The accuracy of a fiberoptic oximeter over a wide range of arterial oxygen saturation values in piglets

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Abstract
A piglet model was used to evaluate the accuracy of a fiberoptic oximeter over a wide range of arterial oxygen saturation (SaO2) values. In eight anaesthetized piglets, the inspired oxygen concentration was varied from 30% to 6% resulting in a SaO2 range from 100% to 15%. Paired data of the Opticath fiberoptic catheter, which was placed in the descending aorta, and blood sample SaO2 values assessed by a multiwavelength oximeter, were analysed. After in vitro calibration according to the manufacturer's instruction, the fiberoptic catheter started to underestimate the SaO2 below 78%, worsening towards lower SaO2 values. The overall bias was -3.4% and the precision 3.8%. An off-line fit with a non-linear model resulted in a standard deviation of residuals of 2.6%. After several in vivo calibration adjustments when the fiberoptic oximeter deviated more than 4% from the blood sample value, the bias was eliminated over the total SaO2 range and the precision was 3.7%. The Opticath fiberoptic oximeter could have an accuracy for the whole SaO2 range between 15-100% close to the accuracy of the multiwavelength oximeter, when the fiberoptic oximeter is adapted for the underestimation below 78% SaO2.