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

Abstract

Background: Arterial blood gas analysis (ABG) serves as the gold standard for the measurement of partial pressure of oxygen (PO 2 ). Capillary blood gas analysis (CBG) is available as a substitute and has become standard of care for PO 2 -analysis in the non-ICU-setting in several countries. Nevertheless, the agreement of ABG and CBG in regard to PO 2 has not been evaluated in hypoxemic COPD patients. Objectives: The aim of the present study was to compare arterial (P a O 2 ) and capillary PO 2 (P c O 2 ) in hypoxemic COPD patients. Methods: Bland-Altman-comparison of P a O 2 and P c O 2 in P c O 2 -values ≤ 60mmHg served as the primary outcome parameter and in P c O 2 -values ≤ 55mmHg as a secondary outcome parameter. Pain associated with the measurements was assessed using a 100-mm visual analogue scale (VAS). Results: 102 measurement pairs were obtained. The mean difference between P a O 2 and P c O 2 in P c O 2 values ≤60 mmHg was 5.99 ± 6.05 mmHg (lower limit of agreement (LLA) -5.88 mmHg, upper limit of agreement (ULA) 17.85 mmHg). The mean difference between P a O 2 and P c O 2 in P c O 2 values ≤55 mmHg (n=73) was 5.33 ±5.52 mmHg (LLA –5.48 mmHg, ULA 16.15 mmHg). 28.8% of this cohort would have inappropriately been prescribed long-term oxygen therapy (LTOT) if P a O 2 ≤55 mmHg was set as the cut-off value, 30.4% in the case of P a O 2 ≤60 mmHg. ABG was rated as more painful on the VAS (23.86 ±22.72 mm) compared to CBG (13.98 ±16.19 mmHg), p-value Conclusions: P c O 2 did not adequately reflect P a O 2 in hypoxemic COPD patients, which would have led to a relevant number of unnecessary LTOT prescriptions in this cohort. ABG was rated as more painful compared to CBG. However, overall rating of pain was moderate.