Comparison of the durations of mild therapeutic hypothermia on outcome after cardiopulmonary resuscitation in the rat.

BACKGROUND: Current studies have demonstrated that applying therapeutic hypothermia for 12 to 24 hours after resuscitation from cardiac arrest improves the outcomes of cardiopulmonary resuscitation. The present study investigated whether a shorter duration of therapeutic hypothermia induced quickly and early after resuscitation would provide an equal improvement in the outcomes of cardiopulmonary resuscitation.

METHODS AND RESULTS: Ventricular fibrillation was induced and untreated for 8 minutes in 24 male Sprague-Dawley rats. Defibrillation was attempted after 8 minutes of cardiopulmonary resuscitation. Seven minutes after resuscitation, animals were randomized into 4 groups (n=6 each): normothermic, hypothermic-2 hours, hypothermic-5 hours, and hypothermic-8 hours. Animals in the hypothermic groups received rapid cooling, which was started 7 minutes after restoration of spontaneous circulation and maintained at 33±0.5°C for 2, 5, or 8 hours. Normothermic animals were maintained at 37±0.2°C. All animals were anesthetized and ventilated for 8 hours after resuscitation. Blood temperature was significantly decreased in the hypothermic groups. Postresuscitation myocardial function, neurological deficit scores, and 72-hour survival were significantly better in animals treated with hypothermia regardless of the duration of cooling. However, significantly better postresuscitation tissue microcirculation, myocardial ejection fraction, and neurological deficit scores were observed in the hypothermic-2 hours animals.

CONCLUSIONS: In a rat model of cardiopulmonary resuscitation, a shorter duration of mild hypothermia induced rapidly and early after restoration of spontaneous circulation improved postresuscitation microcirculation, myocardial and cerebral functions, and survival as well as, or better than, prolonged duration of hypothermia after resuscitation.