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.
