Physiological effects of high-flow oxygen in tracheostomized patients

Abstract

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, 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).

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.

Keywords: Mechanical ventilator weaning; Oxygen inhalation therapy; Positive end-expiratory pressure; Respiratory insufficiency; Tracheostomy.

Fig. 1

PaO₂/FiO₂ (a), PaCO₂ (b) and respiratory rate (c) in the four study steps. Results are displayed as median, interquartile range, maximum and minimum. With HFOT_TRACHEAL device, PaO₂/FiO₂ increases proportionally to gas flow, especially between 10 and 30 L/min. As compared to standard oxygen, 50 L/min, but not 30 L/min nor 10 L/min, ameliorate oxygenation and reduce respiratory rate in isocapnic conditions

Fig. 2

Peak (a), mean expiratory pressure (b) and negative peak of inspiratory pressure. Results are displayed as median, interquartile range, maximum and minimum. During HFOT_TRACHEAL, tracheal expiratory pressure increases proportionally to the gas flow. All HFOT_TRACHEAL settings limit the negative inspiratory pressure, especially as flow is set at 50 L/min, likely due to the capability of the high gas flow in an open system to match patient’s peak inspiratory flow. As compared to standard oxygen, 50 L/min, but not 30 L/min nor 10 L/min, increase tracheal peak and mean tracheal expiratory pressure

Fig. 3

Thirty-second recordings of tracheal pressure tracings during HFOT_TRACHEAL and HFOT_NASAL in 5 patients who underwent tracheostomy decannulation over the course of ICU stay. In both conditions gas flow was set at 50 L/min. Average respiratory rate for the 30-s recording is reported for all conditions. During HFOT_NASAL lower airway pressure during expiration is higher and more inter-individually variable than HFOT_TRACHEAL, despite a non-dissimilar respiratory rate, which was calculated on the same 30-s recording. This suggests that the HFOT_NASAL-induced increase in expiratory pressure depends not only on gas flow, but also on patient’s expiratory pattern and, likely, on individual respiratory system mechanical properties. Please note that, under this condition, tracheal pressure was not constant over the course of the respiratory cycle and became negative during inspiration in 4 patients, which is different from what previously reported for pharyngeal pressure [14]

Fig. 4

Peak and mean expiratory pressure during HFOT_TRACHEAL and HFOT_NASAL and different gas flows delivered. Results are displayed as median and interquartile range; *indicates p ≤ 0.05 for HFOT_TRACHEAL vs. HFOT_NASAL comparisons