Comparison of the effects of hypothermia at 33 degrees C or 35 degrees C after cardiac arrest in rats.
OBJECTIVE
Hypothermia of 32 degrees C-34 degrees C induced after resuscitation from cardiac arrest improves neurologic recovery, but the optimal depth of cooling is unknown. Using a rat model, the authors tested the hypothesis that cooling to 35 degrees C between hours 1 and 24 after resuscitation would improve neurologic outcome as much as cooling to 33 degrees C.


METHODS
Halothane-anesthetized rats (n = 38) underwent 8 minutes of asphyxial cardiac arrest and resuscitation. Cranial temperature was maintained at 37 degrees C before, during, and after arrest. Between one and 24 hours after resuscitation, cranial temperature was maintained at 33 degrees C, 35 degrees C, or 37 degrees C using computer-controlled cooling fans and heating lamps. Neurologic scores were measured daily, and rats were killed at 14 days for histologic analysis. Neurons per high-powered field were counted in the CA1 region of the anterior hippocampus using neuronal nuclear antigen staining.


RESULTS
After 14 days, 12 of 12 rats (100%) cooled to 33 degrees C, 11 of 12 rats (92%) cooled to 35 degrees C, and ten of 14 rats (71%) cooled to 37 degrees C survived, with hazard of death greater in the rats cooled to 37 degrees C than in the combined hypothermia groups. Neurologic scores were worse in the rats cooled to 37 degrees C than in the hypothermia groups on days 1, 2, and 3. Numbers of surviving neurons were similar between the groups cooled to 33 degrees C and 35 degrees C and were higher than in the group cooled to 37 degrees C.


CONCLUSIONS
These data illustrate that hypothermia of 35 degrees C or 33 degrees C over the first day of recovery improves neurologic scores and neuronal survival after cardiac arrest in rats. The benefit of induced hypothermia of 35 degrees C appears to be similar to the benefit of 33 degrees C.
Logue
Eric S
ES
Department of Emergency Medicine, Safar Center for Resuscitation Research, University of Pittsburgh, Pittsburgh, PA, USA.
McMichael
Melissa J
MJ
Callaway
Clifton W
CW
D000818:Animals; D002545:Brain Ischemia / Q000503:physiopathology* / Q000517:prevention & control*; D006323:Heart Arrest / Q000503:physiopathology*; D007036:Hypothermia, Induced / Q000379:methods*; D008297:Male; D016016:Proportional Hazards Models; D051381:Rats; D017207:Rats, Sprague-Dawley; D018709:Statistics, Nonparametric