Cardiovascular effects of intravenous vatinoxan (MK-467) in medetomidine-tiletamine-zolazepam anaesthetised red deer (Cervus elaphus)

CARDIORESPIRATORY EFFECTS OF VATINOXAN IN BLESBOK (DAMALISCUS PYGARGUS PHILLIPSI) IMMOBILIZED WITH THIAFENTANIL-MEDETOMIDINE

Combinations of a low dose of opioid, such as thiafentanil, and a high dose of medetomidine, are increasingly being used for immobilization of African ungulates. Both drugs can have undesirable cardiorespiratory effects. In this study we assessed whether vatinoxan, a peripherally acting alpha2-adrenergic receptor antagonist, can be used to alleviate some of these effects without affecting the immobilization quality. Eight healthy, female, boma-confined blesbok (Damaliscus pygargus phillipsi), weighing a mean (SDtion) of 56.8 (4.4) kg, were immobilized twice in a randomized cross-over study with a 2-wk washout period using (1) 0.5 mg thiafentanil + 1.5 mg medetomidine (TM), (2) TM + vatinoxan: 0.5 mg thiafentanil + 1.5 mg medetomidine + 15 mg vatinoxan per milligram medetomidine (total of 22.5 mg, administered intramuscularly at 10 min post recumbency). Heart rate, respiratory rate, rectal temperature, oxygen saturation (SpO2), arterial blood pressure, and sedation scores from 1 to 5 (1 = limited effect; 5 = excessively deep) were measured every 5 min. Arterial blood gases (PaO2 and PaCO2) were measured at 10, 15, 25, and 35 min postrecumbency and the alveolar--arterial oxygen gradient (P[A-a]O2) was calculated. Induction times and immobilization quality did not differ between groups. The heart rate was significantly higher and the mean arterial pressure significantly lower in blesbok after receiving vatinoxan. All animals were hypoxemic and there were no significant differences in the respiratory rates, PaO2, PaCO2, SpO2, or P(A-a)O2 gradients at any time point. Although vatinoxan did not improve respiratory variables and blood oxygenation in these animals, the change in cardiovascular variables may suggest that it improves tissue perfusion, a positive outcome that requires further investigation.

EFFICACY OF TOLAZOLINE AND VATINOXAN IN REDUCING ADVERSE EFFECTS OF BUTORPHANOL-AZAPERONE-MEDETOMIDINE IMMOBILIZATION IN ROCKY MOUNTAIN ELK (CERVUS CANADENSIS)

A mixture of butorphanol, azaperone, and medetomidine (BAM) is frequently used for immobilization of North American hoofstock. Common adverse effects include respiratory depression, hypoxemia, and bradycardia. In this nonblinded crossover study the efficacy of two a-2 adrenergic antagonists, tolazoline and vatinoxan, were evaluated in alleviating adverse effects of BAM in Rocky Mountain elk (Cervus canadensis). Early administration of these antagonists was hypothesized to cause an increase in heart rate, respiratory rate, partial pressure of oxygen (PaO2) and hemoglobin oxygen saturation (SpO2), as well as reduction in mean arterial blood pressure without affecting sedation levels. Eight captive adult female elk were immobilized on three separate occasions at least 14 d apart with 0.15 mg/kg butorphanol, 0.05 mg/kg azaperone, and 0.06 mg/kg medetomidine. Tolazoline (2 mg/kg IM), vatinoxan (3 mg/mg medetomidine IV) or sterile saline (2 ml IM) were administered 20 min postinduction. The BAM caused hypoxemia, bradycardia, and moderate hypertension, and because of the severe hypoxemia observed, all animals received intratracheal oxygen throughout immobilization. Heart rate, respiratory rate, rectal temperature, SpO2, PaO2, and systolic, diastolic, and mean arterial blood pressure were monitored every 5 min throughout the immobilization. Intramuscular tolazoline caused a brief but significant drop in mean arterial pressure compared with controls and a brief but nonsignificant increase in heart rate. Vatinoxan caused a significant drop in blood pressure and a brief significant increase in heart rate. Changes in respiratory rates and PaO2 were not observed with either antagonist; however, all animals received oxygen, which may have influenced this result. The depth of sedation was unchanged after administration of either drug.

