Hypoxia following etorphine administration in goats (Capra hircus) results more from pulmonary hypertension than from hypoventilation

Effects of Butorphanol on Respiration in White Rhinoceros (Ceratotherium simum) Immobilized with Etorphine-Azaperone

This article reports on respiratory function in white rhinoceros (Ceratotherium simum) immobilized with etorphine-azaperone and the changes induced by butorphanol administration as part of a multifaceted crossover study that also investigated the effects of etorphine or etorphine-butorphanol treatments. Six male white rhinoceros underwent two immobilizations by using 1) etorphine-azaperone and 2) etorphine-azaperone-butorphanol. Starting 10 min after recumbency, arterial blood gases, limb muscle tremors, expired minute ventilation, and respiratory rate were evaluated at 5-min intervals for 25 min. Alveolar to arterial oxygen gradient, expected respiratory minute volume, oxygen consumption, and carbon dioxide production were calculated. Etorphine-azaperone administration resulted in hypoxemia and hypercapnia, with increases in alveolar to arterial oxygen gradient, oxygen consumption, and carbon dioxide production, and a decrease in expired minute ventilation. Muscle tremors were also observed. Intravenous butorphanol administration in etorphine-azaperone-immobilized white rhinoceros resulted in less hypoxemia and hypercapnia; a decrease in oxygen consumption, carbon dioxide production, and expired minute ventilation; and no change in the alveolar to arterial oxygen gradient and rate of breathing. We show that the immobilization of white rhinoceros with etorphine-azaperone results in hypoxemia and hypercapnia and that the subsequent intravenous administration of butorphanol improves both arterial blood oxygen and carbon dioxide partial pressures.

Ketamine-butorphanol-medetomidine for the immobilisation of free-living hyenas (Crocuta crocuta)

Free-ranging spotted hyenas (Crocuta crocuta) are immobilised for a variety of purposes, including wildlife-human conflict mitigation, research, and veterinary treatment. Combinations of tiletamine-zolazepam (Zoletil) and medetomidine are commonly used for immobilisation of hyenas, however, recovery times are long. In this descriptive study, a total of 20 adult or subadult free-ranging hyenas were immobilised near Skukuza in the Kruger National Park using ketamine, butorphanol, and medetomidine. The goal of the study was to evaluate a suitable dose and measure cardiorespiratory effects of this combination. The quality of induction and recovery were scored using an established scoring system from 1 (excellent) to (poor). Twelve of the 20 hyenas were given an induction score of 1 (excellent), five an induction score of 2 (good), and three an induction score of 3 (fair). Of the animals with induction score = 1, the mean drug dose was 1.17 mg/kg ketamine, 0.25 mg/kg butorphanol and 0.03 mg/kg medetomidine, and the mean induction time and time to handling 6:25 minutes and 9:46 minutes respectively. The mean recovery time (from reversal to standing) was 10:16 min, which is shorter than what has been reported for tiletaminezolazepam- based combinations in hyenas. Most hyenas were bradycardic (< 40 beats per minute) and the mean PaO2 69.5 mmHg. Three hyenas, one with induction score = 2, and two with induction scores = 3 spontaneously recovered at 33, 44 and 56 minutes post approach respectively. Regardless of induction time, all hyenas reached a level of surgical anaesthesia while immobilised. Overall, ketamine-butorphanol-medetomidine (KBM) was effective in immobilising hyenas but induction times varied, and animals were bradycardic during immobilisation.

Effects of sub-lethal doses of fentanyl on vital physiologic functions and withdrawal-like behaviors in adult goats

Synthetic opioids like fentanyl have improved the standard of care for many patients in the clinical setting, but their abuse leads to tens of thousands of overdose deaths annually. The current opioid epidemic underscores a critical need for insights into the physiological effects of fentanyl on vital functions. High doses of opioids in small mammals cause opioid-induced respiratory depression (OIRD) leading to hypoventilation, hypoxemia, and hypercapnia. In addition, opioids can also increase the alveolar to arterial oxygen (A-a) gradient and airway dysfunction. However, little is known about the physiologic effects of sub-lethal doses of opioids in large mammals. Here we report the effects of a sub-lethal dose range of fentanyl (25-125 μg/kg; IV) on vital physiologic functions over 90 min (min) and withdrawal-like behaviors over the subsequent 4 h (h) in adult female goats (n = 13). Fentanyl induced decreases in breathing frequency in the first few min post-injection, but then led to a sustained increase in tidal volume, total ventilation, and blood pressure with a reduced heart rate for ≥90 min. These ventilatory changes resulted in time-dependent arterial hypocapnia and hypoxemia and an increased alveolar to arterial oxygen gradient ∼30 min post-injection indicative of impaired gas exchange in the lung. The predominant effects of fentanyl on breathing were stimulatory, underscored by an increased rate of rise of the diaphragm muscle activity and increased activation of upper airway, intercostal and abdominal muscles. Beginning 90 min post-injection we also quantified withdrawal-like behaviors over 4 h, demonstrating dose- and time-dependent increases in locomotor, biting, itching, and pawing behaviors. We conclude that fentanyl at sublethal doses induces multiple physiologic and behavior changes that emerge along different time courses suggesting multiple independent mechanisms underlying effects of opioids.

Development of a novel immobilisation protocol for black-faced impala (Aepyceros melampus ssp. petersi) in Etosha National Park

Black-faced impala (Aepyceros melampus ssp. petersi) are endemic to Namibia where conservation management involves immobilisation and translocation, and mortality with current protocols is common. Critically evaluated field immobilisation protocols are needed to maximise animal safety. This prospective study was done in two phases: the first compared etorphine- and thiafentanil-based combinations, the second evaluated the influence of oxygen in impala receiving the thiafentanil-based combination. Animals (10 per group) received 50 mg ketamine (K) and 10 mg butorphanol (B), with either 2.0 mg etorphine (E) or 2.0 mg thiafentanil (T). A third group of ten impala were anaesthetised using TKB with supplemental nasal oxygen (O) at a rate of 5 L/minute. Behavioural, metabolic and physiological variables were assessed within five minutes of recumbency and at 10, 15, and 20 minutes post-recumbency. Statistical analyses for non-parametric data were performed to compare the treatment groups as well as time points; p ≤ 0.05 considered significant. Following darting, 7/10 EKB animals were standing when approached, compared to 2/20 in the thiafentanil treatment groups. Time to first effect was significantly higher for EKB (155 ± 105.7 seconds) compared to TKBO (61.5 ± 21.4 seconds). Time to sternal after darting was significantly higher with EKB (411.6 ± 174 seconds) compared to TKB (160.5 ± 85.4 seconds) and TKBO (166 ± 77.3 seconds). This study builds on previous work investigating the effects of potent opioids on impala and is the first evaluating their use in a field setting. The thiafentanil combination had a faster onset and resulted in a smoother induction than the etorphine combination. Additionally, oxygenation improved in animals receiving oxygen supplementation.

