Response of ventilation and of intracranial pressure during rebreathing of carbon dioxide in patients with acute brain damage.

A study of the ventilatory response to rising CO2 in 43 patients with acute brain damage, using a rebreathing method, has revealed several instances of abnormally low responsiveness. The increased responsiveness previously reported in chronic brain damage was not observed in these patients by this method. The incidence of a very low response to CO2 tended to be associated with hyperventilation and brain-stem damage, but the numbers were insufficient to define a statistical relationship. There was no association between responsiveness to CO2 and either bilateral forebrain damage or periodic breathing. Studies of changes in intracranial pressure with rising CO2 suggest that such a rebreathing test might provide a simple means of confirming the presence or absence of cerebrovascular response to changing CO2.