Thirty-two swine (mean+/-SE weight, 23.0+/-0.6 kg) were divided into 4 groups: normothermia (n=8), mild
hypothermia (35 degrees C) (n=8), moderate
hypothermia (33 degrees C) (n=8), and severe
hypothermia (30 degrees C) (n=8).
Hypothermia was induced by surrounding the animal with
ice, and VF was electrically induced. After 8 minutes of unsupported VF (no
CPR), the swine were defibrillated (biphasic waveform) with successive shocks as needed and underwent
CPR until resumption of spontaneous circulation or no response (> or =10 minutes). First-
shock defibrillation success was higher in the moderate
hypothermia group (6 of 8
hypothermia versus 1 of 8 normothermia; P=0.04). The number of shocks needed for late defibrillation (> or =1 minute after initial
shock) was less in all 3
hypothermia groups compared with normothermia (all P<0.05). None of the 8 animals in the normothermia group achieved resumption of spontaneous circulation compared with 3 of 8 mild
hypothermia (P=
NS), 7 of 8 moderate
hypothermia (P=0.001), and 5 of 8 severe
hypothermia (P=0.03) animals. Coronary perfusion pressure during
CPR was not different between the groups.
CONCLUSIONS: When VF was induced in the setting of moderate or severe
hypothermia, resuscitative measures were facilitated with significantly improved defibrillation success and
resuscitation outcome. The beneficial effect of
hypothermia was not due to alteration of coronary perfusion pressure, which suggests that changes in the mechanical, metabolic, or electrophysiological properties of the myocardium may be responsible.