The effect of passive hyperventilation on intraventricular pressure in the dog.

The effectiveness of passive hyperventilation in reducing intracranial pressure was studied in mongrel dogs by varying the levels of end-tidal pCO2 and airway pressure, and comparing the positive-negative and positive-atmospheric pressure. It has been shown that there is a point beyond which reduction of pCO2 does not affect cerebral blood flow. The present study demonstrates that another limiting factor is the degree of positive or negative airway pressure. Positive airway pressure impedes venous drainage, thereby increasing intracranial pressure. This increase could only partly be offset by applying negative expiratory airway pressure, since it was found that excessive negative airway pressure (greater than static recoil pressure of the lung) may trap air in alveoli. An optimal range of positive and negative airway pressures is defined.