Transcutaneous CO2 and O2 monitoring during walking with a high-flow nasal cannula in patients with chronic obstructive pulmonary disease.

BACKGROUND

Patients with advanced chronic obstructive pulmonary disease (COPD) experience dyspnea on exertion, and require rehabilitation using physical therapy. COPD results in deoxygenation through both alveolar hypoventilation and ventilation/perfusion mismatch. In this study, we examined the time courses of transcutaneous partial pressures of CO2 (PtcCO2) and O2 (PtcO2) during walking in COPD patients with and without O2 supplementation by using a high-flow nasal cannula (HFNC).

METHODS

PtcCO2, PtcO2, and arterial O2 saturation by pulse oximetry (SpO2) were monitored during the 6-min walking test (6MWT) under room air (n = 14) or O2 supplementation by HFNC (FiO2 0.3-0.5) (n = 20) in COPD patients with dyspnea on exertion. Trajectory data of n = 237 from 20 patients with HFNC-supplemented walking rehabilitation were evaluated.

RESULTS

Both PtcO2 and SpO2 were significantly decreased during 6MWT under room air (p < 0.001 and p < 0.01, respectively), but PtcCO2 did not show a significant change. During walking under HFNC, PtcCO2 was significantly increased in an O2-dependent manner (p < 0.001), but decreasing PtcO2 change under FiO2 0.3 was significantly larger than under 0.5 (p < 0.001). In two patients, we observed monthly or weekly increases in PtcCO2 (> 70 mmHg) at one month before acute exacerbations.

CONCLUSIONS

Deoxygenation during walking in patients with COPD is not related to worsening of alveolar hypoventilation under room air. When O2 supplementation is performed, PtcCO2 monitoring is advised to detect PtcCO2 increases during walking rehabilitation. HFNC-assisted walking decreases PtcO2, but adequate O2 supply may mitigate this decrease.