Abstract 2016: Duration of Cooling and Time From Out-of-Hospital Cardiac Arrest to Spontaneous Circulation in Patients Treated With Mild Hypothermia
BACKGROUND Although 2005 AHA guidelines for CPR recommended that unconscious adult patients with return of spontaneous circulation (ROSC) after out-of-hospital VF arrest should be cooled to 32°C to 34°C for 12 to 24 hours (Class 2a), there was an insufficient evidence of optimal cooling duration. We studied the relationship between cooling duration and time from collapse to ROSC.
METHODS Comatose adult patients who achieved ROSC by standard CPR after witnessed out-of-hospital cardiac arrest due to cardiac etiology were eligible in this study of mild hypothermia (34°C, measured in the pulmonary arterial blood temperature). The cooling was initiated rapidly using intravenous infusion of extracellular fluid (2 liters at 4 °C over 30 minutes) and was continued precisely using extracorporeal cooling method with KTEK-3 as reported previously. The cooling duration was determined by the time from collapse to ROSC. The patients who had collapse-to-ROSC interval of ≤ 20 minutes were cooled for 24 hours, 20 to 30 minutes for 48 hours and >30 minutes for 72 hours. The primary endpoints were neurologic outcomes at the time of hospital discharge.
RESULTS Of the 461 patients with out-of-hospital cardiac arrest, 46 (10%) were eligible. Mean (±SD) collapse-to-ROSC interval was 23.5±16.5 minutes, and 28 (61%) were cooled for 24 hours, 7(15%) for 48 hours and 11(24%) for 72 hours. A total of 27 of the 28 patients (96%) in the 24-hour cooling group had the favorable neurologic outcome vs. 6 of the 7(86%) in the 48-hour cooling group vs. 0 of the 11(0%) in the 72-hour cooling group (p<0.0001). In the patients with survival to hospital discharge, 1 of the 28 patients (4%) in the 24-hour cooling group had the unfavorable neurologic outcome vs. 0 of the 6(0%) in the 48-hour cooling group vs. 7 of the 7(100%) in the 72-hour cooling group (p<0.0001). The adjusted odds ratio for the favorable neurologic outcome after collapse-to-ROSC interval was 0.75(95% CI, 0.61–0.92; p=0.007).
CONCLUSIONS The cooling duration for 24 to 48 hours produced excellent outcome when the collapse-to-ROSC interval was ≤ 30 minutes, but the duration for 72 hours did not improve the outcome when its interval was >30 minutes. Further research is needed to determine cooling duration for comatose survivors after prolonged CPR.