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  • Title: Work of breathing during constant- and variable-flow nasal continuous positive airway pressure in preterm neonates.
    Author: Pandit PB, Courtney SE, Pyon KH, Saslow JG, Habib RH.
    Journal: Pediatrics; 2001 Sep; 108(3):682-5. PubMed ID: 11533336.
    Abstract:
    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 H(2)O. 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 H(2)O. 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 H(2)O, whereas it increased only at 8 cm H(2)O 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 H(2)O 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.
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