Determining whether blood colour can be used to assess arterial blood oxygenation in immobilised impala (Aepyceros melampus)

Abstract

Hypoxaemia (oxyhaemoglobin saturation < 90%) often occurs during wildlife immobilisation and poses a risk of morbidity and mortality. Several methods have been used to assess blood oxygenation in immobilised impala (Aepyceros melampus). Pulse oximetry has been shown to be unreliable, co-oximetry and blood gas analysis are the gold standard but are limited by practicality and cost. With the advent of digital cameras and spectrocolourimeters the assessment of blood colour could be of value for determining blood oxygenation. This study set out to determine whether there is good association between arterial blood colour, as assessed by CIE L*a*b* (Commission on international illumination; L*: luminosity; a*: green to red; b*: blue to yellow) colour components, and blood oxygenation, as determined by functional oxyhaemoglobin saturation (SaO2) and fractional oxyhaemoglobin saturation (FO2Hb). To obtain arterial blood samples with different blood oxygen levels 11 impala were immobilised with either etorphine or thiafentanil. Arterial blood samples were collected from the auricular artery at five-minute intervals and immediately analysed by means of co-oximetry to measure blood oxygenation, and spectrocolourimetry to measure the CIE L*a*b* colour components. The colour components associated better with blood oxygenation (SaO2 and FO2Hb) using a quadratic rather than a linear model (p < 0.001). The association was strong for each of the colour components (CIE L*a*b*). Therefore both SaO₂ and FO2Hb are reliable predictors of all three CIE L*a*b* components of arterial blood colour, and hence blood colour can be used to reliably estimate arterial blood oxygenation of impala. These findings could pave the way for developing colour charts and devices that can be used in the field to inexpensively determine blood oxygenation, and detect hypoxaemia, in immobilised or anaesthetised animals.