Effect of intermittently raised intracranial pressure on breathing pattern, ventilatory response to CO2, and blood gases in anesthetized cats.

In anesthetised cats, breathing pattern, blood gases, and ventilatory response to CO2 were recorded before and during intermittent 10-minute episodes of hydrostatically raised intracranial pressure. The first effect on breathing was a stimulation which was followed at higher pressures by irregularity, depression, and periods of apnea; hyperventilation at high intracranial pressure (ICP was rare. Raised ICP did not consistently depress the ventilatory response to CO2 until ventilation during airbreathing was already depressed; therefore, we cannot experimentally justify applying this test clinically to detect incipient ventilatory depression. When hypoxemia developed during raised ICP, it was compatible with the degree of hypoventilation due to central depression of breathing; thus, there was no evidence of a neurally mediated effect on the lungs, causing defective gas exchange.