Effects of skin pigmentation on pulse oximeter accuracy at low saturation

Abstract

Background: It is uncertain whether skin pigmentation affects pulse oximeter accuracy at low HbO2 saturation. Methods: The accuracy of finger pulse oximeters during stable, plateau levels of arterial oxygen saturation (SaO2) between 60 and 100% were evaluated in 11 subjects with darkly pigmented skin and in 10 with light skin pigmentation. Oximeters tested were the Nellcor N-595 with the OxiMax-A probe (Nellcor Inc., Pleasanton, CA), the Novametrix 513 (Novametrix Inc., Wallingford, CT), and the Nonin Onyx (Nonin Inc., Plymouth, MN). Semisupine subjects breathed air-nitrogen-carbon dioxide mixtures through a mouthpiece. A computer used end-tidal oxygen and carbon dioxide concentrations determined by mass spectrometry to estimate breath-by-breath SaO2, from which an operator adjusted inspired gas to rapidly achieve 2- to 3-min stable plateaus of desaturation. Comparisons of oxygen saturation measured by pulse oximetry (SpO2) with SaO 2 (by Radiometer OSM3) were used in a multivariate model to determine the interrelation between saturation, skin pigmentation, and oximeter bias (SpO2 - SaO2). Results: At 60-70% SaO2, SpO2 (mean of three oximeters) overestimated SaO2 (bias ± SD) by 3.56 ± 2.45% (n = 29) in darkly pigmented subjects, compared with 0.37 ± 3.20% (n = 58) in lightly pigmented subjects (P < 0.0001). The SD of bias was not greater with dark than light skin. The dark-light skin differences at 60-70% SaO2 were 2.35% (Nonin), 3.38% (Novametrix), and 4.30% (Nellcor). Skin pigment-related differences were significant with Nonin below 70% SaO2, with Novametrix below 90%, and with Nellcor at all ranges. Pigment-related bias increased approximately in proportion to desaturation. Conclusions: The three tested pulse oximeters overestimated arterial oxygen saturation during hypoxia in dark-skinned individuals. © 2005 American Society of Anesthesiologists, Inc. Lippincott Williams & Wilkins, Inc.