Immobilization of Captive Kulans (Equus hemionus kulan) Without Using Ultrapotent Opioids

Etorphine is widely used in zoological medicine for the immobilization of large herbivores. All reported immobilization protocols for kulans use etorphine as the primary immobilizing agent. However, etorphine can trigger severe side effects and is highly toxic for humans, its availability is occasionally limited for use in wildlife medicine. Therefore, two different alpha-2 agonist-based protocols for the general anesthesia of kulans were investigated and compared with the standard etorphine immobilization. In total, 21 immobilizations were performed within the scope of routine husbandry management at the Serengeti-Park Hodenhagen. Kulans were darted using a ketamine–medetomidine–midazolam–butorphanol (KMMB) protocol (n = 8, treatment group (TG) 1), a tiletamine–zolazepam–medetomidine–butorphanol (TZMB) protocol (n = 7, treatment group (TG) 2), or an etorphine–acepromazine–detomidine–butorphanol (EADB) protocol (n = 6, control group). Vital parameters included heart rate, respiratory rate, arterial blood pressure (invasive), end tidal CO₂ (etCO₂), electromyography and core body temperature, which were all assessed every 10 min. For blood gas analysis, arterial samples were collected 15, 30, 45 and 60 min after induction. Subjective measures of quality and efficacy included quality of induction, immobilization, and recovery. Time to recumbency was longer for TG 1 (9.00 ± 1.67 min) and TG 2 (10.43 ± 1.79 min) compared to the induction times in the control group (5.33 ± 1.93 min). Treatment group protocols resulted in excellent muscle relaxation, normoxemia and normocapnia. Lower pulse rates combined with systolic arterial hypertension were detected in the alpha-2 agonist-based protocols. However, only in TZMB-immobilized kulans, sustained severe systolic arterial hypertension was observed, with significantly higher values than in the TG 1 and the normotensive control group. At 60 min following induction, medetomidine and detomidine were antagonized with atipamezole IM (5 mg/mg medetomidine or 2 mg/mg detomidine), etorphine and butorphanol with naltrexone IV (2 mg/mg butorphanol or 50 mg/mg etorphine), and midazolam and zolazepam with flumazenil IV (0.3 mg per animal). All three combinations provided smooth and rapid recoveries. To conclude, the investigated treatment protocols (KMMB and TZMB) provided a safe and efficient general anesthesia in kulans with significantly better muscle relaxation, higher respiration rates and improved arterial oxygenation compared with the immobilizations of the control group. However, the control group (EADB) showed faster recoveries. Therefore, EADB is recommended for ultra-short immobilizations (e.g., microchipping and collaring), especially with free-ranging kulans where individual recovery is uncertain, whereas the investigated treatment protocols are recommended for prolonged medical procedures on captive kulans.

Arterial Blood Gases and Cardiorespiratory Parameters in Etorphine-Medetomidine-Midazolam Immobilized Free-Ranging and Game-Farmed Southern White Rhinoceroses (Ceratotherium simum simum) Undergoing Electro-Ejaculation

With the rapid loss of individuals in the wild, semen cryopreservation has gained importance to safeguard the genetic diversity of white rhinoceroses (Ceratotherium simum). For semen collection via electro-ejaculation, immobilization of free-ranging individuals requires the potent opioid etorphine, which is routinely combined with azaperone, but causes hypoxemia, hypercarbia, acidemia, muscle rigidity, tachycardia, and systemic hypertension. In this study, the suitability of two alternative immobilization protocols including etorphine, medetomidine, and midazolam at different doses (high vs. low etorphine) was evaluated in adult white rhinoceros bulls in two different management systems (free-ranging vs. game-farmed) and undergoing electro-ejaculation. Fourteen free-ranging (Group 1) and 28 game-farmed rhinoceroses (Group 2) were immobilized with ≈2.5 μg/kg etorphine (high dose), ≈2.5 μg/kg medetomidine, ≈25 μg/kg midazolam and 1,500–1,700 IU hyaluronidase and received ≈2.5 μg/kg of butorphanol intravenously at first handling. Twenty game-farmed animals (Group 3) received ≈1 μg/kg etorphine (low dose), ≈5 μg/kg medetomidine, ≈25 μg/kg midazolam and 1,700 IU hyaluronidase. Respiratory rate, heart rate and peripheral hemoglobin oxygen saturation (SpO₂) were measured at 5-min intervals; non-invasive oscillometric blood pressures and arterial blood gases at first handling and before reversal of the immobilization; serum clinical chemistry analytes and hematocrit at first handling. Generalized mixed models (fixed factors: group, time, recumbency; random factor: individual rhinoceros) were applied to compare longitudinal changes between free-ranging and game-farmed rhinoceroses immobilized with the higher etorphine dose (Groups 1 and 2), and between the two protocols tested in the game-farmed rhinoceroses (Groups 2 and 3). All animals were successfully immobilized, presented with normal lactate concentrations (<5 mmol/L), experienced no muscle tremors and recovered uneventfully. Hypoxemia and hypertension persisted throughout the immobilization in all groups. Acidemia and hypercarbia were absent in Group 1, but present in the game-farmed animals. The lower etorphine dose in Group 3 resulted in significantly longer induction times, however, tachycardia was not observed. SpO₂ was higher for sternal vs. lateral recumbency. Semen-rich fractions were recovered following electro-stimulation in 46 out of the 62 animals. Our findings suggest that etorphine-medetomidine-midazolam provides effective immobilization with fewer side effects compared to previous reports in white rhinoceroses and is suitable for successful electro-ejaculation.

Cardiopulmonary Parameters and Arterial Blood Gases During Etorphine-Medetomidine-Midazolam Immobilization in Free-Ranging Black Rhinoceroses (Diceros bicornis) Undergoing Electro-Ejaculation-A Preliminary Study

Conservation management interventions for the critically endangered black rhinoceros (Diceros bicornis) require immobilization, which offer opportunities for semen collection and cryopreservation to establish genetic reservoirs. In free-ranging rhinoceroses, a combination of the potent opioid etorphine and the tranquilizer azaperone is routinely used for chemical immobilization but is associated with muscle rigidity and severe cardiopulmonary changes. Additionally, azaperone inhibits semen emission. Seven free-ranging, male, sexually mature black rhinoceroses were immobilized with an alternative protocol consisting of 4.5 mg etorphine, 5 mg medetomidine, 50 mg midazolam and 2,500 IU hyaluronidase delivered remotely by darting from a helicopter. During the immobilization, electro-ejaculation was performed with a portable electro-ejaculator, and a species-specific rectal probe. Animals were observed for muscle tremors. Longitudinal changes in respiratory rate, heart rate and peripheral oxyhemoglobin saturation, measured at 5 min intervals, were assessed using a general mixed model. Non-invasive oscillometric blood pressure and arterial blood gas variables were measured at first handling and before reversal and compared using the Wilcoxon rank sum test. All animals were successfully immobilized, showed no muscle tremors, presented with normal heart rates and lactate concentration (<5 mmol/L), recovered uneventfully, but experienced acidemia, hypoxemia and hypercapnia. Induction time and total time in recumbency were 4.2 ± 0.41 and 38.4 ± 6.9 min, respectively. Electro-stimulation commenced after 11.7 ± 3.98 min and completed after 24.3 ± 6.65 min. Semen-rich fractions were successfully collected from six animals. Our observations indicate that etorphine-medetomidine-midazolam provides a promising immobilization protocol for free-ranging black rhinoceroses, that allows for successful electro-ejaculation.

Immobilization of African buffaloes (Syncerus caffer) using etorphine-midazolam compared with etorphine-azaperone

OBJECTIVE

To compare induction times and physiological effects of etorphine-azaperone with etorphine-midazolam immobilization in African buffaloes.

STUDY DESIGN

Randomized crossover study.

ANIMALS

A group of 10 adult buffalo bulls (mean body weight 353 kg).

