Hydrostatically raised intracranial pressure

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.

Respiration and acid-base balance of blood after diffuse experimental brain injury

Diffuse brain injury in rabbits was caused by injecting olive oil and saline into one internal carotid artery. In this report, the fourth of a series, the effects of this experimental brain injury on respiration and acid-base balance of blood are analyzed. The animals that withstood the injury best were those that had a lower pre-traumatic pCO2; the animals that suffered a rise in intracranial pressure and succumbed to the injury quickly did so in spite of pronounced hyperventilation after the injury. Arterial pCO2 immediately before the injury was the only significant prognostic factor in this analysis. Respiratory rate only dropped immediately before respiratory arrest and death. The findings concerning pCO2 tally with results after experimental ligation of a cerebral artery, but less so with results after other types of experimental brain injury. This emphasizes again that conclusions drawn from one type of brain injury must not be extrapolated to other types.