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Work of breathing during constant- and variable-flow nasal continuous positive airway pressure in preterm neonates
Pandit PB, Courtney SE, Pyon KH, Saslow JG, Habib RH
Pediatrics 2001 Sep;108(3):682-685
clinical trial
3/10 [Eligibility criteria: Yes; Random allocation: Yes; Concealed allocation: No; Baseline comparability: No; Blind subjects: No; Blind therapists: No; Blind assessors: No; Adequate follow-up: No; Intention-to-treat analysis: No; Between-group comparisons: Yes; Point estimates and variability: Yes. Note: Eligibility criteria item does not contribute to total score] *This score has been confirmed*

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 FIO2 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 (VT) by DC-coupled/calibrated respiratory inductance plethysmography as well as esophageal pressures at NCPAP of 8, 6, 4, and 0 cmH2O. Inspiratory WOB (WOBI) and lung compliance were calculated from the esophageal pressure and VT data using standard methods. WOB was divided by VT to standardize the results. RESULTS: WOBI decreased at all CPAP levels with variable-flow NCPAP, with a maximal decrease at 4 cmH2O. WOBI 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 cmH2O, whereas it increased only at 8 cmH2O with constant-flow NCPAP. Compared with constant-flow NCPAP, WOBI was 13% to 29% lower with variable-flow NCPAP. CONCLUSION: WOBI is decreased with variable-flow NCPAP compared with constant-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 overdistention at CPAP of 6 to 8 cmH2O 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.
Reproduced with permission from Pediatrics. Copyright by the American Academy of Pediatrics.

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