METHODS

Etorphine-azaperone (treatment EA; 0.015 and 0.15 mg kg^-1, respectively) and etorphine-midazolam (treatment EM; 0.015 and 0.15 mg kg^-1, respectively) were administered once to buffaloes, 1 week apart. Once in sternal recumbency, buffaloes were instrumented and physiological variables recorded at 5 minute intervals, from 5 minutes to 20 minutes. Naltrexone (20 mg mg^-1 etorphine dose) was administered intravenously at 40 minutes. Induction (dart placement to recumbency) and recovery (naltrexone administration to standing) times were recorded. Arterial blood samples were analysed at 5 and 20 minutes. Physiological data were compared between treatments using a general linear mixed model and reported as mean ± standard deviation. Time data were compared using Mann-Whitney U test and reported as median (interquartile range) with p ≤ 0.05.

RESULTS

Actual drug doses administered for etorphine, azaperone and midazolam were 0.015 ± 0.001, 0.15 ± 0.01 and 0.16 ± 0.02 mg kg^-1, respectively. Induction time for treatment EA was 3.3 (3.6) minutes and not different from 3.2 (3.2) minutes for treatment EM. The overall mean arterial blood pressure was significantly lower for treatment EA (102 ± 25 mmHg) than that for treatment EM (163 ± 18 mmHg) (p < 0.001). The PaO₂ for treatment EA (37 ± 12 mmHg; 5.0 ± 1.6 kPa) was not different from that for treatment EM (43 ± 8 mmHg; 5.8 ± 1.1 kPa). Recovery time was 0.8 (0.6) minutes for treatment EA and did not differ from 1.1 (0.6) minutes for treatment EM.

CONCLUSIONS AND CLINICAL RELEVANCE

Treatment EA was as effective as treatment EM for immobilization in this study. However, systemic arterial hypertension was a concern with treatment EM, and both combinations produced clinically relevant hypoxaemia. Supplemental oxygen administration is recommended with both drug combinations.

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.

EVALUATION OF TWO DOSES OF BUTORPHANOL-MEDETOMIDINE-MIDAZOLAM FOR THE IMMOBILIZATION OF WILD VERSUS CAPTIVE BLACK-FOOTED CATS (FELIS NIGRIPES)

The efficacy, safety, physiologic effects, and reversibility of butorphanol-medetomidine-midazolam (BMM) immobilization were evaluated in black-footed cats (Felis nigripes) and compared between captive and wild animals. Nine captive and 14 wild black-footed cats were hand injected into an accessible hind limb muscle group with the BMM combination. The captive cats (captive group) received a lower dose of the combination (butorphanol, 0.25 ± 0.03 mg/kg; medetomidine, 0.06 ± 0.01 mg/kg; midazolam, 0.13 ± 0.02 mg/kg), whereas the wild cats received a higher dose (butorphanol, 0.53 ± 0.11 mg/kg, medetomidine, 0.13 ± 0.03 mg/kg, midazolam, 0.27 ± 0.05 mg/kg). Two capture methods were required to restrain the wild cats; previously collared cats were tracked and excavated out of their burrows during daylight hours (excavated group), whereas uncollared cats were randomly located using spotlights and pursued by a vehicle at night (pursued group). Inductions were rapid and no spontaneous arousals occurred. Mean arterial blood pressure in all cats was within normal limits for domestic cats. Initial rectal temperatures varied greatly among the groups, but decreased in all groups as the immobilization progressed. In the pursued animals, heart rates and respiratory rates were initially elevated. All cats had moderate hypoxemia, hypocapnia, and metabolic acidosis. Intramuscular administration of naltrexone, atipamezole, and flumazenil resulted in rapid, uncomplicated recoveries. BMM is thus a safe, effective immobilizing drug combination for both captive and wild black-footed cats, but higher doses are required in wild animals. The capture methods exerted a greater influence on the physiology of the immobilized animals than did the doses of the drugs used. Although this drug combination can be used safely to immobilize black-footed cats, supplemental oxygen should always be available for use, especially in pursued animals due to hypoxia.

Investigation of cardiorespiratory effects of the selective 5-HT4 agonist BIMU-8 in etorphine-immobilised goats (Capra aegagrus hircus) in a randomized, blinded and controlled trial

BACKGROUND

Opioid-induced respiratory compromise remains a significant challenge in etorphine-immobilised wildlife. Serotonergic agonists offer a potential avenue for preventing or treating opioid-induced respiratory compromise. We therefore aimed to determine whether the selective 5-hydroxytryptamine receptor 4 (5-HT4) agonist, BIMU-8, reverses opioid-induced respiratory compromise in etorphine-immobilised goats.

METHODS

Seven healthy adult goats were immobilised with etorphine, then treated with BIMU-8 or sterile water 5 minutes later in a randomised, prospective cross-over study. Cardiorespiratory variables were measured at 1-minute intervals from 4 minutes before etorphine to 15 minutes after its administration. Arterial blood gas analyses were also performed before and after etorphine administration and the respective treatments.

RESULTS

Intravenous injection of BIMU-8 attenuated etorphine-induced respiratory compromise, as indicated by improvements, compared to baseline and between treatments, in respiratory rate (f_R ), peripheral arterial blood oxygen saturation (SpO₂ ), partial pressure of arterial oxygen (PaO₂ ) and the alveolar-arterial oxygen partial pressure gradient (P(A-a)O₂ ). BIMU-8 caused an increase in heart rate and a temporary decrease in arterial blood pressure. Mild movements and slight muscle spasm occurred but BIMU-8 did not reverse immobilisation.

CONCLUSION

Our results indicate that BIMU-8 may be a potential drug candidate for the treatment, or prevention, of etorphine-induced respiratory compromise in immobilised ungulates.

What hinders pulmonary gas exchange and changes distribution of ventilation in immobilized white rhinoceroses (Ceratotherium simum) in lateral recumbency?

This study used electrical impedance tomography (EIT) measurements of regional ventilation and perfusion to elucidate the reasons for severe gas exchange impairment reported in rhinoceroses during opioid-induced immobilization. EIT values were compared with standard monitoring parameters to establish a new monitoring tool for conservational immobilization and future treatment options. Six male white rhinoceroses were immobilized using etorphine, and EIT ventilation variables, venous admixture, and dead space were measured 30, 40, and 50 min after becoming recumbent in lateral position. Pulmonary perfusion mapping using impedance-enhanced EIT was performed at the end of the study period. The measured impedance (∆Z) by EIT was compared between pulmonary regions using mixed linear models. Measurements of regional ventilation and perfusion revealed a pronounced disproportional shift of ventilation and perfusion toward the nondependent lung. Overall, the dependent lung was minimally ventilated and perfused, but remained aerated with minimal detectable lung collapse. Perfusion was found primarily around the hilum of the nondependent lung and was minimal in the periphery of the nondependent and the entire dependent lung. These shifts can explain the high amount of venous admixture and physiological dead space found in this study. Breath holding redistributed ventilation toward dependent and ventral lung areas. The findings of this study reveal important pathophysiological insights into the changes in lung ventilation and perfusion during immobilization of white rhinoceroses. These novel insights might induce a search for better therapeutic options and is establishing EIT as a promising monitoring tool for large animals in the field.NEW & NOTEWORTHY Electrical impedance tomography measurements of regional ventilation and perfusion applied to etorphine-immobilized white rhinoceroses in lateral recumbency revealed a pronounced disproportional shift of the measured ventilation and perfusion toward the nondependent lung. The dependent lung was minimally ventilated and perfused, but still aerated. Perfusion was found primarily around the hilum of the nondependent lung. These shifts can explain the gas exchange impairments found in this study. Breath holding can redistribute ventilation.

Comparison of cardiopulmonary effects of etorphine and thiafentanil administered as sole agents for immobilization of impala (Aepyceros melampus)

OBJECTIVE

To compare the cardiopulmonary effects of the opioids etorphine and thiafentanil for immobilization of impala.

