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Comparison of the Effects of Hypothermia at 33°C or 35°C after Cardiac Arrest in Rats
Author(s) -
Logue Eric S.,
McMichael Melissa J.,
Callaway Clifton W.
Publication year - 2007
Publication title -
academic emergency medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.221
H-Index - 124
eISSN - 1553-2712
pISSN - 1069-6563
DOI - 10.1197/j.aem.2006.10.097
Subject(s) - medicine , hypothermia , resuscitation , anesthesia , cardiopulmonary resuscitation
Objectives:Hypothermia of 32°C–34°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°C between hours 1 and 24 after resuscitation would improve neurologic outcome as much as cooling to 33°C.Methods:Halothane‐anesthetized rats ( n = 38) underwent 8 minutes of asphyxial cardiac arrest and resuscitation. Cranial temperature was maintained at 37°C before, during, and after arrest. Between one and 24 hours after resuscitation, cranial temperature was maintained at 33°C, 35°C, or 37°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°C, 11 of 12 rats (92%) cooled to 35°C, and ten of 14 rats (71%) cooled to 37°C survived, with hazard of death greater in the rats cooled to 37°C than in the combined hypothermia groups. Neurologic scores were worse in the rats cooled to 37°C than in the hypothermia groups on days 1, 2, and 3. Numbers of surviving neurons were similar between the groups cooled to 33°C and 35°C and were higher than in the group cooled to 37°C.Conclusions:These data illustrate that hypothermia of 35°C or 33°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°C appears to be similar to the benefit of 33°C.