Accuracy and trending capability of haemoglobin measurement by noninvasive pulse co-oximetry in anaesthetized horses.

ABSTRACT

OBJECTIVE: To assess the accuracy and trending capability of continuous measurement of haemoglobin concentration [Hb], haemoglobin oxygen saturation (SaO2) and oxygen content (CaO2) measured by the Masimo Radical-7 pulse co-oximeter in horses undergoing inhalational anaesthesia. STUDY DESIGN: Prospective observational clinical study. ANIMALS A group of 23 anaesthetized adult horses. METHODS: In 23 healthy adult horses undergoing elective surgical procedures, paired measurements of pulse co-oximetry-based haemoglobin concentration (SpHb), SaO2 (SpO2), and CaO2 (SpOC) and simultaneous arterial blood samples were collected at multiple time points throughout anaesthesia. The arterial samples were analysed by a laboratory co-oximeter for total haemoglobin (tHb), SaO2 and manually calculated CaO2. Bland-Altman plots, linear regression analysis, error grid analysis, four-quadrant plot and Critchley polar plot were used to assess the accuracy and trending capability of the pulse co-oximeter. Data are presented as mean differences and 95% limits of agreement (LoA). RESULTS: In 101 data pairs analysed, the pulse co-oximeter slightly underestimated tHb (bias 0.06 g dL-1; LoA -1.0 to 1.2 g dL-1), SaO2 (bias 1.4%; LoA -2.0% to 4.8%), and CaO2 (bias 0.3 mL dL-1; LoA -2.1 to 2.7 mL dL-1). Zone A of the error grid encompassed 99% of data pairs for SpHb. Perfusion index (PI) ≥ 1% was recorded in 58/101 and PI < 1% in 43/101. The concordance rate for consecutive changes in SpHb and tHb with PI ≥ 1% and < 1% was 80% and 91% with four-quadrant plot, and 45.8% and 66.6% with Critchley polar plot. CONCLUSIONS: Pulse co-oximetry has acceptable accuracy for the values measured, even with low PI, whereas its trending ability requires further investigation in those horses with a higher [Hb] variation during anaesthesia.