Selective head cooling has been proposed as a neuroprotective intervention
after hypoxia-ischemia in which the brain is cooled without subjecting the
rest of the body to significant hypothermia, thus minimizing adverse system
ic effects. There are little data showing it is possible to cool the brain
more than the body. We have therefore applied selective head cooling to our
hypoxia-ischemia piglet model to establish whether it is possible. Nine pi
glets were anesthetized, and brain temperature was measured at the surface
and in the superficial (0.2 cm) and deep (1.7-2.0 cm) gray matter. Rectal (
6-cm depth), skin, and scalp temperatures (T) were recorded continuously. L
owering T-rectal from normothermia (39 degreesC) to hypothermia (33.5-33.8
degreesC) using a head cap perfused with cold (6-24 degreesC) water was und
ertaken for up to 6 h. To assess the impact of the 45-min hypoxia-ischemia
insult on the effectiveness of selective head cooling, four piglets were co
oled both before and after the insult, and four, only afterward. During sel
ective head cooling, it waspossible to achieve a lower T-deep brain than T-
rectal in all animals both before and after hypoxia. However, this was only
possible when overhead body heating was used. The T-rectal to T-deep brain
gradient was significantly smaller after the insult (median, 5.3 degreesC;
range, 4.2-8.5 degreesC versus 3.0 degreesC; 1.7-7.4 degreesC; p = 0.008).
During rewarming to normothermia, the gradient was maintained at 4.5 degre
esC. We report for the first time a study, which by direct measurement of d
eep intracerebral temperatures, validates the cooling cap as an effective m
ethod of selective brain cooling in a newborn animal hypoxia-ischemia model
.