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

Farzi S, Hausler F, Wallner S, Spindelböck W, Prause G, Gemes G

Departamento de Anestesiología y Medicina Intensiva, Departamento de Medicina Interna, Universidad de Medicina de Graz, Austria, Medizinercorps Graz, Cruz Roja Austriaca, Graz, Austria.

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 system
calls responding to cardiac arrest in the period from Jan 1st, 2003 to Dec 31st, 2010.
126 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 parameters 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, 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.

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