High-flow nasal cannula oxygen therapy for outpatients undergoing flexible bronchoscopy: a randomised controlled trial.

INTRODUCTION: High-flow nasal cannula (HFNC) provides benefits to patients undergoing flexible bronchoscopy (FOB). We compared the effects of HFNC versus standard therapy (ST) on gas exchange, lung volume and diaphragm function in patients undergoing FOB for bronchoalveolar lavage (BAL). METHODS: 36 outpatients were randomised to ST or HFNC. Arterial blood gases, episodes of severe desaturation, changes of end-expiratory lung impedance (ΔEELI), diaphragm ultrasound were recorded. Measurements were done at baseline (T0), after bronchoscope insertion (T1), at the end of the procedure (T2) and 10 min afterwards (T3). RESULTS: Arterial partial oxygen pressure (PaO2) was not different between T0 (10.8 (95% CI 8.7 to 12.0) kPa and T2 (11.1 (95% CI 10.4 to 12.0) kPa) with HFNC, while decreased from 11.1 (95% CI 10.5 to 12.1) to 9.1 (95% CI 8.4 to 9.8) kPa with ST. At T2, PaO2 was significantly higher with HFNC than with ST (p<0.001). Also, with HFNC, compared with ST, fewer desaturations occurred (11% vs 56%; p<0.01). ΔEELI was no different at the different time points with HFNC, while with ST there was a significant decrease at T1 (-170 (95% CI -382 to -32) mL, p=0.003), T2 (-211 (95% CI -425 to -148) mL, p<0.001) and T3 (-213 (95% CI -398 to -81) mL, p<0.001), as opposed to T0. EELI was lower with ST than HFNC at T1 (p=0.006), T2 (p=0.001) and T3 (p=0.002). Diaphragm displacement was no different between groups (p=0.748), while the thickening fraction significantly increased at T1 and T2 with ST only (p<0.01). CONCLUSIONS: During FOB for BAL, HFNC improves gas exchange, avoiding loss of end-expiratory lung volume and preventing increase of diaphragm activation. TRIAL REGISTRATION NUMBER: NCT04016480.