Surface cooling for rapid induction of mild hypothermia after cardiac arrest: design determines efficacy

Recently, a novel cooling pad was developed for rapid induction of mild hypothermia after cardiac arrest. The aim of this study was to evaluate the cooling efficacy of three different pad designs for in-hospital cooling.

Included in this prospective interventional study were patients with esophageal temperature (Tes) > 34 degrees C on admission. The cooling pad consists of multiple cooling units, filled with a combination of graphite and water, which is precooled to -18 degrees C (design A) or to -9 degrees C (designs B and C) before use. The designs of the cooling pad differed in number, shape, and thickness of the cooling units, with weights of 9.7 kg (design A), 5.3 kg (design B), and 6.2 kg (design C). All three designs were tested in sequential order and were changed according to the results found in the previous trial. Cooling was started after admission until Tes = 34 degrees C, when the cooling pad was removed. The target temperature of Tes = 32-34 degrees C was maintained for 24 hours. Data are presented as medians and interquartile ranges (IQRs = 25%-75%) or proportions.

Cooling rates were 3.4 degrees C/hour (IQR = 2.5-3.7) with design A (n = 12), 2.8 degrees C/hour (IQR = 1.6-3.3) with design B (n = 7), and 2.9 degrees C/hour (IQR = 1.9-3.6) with design C (n = 10; p = 0.5). To reach 34 degrees C, the cooling pad had to be exchanged with a new one due to melting and therefore depleting cooling capacity in three patients with design A, in five patients with design B, and in no patient with design C (p = 0.004).

With adequate design and storage temperature, the cooling pad proved to be efficient for rapid in-hospital cooling of patients resuscitated from cardiac arrest.