• G D Jay, L Hughes, and F P Renzi.
• Department of Emergency Medicine, Brown University School of Medicine, Rhode Island Hospital, Providence.
• Ann Emerg Med. 1994 Jul 1;24(1):32-5.

HypothesisPulse oximetry is an accurate, noninvasive assay of oxygen saturation percentage (SaO2) in acutely severe anemia (less than 5 g/dL).DesignA 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%.SettingAn academic emergency department in a tertiary referral hospital with a Level I trauma center.ParticipantsSeventeen nonhypoxic patients were identified with initial hematocrit of less than 20% over a 9-month period.Measurements And Main ResultsDetermination 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.ConclusionDespite 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.

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