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.