Nasal high flow does not improve exercise tolerance in COPD patients after exacerbation

Nasal high flow (NHF) during exercise has failed to boost endurance time in patients with chronic obstructive pulmonary disease (COPD) who are recovering from acute exacerbation, as shown in a recent study.

In this monocentric, randomized, controlled crossover study, the investigators hypothesized that NHF would improve exercise tolerance in COPD patients following exacerbation by reducing respiratory work and improving gas exchange. To test this hypothesis, patients with severe to very severe COPD performed two high-intensity constant work-rate exercise tests (CWRET) with and without NHF for 2 consecutive days.

The mean difference in endurance time between both conditions was the main outcome. Secondary outcomes included vastus lateralis oxygenation (StO₂), dyspnoea, leg discomfort, maximal inspiratory pressure (MIP), transcutaneous CO₂ pressure (PtcCO₂), respiratory rate (RR), heart rate (HR) and pulsed O₂ saturation (SpO₂), as well as the patients' opinions of the device.

Nineteen patients (mean age, 62.1±9.1 years) were included in the analysis, with mean forced expiratory volume in 1 s of 28.7±10.8 percent.

There were no significant differences seen between the two test conditions in terms of endurance time during the CWRET (–66.58 s, 95 percent CI, –155.9 to 22.7, p=0.12). However, NHF led to a reduction in StO₂ (–2.1 percent, –4.3 to 0.0), PtCO₂ (–1.3 mm Hg, –2.5 to –0.2) and HR (–2.7 bpm, –5.0 to –0.5) at the end of the exercise (p≤0.05). No significant differences were found for any of the other secondary outcomes. [Respirology 2019;24:1088-1094]

In addition, half of the patients found the device to be moderately or very uncomfortable to use.

A single-centre randomized controlled cross-over trial in 24 hospital inpatients with acute exacerbations of COPD receiving oxygen via standard nasal prongs (SNPs) reported a small reduction in PtCO₂ with short-term use of NHF compared with SNP. However, the researchers were uncertain whether this finding was clinically significant. [Respirology 2017;22:1149-1155]

This was supported by another single-blind randomized controlled crossover trial which involved 48 COPD patients. Results showed that NHF led to a small flow-dependent reduction in in PtCO₂ and respiratory rate in patients with stable COPD. [Respirology 2018;23:378-384]

On the other hand, a recent single-blind randomized controlled two-way crossover single-centre trial conducted in New Zealand and included 24 patients with stable hypercapnic COPD found that noninvasive ventilation reduced the PtCO₂ more than NHF. However, participants evaluated NHF as significantly better for ease of application, comfort and fit. [Respirology 2019;24:1081-1087]

NHF is a device that delivers heated and humidified oxygen up to 60 L/min. Its potential benefits are as follows: the improvement of lung mucociliary clearance, the washout of upper airway dead space, the generation of a low level of positive airway pressure (PEEP effect), the decrease in inspiratory resistance and the increase in expiratory resistance. [COPD 2017;14:346-350]