High-frequency Jet Ventilation in Postoperative Respiratory Failure

Abstract

Critically ill patients (24) in postoperative respiratory failure received high-frequency jet ventilation (HFJV). In 15 patients (Group A), respiratory frequency was maintained at 100/min and 3 different inspiratory/expiratory time (I/E) ratios were used at random: 0.25, 0.43 and 0.67. In 9 patients (Group B) I/E ratio was maintained at 0.43, and 6 respiratory frequencies were used at random: 100/min, 200/min; 300/min, 400/min, 500/min and 600/min. HFJV significantly increased PaO2 [arterial partial pressure of O2] in both groups. Mean airway pressure did not alter with respiratory frequency but increased with I/E ratio. In Group A patients, a significant relationship was found between improvement in PaO2 and the increase in mean airway pressure (r = 0.897, P < 0.001). A very close relationship was observed between mean alveolar pressure and mean airway pressure (r = 0.973, P < 0.001), suggesting that a PEEP [positive end-expiratory pressure] effect was created at the alveolar level. The increase in mean airway pressure induced an increase in pulmonary volume. In Group A patients, the mean increase in pulmonary volume above apneic functional residual capacity was +362 ml for an I/E ratio of 0.25, +1095 ml for an I/E ratio of 0.43 and +1936 ml for an I/E ratio of 0.67. In Group B patients, the mean increase in pulmonary volume above apneic functional residual capacity did not alter significantly with respiratory frequency. For a given ventilatory setting, the greater the static respiratory compliance, the greater was the increase in pulmonary volume. Mean airway pressure is apparently a principal determinant of arterial O2 tension during HFJV and I/E ratio rather than respiratory frequency influences PaO2 during this type of ventilation.