Impact of time to cooling initiation and time to target temperature in patients treated with hypothermia after cardiac arrest

Purpose: Little is known about the role of time to initiation of therapeutic hypothermia and time to target temperature (TTT) in the prognosis of patients resuscitated from cardiac arrest.

Methods: A retrospective analysis was performed in 145 survivors of cardiac arrest who underwent therapeutic hypothermia between January 2003 and January 2013. The objective was to identify predictors of survival free from significant neurological sequelae (Cerebral Performance Categories Scale (CPC): >2) six months after cardiac arrest. We evaluated the effect of faster and earlier cooling.

Results: Overall survival at six months was 42.1% (61 patients); 59 of these were considered to have a good neurological status (CPC ≤ 2), and in whom therapeutic hypothermia was initiated earlier (87 ± 17 min vs. 111 ± 14 min; p=0.042), and the target temperature was reached at an earlier time (TTT: 316 ± 30 min vs. 365 ± 27 min; p=0.017). Multivariate analysis selected longer duration of cardiac arrest (odds ratio (OR) = 1.06 per min), a non-shockable initial rhythm (OR=13.8), severe acidosis (OR=0.009 per 0.01 unit), older age (OR=1.04 per year) and longer TTT (OR=1.005 per min) as associated with poor prognosis.

Conclusion: The most important prognostic factors for death or lack of neurological recovery in patients with cardiac arrest treated with therapeutic hypothermia are initial-rhythm, time from cardiac arrest to return of spontaneous circulation and arterial-pH at admission. Although the speed of cooling initiation and the time to reach target temperature may play a role, its influence on prognosis seems to be less important.