Therapeutic Hypothermia After Out-of-Hospital Cardiac Arrest: Evaluation of a Regional System to Increase Access to Cooling
What are the key aspects of the Cool It protocol and outcomes of resuscitated out-of-hospital cardiac arrest (OHCA) patients treated with therapeutic hypothermia (TH) during the initial 4 years of the program?
The Cool It protocol has established TH as the standard of care for OHCA across a regional network of hospitals transferring patients to a central TH-capable hospital. Between February 2006 and August 2009, 140 OHCA patients who remained unresponsive after return of spontaneous circulation were cooled and rewarmed with the use of an automated, noninvasive cooling device. Three quarters of the patients (n = 107) were transferred to the TH-capable hospital from referring network hospitals. Positive neurological outcome was defined as Cerebral Performance Category 1 or 2 at discharge.
Patients with nonventricular fibrillation arrest or cardiogenic shock were included, and patients with concurrent ST-segment elevation myocardial infarction (STEMI) (n = 68) received cardiac intervention and cooling simultaneously. Overall survival to hospital discharge was 56%, and 92% of survivors were discharged with a positive neurological outcome. Survival was similar in transferred and nontransferred patients. Nonventricular fibrillation arrest and presence of cardiogenic shock were associated strongly with mortality, but survivors with these event characteristics had high rates of positive neurological recovery (100% and 89%, respectively). A 20% increase in the risk of death (95% confidence interval, 4-39%) was observed for every hour of delay to initiation of cooling.
The authors concluded that a comprehensive TH protocol can be integrated into a regional STEMI network that achieves broad dispersion of this essential therapy for OHCA.
In this TH-treated cohort, 56% of patients survived to hospital discharge, and among those who survived, 92% experienced a return to normal or near-normal neurological functioning. With the efficacy of TH more established, the opportunity to improve outcomes from OHCA may lie in the study of how best to deploy the therapy to larger numbers of patients. This study suggests that TH protocols that incorporate simple, noninvasive surface cooling before hospital arrival may provide an effective rescue therapy for OHCA and be readily adopted within the context of existing STEMI networks. In addition, enhanced monitoring of complications should be done in future TH studies so that the risks associated with TH can be understood and minimized.
Keywords: Survivors, Shock, Cardiogenic, Myocardial Infarction, Out-of-Hospital Cardiac Arrest, Hypothermia
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