High-Frequency Ventilation

Abstract

High-frequency ventilation (HFV) is a difficult subject to deal with because we still lack a definition of high frequency. Basically HFV comes in three flavors: high-frequency positive pressure ventilation (HFPPV) introduced by Jonzon et al. (1); high-frequency jet ventilation (HFJV) introduced by Klain et al. (2); and high-frequency oscillation (HFO) introduced by Lunkenheimer et al. (3). The definition of high frequency depends on the system: HFPPV generally operates at 60+/min, HFJV at 150+/min and HFO at 900+/min. They can all achieve effective gas exchange in the normal lung. There are, as yet, no good comparative studies between the systems, nor any convincing evidence that any of them are superior to conventional mechanical ventilation (CMV) in diffuse parenchymal lung disease with hypoxia in humans. Despite this there are compelling theoretical reasons to suspect that HFV may be superior to CMV in this group of diseases. CMV creates large phasic volume distensions in sick lungs which have a nonuniform distribution of compliance, inevitably creating local overdistension. This can, at the macroscopic level, lead to air leaks (pneumothorax, etc.) and at the microscopic level cause hyaline membrane formation. Therefore, a mode of ventilation which reduces the magnitude of the volume distension might reduce the degree of barotrauma.