The Influence of Photoperiod, Intake of Polyunsaturated Fatty Acids, and Food Availability on Seasonal Acclimatization in Red Deer (Cervus elaphus)

Hypometabolism and hypothermia are common reactions of birds and mammals to cope with harsh winter conditions. In small mammals, the occurrence of hibernation and daily torpor is entrained by photoperiod, and the magnitude of hypometabolism and decrease of body temperature (T_b) is influenced by the dietary supply of essential polyunsaturated fatty acids. We investigated whether similar effects exist in a non-hibernating large mammal, the red deer (Cervus elaphus). We fed adult females with pellets enriched with either linoleic acid (LA) or α-linolenic acid (ALA) during alternating periods of ad libitum and restricted feeding in a cross-over experimental design. Further, we scrutinized the role of photoperiod for physiological and behavioral seasonal changes by manipulating the amount of circulating melatonin. The deer were equipped with data loggers recording heart rate, core and peripheral T_b, and locomotor activity. Further, we regularly weighed the animals and measured their daily intake of food pellets. All physiological and behavioral parameters measured varied seasonally, with amplitudes exacerbated by restricted feeding, but with only few and inconsistent effects of supplementation with LA or ALA. Administering melatonin around the summer solstice caused a change into the winter phenotype weeks ahead of time in all traits measured. We conclude that red deer reduce energy expenditure for thermoregulation upon short daylength, a reaction amplified by food restriction.

Cardiorespiratory effects of isoflurane and medetomidine-tiletamine-zolazepam in 12 bonobos (Pan paniscus)

BACKGROUND

Cardiovascular disease is a significant cause of mortality in captive great apes. However, data from bonobos are lacking due to a paucity of collections in Europe. Comprehensive preventive screening is required to understand the aetiopathogenesis of cardiovascular disease, but the provision of a stable and predictable anaesthetic protocol with minimal cardiovascular effects is challenging.

METHODS

This prospective, observational case series reports anaesthesia of 12 bonobos using hand-injected medetomidine and tiletamine-zolazepam followed by maintenance with isoflurane in oxygen. Comprehensive clinical examinations, including arterial blood gases and echocardiography were undertaken.

RESULTS

Induction of anaesthesia with hand injection was successful in all but one individual. Respiratory acidosis with metabolic alkalosis and respiratory alkalosis with metabolic acidosis were documented. Hypochloraemia may have contributed to non-respiratory alkalosis in one individual. Ten bonobos experienced hypotension and required haemodynamic support. Both N-terminal pro b-type natriuretic peptide and troponin I cardiac biomarkers correlated with left ventricular ejection fraction (percentage). Recovery was smooth, rapid and uneventful in all animals.

LIMITATIONS

The effects of the anaesthetic must be considered during echocardiographical interpretation.

CONCLUSIONS

The anaesthesia protocol provided a safe, predictable induction and recovery, facilitating diagnostics (including echocardiography) and minor surgical procedures. Comprehensive monitoring, including invasive blood pressure monitoring and haemodynamic support, is highly recommended.

Comparison of the cardiovascular effects of immobilization with three different drug combinations in free-ranging African lions

Thirty-six free-ranging lions (12 per group) were immobilized with tiletamine-zolazepam (Zoletil 0.6 mg/kg i.m.) plus medetomidine (0.036 mg/kg i.m.) (TZM), ketamine (3.0 mg/kg i.m.) plus medetomidine (0.036 mg/kg i.m.) (KM) or ketamine (1.2 mg/kg i.m.) plus butorphanol (0.24 mg/kg i.m.) plus medetomidine (0.036 mg/kg i.m.) (KBM). During immobilization cardiovascular variables were monitored at 5-minute intervals for a period of 30 minutes. Lions immobilized with all three drug combinations were severely hypertensive. Systolic arterial pressure was higher at initial sampling in lions immobilized with KM (237.3 ± 24.8 mmHg) than in those immobilized with TZM (221.0 ± 18.1 mmHg) or KBM (226.0 ± 20.6 mmHg) and decreased to 205.8 ± 19.4, 197.7 ± 23.7 and 196.3 ± 17.7 mmHg, respectively. Heart rates were within normal ranges for healthy, awake lions and decreased throughout the immobilization regardless of drug combination used. Lions immobilized with TZM had a higher occurrence (66%) of skipped heart beats than those immobilized with KBM (25%). The three drug combinations all caused negative cardiovascular effects, which were less when KBM was used, but adverse enough to warrant further investigations to determine if these effects can be reversed or prevented when these three combinations are used to immobilize free-living lions.

