Objective To determine whether continuous positive airway pressure (CPAP) compared with heated humidified, high-flow nasal cannula (HHFNC) in infants with evolving or established bronchopulmonary dysplasia (BPD) reduced the work of breathing (WOB) and thoracoabdominal asynchrony (TAA) and improved oxygen saturation (SaO₂).

Design Randomised crossover study.

Setting Tertiary neonatal unit.

Patients 20 infants (median gestational age of 27.6 weeks (range 24.6–31.9 weeks)) were studied at a median postnatal age of 30.9 weeks (range 28.1–39.1 weeks).

Interventions Infants were studied on 2 consecutive days. On the first study day, they were randomised to either CPAP or HHFNC each for 2 h, the order being reversed on the second day.

Main outcome measures The WOB was assessed by measuring the pressure time product of the diaphragm (PTPdi). PTPdi, TAA and SaO₂ were assessed during the final 5 min of each 2 h period and the results on the two study days were meaned.

Results There were no significant differences in the results on CPAP versus HHFNC: mean PTPdi 226 (range 126–294) versus 224 cm H₂O/s/min (95% CI for difference: −27 to 22; p=0.85) (range 170–318) (p=0.82), mean TAA 13.4° (range 4.51°–23.32°) versus 14.01° (range 4.25°–23.86°) (95% CI for difference: −3.9 to 2.8: p=0.73) (p=0.63) and mean SaO₂ 95% (range 93%–100%) versus 95% (94%–99%), (95% CI for difference −1.8 to 0.5; p=0.25) (p=0.45).

Conclusion In infants with evolving or established BPD, CPAP compared with HHFNC offered no significant advantage with regard to the WOB, degree of asynchrony or oxygen saturation.