Optimal mean airway pressure during high-frequency oscillatory ventilation determined by measurement of respiratory system reactance

Background: The aims of the present study were (i) to characterize the relationship between mean airway pressure ( P AW ) and reactance measured at 5 Hz (reactance of the respiratory system ( X RS ) , forced oscillation technique) and (ii) to compare optimal P AW ( P opt ) defined by X RS , oxygenation, lung volume ( V L ), and tidal volume ( V T ) in preterm lambs receiving high-frequency oscillatory ventilation (HFOV). Methods: Nine 132-d gestation lambs were commenced on HFOV at P AW of 14 cmH 2 O ( P start ). P AW was increased stepwise to a maximum pressure ( P max ) and subsequently sequentially decreased to the closing pressure ( P cl , oxygenation deteriorated) or a minimum of 6 cmH 2 O, using an oxygenation-based recruitment maneuver. X RS , regional V L (electrical impedance tomography), and V T were measured immediately after ( t 0min ) and 2 min after ( t 2min ) each P AW decrement. P opt defined by oxygenation, X RS , V L , and V T were determined. Results: The P AW – X RS and P AW – V T relationships were dome shaped with a maximum at P cl +6 cmH 2 O, the same point as P opt defined by V L . Below P cl +6 cmH 2 O, X RS became unstable between t 0min and t 2min and was associated with derecruitment in the dependent lung. P opt , as defined by oxygenation, was lower than the P opt defined by X RS , V L , or V T . Conclusion: X RS has the potential as a bedside tool for optimizing P AW during HFOV.