The aim of the study was to identify the optimal level of hypothermia during cardiac arrest, just prior to resuscitation with an extracorporal cooling system and without fluid overload, for neurological outcome at day 9 in pigs.
In a prospective randomised laboratory investigation, 24 female Large White pigs (31-38 kg) underwent ventricular fibrillation cardiac arrest for 15 min, followed by 1 min, 3 min, or 5 min (n =8 per group) of 4°C cooling with an extracorporal cooling system via an aortic balloon catheter and resuscitation with cardiopulmonary bypass. Sixty minutes following induction of cardiac arrest, defibrillation attempts were started. Mild hypothermia (34.5°C) and intensive care were continued for 20 h and final outcome was evaluated after 9 days.
Brain temperature decreased from 38.5°C to 30.4±1.6°C within 221±81 s in the 1min-group; to 24.2±4.6°C within 375±127 s in the 3min-group; and to 18.8±4.0°C within 450±121 s in the 5min-group. Restoration of spontaneous circulation was achieved in seven (1min-group), six (3min-group) and six (5min-group) animals (p = 0.78), whereas survival to 9 days was only achieved in six, three, and three animals in each group (p = 0.22), respectively.
Differences in outcome were not statistically significant amongst the three groups with various levels of hypothermia (30°C, 24°C, and 18°C) during cardiac arrest prior to resuscitation. However, the animals with the least temperature reduction showed a trend to better survival for 9 days. Further studies are necessary to investigate optimized methods for induction, as well as level, of cerebral hypothermia.