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 m odest reduction in brain temperature (2-3 degrees C) before ischemia p rovides 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 rec tal temperatures of either 38.3 +/- 0.4 degrees C (n = 10, normothermi c) or 35.4 +/- 0.5 degrees C (n = 10, hypothermic). The relationship b etween rectal and brain temperature was delineated in preliminary expe riments on four swine. Animals with intraischemic rectal temperatures maintained at either 39.5 degrees C or 35.5 degrees C were associated with a similar magnitude of difference in brain temperature. Therefore , rectal temperature was used to monitor brain temperature for 20 anim als studied subsequently. Ischemia was induced by combining neck compr ession with hemorrhagic hypotension and resulted in similar group valu es for mean arterial pressure and changes in pH and blood gases at the completion of ischemia. A clinical overall performance score and brai n tissue structure were evaluated after 72 h (or earlier if animals di ed prematurely). Hypothermic animals had less severe stages of impairm ent compared with the normothermic group (p = 0.023). Hypothermic pigl ets 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 po ns/midbrain (p = 0.04) and the same direction of effect in neocortex a t 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 degrees C reduction in brain temperature during 15 min of incomplete ischemia provides partial neuroprotection in neonatal swine.