Effect of hyperventilation on brain tissue oxygenation and cerebrovenous PO2 in rats

Previous studies have shown that cortical tissue oxygenation is impaired du ring hyperventilation. However, it is important to quantify the effect of h yperventilation on brain tissue PO2 and cerebrovenous PO2 simultaneously es pecially since cerebral Venous oxygenation is often used to assess brain ti ssue oxygenation. The present study was designed to measure the sagittal si nus PO2 (PvO(2)), brain tissue PO2 In the thalamus (PtO2), and brain temper ature (Bt) simultaneously during acute hyperventilation. Isoflurane-anesthe tized rats were hyperventilated for 10 min during which time the arterial c arbon dioxide tension (PaCO2) dropped from 40.3+/-4.9 mmHg to 23.5+/-2.8 mm Hg. PtO2 declined from 26.0+/-4.2 mmHg to 14.8+/-5.2 mmHg (P=0.004) while b rain temperature decreased from 36.5+/-0.3 degrees C to 36.2+/-0.3 degrees C (P=0.02). However, PvO(2) and arterial blood pressure (BP) did not change during hyperventilation. The maintenance of PvO(2) when perfusion is thoug ht to decline and PtO2 decreases suggests that there may be a diffusion lim itation, possibly due to selective perfusion. Therefore, cerebrovenous PO2 may not give a good assessment of bran tissue oxygenation especially in con ditions of acute hyperventilation. and deeper brain regions other than the cortex also show impaired tissue oxygenation following hyperventilation, (C ) 2000 Elsevier Science B.V. All rights reserved.