Physiological effects of high-flow oxygen in tracheostomized patients.

Background: High-flow oxygen therapy via nasal cannula (HFOT) increases airway pressure, ameliorates oxygenation and reduces work of breathing. High-flow oxygen can be delivered through tracheostomy (HFOT), but its physiological effects have not been systematically described. We conducted a cross-over study to elucidate the effects of increasing flow rates of HFOT on gas exchange, respiratory rate and endotracheal pressure and to compare lower airway pressure produced by HFOT and HFOT METHODS: Twenty-six tracheostomized patients underwent standard oxygen therapy through a conventional heat and moisture exchanger, and then HFOT through a heated humidifier, with gas flow set at 10, 30 and 50 L/min. Each step lasted 30 min; gas flow sequence during HFOT was randomized. In five patients, measurements were repeated during HFOT before tracheostomy decannulation and immediately after during HFOT. In each step, arterial blood gases, respiratory rate, and tracheal pressure were measured.

Results: During HFOT, PaO/FiO ratio and tracheal expiratory pressure slightly increased proportionally to gas flow. The mean [95% confidence interval] expiratory pressure raise induced by 10-L/min increase in flow was 0.2 [0.1-0.2] cmHO (ρ = 0.77, p < 0.001). Compared to standard oxygen, HFOT limited the negative inspiratory swing in tracheal pressure; at 50 L/min, but not with other settings, HFOT increased mean tracheal expiratory pressure by (mean difference [95% CI]) 0.4 [0.3-0.6] cmHO, peak tracheal expiratory pressure by 0.4 [0.2-0.6] cmHO, improved PaO/FiO ratio by 40 [8-71] mmHg, and reduced respiratory rate by 1.9 [0.3-3.6] breaths/min without PaCO changes. As compared to HFOT, HFOT produced higher tracheal mean and peak expiratory pressure (at 50 L/min, mean difference [95% CI]: 3 [1-5] cmHO and 4 [1-7] cmHO, respectively).

Conclusions: As compared to standard oxygen, 50 L/min of HFOT are needed to improve oxygenation, reduce respiratory rate and provide small degree of positive airway expiratory pressure, which, however, is significantly lower than the one produced by HFOT.