Evaluation of Masimo signal extraction technology pulse oximetry in anaesthetized pregnant sheep

Evaluation of the accuracy of Masimo signal extraction technology (SET) pulse oximetry in anaesthetized late gestational pregnant sheep. Prospective experimental study. Seventeen pregnant Merino ewes. Animals included in study were late gestation ewes undergoing general anaesthesia for Caesarean delivery or foetal surgery in a medical research laboratory. Masimo Radical-7 pulse oximetry (SpO2) measurements were compared to co-oximetry (SaO2) measurements from arterial blood gas analyses. The failure rate of the pulse oximeter was calculated. Accuracy was assessed by Bland & Altman's (2007) limits of agreement method. The effect of mean arterial blood pressure (MAP), perfusion index (PI) and haemoglobin (Hb) concentration on accuracy were assessed by regression analysis. Forty arterial blood samples paired with SpO2 and blood pressure measurements were obtained. SpO2 ranged from 42 to 99% and SaO2 from 43.7 to 99.9%. MAP ranged from 24 to 82 mmHg, PI from 0.1 to 1.56 and Hb concentration from 71 to 114 g L−1. Masimo pulse oximetry measurements tended to underestimate oxyhaemoglobin saturation compared to co-oximetry with a bias (mean difference) of −2% and precision (standard deviation of the differences) of 6%. Accuracy appeared to decrease when SpO2 was