Agreement between arterial partial pressure of carbon dioxide and saturation of hemoglobin with oxygen values obtained by direct arterial blood measurements versus noninvasive methods in conscious healthy and ill foals

Abstract

Objective-To determine agreement between indirect measurements of end-tidal partial pressure of carbon dioxide (Petco2) and saturation of hemoglobin with oxygen as measured by pulse oximetry (Spo2) with direct measurements of Paco2 and calculated saturation of hemoglobin with oxygen in arterial blood (Sao2) in conscious healthy and ill foals. Design-Validation study. Animals-10 healthy and 21 ill neonatal foals. Procedures-Arterial blood gas analysis was performed on healthy and ill foals examined at a veterinary teaching hospital to determine direct measurements of Paco2 and Pao2 along with Sao2. Concurrently, Petco2 was measured with a capnograph inserted into a naris, and Spo2 was measured with a reflectance probe placed at the base of the tail. Paired values were compared by use of Pearson correlation coefficients, and level of agreement was assessed with the Bland-Altman method. Results-Mean ± SD difference between Paco2 and Petco2 was 0.1 ± 5.0 mm Hg. There was significant strong correlation (r = 0.779) and good agreement between Paco2 and Petco2. Mean ± SD difference between Sao2 and Spo2 was 2.5 ± 3.5%. There was significant moderate correlation (r = 0.499) and acceptable agreement between Sao2 and Spo2.

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

“…Prior studies assessing the accuracy of pulse oximetry for the measurement of SaO 2 in neonatal foals have used calculated saturation based on an equation developed for adult horses as the reference method . The present study demonstrates that calculated saturation based on an equation developed for adult equine hemoglobin is inaccurate, particularly at low saturation with overestimation of SaO 2 by as much as 25% in some samples.…”

“…Prior studies assessing the accuracy of pulse oximetry for the measurement of SaO 2 in neonatal foals have used calculated saturation based on an equation developed for adult horses as the reference method. 7,8 The present study demonstrates that calculated saturation based on an equation developed for adult equine hemoglobin is inaccurate, particularly at low saturation with overestimation of SaO 2 by as much as 25% in some samples. The poor performance of an equation developed for adult horses is not unexpected because the oxygen saturation curve of newborn animals of most species is shifted to the left relative to adult blood, indicating greater affinity for oxygen.…”

“…In one study, placement of a reflectance sensor at the base of the tail of conscious neonatal foals gave SaO 2 values similar to values calculated using the equation for equine hemoglobin. 8 However, it is unknown whether placement of a reflectance sensor at the base of the tail provides accurate measurement of SaO 2 compared to co-oximetry.…”

“…Studies in dogs, cats, and adult horses have underscored considerable differences in accuracies between various monitors, sensors, and site of sensor placement . Prior studies evaluating the accuracy of SpO 2 in neonatal foals have used calculated SaO 2 as the reference method . Given that calculated SaO 2 might be less accurate than SpO 2 , there is a need to assess the accuracy of SpO 2 relative to co‐oximetry at various levels of saturation in neonatal foals.…”

Evaluation of the optical interference in a combined measurement system used for assessment of tissue blood flow

“…Photoplethysmography, (PPG) a non-invasive electro-optical technique used mainly to determine and register the variation in blood volume or blood flow in the body caused by cardiovascular pulsations in the bed of tissue [5][6]. A photoplethysmographic signal is obtained by illuminating a region of tissue containing a vascular bed and acquiring either the reflected or transmitted light.…”