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. Physical model studies indicate that a variable-flow NCPAP device provides more stable volume recruitment with less imposed work of breathing (WOB). Although superior lung recruitment with variable-flow NCPAP has been demonstrated in preterm neonates, corroborating WOB data are lacking.

Objective. To measure and compare WOB associated with the use of variable-flow 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 Fio ₂ of 0.3 ± 0.1 were studied. Variable-flow and constant-flow NCPAP were applied in random order. We measured changes in lung volume and tidal ventilation (V_T) by DC-coupled/calibrated respiratory inductance plethysmography as well as esophageal pressures at NCPAP of 8, 6, 4, and 0 cm H₂O. Inspiratory WOB (WOB_I) and lung compliance were calculated from the esophageal pressure and V_T data using standard methods. WOB was divided by V_T to standardize the results.

Results. WOB_I decreased at all CPAP levels with variable-flow NCPAP, with a maximal decrease at 4 cm H₂O. WOB_I increased at all CPAP levels with constant-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, WOB_I was 13% to 29% lower with variable-flow NCPAP.

Conclusion. WOB_I is decreased with variable-flow NCPAP compared with constant-flow NCPAP. The increase in WOB_I 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 overdistention 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 neonates with significant lung disease and its use over extended periods of time.continuous-flow and variable-flow NCPAP, work of breathing, premature neonates, lung compliance.