Cerebral and Cardiopulmonary Responses to High-Frequency Jet Ventilation and Conventional Mechanical Ventilation in a Model of Brain and Lung Injury

Abstract

The cardiopulmonary and intracranial effects of high-frequency jet ventilation (HFJV) were evaluated in four groups of 10 mongrel dogs and compared to conventional mechanical ventilation with and without positive and expiratory pressure (PEEP). Each group of animals was studied with various combinations of normal and abnormal brain and lung function. Experimental brain injury (abnormal cerebral elastance) was produced by infusion of saline into the subarachnoid space to increase intracranial pressure (ICP), while lung injury resulted from intratracheal instillation of 0.1N HCl. Animals responded similarly to HFJV and conventional ventilation except for those with abnormal lungs, in whom peak airway pressures were significantly lower with HFJV (P less than 0.05). The application of PEEP (10 and 20 cm H2O) produced significant increases in mean airway pressure compared to HFJV (P less than 0.05). Animals with abnormal lungs demonstrated significantly improved mean PaO2 (194 vs 104 mm Hg) and shunt fraction (0.20 vs 0.45) with 20 cm H2O PEEP compared to HFJV. In all dogs subjected to 20 cm H2O PEEP, cardiac index and mean arterial pressure were decreased significantly (P less than 0.05) below values with HFJV. ICP responses did not vary significantly with the different modes of ventilation and were not influenced by the status of lung or brain function. However, significant reductions in cerebral perfusion pressure were noted with 20 cm H2O PEEP compared to HFJV. We conclude that unless high levels of PEEP (15-20 cm H2O) are required for adequate oxygenation, the cardiovascular and cerebral effects of HFJV do not differ significantly from those of conventional mechanical ventilation.