Effect of hyperventilation on brain tissue oxygen pressure, carbon dioxide pressure, pH value and intracranial pressure during intracranial hypertension in pigs.

OBJECTIVE

To study the effect of hyperventilat ion on brain tissue oxygen pressure (P(ti)O(2)), brain tissue carbon dio xide pressure (P(ti)O(2)), pH value and intracranial pressure (ICP) dur ing intracranial hypertension in pigs.

METHODS

Autologous arterial blood (5.5 mlplus minus0.5 ml) was injected into the left frontal lobe by micropump to establish the model of intr acerebral hematoma in pigs. After blood injection, the animals were hyperventila ted for 15 minutes to decrease the pressure of carbon dioxide in arterial blood (P(a)CO(2)) to 27.35 mm Hgplus minus11.97 mm Hg (1 mm Hg=0.133 kPa). The mean arterial pressure (MAP), intracranial pressure (ICP), cerebral perfusion pressure (CPP), P(ti)O(2), (P(ti)CO(2)), pH value and [HCO(3)(-)] were continuously monitored and the blood gas was analyzed.

RESULTS

After hyperventilation, the ICP significantly decr eased (P<0.01), the CPP significantly increased (P<0.05), while the P(ti)O(2) greatly decreased to t he ischemic level (8.20 mm Hgplus minus2.50 mm Hg) (P<0.01), the P(ti)CO(2) decreased (P<0.01) and the pH value increased (P<0.01). At the same time, bl ood gas analysis showed that the P(a)CO(2) greatly decreased and the pH valu e increased.

CONCLUSIONS

Hyperventilation can decrease the ICP and the P(ti)O(2) significantly. Therefore, hyperventilation should be avoided earl y after brain injury. The P(ti)O(2) monitoring will be helpful for detec ting cerebral ischemia early.