Pilot Randomized Clinical Trial of Prehospital Induction of Mild Hypothermia in Out-of-Hospital Cardiac Arrest Patients With a Rapid Infusion of 4°C Normal Saline

TLDR

Although delayed hospital cooling improves outcomes after cardiac arrest, initiating cooling immediately after return of spontaneous circulation in the field may be more beneficial. The study aimed to evaluate the feasibility, safety, and effectiveness of in-field cooling and to suggest larger trials focusing on neurological outcomes, particularly in patients with ventricular fibrillation. A randomized pilot trial enrolled 125 patients, assigning 63 to receive intravenous cooling with 500–2000 mL of 4 °C normal saline before hospital arrival, while 62 received standard care. In-field cooling reduced esophageal temperature by 1.24 °C (arrival 34.7 °C) versus a 0.10 °C increase in controls (arrival 35.7 °C, P < 0.0001) without adverse hemodynamic or respiratory effects, and trended toward better awakening and survival in ventricular fibrillation patients.

Abstract

Although delayed hospital cooling has been demonstrated to improve outcome after cardiac arrest, in-field cooling started immediately after the return of spontaneous circulation may be more beneficial. The aims of the present pilot study were to assess the feasibility, safety, and effectiveness of in-field cooling.We determined the effect on esophageal temperature, before hospital arrival, of infusing up to 2 L of 4 degrees C normal saline as soon as possible after resuscitation from out-of-hospital cardiac arrest. A total of 125 such patients were randomized to receive standard care with or without intravenous cooling. Of the 63 patients randomized to cooling, 49 (78%) received an infusion of 500 to 2000 mL of 4 degrees C normal saline before hospital arrival. These 63 patients experienced a mean temperature decrease of 1.24+/-1 degrees C with a hospital arrival temperature of 34.7 degrees C, whereas the 62 patients not randomized to cooling experienced a mean temperature increase of 0.10+/-0.94 degrees C (P<0.0001) with a hospital arrival temperature of 35.7 degrees C. In-field cooling was not associated with adverse consequences in terms of blood pressure, heart rate, arterial oxygenation, evidence for pulmonary edema on initial chest x-ray, or rearrest. Secondary end points of awakening and discharged alive from hospital trended toward improvement in ventricular fibrillation patients randomized to in-field cooling.These pilot data suggest that infusion of up to 2 L of 4 degrees C normal saline in the field is feasible, safe, and effective in lowering temperature. We propose that the effect of this cooling method on neurological outcome after cardiac arrest be studied in larger numbers of patients, especially those whose initial rhythm is ventricular fibrillation.