Odd haemoglobins in odd-toed ungulates: Impact of selected haemoglobin characteristics of the white rhinoceros (<i>Ceratotherium simum</i>) on the monitoring of the arterial oxygen saturation of haemoglobin

Background Due to the current poaching crisis in Africa, increasing numbers of white rhinoceroses (Ceratotherium simum) require opioid immobilisation for medical interventions or management procedures. Alarmingly, the results of both blood gas analysis and pulse oximetry regularly indicate severe hypoxaemia. Yet, the recovery of the animals is uneventful. Thus, neither of the techniques seems to represent the real oxygenation level. We hypothesized that unusual haemoglobin characteristics of this species interfere with the techniques developed and calibrated for the use in human patients. Methods Haemoglobin was isolated from blood samples of four adult, white rhinoceroses. Oxygen dissociation curves at pH 7.2 and 7.4 (37°C) were determined based on the absorbance change of haemoglobin in the Soret-region (around 420 nm). Absorbance spectra of oxy- and deoxyhaemoglobin extending into the infrared region were measured. Results Oxygen dissociation curves of rhinoceros haemoglobin showed the typical high oxygen affinity (p50 of 2.75 ± 0.07 and 2.00 ± 0.04 kPa for pH 7.2 and 7.4, respectively) under near-physiological conditions with respect to pH, temperature and DPG. The infrared absorbance spectra of oxy- and deoxyhaemoglobin showed only marginal deviations from standard human spectra, possibly due to the presence of a few percent of methaemoglobin in vitro. Conclusions Our data enables the development of a rhinoceros-specific blood gas analysis algorithm, which allows for species-specific calculation of SaO2 levels in anaesthetized animals. The inconspicuous absorbance spectra do not contribute to the systematic underestimation of SpO2 by pulse-oximetry.背景 受当前非洲盗猎危机影响，需接受医疗干预或管理操作的白犀牛（Ceratotherium simum）数量日益增多，且此类操作多需采用阿片类药物进行制动保定。令人警觉的是，血气分析与脉搏血氧饱和度测定的结果常显示动物存在严重低氧血症，但这些动物的术后恢复却平稳顺利。由此可见，上述两种检测技术均无法准确反映白犀牛的真实氧合水平。我们推测，该物种独特的血红蛋白特性会干扰为人类患者开发并校准的血氧检测技术的准确性。 方法 本研究从4头成年白犀牛的血液样本中分离得到血红蛋白。在pH 7.2与7.4、37℃条件下，基于血红蛋白在索雷区（Soret-region，约420nm）的吸光度变化，测定其氧解离曲线；同时测定了氧合血红蛋白与去氧血红蛋白延伸至红外区域的吸光度光谱。 结果 在pH、温度及二磷酸甘油酸（DPG）接近生理状态的条件下，犀牛血红蛋白的氧解离曲线呈现典型的高氧亲和力特征：pH 7.2时半饱和氧分压（p50）为2.75±0.07 kPa，pH 7.4时为2.00±0.04 kPa。氧合血红蛋白与去氧血红蛋白的红外吸光度光谱与标准人类光谱仅存在微小偏差，该偏差可能源于体外环境中存在少量高铁血红蛋白。 结论 本研究数据可用于开发针对白犀牛的特异性血气分析算法，实现对麻醉动物动脉血氧饱和度（SaO2）的物种特异性计算。本次测得的吸光度光谱无显著异常，无法解释脉搏血氧饱和度测定法（SpO2）系统性低估血氧水平的现象。