Tremors in white rhinoceroses (<i>Ceratotherium simum</i>) during etorphine–azaperone immobilisation

Abstract

Little is known about the mechanisms causing tremors during immobilisation of rhinoceros and whether cardiorespiratory supportive interventions alter their intensity. Therefore, we set out to determine the possible mechanisms that lead to muscle tremors and ascertain whether cardiorespiratory supportive interventions affect tremor intensity. We studied tremors and physiological responses during etorphine–azaperone immobilisation in eight boma-held and 14 free-living white rhinoceroses. Repeated measures analysis of variance and a Friedman test were used to determine differences in variables over time and between interventions. Spearman and Pearson correlations were used to test for associations between variables. Tremor intensity measured objectively by activity loggers correlated well (p < 0.0001; r2 = 0.9) with visual observations. Tremor intensity was greatest when animals were severely hypoxaemic and acidaemic. Tremor intensity correlated strongly and negatively with partial pressure of oxygen (PaO2) (p = 0.0003; r2 = 0.9995) and potential of hydrogen (pH) (p = 0.02, r2 = 0.97). It correlated strongly and positively with adrenaline concentrations (p = 0.003; r2 = 0.96), and adrenaline correlated strongly and negatively with PaO2 (p = 0.03; r2 = 0.95) and pH (p = 0.03; r2 = 0.94). Therefore, hypoxaemia and acidaemia were likely associated with the intensity of tremors through their activation of the release of tremorgenic levels of adrenaline. Tremors can be reduced if circulating adrenaline is reduced, and this can be achieved by the administration of butorphanol plus oxygen insufflation. Furthermore, to assist with reducing the risks associated with rhinoceros immobilisation, tremor intensity could be used as a clinical indicator of respiratory and metabolic compromise.

Releasing Three Orphaned White Rhinoceroses (Ceratotherium simum) to the Game Reserve in South Africa. Rehabilitation, Translocation and Post-Release Observations

“…The addition of azaperone to etorphine in the dart, allows a reduction in blood pressure and reduces muscle tremors which further reduces blood oxygen levels, while intravenous administration of butorphanol in recumbent animals causes the heart to slow down to normal values, most likely due to reduce the hypoxemia [40]. The study conducted in two groups of rhinoceroses, free-ranging and boma-held individuals, confirmed the effect of intravenously administered butorphanol on decreasing the muscle tremor intensity in both groups of animals [41].…”

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

“…Acidosis, hypercapnia and a low arterial partial pressure of oxygen (PaO 2 ) are common in opioid-immobilised white rhinoceroses, indicating marked cardiorespiratory depression [1,4–6]. Our findings help to explain why despite the seemingly extremely low SaO 2 values reported in these animals, recovery is usually uneventful, without obvious clinical signs of long-term damage associated with such severe hypoxaemia.…”

“…Severe side effects (e.g. muscle tremors, tachycardia, hypertension, hypercapnia, low partial pressure of oxygen (pO 2 ) and acidosis) occur regularly and are well described [1].…”

“…Standard blood gas analysis and pulse oximetry indicate an alarmingly low oxygenation status under opioid immobilisation that is in conflict with uneventful recoveries [1,4–6]. Haymerle et al reported SaO 2 values as low as 39% and SpO 2 values as low as 42% in clinically healthy, opioid-immobilised animals generated by commercially available devices [7].…”

A Comparison of Hematological, Immunological, and Stress Responses to Capture and Transport in Wild White Rhinoceros Bulls (Ceratotherium simum simum) Supplemented With Azaperone or Midazolam

“…Rhinoceroses immobilized with etorphine based drugcombinations are known to exhibit severe tachycardia and systemic hypertension resulting from the effects of the potent opioid combined with sympathetic activation (48,49). Elevated plasma epinephrine concentrations at TC compared to the other sample time points indicated that our rhinoceroses likely experienced tachycardia and hypertension, which for logistical reasons, we were not able to measure.…”