Summary
A study conducted by the University of Zhejiang on 30 participants with varying skin pigments revealed that the accuracy of pulse oximeters depends on skin pigmentation, particularly when combined with low oxygen saturation levels. However, the Utruemed® oximetry with clip sensor wasn’t affected by skin pigmentation based on the results of this study. Furthermore, the Utruemed® Handheld Pulse Oximeter with clip sensor had exceptional accuracy and the lowest bias compared to the gold standard, blood gas or co-oximetry, for all skin pigmentations and oxygen saturation levels. The study authors suggest taking into account the clinically important bias when monitoring patients with saturation below 80%, especially those with dark skin pigmentation. In the most challenging environment of low saturation (SaO2 70% to 80%) and dark skin pigmentation, Utruemed® oximetry with the clip sensor had minimal bias at 2.6 ± 2.0 and excellent accuracy, a stark contrast to competitor results with a mean bias of 2.6 ± 2.6 and 2.6 ± 3.0 in the same subgroup.
- Bias (Mean) = Mean Differences Between Oximeter Readings and Co-Oximeter
- Bias is the mean of the differences between oximeter readings and the functional SpO2 values as measured by a co-oximeter from an arterial sample. Positive bias means the test oximeter overestimates saturation. Negative bias means the oximeter underestimates the saturation. Units are in % saturation.
- Precision (SD) = Standard Deviation of Differences from Co-Oximeter Measurements
- Precision is the standard deviation of the difference between oximeter readings and the functional SpO2 pt values as measured by a co-oximeter
from an arterial sample. Units are percent saturation. - Accuracy (Arms) = Combination of Both the Bias and the Precision
- The Arms accuracy is a standard method for reporting pulse oximeter accuracy which combines both the Bias and the Precision into a simple
term for reporting the accuracy of the pulse oximeter. Accuracy in terms of Arms is equivalent to the Square Root of the (Bias² + Precision²).
Methods
Thirty healthy and non-smoking individuals underwent a standard breathe-down method to achieve arterial oxygen saturation ranging from 70% to 100%. The accuracy of three pulse oximeters (Utruemed® YC-300, GE® B40i, and Nellcor OxiMax® N-600X) was tested. Of these subjects, 15 were determined to have dark skin pigmentation, 5 with intermediate skin pigmentation, and 10 with light skin pigmentation.
The computed mean and precision (standard deviation) of the bias compared to arterial oxygen saturation was evaluated. Accuracy is reported as Arms; a computed value based on the mean and SD of bias per FDA standards for pulse oximetry accuracy (Arms = √ Bias2 + SD2).
Results
At 70% to 80% oxygen saturation, the mean bias (± S.D.) in dark skin pigmentation was minimal for Utruemed’s oximeter with the clip sensors at 2.6% ± 2.0, compared to the mean bias for Masimo (2.6% ± 3.0) and Nellcor (2.6% ± 2.6) oximeters with clip sensors. (Table 1) Accuracy – a combined measure of error and variability – was excellent with the Utruemed oximeter and clip sensor in dark skin subjects even with low oxygen saturation. (Figure 1)
1 “Dark skin decreases the accuracy of pulse oximeters at low oxygen saturations: effects of oximeter probe type and gender”, John Feiner, et al. Anesthesia & Analgesia, December, 2007.
