High-frequency oscillatory ventilation in neonatal RDS: initial volume optimization and respiratory mechanics

To determine whetherinitial lung volume optimization influences respiratory mechanics,which could indicate the achievement of optimal volume, we studied 17 premature infants with respiratory distress syndrome (RDS) assisted byhigh-frequency oscillatory ventilation. The continuous distendingpressure (CDP) was increased stepwise from 6-8 cmH₂Oup to optimal CDP (OCDP), i.e., that allowing good oxygenation with thelowest inspired O₂ fraction. Respiratory systemcompliance (Crs) and resistance were concomitantlymeasured. Mean OCDP was 16.5 ± 1.2 cmH₂O. InspiredO₂ fraction could be reduced from an initial level of 0.73 ± 0.17 to 0.33 ± 0.07. However, Crs (0.45 ± 0.14ml · cmH₂O¹ · kg¹at starting CDP point) remained unchanged through lung volume optimization but appeared inversely related to OCDP. Similarly, respiratory system resistance was not affected. We conclude that thereis a marked dissociation between oxygenation improvement and Crsprofile during the initial phase of lung recruitment by earlyhigh-frequency oscillatory ventilation in infants with RDS. Thusoptimal lung volume cannot be defined by serial Crs measurement. At themost, low initial Crs suggests that higher CDP will be needed.