STUDY DESIGN

Two-way crossover, randomized study.

ANIMALS

A group of eight adult female impala.

METHODS

Impala were given two treatments: 0.09 mg kg^-1 etorphine or 0.09 mg kg^-1 thiafentanil via remote dart injection. Time to recumbency, quality of immobilization and recovery were assessed. Respiratory rate, heart rate (HR), mean arterial blood pressure (MAP) and arterial blood gases were measured. A linear mixed model was used to analyse the effects of treatments, treatments over time and interactions of treatment and time (p < 0.05).

RESULTS

Time to recumbency was significantly faster with thiafentanil (2.0 ± 0.8 minutes) than with etorphine (3.9 ± 1.6 minutes; p = 0.007). Both treatments produced bradypnoea, which was more severe at 5 minutes with thiafentanil (7 ± 4 breaths minute^-1) than with etorphine (13 ± 12 breaths minute^-1; p = 0.004). HR increased with both treatments but significantly decreased over time when etorphine (132 ± 17 to 82 ± 11 beats minute^-1) was compared with thiafentanil (113 ± 22 to 107 ± 36 beats minute^-1; p < 0.001). Both treatments caused hypertension which was more profound with thiafentanil (mean overall MAP = 140 ± 14 mmHg; p < 0.001). Hypoxaemia occurred with both treatments but was greater with thiafentanil [PaO₂ 37 ± 13 mmHg (4.9 kPa)] than with etorphine [45 ± 16 mmHg (6.0 kPa)] 5 minutes after recumbency (p < 0.001). After 30 minutes, PaO₂ increased to 59 ± 10 mmHg (7.9 kPa) with both treatments (p < 0.001).

CONCLUSIONS AND CLINICAL RELEVANCE

The shorter time to recumbency with thiafentanil may allow easier and faster retrieval in the field. However, thiafentanil caused greater hypertension, and ventilatory effects during the first 10 minutes, after administration.

Comparison of some cardiopulmonary effects of etorphine and thiafentanil during the chemical immobilization of blesbok (Damaliscus pygargus phillipsi)

OBJECTIVE

To determine the cardiopulmonary effects of etorphine and thiafentanil for immobilization of blesbok.

STUDY DESIGN

Blinded, randomized, two-way crossover study.

ANIMALS

A group of eight adult female blesbok.

METHODS

Animals were immobilized twice, once with etorphine (0.09 mg kg^-1) and once with thiafentanil (0.09 mg kg^-1) administered intramuscularly by dart. Immobilization quality was assessed and analysed by Wilcoxon signed-rank test. Time to final recumbency was compared between treatments by one-way analysis of variance. Cardiopulmonary effects including respiratory rate (ƒ_R), arterial blood pressures and arterial blood gases were measured. A linear mixed model was used to assess the effects of drug treatments over the 40 minute immobilization period. Significant differences between treatments, for treatment over time as well as effect of treatment by time on the variables, were analysed (p < 0.05).

RESULTS

There was no statistical difference (p = 0.186) between treatments for time to recumbency. The mean ƒ_R was lower with etorphine (14 breaths minute^-1) than with thiafentanil (19 breaths minute^-1, p = 0.034). The overall mean PaCO₂ was higher with etorphine [45 mmHg (6.0 kPa)] than with thiafentanil [41 mmHg (5.5 kPa), p = 0.025], whereas PaO₂ was lower with etorphine [53 mmHg (7.1 kPa)] than with thiafentanil [64 mmHg (8.5 kPa), p < 0.001]. The systolic arterial pressure measured throughout all time points was higher with thiafentanil than with etorphine (p = 0.04). The difference varied from 30 mmHg at 20 minutes after recumbency to 14 mmHg (standard error difference 2.7 mmHg) at 40 minutes after recumbency. Mean and diastolic arterial pressures were significantly higher with thiafentanil at 20 and 25 minute measurement points only (p < 0.001).

CONCLUSIONS

Both drugs caused clinically relevant hypoxaemia; however, it was less severe with thiafentanil. Ventilation was adequate. Hypertension was greater and immobilization scores were lower with thiafentanil.

Do potent immobilising-opioids induce different physiological effects in impala and blesbok?

Potent opioids are known to cause negative alterations to the physiology of immobilised antelope. How these effects differ between species has not been studied. This study aimed to compare time to recumbence and effects of opioid-based immobilisation on the physiology of impala (Aepyceros melampus) and blesbok (Damaliscus pygargus phillipsi). Eight animals of each species were immobilised, with 0.09 mg/kg etorphine and 0.09 mg/kg thiafentanil respectively, in a randomised two-way cross-over study. Variables measured and analysed by means of a linear mixed model included time to recumbence, heart rate, respiratory rate, arterial blood pressure, blood gases, lactate and glucose. In blesbok, mean time to recumbence was not significantly different with either drug (2.5 minutes and 2.2 min, respectively), but in impala thiafentanil achieved a shorter time to recumbence (2.0 min) than etorphine (3.9 min). Mean heart rates of immobilised impala were within reported physiological limits, but lower in immobilised blesbok when both opioids were used (35 beats/min to 44 beats/min vs. 104 ± 1.4 beats/min resting heart rate). Impala developed severe respiratory compromise and hypoxaemia from both opioids (overall mean PaO2 values ranged from 38 mmHg to 59 mmHg over 30 min). In contrast, blesbok developed only moderate compromise. Therefore, significantly different species-specific physiological responses to potent opioid drugs exist in blesbok and impala. Given that these different responses are clinically relevant, extrapolation of immobilising drug effects from one species of African ungulate to another is not recommended.

Immobilization quality and cardiopulmonary effects of etorphine alone compared with etorphine-azaperone in blesbok (Damaliscus pygargus phillipsi)

OBJECTIVE

To evaluate the immobilization quality and cardiopulmonary effects of etorphine alone compared with etorphine-azaperone in blesbok (Damaliscus pygargus phillipsi).

STUDY DESIGN

Blinded, randomized, crossover design.

ANIMALS

A total of 12 boma-habituated female blesbok weighing [mean ± standard deviation (SD)] 57.5 ± 2.5 kg.

METHODS

Each animal was administered etorphine (0.09 mg kg^-1) or etorphine-azaperone (0.09 mg kg^-1; 0.35 mg kg^-1) intramuscularly with 1-week intertreatment washout period. Time to first sign of altered state of consciousness and immobilization time were recorded. Physiological variables were recorded, arterial blood samples were taken during a 40-minute immobilization period, and naltrexone (mean ± SD: 1.83 ± 0.06 mg kg^-1) was intravenously administered. Recovery times were documented, and induction, immobilization and recovery were subjectively scored. Statistical analyses were performed; p < 0.05 was significant.

RESULTS

No difference was observed in time to first sign, immobilization time and recovery times between treatments. Time to head up was longer with etorphine-azaperone (0.5 ± 0.2 versus 0.4 ± 0.2 minutes; p = 0.015). Etorphine caused higher arterial blood pressures (mean: 131 ± 17 versus 110 ± 11 mmHg, p < 0.0001), pH, rectal temperature and arterial oxygen partial pressure (59.2 ± 7.7 versus 42.2 ± 9.8 mmHg), but lower heart (p = 0.002) and respiratory rates (p = 0.01). Etorphine-azaperone combination led to greater impairment of ventilatory function, with higher end-tidal carbon dioxide (p < 0.0001) and arterial partial pressure of carbon dioxide (58.0 ± 4.5 versus 48.1 ± 5.1 mmHg). Immobilization quality was greater with etorphine-azaperone than with etorphine alone (median scores: 4 versus 3; p < 0.0001).

