EFFECT OF MEAN AIRWAY PRESSURE ON LUNG-VOLUME DURING HIGH-FREQUENCY OSCILLATORY VENTILATION OF PRETERM INFANTS

Measurement of mean lung volume (MLV) in high-frequency oscillatory ve ntilation (HFO) may be useful for optimizing the high lung volume stra tegy, but has not been available until now. We have measured MLV by me ans of the sulfur hexafluoride (SF6) washout method in 13 premature in fants ventilated with HFO because of respiratory distress syndrome (ge stational age, 23 to 31 wk [median, 25 + 6/7 wk]; birthweight, 630 to 1,140 g [790 g]; age at measurement, 2 to 10 d [4 d]; weight, 675 to 1 ,250 g [850 g]). To evaluate the relationship between MLV and mean air way pressure (MAP), the latter was systematically varied between the m easurements. With clinically selected MAP, MLV was between 23.3 and 41 .9 ml/kg (median, 33.5 ml/kg) and was strongly dependent on MAP in eac h patient; linear regression analyses resulted in slope factors betwee n 1.0 and 6.9 ml/cm H2O/kg (median, 2.83 ml/cm H2O/kg), with correlati on coefficients between 0.77 and 0.99 (median, 0.94). Stabilization of MLV after modification of MAP took 2 to 25 min (median, 9 min). We co nclude that the selection of MAP on a clinical basis leads to a wide r ange of different MLVs. Despite the strong dependence of MLV on MAP, t he prediction of MLV solely based on MAP was impossible because of lar ge patient to patient variability of linear regressions. Alveolar recr uitment and derecruitment may take up to 25 min after MAP changes.