Reflections on pediatric high-frequency oscillatory ventilation from a physiologic perspective

Abstract

Mechanical ventilation using low tidal volumes has become universally accepted to prevent ventilator-induced lung injury. High-frequency oscillatory ventilation (HFOV) allows pulmonary gas exchange using very small tidal volume (1-2 mL/kg) with concomitant decreased risk of atelectrauma. However, its use in pediatric critical care varies between only 3% and 30% of all ventilated children. This might be explained by the fact that the beneficial effect of HFOV on patient outcome has not been ascertained. Alternatively, in contrast with present recommendations, one can ask if HFOV has been employed in its most optimal fashion related especially to the indications for and timing of HFOV, as well as to using the best oscillator settings. The first was addressed in one small randomized study showing that early use of HFOV, instead of rescue use, was associated with improved survival. From a physiologic perspective, the oscillator settings could be refined. Lung volume is the main determinant of oxygenation in diffuse alveolar disease, suggesting using an open-lung strategy by recruitment maneuvers, although this is in practice not custom. Using such an approach, the patient can be oscillated on the deflation limb of the pressure-volume (P-V) curve, allowing less pressure required to maintain a certain amount of lung volume. Gas exchange is determined by the frequency and the oscillatory power setting, controlling the magnitude of the membrane displacement. Experimental work as well as preliminary human data have shown that it is possible to achieve the smallest tidal volume with concomitant adequate gas exchange when oscillating at high frequency and high fixed power setting. Future studies are needed to validate these novel approaches and to evaluate their effect on patient outcome.