CONCLUSIONS AND CLINICAL RELEVANCE

Both treatments provided satisfactory immobilization of blesbok; however, in addition to a deeper level of immobilization, etorphine-azaperone caused greater ventilatory impairment. Oxygen supplementation is recommended with both treatments.

Kölliker-Fuse/Parabrachial complex mu opioid receptors contribute to fentanyl-induced apnea and respiratory rate depression

Overdoses caused by the opioid agonist fentanyl have increased exponentially in recent years. Identifying mechanisms to counter progression to fatal respiratory apnea during opioid overdose is desirable, but difficult to study in vivo. The pontine Kölliker-Fuse/Parabrachial complex (KF/PB) provides respiratory drive and contains opioid-sensitive neurons. The contribution of the KF/PB complex to fentanyl-induced apnea was investigated using the in situ arterially perfused preparation of rat. Systemic application of fentanyl resulted in concentration-dependent respiratory disturbances. At low concentrations, respiratory rate slowed and subsequently transitioned to an apneustic-like, 2-phase pattern. Higher concentrations caused prolonged apnea, interrupted by occasional apneustic-like bursts. Application of CTAP, a selective mu opioid receptor antagonist, directly into the KF/PB complex reversed and prevented fentanyl-induced apnea by increasing the frequency of apneustic-like bursting. These results demonstrate that countering opioid effects in the KF/PB complex is sufficient to restore phasic respiratory output at a rate similar to pre-fentanyl conditions, which could be beneficial in opioid overdose.

Dose-effect study of the serotonin agonist R-8-OH-DPAT on opioid-induced respiratory depression in blesbok (Damaliscus pygargus philipsi) and impala (Aepyceros melampus)

OBJECTIVE

To determine whether the R-enantiomer of 8-hydroxy-2-(di-n-propylamino) tetralin (R-8-OH-DPAT) alleviates respiratory depression in antelope species immobilized with etorphine. The experiment also aimed to establish the most clinically effective dose of this serotonin 5- HT_1A receptor agonist.

ANIMALS

A group of six female blesbok and six female impala.

STUDY DESIGN

Each animal was subjected to four immobilization treatments in a prospective four-way crossover design-control treatment consisting of only etorphine at 0.09 mg kg^-1 and three treatments consisting of etorphine at 0.09 mg kg^-1 combined with 0.005, 0.02 and 0.07 mg kg^-1 of R-8-OH-DPAT, respectively. Induction, quality of immobilization and recovery were monitored in each treatment. Physiological variables including heart rate, respiratory rate, arterial blood pressure and blood gases were measured for 35 minutes during immobilization. A linear mixed model was used to assess the effects of treatments over the recumbency period.

RESULTS

R-8-OH-DPAT did not influence induction, immobilization or recovery scores. Respiratory rate in blesbok was increased in the medium- and high-dosage R-8-OH-DPAT treatment group. However, this increased respiratory rate did not translate into improvements of arterial partial pressure of oxygen (PaO₂) values in the blesbok. The medium and higher dosages of R-8-OH-DPAT in impala led to an improved PaO₂ as well as to decreased opioid-induced tachycardia during the first 10 minutes of immobilization.

CONCLUSIONS AND CLINICAL RELEVANCE

Previous reports indicated that the racemic mixture of 8-OH-DPAT injected intravenously had a positive effect on blood-gas values in etorphine-treated hypoxemic goats. In this experiment, similar effects could be seen in impala at the higher dosage rates of R-8-OH-DPAT. However, failure to achieve an improvement of blood-gas values in blesbok was an unexpected result. It could be speculated that the dosage, species-specific differences of serotonin receptors or the use of the R-enantiomer of 8-OH-DPAT might play a role.

CAPTIVE MANAGEMENT OF WILD IMPALA ( AEPYCEROS MELAMPUS) DURING INTENSIVE IMMOBILIZATION AND GENERAL ANESTHESIA STUDY TRIALS

Immobilization and anesthesia of impala ( Aepyceros melampus) has become a popular research theme. This demand is brought about by the increased need to immobilize and anesthetize impala and other medium-sized wild ungulates because of their increased value in game ranching and zoological collections. To improve our understanding of immobilization and general anesthesia in these species, it is paramount to be able to study them in a practical, safe research environment that does not cause harm or unnecessary stress to the animals. This study aimed to scrutinize our management and welfare practices and scientific methods of 15 wild-caught impala placed in captive confinement during a 16-wk intensive research project. The scientific methods of the project were scrutinized to identify procedures that attributed to morbidity and mortality. Indicators of impala welfare during captivity were monitored by documenting serial physical (body weight, coat condition), physiological (biochemistry and hematology), and psychologic (behavioral) aspects. Two impala suffered irreparable femoral fractures during darting and were humanly euthanized. One impala suffered cardiovascular collapse during immobilization and could not be resuscitated. The procedure of chemical capture had a morbidity and mortality rate of 14.8% and 4.4%, respectively. The impala maintained acceptable physical and physiologic parameters, including stable body weights, well-groomed coats, and values for total serum protein, serum creatinine, and hematologic parameters that were within reference ranges for the species. There were improvements in the impalas' psychological parameters, which included a decrease in the number of aggressive interactions (head butting and ramming) and an increase in the number of reciprocal allogrooming interactions. The monitored welfare indicators suggest adaptation to captivity. The study showed that impala could be successfully managed in captivity for 16 wk. However, scientific methods (namely darting) increased the risk of injury and caused fatalities.

Compared to etorphine-azaperone, the ketamine-butorphanol-medetomidine combination is also effective at immobilizing zebra (Equus zebra)

OBJECTIVE

To compare immobilization efficacy of a nonpotent opioid drug combination, ketamine-butorphanol-medetomidine (KBM) to the preferred etorphine-azaperone (EA) combination in zebras.

STUDY DESIGN

Randomized crossover trial.

ANIMALS

A group of ten adult zebra (six females and four male).

METHODS

KBM and EA were administered once to the zebras in random order by dart, 3 weeks apart. Once a zebra was recumbent and instrumented, physiological parameters were measured and recorded at 5-minute intervals until 20 minutes. Antagonist drugs were administered at 25 minutes. KBM was antagonised using atipamezole (7.5 mg mg^-1 medetomidine dose) and naltrexone (2 mg mg^-1 butorphanol dose). EA was antagonized using naltrexone (20 mg mg^-1 etorphine dose). Induction and recovery (following antagonist administration) times were recorded. Physiological parameters, including invasive blood pressure and blood gas analysis, were compared between combinations using a general linear mixed model. Data are reported as mean ± standard deviation or median (interquartile range).

RESULTS

The doses of KBM and EA administered were 3.30 ± 0.18, 0.40 ± 0.02 and 0.16 ± 0.01 mg kg^-1; and 0.02 ± 0.001 and 0.20 ± 0.01 mg kg^-1, respectively. KBM and EA induction times were 420 (282-564) and 240 (204-294) seconds, respectively (p = 0.03). Zebras remained recumbent throughout the study procedures. Systolic blood pressure (226 ± 42 and 167 ± 42 mmHg) and oxygen partial pressure (64 ± 12 and 47 ± 13 mmHg) were higher for KBM compared to EA (p < 0.01). Recovery time, after administering antagonists, was 92 (34-1337) and 26 (22-32) seconds for KBM and EA, respectively (p = 0.03).

