ACCURACY AND RELIABILITY OF PULSE OXIMETRY AT DIFFERENT PaCO2 LEVELS

Aim: To assess whether arterial carbon dioxide pressure (PaCO2) has an impact on agreement between oxygen saturation measured with pulse oximetry (SpO2) or arterial blood gas co-oximetry (SaO2). Methods: A study was performed on SaO2 and SpO2 determinations obtained simultaneously from 846 patients under assessment for long-term home oxygen therapy in a specialized outpatient clinic. Both measurements were taken with patients seated and breathing room air. Agreement between SaO2 and SpO2 results was analyzed by the Bland-Altman method and the Lin concordance coefficient. In addition, potential interactions of PaO2 or PaCO2 on agreement were analyzed by adjusted multivariate analysis. Results: At comparison of SaO2 and SpO2 results, the Bland-Altman technique yielded a bias (95 % CI) of-1.24 (-6.86; 4.38) and-1.32 (-7.78; 5.15) when PaCO2 was higher than 48 mmHg or PaO2 lower than 54 mmHg, respectively. Estimate by Lin’s coefficient (95 % CI) in these cases was 0.88 (0.85;0.90) and 0.81 (0.77;0.85). Adjusted multivariate analysis performed to assess the impact of pH, PaO2, PaCO2, and bicarbonate on bias showed that PaO2, PaCO2 an