Capillary PO ₂ does not adequately reflect arterial PO ₂ in hypoxemic COPD patients

Abstract

Purpose

To compare arterial (P _aO ₂) with capillary (P _cO ₂) 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 _cO ₂ and P _aO ₂ has not been evaluated in hypoxemic COPD patients.

Patients and methods

Bland–Altman comparison of P _aO ₂ and P _cO ₂ served as the primary outcome parameter if P _cO ₂ values were ≤60 mmHg and the secondary outcome parameter if P _cO ₂ values were ≤55 mmHg. Pain associated with the measurements was assessed using a 100-mm visual analog scale.

Results

One hundred and two P _aO ₂/P _cO ₂ measurement pairs were obtained. For P _cO ₂ values ≤60 mmHg, the mean difference between P _aO ₂ and P _cO ₂ was 5.99±6.05 mmHg (limits of agreement: −5.88 to 17.85 mmHg). For P _cO ₂ 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 _aO ₂ ≤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 _cO ₂ would have been assessed. ABG was rated as more painful compared with CBG.

Conclusions

P _cO ₂ does not adequately reflect P _aO ₂ in hypoxemic COPD patients, which can lead to a relevant number of unnecessary long-term oxygen therapy prescriptions.