Capillary PO₂ does not adequately reflect arterial PO₂ in hypoxemic COPD patients

To compare arterial (P_aO₂) with capillary (P_cO₂) partial pressure of oxygen in hypoxemic COPD patients because capillary blood gas analysis (CBG) is increasingly being used as an alternative to arterial blood gas analysis (ABG) in a non-intensive care unit setting, although the agreement between P_cO₂ and P_aO₂ has not been evaluated in hypoxemic COPD patients.

Bland-Altman comparison of P_aO₂ and P_cO₂ served as the primary outcome parameter if P_cO₂ values were ≤60 mmHg and the secondary outcome parameter if P_cO₂ values were ≤55 mmHg. Pain associated with the measurements was assessed using a 100-mm visual analog scale.

One hundred and two P_aO₂/P_cO₂ measurement pairs were obtained. For P_cO₂ values ≤60 mmHg, the mean difference between P_aO₂ and P_cO₂ was 5.99±6.05 mmHg (limits of agreement: -5.88 to 17.85 mmHg). For P_cO₂ values ≤55 mmHg (n=73), the mean difference was 5.33±5.52 mmHg (limits of agreement: -5.48 to 16.15 mmHg). If P_aO₂ ≤55 (≤60) mmHg was set as the cut-off value, in 20.6% (30.4%) of all patients, long-term oxygen therapy have been unnecessarily prescribed if only P_cO₂ would have been assessed. ABG was rated as more painful compared with CBG.

P_cO₂ does not adequately reflect P_aO₂ in hypoxemic COPD patients, which can lead to a relevant number of unnecessary long-term oxygen therapy prescriptions.