Physiological effects of high-flow oxygen in tracheostomized patients

High-flow oxygen therapy via nasal cannula (HFOT_NASAL) increases airway pressure, ameliorates oxygenation and reduces work of breathing. High-flow oxygen can be delivered through tracheostomy (HFOT_TRACHEAL), 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_TRACHEAL on gas exchange, respiratory rate and endotracheal pressure and to compare lower airway pressure produced by HFOT_NASAL and HFOT_TRACHEAL. METHODS: Twenty-six tracheostomized patients underwent standard oxygen therapy through a conventional heat and moisture exchanger, and then HFOT_TRACHEAL 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_TRACHEAL was randomized. In five patients, measurements were repeated during HFOT_TRACHEAL before tracheostomy decannulation and immediately after during HFOT_NASAL. In each step, arterial blood gases, respiratory rate, and tracheal pressure were measured.

During HFOT_TRACHEAL, PaO₂/FiO₂ 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] cmH₂O (ρ = 0.77, p < 0.001). Compared to standard oxygen, HFOT_TRACHEAL limited the negative inspiratory swing in tracheal pressure; at 50 L/min, but not with other settings, HFOT_TRACHEAL increased mean tracheal expiratory pressure by (mean difference [95% CI]) 0.4 [0.3-0.6] cmH₂O, peak tracheal expiratory pressure by 0.4 [0.2-0.6] cmH₂O, improved PaO₂/FiO₂ ratio by 40 [8-71] mmHg, and reduced respiratory rate by 1.9 [0.3-3.6] breaths/min without PaCO₂ changes. As compared to HFOT_TRACHEAL, HFOT_NASAL produced higher tracheal mean and peak expiratory pressure (at 50 L/min, mean difference [95% CI]: 3 [1-5] cmH₂O and 4 [1-7] cmH₂O, respectively).

As compared to standard oxygen, 50 L/min of HFOT_TRACHEAL 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_NASAL.