Arterial blood gases during raised intracranial pressure in anesthetized cats under controlled ventilation

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Abstract
In anesthetized paralyzed cats ventilated with air, blood gases were analyzed repeatedly before and during episodes of raised intracranial pressure (ICP). The ICP was raised by infusion via the lumbar subarachnoid or intraventricular route, and increases were maintained for at least 30 min. A minor degree of hypoxemia commonly developed, but was always associated with hypercapnia; normoxia was restored by increasing the ventilation sufficiently to restore normocapnia. Relative underventilation is thus liable to develop if the minute volume is maintained constant when ICP is raised, probably because of increased metabolic rate which may be associated with a rise in temperature; there is no evidence to implicate more obscure causes of hypoxemia in this circumstance. Pulmonary hemorrhage and edema were found post mortem in 9 of 20 animals, but only 2 of these had developed greater hypoxemia than could be accounted for by under-ventilation. Phrenic electroneurograms were recorded, and respiratory activity persisted during prolonged periods of cerebral ischemia.