Sustained inflation during HFOV improves pulmonary mechanics and oxygenation

Effective use of high-frequency oscillatory ventilation (HFOV) may require maintenance of adequate lung volume to optimize gas exchange. To determine the impact of inflation during HFOV, sustained inflation was applied at pressures of 5, 10, and 15 cmH2O above mean airway pressure for 3, 10, and 30 s to 15 intubated, paralyzed, anesthetized rabbits after saline lavage to induce surfactant deficiency. Arterial blood gases were recorded in all rabbits while static compliance, resistance, time constant, and changes in functional residual capacity were recorded using the interrupter technique and plethysmograph in seven rabbits. Parameters were recorded before and 2 min after sustained inflation. Arterial PO2, compliance of the respiratory system, and functional residual capacity increased after sustained inflation at pressure levels of at least 10 cmH2O and 10-s duration. As the presence or duration of a sustained inflation was increased, oxygenation improved (P less than or equal to 0.01), but arterial PCO2 increased as longer sustained inflations were used (P less than or equal to 0.005). Sustained inflations of 5 cmH2O above mean airway pressure or of 3-s duration were ineffective. We conclude that either a critical pressure or duration of sustained inflation is needed to improve oxygenation and pulmonary mechanics during HFOV.