ACCURACY AND RELIABILITY OF PULSE OXIMETRY AT DIFFERENT PaCO₂ LEVELS

¹ Servei de Pneumologia, Hospital Universitari Vall d'Hebron, Barcelona, Spain; Dept de Biología Cel·lular, de Fisiologia i d'Immunologia, UAB, Barcelona, Spain; and CIBER de Enfermedades Respiratorias (Ciberes)
² Laboratorio de Bioestadística i Epidemiología (Universitat Autònoma de Barcelona); Servei de Farmacologia Clínica, IDIBAPS, (Hospital Clínic), Barcelona
³ Servei de Pneumologia, Hospital Universitari Vall d'Hebron, Barcelona, Spain; and CIBER de Enfermedades Respiratorias (Ciberes)
⁴ Dept de Biología Cel·lular, de Fisiologia i d'Immunologia, UAB, Barcelona, Spain

^* To whom correspondence should be addressed. E-mail: xmunoz{at}vhebron.net.

	Abstract

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).

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.

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 and their interaction term were the most important predictors of the bias (standardized estimates of -0.54, -0.94, and 0.85, respectively). The effect of pH, although statistically significant, was small and bicarbonate had no significant effect.

PaCO₂ status can contribute to impairing agreement between SaO₂ and SpO₂, particularly in patients with hypercapnia.