Pulse oximetry is accurate in acute anemia from hemorrhage.

HYPOTHESIS

Pulse oximetry is an accurate, noninvasive assay of oxygen saturation percentage (SaO2) in acutely severe anemia (less than 5 g/dL).

DESIGN

A paired comparison of SaO2 by pulse oximetry (SpO2) and arterial blood gas analysis (SaO2) in patients with either acute gastrointestinal bleeding or blunt trauma with hematocrit of less than 20%.

SETTING

An academic emergency department in a tertiary referral hospital with a Level I trauma center.

PARTICIPANTS

Seventeen nonhypoxic patients were identified with initial hematocrit of less than 20% over a 9-month period.

MEASUREMENTS AND MAIN RESULTS

Determination of SaO2 by pulse oximetry and arterial blood analysis was not statistically significantly different (P < .05) over a range of hemoglobin levels from 2.3 to 8.7 g/dL. The observed mean difference between SpO2 and SaO2 was 0.53 +/- 0.23% (mean +/- SEM; n = 17). The 95% confidence interval associated with this difference score ranged from 0.044 to 1.014.

CONCLUSION

Despite reports that pulse oximetry is inaccurate below a hemoglobin concentration of 5 g/dL, our study suggested that this technology is accurate and reliable at 2.3 g/dL for nonhypoxic SaO2 values (SaO2 of more than 93%). The anemic endpoint where pulse oximetry either becomes inaccurate or simply fails to work has not been determined. Pulse oximetry overestimates SaO2 on average by 0.53% over a range of hemoglobin concentrations from 2.3 to 8.7 g/dL.