Impact of high-flow oxygen therapy delivered through a tracheostomy on arterial blood gases and endotracheal pressure

Introduction

High-flow oxygen therapy (HFOT) delivered through nasal cannulas can improve oxygenation as compared with low-flow oxygen devices. It has been shown that nasal HFOT can generate a positive airway pressure, which increases linearly with the gas flow rate. Data on the use of HFOT delivered through a tracheostomy are scarce. The aim of the present randomized, controlled, cross-over trial was to assess the effects of HFOT delivered through a tracheostomy on arterial blood gases and endotracheal pressure in critically ill patients.

Methods

Tracheostomized patients underwent HFOT with three gas flow rates (10 l/minute, 30 l/minute and 50 l/minute), randomly applied for 20-minute periods. At the end of each period, arterial blood gases, respiratory rate, and endotracheal pressure (Ptrach) were measured. Ptrach was recorded over the last 3 minutes of each study period: the maximum expiratory pressure (MEPtrach) and mean expiratory pressure were measured and averaged for all respiratory cycles during 1-minute recording with stable breathing. FiO₂ was kept constant during the whole study.

Results

Seventeen tracheostomized patients were enrolled (SAPS II 52 ± 10, PaO₂ 96 ± 27 mmHg, PaCO₂ 33 ± 10 mmHg). Increasing the gas flow rate from 10 l/minute to 30 l/minute was associated with an increase in PaO₂/FiO₂ that did not improve further when 50 l/minute was used (259 ±66, 317 ± 79, and 325 ± 76, respectively, P < 0.001). The same trend was observed with PaO₂ (89 ± 19 mmHg, 109 ± 26 mmHg, and 113 ± 29 mmHg, respectively, P < 0.001) and SaO₂ (96 ± 3%, 98 ± 2%, 98 ± 2%, respectively, P < 0.001). PaCO₂ (32 ± 8² mmHg on average) and respiratory rate (27 ± 7 breaths/minute on average) did not change with different gas flow rates. MEPtrach (0.96 ± 0.43 cmH₂O, 1.32 ± 0.4 cmH₂O, and 1.89 ± 0.5 cmH₂O at 10 l/minute, 30 l/minute and 50 l/minute, respectively, P < 0.01) and mean expiratory pressure (0.54 ± 0.27 cmH₂O, 0.91 ± 0.29 cmH₂O, and 1.36 ± 0.35 cmH₂O, at 10 l/ minute, 30 l/minute and 50 l/minute, respectively, P < 0.01) increased with flow. Changes in PaO₂/FiO₂ were not correlated with changes in expiratory pressures.

Conclusion

When HFOT is used through a tracheostomy at increasing gas flow rate, oxygenation increases up to 30 l/minute while CO₂ clearance and the respiratory rate do not vary. Tracheal expiratory pressure increases with flow, but changes are small and probably of limited clinical relevance. Changes in oxygenation are not related to the variations of tracheal expiratory pressure. HFOT through a tracheostomy has different effects from when a nasal interface is used.