PREDICTIVE VALUE OF MEASUREMENTS OF RESPIRATORY MECHANICS IN PRETERM INFANTS WITH HMD

Conventional methods for measuring respiratory mechanics model the res piratory system as a single compartment. The interrupter technique all ows the respiratory system to be considered as a two compartment model with ''flow resistance'' of the conducting airways (Rinit), calculate d from the initial pressure drop (Pinit), considered separately from P diff, as a measure of the viscoelastic properties of the lung and ches t wall and any pendelluft present. The pulmonary mechanics of 50 intub ated and mechanically ventilated preterm infants (less-than-or-equal-t o 1500 g) were studied during the first week of life using conventiona l methods and the interrupter technique to determine whether it was po ssible to predict which infants would develop bronchopulmonary dysplas ia (BPD). Pulmonary mechanics of preterm infants intubated and ventila ted for apnea of prematurity were also studied. The dynamic compliance of the respiratory system (C(rsdyn)) was significantly lower on day 1 (P < 0.001) and during the first week of life in the infants with HMD who developed BPD (ANOVA, P < 0.0001). There was no significant diffe rence in the respiratory system resistance (R(rs)), Rinit, or Pdiff be tween BPD and no-BPD groups. However, Pdiff was significantly higher i n infants with HMD, regardless of the outcome, when compared to the in fants ventilated for apnea of prematurity. This suggests that the path ology of HMD is distal to the conducting airways and significantly alt ers the viscoelastic properties of the lung on day 1. Using stepwise l ogistic regression, C(rsdyn) on day 1 and birth weight or gestational age were significant independent predictors of the development of BPD, correctly classifying 92% of infants. Due to the correlation between birth weight and gestational age (r = 0.72, P < 0.0001), only one of t hese variables was necessary in the prediction model. In conclusion, C (rsdyn) is a better independent predictor of the development of BPD in preterm infants with HMD than gestational age or birth weight. (C) 19 93 Wiley-Liss, Inc.