Effect of high-frequency ventilation versus conventional mechanical ventilation on ICP in head-injured dogs

Changes in intrathoracic pressure may influence intracranial pressure (ICP), presumably by affecting venous return. High-frequency ventilation (HFV) has been associated with lower intrapleural and airway pressures and has the potential to lower ICP. To evaluate the effects of HFV compared to conventional ventilation on ICP, normocarbia was maintained in nine dogs while alternating between conventional ventilation and HFV at 200 breaths/min. The mean ICP was raised from 6.3 +/- 6.1 to 24.7 +/- 1.04 mm Hg by inflation of Fogarty balloons implanted in the epidural space. The ICP peaks associated with positive inflation pressures were eliminated with HFV, but mean ICP was not significantly different between the two ventilatory modes (23.4 +/- 9.7 mm Hg for the conventional system versus 26.0 +/- 10.0 mm Hg for HFV). Four dogs exhibited neurogenic pulmonary edema: they developed elevated pulmonary artery and intrathoracic pressures and required increased inspiratory flow with HFV to maintain normocarbia. The authors conclude that, in this head-injury model, there did not seem to be an advantage of HFV over conventional ventilation.