Identification of optimal lung volume during high-frequency oscillatory ventilation using respiratory inductive plethysmography

OBJECTIVES First, to define the relationships between critical opening and closing pressures and oxygenating efficiency, and second, to address whether respiratory inductive plethysmography (RIP) could be used to monitor changes in thoracic volume that follow changes in mean airway pressure during high- frequency oscillatory ventilation (HFOV). DESIGN Prospective, interventional animal study. SETTING University research laboratory. SUBJECTS Five anesthetized, paralyzed, and ventilated pigs. INTERVENTIONS The animals were ventilated by using HFOV after lung injury. Pre- and post-HFOV pressure-volume curves were obtained by supersyringe. A pressure-volume curve was constructed during HFOV as mean airway pressure was increased from 10 to 40 cm H2O and then weaned back down to the minimum sustainable. Hemodynamic and oxygenation data were obtained at each data point. MEASUREMENTS AND MAIN RESULTS RIP-derived thoracic volumes correlated with known lung volumes during supersyringe (r = .78, p < .00001). During HFOV, three of five animals had an identifiable critical opening pressure of the lung, and four of five had an identifiable critical closing pressure. No consistent relationship between critical opening and critical closing pressures was observed. During the weaning phase of HFOV, a relative decrease in RIP-measured volume of >10% predicted the decrease in oxygenation associated with reaching the critical closing pressure. CONCLUSIONS The ability of RIP to detect optimal lung volume during the weaning of mean airway pressure may allow clinicians to more directly monitor lung volume changes during HFOV and use the lowest possible airway pressures after lung recruitment.