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


Christopher Quinn, School of Animal and Veterinary Sciences, Charles Sturt University, Wagga Wagga, NSW 2650, Australia. E-mail: cquinn@csu.edu.au


Objective  Evaluation of the accuracy of Masimo signal extraction technology (SET) pulse oximetry in anaesthetized late gestational pregnant sheep.

Study design  Prospective experimental study.

Animals  Seventeen pregnant Merino ewes.

Methods  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.

Results  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 <75%, however numbers were too small for statistical comparisons. Hb concentration and PI had no significant effect on accuracy, whereas MAP was negatively correlated with SpO2 bias.

Conclusions and clinical relevance  Masimo SET pulse oximetry can provide reliable and continuous monitoring of arterial oxyhaemoglobin saturation in anaesthetized pregnant sheep during clinically relevant levels of cardiopulmonary dysfunction. Further work is needed to assess pulse oximeter function during extreme hypotension and hypoxaemia.