Therapeutic mild hypothermia after cardiac arrest in shockable and nonshockable rhythms: does it improve both survival and neurological outcome?

Abstract

INTRODUCTION. Though therapeutic mild hypothermia (TMH) after resuscitation from cardiac arrest (CA) has been postulated and studied to be associated with good outcome of the patients, there is no dearth of data which doesn't favour TMH. Also, there is lack of data which has separately compared the efficacy of TMH in patients after cardiac arrest in ventricular tachycardia/ventricular fibrillation, the shockable rhythm (SR) and pulseless electrical activity/asystole (PEA/Asys), the nonshockable rhythm (NR) for two separate but important parameters of outcome: survival and neurological outcome. OBJECTIVES. To find out whether TMH is associated with good outcome after CA in shockable rhythm compared to nonshockable rhythm, in terms of survival as well as neurological outcome. METHODS. We reviewed medical records of all CA patients (in-hospital or out of hospital arrest) in whom cardiopulmonary resuscitation (CPR) was done at our hospital from 1st February 2011 to 31st January 2012 (12 months). The following information was collected: first documented rhythm (FDR), whether TMH done or not, and two outcome measures including: survival to hospital discharge and neurological outcome at the time of hospital discharge. Measure of good neurological outcome was cerebral performance category score 1 or 2 (CPC, 5 point scale; 1 = good cerebral performance, to 5 = brain death). Then we quantified the association of TMH with SR as well as nonshockable rhythm for both the parameters of outcome i.e. survival to hospital discharge and good neurological outcome, by logistic regression analysis. RESULTS. We had 297 CA patients (168 SR, 129 NR) in whom CPR was done. Return of spontaneous circulation was achieved in 90 patients. TMH was induced in 57 patients (33 SR, 24 NR). Survival to hospital discharge was observed in 27 patients (18/33 [54.5 %] SR, 9/24 [37.5 %] NR), out of which 18 patients (10/33 [30 %] SR, 8/24 [33 %] NR) had good neurological outcome. On analysis, TMH was found to be associated with increased odds of survival to hospital discharge (though statistically not significant) in SR patients compared to nonshockable rhythm patients (Odds ratio [OR] 2.00; 95 % confidence interval [CI] 0.68-5.85; p 0.20), but it was not associated with any better neurological outcome in terms of CPC score in patients presenting with SR rather than nonshockable rhythm (OR 0.87; 95 % CI 0.28-2.68; p 0.81). Rather, odds for good neurological outcome were more in favour of nonshockable rhythm (PEA/Asys). CONCLUSION. Though TMH might be associated with better survival chances in patients presenting with shockable rhythm, neurological outcome was no better (rather worse) in this group of patients when compared to patients with nonshockable rhythm as the first documented rhythm.