Intraocular and intracranial pressure during respiratory alkalosis and acidosis

Intraocular and intracranial pressures (IOP and ICP) were measured at four different arterial carbon dioxide tensions by direct continuous techniques in Rhesus monkeys during anaesthesia with halothane and nitrous oxide. Increases in IOP correlated significantly with PaCO2 ranging from 2.66 to 10.24kPa (P less than 0.001). Increases in ICP correlated significantly (P less than 0.001) with PaCO2 between 2.66 and 7.71 kPa, but plateaued thereafter. When PaCO2 was decreased rapidly, PaCO2, IOP and ICP decreased exponentially with similar half-times. The fast changes in IOP and ICP can probably be explained by an alteration of intraocular and intracranial blood volumes. IOP usually remained within the normal range, even at maximum PaCO2.