CONCLUSIONS AND CLINICAL RELEVANCE

Compared to EA, KBM also immobilized zebras effectively. Systemic hypertension and moderate hypoxaemia are clinical concerns of KBM and severe hypoxaemia is a concern of EA. This occurrence of hypoxaemia highlights the importance of oxygen administration during immobilization.

Use of butorphanol and diprenorphine to counter respiratory impairment in the immobilised white rhinoceros (Ceratotherium simum)

Opioid-induced immobilisation results in severe respiratory impairment in the white rhinoceros. It has therefore been attempted in the field to reverse this impairment with the use of opioid agonist-antagonists, such as nalorphine, nalbuphine, butorphanol and diprenorphine; however, the efficacy of some of these treatments has yet to be determined. The efficacy of butorphanol, either alone or in combination with diprenorphine both with and without oxygen insufflation, in alleviating opioid-induced respiratory impairment was evaluated. The study was performed in two parts: a boma trial and a field trial. Rhinoceroses were immobilised specifically for the study, according to a strict protocol to minimise confounding variables. A two-way analysis of variance was used to compare the physiological responses of the rhinoceroses to the different treatments and their effects over time. The intravenous administration of butorphanol (at 3.3 mg per mg etorphine) plus diprenorphine (at 0.4 mg per mg etorphine) did not offer any advantage over butorphanol (at 15 mg per mg etorphine) alone with regard to improving P_aO₂, P_aCO₂ and respiratory rates in etorphine-immobilised white rhinoceroses. Both butorphanol + diprenorphine + oxygen and butorphanol + oxygen, at the doses used, significantly improved the etorphine-induced hypoxaemia in both boma- and field-immobilised white rhinoceroses. Clinically acceptable oxygenation in field-immobilised white rhinoceroses can be achieved by using either treatment regimen, provided that it is combined with oxygen insufflation.

Ameliorating the adverse cardiorespiratory effects of chemical immobilization by inducing general anaesthesia in sheep and goats: implications for physiological studies of large wild mammals

Chemical immobilization is necessary for the physiological study of large wild animals. However, the immobilizing drugs can adversely affect the cardiovascular and respiratory systems, yielding data that do not accurately represent the normal, resting state. We hypothesize that these adverse effects can be ameliorated by reversing the immobilizing agent while holding the animal under general anaesthesia. We used habituated sheep Ovis aries (N = 5, 46.9 ± 5.3 kg body mass, mean ± SEM) and goats Capra hircus (N = 4, 27.7 ± 2.8 kg) as ungulate models for large wild animals, and measured their cardiorespiratory function under three conditions: (1) mild sedation (midazolam), as a proxy for the normal resting state, (2) immobilization (etorphine and azaperone), and (3) general anaesthesia (propofol) followed by etorphine antagonism (naltrexone). Cardiac output for both sheep and goats remained unchanged across the three conditions (overall means of 6.2 ± 0.9 and 3.3 ± 0.3 L min^-1, respectively). For both sheep and goats, systemic and pulmonary mean arterial pressures were significantly altered from initial midazolam levels when administered etorphine + azaperone, but those arterial pressures were restored upon transition to propofol anaesthesia and antagonism of the etorphine. Under etorphine + azaperone, minute ventilation decreased in the sheep, though this decrease was corrected under propofol, while the minute ventilation in the goats remained unchanged throughout. Under etorphine + azaperone, both sheep and goats displayed arterial blood hypoxia and hypercapnia (relative to midazolam levels), which failed to completely recover under propofol, indicating that more time might be needed for the blood gases to be adequately restored. Nonetheless, many of the confounding cardiorespiratory effects of etorphine were ameliorated when it was antagonized with naltrexone while the animal was held under propofol, indicating that this procedure can largely restore the cardiovascular and respiratory systems closer to a normal, resting state.

Effective thiafentanil immobilization and physiological responses of free-ranging moose (Alces alces) in northern Sweden

OBJECTIVE

To evaluate clinical and physiological responses in moose to thiafentanil administration for immobilization.

STUDY DESIGN

Cross-sectional clinical study.

ANIMALS

Eleven (six males and five females) free-ranging adult moose (Alces alces).

METHODS

Each moose was darted from a helicopter with 7.5 mg thiafentanil during March 2014 in northern Sweden. Physiological evaluation included vital signs and blood gases. Arterial blood was collected after induction and again after 10 minutes of intranasal oxygen administration and analyzed immediately with an i-STAT analyzer. A total of 10 mg naltrexone per milligram of thiafentanil was administered to all animals for reversal. Data were analyzed using descriptive statistics.

RESULTS

All moose were sufficiently immobilized with a single dart injection. Induction occurred within 3 minutes in 10 of 11 moose. One individual became recumbent while crossing a river and naltrexone was immediately administered. Animals maintained sternal recumbency with their head raised and vital signs were stable. Nine of 10 moose were hypoxemic before oxygen administration, with seven becoming markedly hypoxemic [partial pressure of arterial oxygen (PaO₂) between 40 and 59 mmHg (5.3-7.9 kPa)]. The PaO₂ increased significantly between samples, but six moose remained hypoxemic despite therapy. Hypercapnia was seen in all moose, with eight having marked hypercapnia [partial pressure of arterial carbon dioxide (PaCO₂) > 60 mmHg (>8.0 kPa)]. All moose were acidemic, with nine showing marked acidemia (pH < 7.20). The pH increased significantly with time and lactate decreased. Recoveries were rapid and uneventful, and all moose were living 6 months after capture.

CONCLUSIONS

Thiafentanil provided rapid and sufficient immobilization of moose and its effects were rapidly reversed with naltrexone. As with other opioids, moose showed hypoxemia and varying degrees of respiratory and metabolic acidosis. Arterial oxygenation of moose improved following intranasal oxygen, but hypoxemia was not fully resolved despite therapy.

CLINICAL RELEVANCE

Thiafentanil (7.5 mg per adult) is effective for immobilization of free-ranging moose. Supplemental oxygen may be of benefit when using this regimen; however, further investigation is required to confirm these results.

Blood acid-base status in impala (Aepyceros melampus) immobilised and maintained under total intravenous anaesthesia using two different drug protocols

BACKGROUND

In mammals, homeostasis and survival are dependent on effective trans-membrane movement of ions and enzyme function, which are labile to extreme acid-base changes, but operate efficiently within a narrow regulated pH range. Research in patients demonstrating a pH shifts outside the narrow regulated range decreased the cardiac output and systemic vascular resistance and altered the oxygen binding to haemoglobin. These cardiopulmonary observations may be applicable to the risks associated with anaesthesia and performance of wildlife ungulates on game farms. The aim of this study was to compare blood pH changes over time in impala immobilised and anaesthetised with two different drug protocols (P-TMP - immobilisation: thiafentanil-medetomidine; maintenance: propofol-ketamine-medetomidine; P-EME - immobilisation: etorphine-medetomidine; maintenance: etorphine-ketamine-medetomidine). Additionally, we discuss the resultant blood pH using both the Henderson-Hasselbalch and the Stewart approaches. Two data collection time points were defined, Time1 before maintenance of general anaesthesia and Time 2 at end of maintenance of general anaesthesia. We hypothesise that blood pH would not be different between drug protocols and would not change over time.

