Transcutaneous CO and O 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 CO (PtcCO) and O (PtcO) during walking in COPD patients with and without O supplementation by using a high-flow nasal cannula (HFNC).

Methods: PtcCO, PtcO, and arterial O saturation by pulse oximetry (SpO) were monitored during the 6-min walking test (6MWT) under room air (n = 14) or O supplementation by HFNC (FiO 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 PtcO and SpO were significantly decreased during 6MWT under room air (p < 0.001 and p < 0.01, respectively), but PtcCO did not show a significant change. During walking under HFNC, PtcCO was significantly increased in an O-dependent manner (p < 0.001), but decreasing PtcO change under FiO 0.3 was significantly larger than under 0.5 (p < 0.001). In two patients, we observed monthly or weekly increases in PtcCO (> 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 O supplementation is performed, PtcCO monitoring is advised to detect PtcCO increases during walking rehabilitation. HFNC-assisted walking decreases PtcO, but adequate O supply may mitigate this decrease.