Physiological effects of high-flow oxygen in tracheostomized patients

Abstract

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

Results: During HFOTTRACHEAL, 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, HFOTTRACHEAL limited the negative inspiratory swing in tracheal pressure; at 50 L/min, but not with other settings, HFOTTRACHEAL 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 HFOTTRACHEAL, HFOTNASAL 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 HFOTTRACHEAL 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 HFOTNASAL.

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

Conflict of interest statement

DLG has received payments for travel expenses by Maquet, Getinge and Air Liquide. MA has received payments for Board participation from Maquet, Air Liquide and Chiesi. DLG and MA disclose a research grant by General Electric Healthcare. SMM is the principal investigator of the RINO trial (clinicaltrials.gov, NCT02107183), which was supported by Fisher and Paykel healthcare.

Figures

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 HFOTTRACHEAL 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 HFOTTRACHEAL, tracheal expiratory pressure increases proportionally to the gas flow. All HFOTTRACHEAL 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 HFOTTRACHEAL and HFOTNASAL 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 HFOTNASAL lower airway pressure during expiration is higher and more inter-individually variable than HFOTTRACHEAL, despite a non-dissimilar respiratory rate, which was calculated on the same 30-s recording. This suggests that the HFOTNASAL-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 HFOTTRACHEAL and HFOTNASAL and different gas flows delivered. Results are displayed as median and interquartile range; *indicates p ≤ 0.05 for HFOTTRACHEAL vs. HFOTNASAL comparisons