RESULTS

Significant differences were detected over time but not between the two drug protocols. Overall, the blood pH decreased over time from 7.37 ± 0.04 to 7.31 ± 0.05 (p = 0.001). Overall, over time arterial partial pressure of carbon dioxide changed from 51.3 ± 7.5 mmHg to 72.6 ± 12.4 mmHg (p < 0.001); strong ion difference from 44.6 ± 2.4 mEq/L to 46.9 ± 3.1 mEq/L (p < 0.001); anion gap from 15.0 ± 3.1 mEq/L to 10.9 ± 2.2 mEq/L (p < 0.001); and total weak acids from 16.1 ± 1.2 mmol/L to 14.0 ± 1.1 mmol/L (p < 0.001). The bicarbonate changed from 29.6 ± 2.7 mEq/L to 36.0 ± 4.1 mEq/L (p < 0.001); and lactate changed from 2.9 ± 1.5 mEq/L to 0.3 ± 0.03 mEq/L (p < 0.001) over time.

CONCLUSIONS

The profound increase in the partial pressure of carbon dioxide that worsened during the total intravenous anaesthesia in both protocols initiated a substantial metabolic compensatory response to prevent severe acidaemia. This compensation resulted in a clinically acceptable mild acidaemic state, which worsened over time but not between the protocols, in healthy impala. However, these important compensatory mechanisms require normal physiological function and therefore when immobilising ill or anorexic wild ungulates their acid-base status should be carefully assessed.

Comparison of thiafentanil-medetomidine to etorphine-medetomidine immobilisation of impalas (<i>Aepyceros melampus</i>)

Impalas (Aepyceros melampus) are increasingly valuable in the South African wildlife industry, and there is a greater need to chemically immobilise them, ideally with minimal risk. This study aimed to compare the times to recumbency and physiological effects of thiafentanil-medetomidine versus etorphine-medetomidine immobilisation. A combination of thiafentanil (2 mg) + medetomidine (2.2 mg) and etorphine (2 mg) + medetomidine (2.2 mg) was administered (to nine impalas; crossover design) via a dart. After darting, a stopwatch was started to record times to recumbency (time from darting until recumbent without attempts to stand). If apnoea was present, the impalas received one or more boluses of butorphanol (1:1 potent opioid dose). Data collection included arterial blood gas analysis and the number of butorphanol boluses. Two-sample t-tests were used to compare differences between combinations. The time to recumbency for thiafentanil-medetomidine was 12.2 (± 6.8) min and no different from 14.5 (± 5.2) min for etorphine-medetomidine (p = 0.426). The thiafentanil-medetomidine combination required more butorphanol boluses (median: 2; interquartile range: 2–3) compared to etorphine-medetomidine (median: 0; interquartile range: 0–1) (p = 0.001). Despite butorphanol treatment and resolution of apnoea, all impalas suffered hypoxaemia (PaO₂ ± 44.0 mmHg). Thiafentanil-medetomidine did not immobilise impalas more rapidly than etorphine-medetomidine, and resulted in more apnoea that required rescue butorphanol boluses. Marked hypoxaemia resulted from both combinations, mainly because of right-to-left intrapulmonary shunting and not because of hypoventilation. Butorphanol and oxygen supplementation should be considered as essential rescue interventions for all impalas immobilised with these potent opioid combinations.

Chemical capture of impala (Aepyceros melampus): A review of factors contributing to morbidity and mortality

OBJECTIVE

To review the factors that contribute to morbidity and mortality of impala undergoing chemical capture, and discuss how they are potentially mitigated.

DATABASES USED

PubMed, Science Direct, Google Scholar and Onderstepoort Veterinary Academic Hospital records.

CONCLUSIONS AND CLINICAL RELEVANCE

Impala are an important species of antelope in Africa and are often captured during management procedures, veterinary interventions and research projects. Chemical capture is a preferred technique over physical capture and restraint for veterinary interventions as it allows for easier handling and better clinical assessment and treatment. However, this capture technique results in high mortality (4%) and morbidity rates (23%), which translates into animal welfare and economic concerns. Investigation of environmental, drug and drug delivery, and animal factors to elucidate the origin of these high rates was reviewed. The greatest risks emanate from the drug and drug delivery factors where potent opioids (etorphine and thiafentanil) cause profound respiratory compromise, that if left untreated often translates into fatalities. Furthermore, the procedure of darting, an essential tool in game capture, can cause irreparable fractures and other fatal injuries mainly through accidental misplacement of the dart into a long bone, thoracic or peritoneal cavity. Impala are anxious and flighty, and this demeanour (animal related factor) can contribute towards mortality and morbidity rates. Impala that mount an inappropriate stress response to capture tend to die; therefore, procedures that induce an intense stress response (awake clinical examinations) should be avoided. Sequela of a heightened stress response include capture-induced hyperthermia, myopathies, fractures, maladaptation to confinement or new environments and death. Impala serve as a useful model for improving immobilizing and anaesthetic drug protocols, darting techniques or new methods of remote injection in wildlife. However, the risks associated with chemical capture in this species should be understood, and all efforts to mitigate these should be employed.

Postinduction butorphanol administration alters oxygen consumption to improve blood gases in etorphine-immobilized white rhinoceros

OBJECTIVE

To investigate the effects of postinduction butorphanol administration in etorphine-immobilized white rhinoceros on respiration and blood gases.

STUDY DESIGN

Randomized crossover study.

ANIMALS

A group of six sub-adult male white rhinoceros.

METHODS

Etorphine, or etorphine followed by butorphanol 12 minutes after recumbency, was administered intramuscularly [2.5 mg etorphine, 25 mg butorphanol (1000-1250 kg), or 3.0 mg etorphine, 30 mg butorphanol (1250-1500 kg)]. Sampling started at 10 minutes after initial recumbency, and was repeated at 5 minute intervals for 25 minutes. Arterial blood gases, limb muscle tremors, expired minute ventilation and respiratory frequency were measured at each sampling point. Calculated values included alveolar-arterial oxygen gradient [ [Formula: see text] ], expected respiratory minute volume (V˙e), tidal volume (Vt), oxygen consumption ( [Formula: see text] ) and carbon dioxide production ( [Formula: see text] ).

RESULTS

Etorphine administration resulted in an initial median (range) hypoxaemia [arterial partial pressure of oxygen 25.0 (23.0-28.0) mmHg], hypercapnia [arterial partial pressure of carbon dioxide 76.2 (67.2-81.2) mmHg], increased [Formula: see text] [41.7 (36.6-45.1) mmHg, [Formula: see text] [11.1 (10.0-12.0) L minute^-1] and muscle tremors. Butorphanol administration was followed by rapid, although moderate, improvements in arterial partial pressure of oxygen [48.5 (42.0-51.0) mmHg] and arterial partial pressure of carbon dioxide [62.8 (57.9-75.2) mmHg]. In rhinoceros administered butorphanol, [Formula: see text] [4.4 (3.6-5.1) L minute^-1] and [Formula: see text] [4.2 (3.8-4.4) L minute^-1] were lower than in those not administered butorphanol. Increased arterial oxygen tension was associated with lower oxygen consumption (p=0.002) which was positively associated with lower muscle tremor scores (p<0.0001).

CONCLUSIONS AND CLINICAL RELEVANCE

Hypoxaemia and hypercapnia in etorphine-immobilized rhinoceros resulted from an increased [ [Formula: see text] ] and increased [Formula: see text] and [Formula: see text] associated with muscle tremors. Rather than being associated with changes in V˙e, it appears that improved blood gases following butorphanol administration were a consequence of decreased [Formula: see text] associated with reduced muscle tremoring.

