Evaluation of pulse oximetry in horses surgically treated for colic

Abstract

Summary All 43 horses anaesthetised for colic surgery were premedicated with xylazine or diazepam. Anaesthesia was induced with guaifenesin and ketamine, horses were placed in dorsal recumbency and anaesthesia was maintained with isoflurane in oxygen and mechanical ventilation. Haemoglobin saturation readings ( S p o 2 ) were taken with a pulse oximeter and compared with computed haemoglobin saturation ( S p o 2 ) from arterial blood samples. Readings were taken over a range of S p o 2 of 78–100%, mean arterial blood pressure ranged from 24 to 108 mmHg and P a o 2 ranged from 53 to 490 mmHg. Analysis of 107 readings showed that S p o 2 values predicted S p o 2 but time, blood pressure and individual horse did not. Correlation coefficients between S p o 2 and S p o 2 were 0.85 for all values and 0.88 for values at 30 min. Values for bias and precision were calculated for all S p o 2 values and for readings separated into 3 saturation groups: normal, low normal, and abnormal. The pulse oximeter tended to underestimate S p o 2 at all times, and was less precise as the saturation decreased.