Accuracy of calculated arterial saturation in oxygen in neonatal foals and effects of monitor, sensor, site of sensor placement, and degree of hypoxemia on the accuracy of pulse oximetry

Abstract

Objectives: To (1) assess the agreement between calculated values for arterial hemoglobin saturation of oxygen (SaO2 ) and values obtained by co-oximetry, (2) assess the accuracy of 2 pulse oximetry monitors for measurement of SaO2 in foals, and for each monitor, and (3) determine the optimal combination of sensor type and site of sensor placement for SaO2 monitoring.

Design: Prospective experimental study.

Setting: University teaching hospital.

Animals: Six neonatal foals.

Interventions: Foals were anesthetized with isoflurane and SaO2 was manipulated by varying the inspired fraction of oxygen. SaO2 was calculated from oxygen tension or measured by pulse oximetry using 2 monitors equipped with transmission or reflectance sensors attached to the foal's tongue, lip, ear, or inserted rectally (reflectance sensor only). SaO2 values measured by co-oximetry were used as the gold standard to calculate bias.

Measurements and main results: Mean (±SD) SaO2 determined by co-oximetry was 65.2% ± 11.8%, 85.4% ± 2.5%, and 97.2% ± 0.4% at the low, intermediate, and high SaO2 level, respectively. Sensors attached to the ear failed to provide SaO2 readings for most attempts. Reflectance sensors placed on the lip or rectally gave significantly larger biases at low SaO2 (-17.0% and -23.6%, respectively) than at higher levels. Bias of all other combinations of monitors, sensors, and sites (-1.8 to -4.1%) was not significantly influenced by the level of SaO2 or different from each other. The bias of calculated saturation was similar to that of pulse oximetry.

Conclusions: Transmission sensors placed on the lip or tongue or reflectance sensors placed on the tongue give the most accurate assessment of SaO2 in anesthetized neonatal foals. Calculated saturation is not more accurate than pulse oximetry to estimate SaO2 .

Keywords: anesthesia; blood gas analysis; oxygenation monitoring.