Lung volume recruitment in lambs during high-frequency oscillatory ventilation using respiratory inductive plethysmography

Monitoring lung volume is important in the treatment of acute hypoxemic res piratory failure. However, there are no tools available for lung volume mea surement to guide ventilator management during high-frequency oscillatory v entilation (HFOV) and during dynamic changes in conventional ventilation (C V). We studied the performance of a new respiratory inductive plethysmograp h (RIP) with modified software. We measured Delta changes in lung volume ab ove end-expiratory volume (V-RIP) during HFOV and studied whether changes i n V-RIP parallel changes in mean airway pressure. Calibration of the plethy smograph was made by serial injections of a known gas volume in six term (1 40 d gestation) and eight preterm (125 d gestation) lambs. Linear regressio n analysis of the relationship between injected gas volume and V-RIP showed strong correlation (r(2) = 0.93-1.00 term animals, r(2) = 0.86-1.00 preter m animals). The pressure volume curves from the calibration with the inject ed gas volumes also correlated well with the pressure volume curves extrapo lated from changes in V-RIP. Lung hysteresis was clearly demonstrated with RIP after changes in mean airway pressure during HFOV and after changes in positive end-expiratory pressure during CV. We conclude that measurements o f lung volume in term and preterm lambs by use of modified RIP correlate we ll with changes in mean airway pressure during HFOV, with static pressure v olume curves and with changes in positive end-expiratory pressure during CV . We speculate that this technique may provide clinically useful informatio n about changes in lung volume during HFOV and CV. However, evaluation of t he precision and chronic stability of RIP measurements over prolonged perio ds will require further studies.