Does SpO2 correlate with SaO2 in stable COPD patients

Background: Pulse oximetry is commonly used to measure oxygen saturations (SpO 2 ) in assessment of patients with stable COPD. This is considered to be equivalent to oxygen saturations measured on a blood gas analyser (SaO 2 ). The ATS, ERS and GOLD guidelines for COPD define suitability for long term oxygen therapy with PaO 2 less than 7.3kPa or SaO 2 of less than 88%. Aim: To confirm if SpO 2 correlates to SaO 2 in stable COPD patients. Methods: Retrospective study of patients with stable COPD attending oxygen clinics in an acute teaching hospital. Results: N=73, Male 29 %, Mean Age70 (range 53 - 93), Mean FEV1 0.89 L, current smokers 29%, 26% on oxygen, mean MRC grade 4, mean BORG score at rest 2 and mean hematocrit (HCT) 0.41. On9t9 paired testing in all patients, no statistically significant difference was noted between SpO 2 and SaO 2 (p value: 0.972), the mean SpO 2 - SaO 2 is -0.012% (95% CI of -0.71 to 0.69). However, in current smokers subgroup (N=21) high variation between these values was noted, with the mean SpO 2 - SaO 2 1.067%. There was a tendency for SpO 2 to be higher than SaO 2 (95% CI of -1.038 to 3.171). There is no statistically significant relationship between SpO 2 and SaO 2 in COPD patients in relation to sex, age, severity of COPD, smoking status, MRC grade, BORG score, and HCT levels. Conclusions: As the difference between SpO 2 and SaO 2 is high in current smokers, SpO 2 reading using pulse oximetry might not be reliable. Further studies with larger sample size are needed to evaluate this further.