High-Flow Nasal Cannula Reduces Ventilatory Requirements During Endobronchial Ultrasound

Background:

High-flow nasal cannula (HFNC) reduces dead-space ventilation, but this effect is diminished by open-mouth breathing and partial airway obstruction. Consequently, it is uncertain whether HFNC provides respiratory support during endobronchial ultrasound (EBUS) procedures.

Methods:

A single-center randomized controlled crossover study was conducted at the Rijnstate Hospital, Arnhem, the Netherlands, from November 2022 to August 2024.

Patients with severe COPD (Gold III/IV) were evaluated to determine if HFNC reduces dead space ventilation during an EBUS procedure. Exclusion criteria were known neurodegenerative conditions, allergies to propofol or esketamine, pregnancy, upper-airway obstructions, or severe pulmonary hypertension.

Subjects received two sequences of HFNC flow (30 and 70 L/min or vice versa) during EBUS.

The primary outcome was CO₂ washout, determined by a 60-s capnography trace with and without HFNC flow to measure the difference in inspiratory, end-tidal CO₂, and β-angle.

Results:

Twenty subjects with severe COPD (Gold III/IV) were included (Group A n = 10; Group B n = 10), of which one could not complete the bronchial measurements because of an obstructing carcinoma. CO₂ washout at carina was observed at 70 L/min of HFNC flow, demonstrated by a reduced inspiratory CO₂ of mean 6.0 mm Hg (95% CI: 4.5–8.3, P < .001) and end-tidal CO₂ of 5.3 mm Hg (95% CI: 2.3–7.5, P = .002), but not at 30 L/min of HFNC flow (mean inspiratory CO₂ difference of 1.5 mm Hg (95% CI: −2.3 to 6.0, P = .69) and mean end-tidal CO₂ difference of 0.8 mm Hg (95% CI: −2.3 to 3.0, P = .35). A flow of 70 L/min reduced inspiratory CO₂ in the left main bronchus (mean = 5.3 mm Hg; 95% CI: 2.3–8.3, P < .001), but not the end-tidal CO₂ (mean = 3.0 mm Hg; 95% CI: 0.0–6.0, P = .07).

Conclusions:

An HFNC flow of 70 L/min reduced dead-space ventilation in subjects with severe COPD undergoing EBUS procedures during deep sedation, suggesting respiratory support during this procedure.