Cooling of the brain through oxygen flushing of the nasal cavities in intubated rats: an alternative model for treatment of brain injury.

Local cooling of the brain by respiration has been found in several animal species with a rete mirabile in the carotid artery/cavernous sinus complex. The present experiment was made to investigate whether a similar cooling could be found in the rat, which does not have a rete. Eleven rats were anesthetized and intubated. Three thermoprobes were inserted into the brain (two probes) and rectum, and the temperatures measured continuously. The nasal cavities were flushed with oxygen (250-1000 ml/min) during 15-min periods, interrupted by 15-min control periods. The mean brain temperature decreased by 0.43 +/- 0.03 degree C (n = 86, P < 0.005) with individual values up to 1.11 degrees C during the flushing periods. The decrease was oxygen-flow dependent, but not correlated to the rectal temperature. It is concluded that even an animal species without a rete mirabile is able to decrease the brain temperature through nasal cooling. The cooling was probably connected to the blood flow. If the results can be extrapolated to man (no rete mirabile), brain temperature can be decreased by nasal flushing with air or oxygen in intubated patients with hyperthermia. We also suggest that this simple treatment will reduce the infarct volume after head injury, trauma, or brain ischemia.