Physiological effects of high-flow oxygen in tracheostomized patients

BACKGROUND: 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. RESULTS: During HFOT(TRACHEAL), PaO(2)/FiO(2) 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] cmH(2)O (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] cmH(2)O, peak tracheal expiratory pressure by 0.4 [0.2–0.6] cmH(2)O, improved PaO(2)/FiO(2) ratio by 40 [8–71] mmHg, and reduced respiratory rate by 1.9 [0.3–3.6] breaths/min without PaCO(2) 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] cmH(2)O and 4 [1–7] cmH(2)O, respectively). CONCLUSIONS: 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).