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

PURPOSE To compare arterial (PaO2) with capillary (PcO2) 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 PcO2 and PaO2 has not been evaluated in hypoxemic COPD patients. PATIENTS AND METHODS Bland-Altman comparison of PaO2 and PcO2 served as the primary outcome parameter if PcO2 values were ≤60 mmHg and the secondary outcome parameter if PcO2 values were ≤55 mmHg. Pain associated with the measurements was assessed using a 100-mm visual analog scale. RESULTS One hundred and two PaO2/PcO2 measurement pairs were obtained. For PcO2 values ≤60 mmHg, the mean difference between PaO2 and PcO2 was 5.99±6.05 mmHg (limits of agreement: -5.88 to 17.85 mmHg). For PcO2 values ≤55 mmHg (n=73), the mean difference was 5.33±5.52 mmHg (limits of agreement: -5.48 to 16.15 mmHg). If PaO2 ≤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 PcO2 would have been assessed. ABG was rated as more painful compared with CBG. CONCLUSIONS PcO2 does not adequately reflect PaO2 in hypoxemic COPD patients, which can lead to a relevant number of unnecessary long-term oxygen therapy prescriptions.