Accuracy of a pulse oximeter in the measurement of the oxyhaemoglobin saturation

The aim of the present study was to evaluate the accuracy, in comparison with a reference method, of the Nellcor N-20P pulse oximeter in the assessment of oxyhaemoglobin saturation (Sa,O2). Sa,O2 was monitored at rest by the Nellcor N-20P pulse oximeter in 100 subjects (82 males, mean age 68+/-12 yrs) consecutively enroled. At the same time, an arterial blood sample was collected for the measurement of Sa,O2, carboxyhaemoglobin, and methaemoglobin by an IL-282 Co-oximeter. A significant difference was found between Sa,O2 values measured with the two methods (t=11.78, p<0.05), but the two series of measurements were significantly correlated (r=0.97). Both the level and the limits of agreement between the two methods were satisfactory when the more appropriate Bland and Altman method was applied. Nevertheless, a lack of accuracy of the pulse oximeter was found, but only for Sa,O2 values <82% and >94%, as demonstrated by the Youden index. In conclusion, these data show that Nellcor N-20P is sufficiently reliable for the assessment and monitoring of oxyhaemoglobin saturation. The lack of accuracy does not seem clinically relevant since it is appreciable only for values at the extremes of the oxyhaemoglobin saturation range.

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