3 level at a cut off of 87.5μg/dl was 79 %. The negative predictive value of NH3 at levels of more than 189μg/dl was 100 %. In patients with return of spontaneous circulation (ROSC) after out-of-hospital cardiac arrest witnessed by bystanders, there was a significant positive correlation between the NH3 level and time interval from cardiac arrest to ROSC (R=0.54, p<0.0001).
CONCLUSIONS We demonstrated that NH3 level on arrival at the emergency room was elevated in patients with out-of-hospital cardiac arrest and reliably predicted neurological outcome. NH3 is a new candidate marker of neurological outcome after cardiac arrest.