Evaluation of oscillometric blood pressure monitoring during immobilization of free-ranging Baird's tapirs (Tapirus bairdii) in Costa Rica

Abstract

The study of free-ranging, endangered species almost always requires immobilization for collection of biological samples and radiotransmitter placement. Although monitoring assists in assuring safe immobilization, scant information is available regarding physiological monitoring of tapirs. This study was designed to test the effectiveness of noninvasive, oscillometric arterial blood pressure monitoring (NIBP) in wild captured tapirs. Six adult Baird's tapirs (Tapirus bairdii) estimated to weigh 235 ± 23.6 kg (mean ± SEM) were attracted to a capture area using ripe bananas as bait. Animals were darted with a mixture of 50 mg butorphanol (0.23 ± 0.03 mg kg−1) and 100 mg xylazine (0.46 ± 0.07 mg kg−1) using a CO2 pistol. Propofol (100 µg kg−1 minute−1 IV, n = 2; 200 µg kg−1 minute−1 IV, n = 2) or ketamine (0.35 ± 0.05 mg kg−1 IV, n = 1) were delivered to maintain immobilization in all but one case. A commercial blood pressure cuff (cuff bladder width to limb circumference ratio 0.399 ± 0.01) was applied to the thoracic limb, and a 20-ga, 3.8 cm catheter was placed in the facial artery on the nondependent side of the laterally recumbent tapir. A laser line-level and careful positioning were used to assure the cuff center and pressure transducer were at the same level, and were at the approximated level of the right atrium. Systolic (SAP), diastolic (DAP) and mean arterial pressure (MAP) were recorded simultaneously (at end cuff decompression). The lower limits of the range of invasive arterial blood pressure (IBP) were 94 ± 18 mm Hg, 58 ± 18 mm Hg and 74 ± 17 mm Hg for SAP, DAP and MAP, respectively. The upper limits of the range of IBP were 114 ± 13 mm Hg, 74 ± 11 mm Hg and 87 ± 13 mm Hg for SAP, DAP, and MAP, respectively. Mean heart rate was 52 ± 9 beats minute−1. To assess agreement and correlation between IBP and NIBP methods of measurement, both correlation analysis and Bland-Altman analysis of agreement (bias and limits of agreement) were performed. Pearson's correlation coefficients were 0.858, 0.801 and 0.912 for SAP, DAP and MAP, respectively. Bias (mean differences) were − 9 mm Hg, − 12 mm Hg and − 7 mm Hg for SAP, DAP and MAP, respectively. The lower limits of agreement were − 21 mm Hg, − 29 mm Hg and − 24 mm Hg for SAP, DAP and MAP, respectively. The upper limits of agreement were 3 mm Hg, 4 mm Hg and 9 mm Hg for SAP, DAP and MAP, respectively. Both correlation and agreement analysis indicated noninvasive oscillometric blood pressure measurement is satisfactory for field blood pressure monitoring, but tend to read falsely low using the described technique.