Modest hypothermia provides partial neuroprotection for ischemic neonatal brain

Hypothermia is a frequent occurrence in newborns, and thermoregulatory management is a fundamental part of medical stabilization. Although modest reduction in brain temperature (2-3°C) before ischemia provides neuroprotection in adults, the effect of modest hypothermia on immature brain has not been examined. Nine-day-old swine were exposed to 15 min of incomplete global brain ischemia, with intraischemic rectal temperatures of either 38.3 ± 0.4°C (n = 10, normothermic) or 35.4 ± 0.5°C (n = 10, hypothermic). The relationship between rectal and brain temperature was delineated in preliminary experiments on four swine. Animals with intraischemic rectal temperatures maintained at either 39.5°C or 35.5°C were associated with a similar magnitude of difference in brain temperature. Therefore, rectal temperature was used to monitor brain temperature for 20 animals studied subsequently. Ischemia was induced by combining neck compression with hemorrhagic hypotension and resulted in similar group values for mean arterial pressure and changes in pH and blood gases at the completion of ischemia. A clinical overall performance score and brain tissue structure were evaluated after 72 h (or earlier if animals died prematurely). Hypothermic animals had less severe stages of impairment compared with the normothermic group (p = 0.023). Hypothermic piglets had less histologic damage in the neocortex at 0.5 cm beneath the brain surface (p = 0.048), the caudate nucleus (p = 0.038), and the pons/ midbrain (p = 0.04) and the same direction of effect in neocortex at 1 cm beneath the surface (P = 0.07) and the cerebellum (p = 0.07) as compared with normothermic animals. The results demonstrate that a 2-3°C reduction in brain temperature during 15 min of incomplete ischemia provides partial neuroprotection in neonatal swine.