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Accuracy and reliability of pulse oximetry at different arterial carbon dioxide pressure levels

¹ Servei de Pneumologia, Hospital Universitari Vall d'Hebron, ² Dept de Biología Cellular, de Fisiologia i d'Immunologia, UAB, ⁴ Laboratorio de Bioestadística i Epidemiología (Universitat Autònoma de Barcelona); Servei de Farmacologia Clínica, IDIBAPS, (Hospital Clínic), Barcelona, and ³ CIBER de Enfermedades Respiratorias (Ciberes), Spain, ⁵ Both authors contributed equally to the study.

CORRESPONDENCE: X. Muñoz, Servei de Pneumologia, Hospital Vall d'Hebron, P° Vall d'Hebron, 119-129, 08035 Barcelona, Spain. Fax: 34 932746083. E-mail: xmunoz{at}vhebron.net

Keywords: Co-oximetry, hypercapnia, hypoxaemia, oxygen therapy, precision

Received: September 25, 2007
Accepted April 29, 2008

The present study aimed to assess whether arterial carbon dioxide pressure (P_a,CO2) has an impact on agreement between oxygen saturation measured with pulse oximetry (S_p,O2) or arterial blood gas co-oximetry (S_a,O2).

S_a,O2 and S_p,O2 determinations were obtained simultaneously from 846 patients under assessment for long-term home oxygen therapy in a specialised outpatient clinic. Both measurements were taken with patients seated and breathing room air.

Agreement between S_a,O2 and S_p,O2 results was analysed by the Bland–Altman method and the Lin concordance coefficient. In addition, potential interactions of arterial oxygen tension (P_a,O2) or P_a,CO2 on agreement were analysed by adjusted multivariate analysis.

Upon comparison of S_a,O2 and S_p,O2 results, the Bland–Altman technique yielded a bias (95% confidence interval (CI)) of -1.24 (-6.86–4.38) and -1.32 (-7.78–5.15) when P</emph>_a,CO2 >48 mmHg (6.39 kPa) or P_a,O2 <54 mmHg (7.20 kPa), 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, P_a,O2, P_a,CO2 and bicarbonate on bias, showed that P_a,O2, P_a,CO2 and their interaction terms were the most important predictors of the bias (standardised 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.

Arterial carbon dioxide pressure status can contribute to impaired agreement between arterial oxygen saturation and arterial oxygen saturation measured with pulse oximetry, particularly in patients with hypercapnia.

This article has been cited by other articles:

				J. Hinkelbein and H. V. Genzwuerker Hypercapnia as the influencing factor of pulse oximetry Eur. Respir. J., December 1, 2008; 32(6): 1670 - 1670. [Full Text] [PDF]

				X. Munoz, F. Torres, and G. Sampol From the authors Eur. Respir. J., December 1, 2008; 32(6): 1670 - 1671. [Full Text] [PDF]