Out-of-hospital surface cooling with a cooling-blanket to induce mild hypothermia in humans after cardiac arrest: a feasibility trial

Introduction

Mild hypothermia (32–34°C) is a promising new therapy for patients resuscitated from cardiac arrest. Animal studies suggest that early and fast cooling is crucial for beneficial effect on neurological outcome. Inducing mild hypothermia immediately after successful restoration of spontaneous circulation (ROSC) in the out-of-hospital setting remains a challenge. Therefore, a novel cooling-blanket (EMCOOLSpad^®), independent of any energy source during use, was developed. The aim of the study was to evaluate feasibility and safety of out-of-hospital surface cooling with EMCOOLSpad^® in patients successfully resuscitated from cardiac arrest.

Methods

We included patients successfully resuscitated from out-of-hospital cardiac arrest with an oesophageal temperature (T_es)>34°C. The EMCOOLSpad^® consists of multiple cooling units (12 mm thick), filled with a mixture of graphite/water, which are stored in a cooling box at -3°C in the ambulance car. Cooling was initiated as soon as feasible by the first treating paramedics and emergency physicians, and was continued in the emergency room. The cooling-blanket was removed when the T_es reached 34°C. The target temperature of T_es 33°C was maintained for 24 hours. Data are presented as the median and interquartile range (25–75%).

Results

From September 2006 to December 2006, 10 patients, weighing 70 (64–93) kg, were included in the study. Cooling was initiated 14 (7–20) minutes after ROSC. The cooling-blanket decreased the T_es from 36.5 (36.2–36.7)°C at the start of cooling to 34.0°C within 61 (47–93) minutes, and to target temperature T_es 33°C within 83 (61–119) minutes, resulting in a cooling rate of 2.6 (1.6–3.6)°C/hour. Hospital admission was 45 (40–53) minutes after ROSC, and T_es 33°C was achieved 78 (32–107) minutes after admission. In eight patients, precooled parts of the cooling-blanket had to be applied repeatedly on the chest and abdomen to maintain the target temperature of T_es 33°C for 24 hours. No skin lesions were observed.

Conclusion

Noninvasive surface cooling with the EMCOOLSpad^® immediately after resuscitation from cardiac arrest, in the out-of-hospital setting, was shown to be feasible and safe. Whether early cooling, as compared with delayed cooling in the hospital, will improve neurological outcome needs to be determined in a prospective randomized trial.