Prehospital measurement of arterial base excess and its role as a possible predictor of outcome after out-of-hospital cardiac arrest

Objective: Cardiac arrest leads to a state of mixed respiratory and metabolic acidosis. Even after adequate ventilation and restoration of spontaneous circulation, metabolic acidosis as reflected by a negative base excess (BE) persists. We hypothesized that arterial BE measured in out-of-hospital cardiac arrest would be significantly associated with prehospital mortality. Methods: We retrospectively reviewed all protocol sheets of emergency medical responses to cardiac arrest in the period from January 1, 2003 to December 31, 2010. One hundred twenty-six adult nontraumatic cardiac arrest patients in whom cardiopulmonary resuscitation (CPR) was attempted and an arterial blood gas sample was obtained during ongoing CPR were included for further analysis. The following data were collected: age, sex, delay, bystander or emergency medical technician CPR, cause of cardiac arrest, initial rhythm, CPR duration; use of thrombolytic therapy, epinephrine, sodium bicarbonate, and for a cooling device and blood gas sample parameters. The univariate association of all parameters with the endpoint was calculated and a multivariate logistic regression model was built. Results: The association of BE and failure to reach the hospital alive was assessed by a receiver operating characteristic curve. The area under the curve was 0.76 (95% CI, 0.68-0.83). The optimum discriminatory threshold derived was-15.2, yielding a specificity of 70% and a sensitivity of 71%. In a multivariate logistic regression model, a negative BE exceeding-15.2 mmol/L remained significantly associated with prehospital mortality (odds ratio 4.62, 95% CI: 1.63-14.03, P=0.004). Conclusion: During ongoing CPR, BE is a significant predictor of failure to reach the hospital alive. [Emergencias 2013;25:47-50]