High-frequency Percussive Ventilation Improves Oxygenation in Patients With ARDS
High-frequency ventilation has emerged during the last 10 years as a way of maintaining gas exchange while, it is hoped, limiting respirator-associated lung parenchymal injury. This mode of ventilation is mainly administered by three types of equipment: (1) jet ventilators, (2) oscillators, and (3) flow interrupters. Although high-frequency jet ventilation has been extensively tested in pediatric patients with encouraging results, the experience is limited with other types of high-frequency ventilation in this group. Studies in adults have produced conflicting results.
The latest such technique is high-frequency percussive ventilation (HFPV) delivered by the volumetric diffusive respirator (VDR). In an attempt to combine the beneficial effects of high-frequency and conventional ventilation (CV), this device delivers small tidal volumes (Vts) at rapid rates by a reciprocating system. It delivers a series of high-frequency breaths with a shortened expiratory time (Te) to allow breath stacking. This is then interrupted to allow pressure reduction back to baseline, A unique feature of this technique is that exhalation is an active phenomenon. Additionally, the endotracheal tube cuff is partially deflated, allowing air to escape around it and avoiding the generation of potentially damaging intra-alveolar pressures.
In patients with ARDS, lung stiffness is a predictable and dangerous complication. As the maintenance of adequate oxygenation in the face of impending barotrauma is at best a trade-off with CV, HFPV offers an attractive alternative for such patients. There are only a few reports evaluating the efficacy of HFPV in adult patients suffering from ARDS.’’ Even if some of these studies show improvement in respiratory function with HFPV, there are only speculations on mechanisms responsible for favorable outcome.
In this study, we analyzed our experience with HFPV in patients with ARDS. We evaluated the changes in respiratory and hemodynamic function after the patients were switched from CV to HFPV. We propose a mechanism by which these changes occur.