Evaluation of the reliability of pulse oximetry, at different attachment sites, to detect hypoxaemia in immobilized impala (Aepyceros melampus)

Reliability of the Enterprise Point-of-Care (EPOC) blood analyzer's calculated arterial oxygen-hemoglobin saturation in immobilized white rhinoceroses (Ceratotherium simum)

BACKGROUND

Enterprise Point-of-Care (EPOC) blood analysis is used routinely in wildlife veterinary practice to monitor blood oxygenation, but the reliability of the EPOC calculated arterial oxygen-hemoglobin saturation (cSaO2 ) has never been validated in the white rhinoceros (Ceratotherium simum), despite their susceptibility to hypoxemia during chemical immobilization.

OBJECTIVES

We aimed to evaluate the reliability of the EPOC cSaO2 by comparing it against arterial oxygen-hemoglobin saturation (SaO2 ) measured by a co-oximeter reference method in immobilized white rhinoceroses.

METHODS

Male white rhinoceroses in two studies (both n = 8) were immobilized by darting with different etorphine-based drug combinations, followed by butorphanol or saline (administered intravenously). Animals in both studies received oxygen via intranasal insufflation after 60 min. Blood samples were drawn, at predetermined time points, from a catheter inserted into the auricular artery and analyzed using the EPOC and a co-oximeter. Bland-Altman (to estimate bias and precision) and area root mean squares (ARMS) plots were used to determine the reliability of the EPOC cSaO2 compared with simultaneous co-oximeter SaO2 readings.

RESULTS

The rhinoceros were acidotic (pH of 7.3 ± 0.1 [mean ± standard deviation]), hypercapnic (PaCO2 of 73.7 ± 10.5 mmHg), and normothermic (body temperature of 37.4 ± 1.8°C). In total, 389 paired cSaO2 -SaO2 measurements were recorded (the cSaO2 ranged between 13.2% and 99.0%, and the SaO2 ranged between 11.8% and 99.9%). The EPOC cSaO2 readings were unreliable (inaccurate, imprecise, and poor ARMS) across the entire saturation range (bias -6%, precision 5%, and ARMS 8%).

CONCLUSIONS

The EPOC cSaO2 is unreliable and should not be used to monitor blood oxygenation in immobilized white rhinoceroses.

Use of blood colour for assessment of arterial oxygen saturation in immobilized impala (Aepyceros melampus)

OBJECTIVE

To determine the relationship between arterial blood colour [as defined by the International Commission on Illumination (CIE) L∗a∗b∗ colour space] and haemoglobin oxygen saturation [functional saturation (SaO₂) and fractional saturation (FO₂Hb)], and if arterial blood colour can be used to predict arterial haemoglobin oxygen saturation.

STUDY DESIGN

Descriptive study as an adjunct to two prospective randomized crossover studies.

ANIMALS

A group of 10 wild caught adult female impala (Aepyceros melampus) weighing 34.1 ± 5.2 kg (mean ± standard deviation).

METHODS

Impala were immobilized with potent opioids (0.09 mg kg^-1 of etorphine or thiafentanil). A total of 163 arterial blood samples were collected anaerobically into heparinized syringes from arterial cannulae and analysed immediately using spectrocolourimetry and co-oximetry. Data were analysed by modelling the relationship between predicted arterial blood colour CIE L∗a∗b∗ components and SaO₂ and FO₂Hb. The models were then used to predict values for L∗, a∗ and b∗ to produce a colour palette for the range of SaO₂ and FO₂Hb used. The modified version of the Farnsworth-Munsell hue test was used to assess the subjective ordering of the resulting colour palette by 20 observers.

RESULTS

The second-order polynomial (quadratic) model produced the best fit for all three arterial blood colour CIE L∗a∗b∗ components for both SaO₂ and FO₂Hb. The regression models were used to generate predicted arterial blood colour CIE L∗a∗b∗ components for the midpoint of each decile over a range of SaO₂ and FO₂Hb percentages (15% to 95%). The resulting colour palettes were correctly ordered by all observers in the SaO₂ range of 45-95% saturation.

CONCLUSIONS AND CLINICAL RELEVANCE

An association between arterial blood colour (as defined by CIE L∗a∗b∗ components) and SaO₂ and FO₂Hb exists, and arterial blood colour can be used to give a clinically useful estimate of arterial haemoglobin oxygen saturation in impala.