Effect of High-Flow Nasal Cannula Flow on Intrapharyngeal Pressure During Fiberoptic Bronchoscopy Under Deep Sedation

Background: The flow reaching the vocal folds may be lower than that at the output of high-flow nasal cannula (HFNC) system. This could be due to upper-respiratory obstruction, oxygen leakage, or other factors. The objective of this study was to observe the effect of flow through a nasopharyngeal airway on intrapharyngeal pressure (IPP) in subjects undergoing fiberoptic bronchoscopy (FOB).

Methods: Patients scheduled for FOB were invited to participate. Measurements were performed at flows of 0-60 L/min; the subjects wore WN-N95 folding medical protective masks (N95) and either underwent FOB or not. IPP at each flow was recorded following 15 s of ventilation, and the cross-sectional area (CSA) of the gastric sinus was measured before and after FOB. Hypoxemia, reflux aspiration, and other pertinent events were recorded.

Results: Sixty subjects undergoing FOB at the Affiliated Hospital of Jiaxing University participated in this trial from October 2022-September 2023. IPP increased significantly with an increase in flow and also increased after placing the N95 mask with the same flow (P < .001). When results from before to after FOB were compared, the difference in CSA was statistically significant 263.6 (220.7-300.5) mm² vs 305.5 (275.4-329.5) mm², P < .001, but the difference in the risk of reflux aspiration was not statistically significant (0% vs 6.7%, P = .13). Complication rates during treatment were 8.3% for hypoxemia, 0% for reflux aspiration, 1.7% for hypertension, 1.7% for hypotension, 6.7% for tachycardia, 5% for bradycardia, and 10% for postoperative nausea and vomiting.

Conclusions: HFNC can provide effective oxygen therapy for people undergoing FOB, and increases in IPP with flow in the range of 0-60 L/min may not increase the risk of reflux aspiration.