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Pulse oximetry is accurate in acute anemia from hemorrhage
1Department of Emergency Medicine, Brown University School of Medicine, Rhode Island Hospital, Providence.
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.