Work of breathing during constant- and variable-flow nasal continuous positive airway pressure in preterm neonates

Background. Constant-flow nasal continuous positive airway pressure (NCPAP) often is used in preterm neonates to recruit and maintain lung volume. Phy sical model studies indicate that a variable-flow NCPAP device provides mor e stable volume recruitment with less imposed work of breathing (WOB). Alth ough superior lung recruitment with variable-flow NCPAP has been demonstrat ed in preterm neonates, corroborating WOB data are lacking. Objective. To measure and compare WOB associated with the use of variable-f low versus constant-flow NCPAP in preterm neonates. Methods. Twenty-four preterm infants who were receiving constant-flow NCPAP (means, SD) and had birth weight of 1024 +/- 253 g, gestational age of 28 +/-1.7 weeks, age of 14 +/- 13 days, and FIO2 of 0.3 +/-0.1 were studied. V ariable-flow and constant-flow NCPAP were applied in random order. We measu red changes in lung volume and tidal ventilation (V-T) by DC-coupled/calibr ated respiratory inductance plethysmography as well as esophageal pressures at NCPAP of 8, 6, 4, and 0 cm H2O. Inspiratory WOB (WOBI) and lung complia nce were calculated from the esophageal pressure and V-T data using standar d methods. WOB was divided by V-T to standardize the results. Results. WOBI decreased at all CPAP levels with variable-flow NCPAP, with a maximal decrease at 4 cm H2O. WOBI increased at all CPAP levels with const ant-flow CPAP. Lung compliance increased at all NCPAP levels with variable- flow, with a relative decrease at 8 cm H2O, whereas it increased only at 8 cm H2O with constant-flow NCPAP. Compared with constant-flow NCPAP, WOBI wa s 13% to 29% lower with variable-flow NCPAP. Conclusion. WOBI is decreased with variable-flow NCPAP compared with consta nt-flow NCPAP. The increase in WOBI with constant-flow NCPAP indicates the presence of appreciable imposed WOB with this device. Our study, performed in neonates with little lung disease, indicates the possibility of lung ove rdistention at CPAP of 6 to 8 cm H2O with the variable-flow device. Further study is necessary to determine the efficacy of variable-flow NCPAP in neo nates with significant lung disease and its use over extended periods of ti me.