Cryogenic brain oedema: loss of cerebrovascular autoregulation as a cause of intracranial hypertension. Implications for treatment.

Experimental cryogenic brain oedema was created in albino rabbits, and intracranial pressure (ICP), cerebral blood flow (CBF), EEG, blood pressure, central venous pressure, were subsequently studied at a constant PaCO2. Upon completion the brain water content of the gray and white matter was analyzed by gravimetry. The findings were compared to controls and sham-operated. Two subsets of elevated ICP following cryogenic injury were identified: one with a mean of 6.2 +/- 3.3 torr (n = 7) and the other of 19.3 +/- 9 (n = 5) (p less than 0.005). Both these subsets had similar white and gray matter gravimetry values indicating that the magnitude of cerebral oedema was comparable and could not explain the difference in ICP. There was however a significant difference in the CBF of the left hemisphere between these subsets, with Subset A at 49.1 +/- 9 ml/100 g/min and Subset B with 70 +/- 9.1 (p less than 0.001). We conclude that the ICP elevation in the cryogenic oedema model may be due to not only increased brain water of the injured hemisphere, but also to increased cerebral blood volume due to increased CBF.