EVALUATION OF ETORPHINE AND MIDAZOLAM ANESTHESIA, AND THE EFFECT OF INTRAVENOUS BUTORPHANOL ON CARDIOPULMONARY PARAMETERS IN GAME-RANCHED WHITE RHINOCEROSES (CERATOTHERIUM SIMUM)

Nineteen white rhinoceroses ( Ceratotherium simum ) were anesthetized with 4 mg of etorphine hydrochloride; 35-40 mg of midazolam; and 7,500 international units of hyaluronidase for dehorning purposes at a game ranch in South Africa, to investigate this anesthetic combination. Median time to recumbency was 548 sec (range 361-787 sec). Good muscle relaxation and no muscle rigidity or tremors were observed in 18 animals, and only 1 individual showed slight tremors. In addition, all animals received butorphanol i.v. 5 min after recumbency at the ratio of 10 mg of butorphanol per 1 mg of etorphine. Blood gas and selected physiologic parameters were measured in the recumbent animal, immediately before and 10 min after the administration of butorphanol. Statistically significant improvements were observed in blood gas physiologic and cardiopulmonary parameters 10 min after the administration of butorphanol, with a reduction in arterial partial pressure of carbon dioxide, systolic blood pressure, and heart rate and an increase in pH, arterial partial pressure of oxygen, oxygen saturation, and respiratory rate (all P < 0.005). After i.v. naltrexone reversal, recovery was uneventful, and median time to walking or running was 110 sec (range 71-247 sec). The results indicate etorphine and midazolam combination is an effective alternative anesthetic protocol and produces good muscle relaxation. Furthermore, i.v. butorphanol was associated with improved blood gas values and cardiopulmonary function for at least 10 min postinjection.

Ampakine CX1942 attenuates opioid-induced respiratory depression and corrects the hypoxaemic effects of etorphine in immobilized goats (Capra hircus)

OBJECTIVES

To determine whether CX1942 reverses respiratory depression in etorphine-immobilized goats, and to compare its effects with those of doxapram hydrochloride.

STUDY DESIGN

A prospective, crossover experimental trial conducted at 1753 m.a.s.l.

ANIMALS

Eight adult female Boer goats (Capra hircus) with a mean ± standard deviation mass of 27.1 ± 1.6 kg.

METHODS

Following immobilization with 0.1 mg kg(-1) etorphine, goats received one of doxapram, CX1942 or sterile water intravenously, in random order in three trials. Respiratory rate, ventilation and tidal volume were measured continuously. Arterial blood samples for the determination of PaO2 , PaCO2 , pH and SaO2 were taken 2 minutes before and then at 5 minute intervals after drug administration for 25 minutes.

RESULTS

Doxapram corrected etorphine-induced respiratory depression but also led to arousal and hyperventilation at 2 minutes after its administration, as indicated by the low PaCO2 (27.8 ± 4.5 mmHg) and ventilation of 5.32 ± 5.24 L minute(-1) above pre-immobilization values. CX1942 improved respiratory parameters and corrected etorphine's hypoxaemic effects more gradually than did doxapram, with a more sustained improvement in PaO2 and SaO2 in comparison with the control trial.

CONCLUSIONS

CX1942 attenuated opioid-induced respiratory depression and corrected the hypoxaemic effects of etorphine in immobilized goats.

CLINICAL RELEVANCE

Ampakines potentially offer advantages over doxapram, a conventional treatment, in reversing etorphine-induced respiratory depression without causing unwanted side effects, particularly arousal, in immobilized animals.

ETORPHINE-KETAMINE-MEDETOMIDINE TOTAL INTRAVENOUS ANESTHESIA IN WILD IMPALA (AEPYCEROS MELAMPUS) OF 120-MINUTE DURATION

There is a growing necessity to perform long-term anesthesia in wildlife, especially antelope. The costs and logistics of transporting wildlife to veterinary practices make surgical intervention a high-stakes operation. Thus there is a need for a field-ready total intravenous anesthesia (TIVA) infusion to maintain anesthesia in antelope. This study explored the feasibility of an etorphine-ketamine-medetomidine TIVA for field anesthesia. Ten wild-caught, adult impala ( Aepyceros melampus ) were enrolled in the study. Impala were immobilized with a standardized combination of etorphine (2 mg) and medetomidine (2.2 mg), which equated to a median (interquartile range [IQR]) etorphine and medetomidine dose of 50.1 (46.2-50.3) and 55.1 (50.8-55.4) μg/kg, respectively. Recumbency was attained in a median (IQR) time of 13.9 (12.0-16.5) min. Respiratory gas tensions, spirometry, and arterial blood gas were analyzed over a 120-min infusion. Once instrumented, the TIVA was infused as follows: etorphine at a variable rate initiated at 40 μg/kg per hour (adjusted according to intermittent deep-pain testing); ketamine and medetomidine at a fixed rate of 1.5 mg/kg per hour and 5 μg/kg per hour, respectively. The etorphine had an erratic titration to clinical effect in four impala. Arterial blood pressure and respiratory and heart rates were all within normal physiological ranges. However, arterial blood gas analysis revealed severe hypoxemia, hypercapnia, and acidosis. Oxygenation and ventilation indices were calculated and highlighted possible co-etiologies to the suspected etorphine-induced respiratory depression as the cause of the blood gas derangements. Impala recovered in the boma post atipamezole (13 mg) and naltrexone (42 mg) antagonism of medetomidine and etorphine, respectively. The etorphine-ketamine-medetomidine TIVA protocol for impala may be sufficient for field procedures of up to 120-min duration. However, hypoxemia and hypercapnia are of paramount concern and thus oxygen supplementation should be considered mandatory. Other TIVA combinations may be superior and warrant further investigation.

Butorphanol with oxygen insufflation improves cardiorespiratory function in field-immobilised white rhinoceros (Ceratotherium simum)

Opioid-induced immobilisation results in severe respiratory compromise in the white rhinoceros (Ceratotherium simum). The effectiveness of oxygen insufflation combined with butorphanol in alleviating respiratory depression in free-ranging chemically immobilised white rhinoceroses was investigated. In this prospective intervention study 14 free-ranging white rhinoceroses were immobilised with a combination of etorphine, azaperone and hyaluronidase. Six minutes (min) after the animals became recumbent, intravenous butorphanol was administered and oxygen insufflation was initiated. Previous boma trial results were used for comparison, using repeated measures two-way analysis of variance. The initial immobilisation-induced hypoxaemia in free-ranging rhinoceroses (arterial partial pressure of oxygen [P_aO₂] 35.4 mmHg ± 6.6 mmHg) was similar to that observed in boma-confined rhinoceroses (P_aO₂ 31 mmHg ± 6 mmHg, n = 8). Although the initial hypercapnia (P_aCO₂ 63.0 mmHg ± 7.5 mmHg) was not as severe as that in animals in the boma trial (79 mmHg ± 7 mmHg), the field-immobilised rhinoceroses were more acidaemic (pH 7.10 ± 0.14) at the beginning of the immobilisation compared with boma-immobilised rhinoceroses (pH 7.28 ± 0.04). Compared with pre-intervention values, butorphanol with oxygen insufflation improved the P_aO₂ (81.2 mmHg ± 23.7 mmHg, p < 0.001, 5 min vs 20 min), arterial partial pressure of carbon dioxide (55.3 mmHg ± 5.2 mmHg, p < 0.01, 5 min vs 20 min), pH (7.17 ± 0.11, p < 0.001, 5 min vs 20 min), heart rate (78 breaths/min± 20 breaths/min, p < 0.001, 5 min vs 20 min) and mean arterial blood pressure (105 mmHg ± 14 mmHg, p < 0.01, 5 min vs 20 min). Oxygen insufflation combined with a single intravenous dose of butorphanol improved oxygenation and reduced hypercapnia and acidaemia in immobilised free-ranging white rhinoceroses.