- Unconscious adults with spontaneous circulation after out-of-hospital cardiac arrest should be cooled to 32-34 degrees C (ILCOR recommendations, 2003) when the initial rhythm is ventricular fibrillation. To assess the technique, safety and efficacy of mild induced hypothermia in patients after OHCA due to VF. Patients were cooled using the MTRE CritiCool external cooling system. Cold intravenous fluids were added to achieve faster cooling in 17 patients. Data were collected prospectively and patients were analyzed according to their neurological outcome on discharge, defined by their cerebral performance category. From February 2002 to September 2006, 51 comatose VF patients with OHCA underwent MIH. Treatment was discontinued early in five because of hemodynamic instability; goal temperature was reached in 98% and maintained for an average of 19.5 hours; 61% had a favorable outcome (CPC 1-2) and 37% died. Improved outcome was observed with longer hypothermia time and possibly when time from collapse to return of spontaneous circulation was < 25 minutes. MIH, using an external cooling system, is simple and feasible, reduces mortality and protects neurological function. Four major factors seem to influence outcome: age, co-morbidities, duration of hypothermia, and possibly the length of time from collapse to return of spontaneous circulation.