Australian Hypothermia Study

The Australian study (9) enrolled comatose patients after ROSC who presented with an initial cardiac rhythm of ventricular fibrillation. Seventy-seven patients were randomly assigned to hypothermia or normothermia, according to the day of the month, with patients assigned to hypothermia on odd-numbered days. The hypothermia arm had 43 patients, and the normothermia arm had 34 patients. Paramedics initiated hypothermia by removing the patient's clothing and applying cold packs to the head and torso. In the hospital, patients underwent vigorous cooling by means of extensive application of ice packs around the head, neck, torso, and limbs to a target core temperature of 33°C, which was monitored by tympanic or bladder thermometer. The target temperature was maintained for 12 hours, and the patient was sedated and paralyzed with small doses of midazolam and vecuronium, as needed to prevent shivering. The patients were actively rewarmed by external warming with a heated-air blanket, beginning at the 18th hour after arrival, with continued sedation and neuromuscular blockade to suppress shivering. Similar sedation and paralysis protocol was provided to patients assigned to the nor-mothermic group, but the target core temperature was maintained at 37°C. Passive rewarming was used in these patients if they presented with mild spontaneous hypothermia.

The primary outcome measures were the places of discharge: to home, to a rehabilitation facility, or to a long-term nursing facility. Prior to discharge from the hospital, patients were evaluated by a specialist in rehabilitation medicine who was blinded to the treatment protocol. Discharge to home or to a rehabilitation facility was regarded as a good outcome, whereas death in the hospital or discharge to a long-term nursing facility, whether the patient was conscious or unconscious, was regarded as a poor outcome. The study found that 49% of patients in the hypothermia arm had good outcome, compared to 26% in the normothermia arm (relative risk for good outcome: 1.85, 95% CI: 0.97-3.49; p = 0.046). The overall mortality between the two groups did not reach statistical significance, with 51% for the hypothermia arm and 68% for the normothermia arm.

Based on the results of these two induced-hypothermia studies (8,9), a recommendation was made by the Task Force of the ILCOR (10,55) such that, "Unconscious adult patients with spontaneous circulation after out-of-hospital cardiac arrest should be cooled to 32°C-34°C for 12-24 hours when the initial rhythm was ventricular fibrillation (VF)." Such cooling may also be beneficial for other rhythms or in-hospital cardiac arrest.

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