Effect of season and diet on heart rate and blood pressure in female red deer (Cervus elaphus) anaesthetised with medetomidine-tiletamine-zolazepam

Temperate zone ungulates like red deer (Cervus elaphus) show pronounced seasonal acclimatisation. Hypometabolism during winter is associated with cardiovascular changes, including a reduction in heart rate (fH) and temporal peripheral vasoconstriction. How anaesthesia with vasoactive substances such as medetomidine affect the seasonally acclimatised cardiovascular system is not yet known. We anaesthetised eleven healthy female red deer with medetomidine (0.1 mg/kg) and tiletamine/zolazepam (3 mg/kg) twice in winter (ad libitum and restricted feed) and in summer (ad libitum and restricted feed), with a two-week washout-period in-between, to test for the effect of season, food availability and supplementation with omega-3 or omega-6 polyunsaturated fatty acid (PUFA) on fH and arterial blood pressure (ABP) during anaesthesia. Six animals received pellets enriched with omega-6 fatty acids (FA), and five animals with omega-3 FA. Anaesthesia significantly decreased fH in summer but not in winter and ABP was lower in winter (p < 0.05). The combination of omega-6 FA enriched pellets and food restriction resulted in a lower fH and higher ABP during anaesthesia with more pronounced changes in winter (p < 0.001). Our results demonstrate that season, food availability and type of PUFA supplementation in red deer affect the cardiovascular system during anaesthesia.

Raptor Sedation and Anesthesia

Sedation and/or anesthesia is routinely and successfully used in raptors for a wide variety of procedures from the routine such as physical examination, radiographs, or venipuncture, to the more complex, such as orthopedic surgeries. Understanding the anatomy and physiology of raptor patients who present for care, and being fully prepared before the start of any procedure, can increase the success of anesthetic procedures. Recent advances in raptor sedation and anesthesia continue to improve the health and welfare of these avian patients.

Comparison of the Cardiovascular Effects of Two Medetomidine Doses Combined with Tiletamine-Zolazepam for the Immobilization of Red Deer Hinds (Cervus elaphus)

Wild animal immobilization often requires high doses of α2-adrenoceptor agonists. Despite their desired sedative and analgetic effects, well-recognized cardiovascular side effects, such as hypertension and bradycardia, remain a major concern. We compared two medetomidine doses on intra-arterial blood pressure and heart rate in 13 captive, female red deer (Cervus elaphus) immobilized during winter. Each animal was randomly assigned to receive either 80 μg/kg (group L) or 100 μg/kg (group H) medetomidine, combined with 3 mg/kg tiletamine-zolazepam administered intramuscularly. Changes in cardiovascular variables over time and differences between the groups were analyzed using linear mixed-effect models. Induction time was faster in group L compared with group H; recovery time did not differ between groups. Initially, the arterial blood pressure was higher in group H compared with group L, but differences between groups diminished during anesthesia. Moreover, the decline in arterial blood pressure in group H was more rapid. Heart rate was significantly lower in group L, but bradycardia was not observed. The higher medetomidine dose did not reduce induction time, and initial hypertension was reduced by administering the lower dose. Therefore, although the sample size was small and, thus, the significance of results might be limited, we suggest using 80 μg/kg instead of 100 μg/kg medetomidine when combined with 3 mg/kg tiletamine-zolazepam for the immobilization of female red deer.

Cardiovascular effects of intravenous vatinoxan in wild boars (Sus scrofa) anaesthetised with intramuscular medetomidine-tiletamine-zolazepam

BACKGROUND

The potent sedative medetomidine is a commonly used adjunct for the immobilisation of non-domestic mammals. However, its use is associated with pronounced cardiovascular side effects, such as bradycardia, vasoconstriction and decreased cardiac output. We investigated the effects of the peripherally-acting alpha-2-adrenoceptor antagonist vatinoxan on cardiovascular properties in medetomidine-tiletamine-zolazepam anaesthetised wild boar (Sus scrofa).

METHODS

Twelve wild boars, anaesthetised twice with medetomidine (0.1 mg/kg) and tiletamine/zolazepam (2.5 mg/kg) IM in a randomised, crossover study, were administered (0.1 mg/kg) vatinoxan or an equivalent volume of saline IV (control). Cardiovascular variables, including heart rate (HR), mean arterial blood pressure (MAP), pulmonary artery pressure (PAP), pulmonary artery occlusion pressure (PAOP) and cardiac output (CO), were assessed 5 min prior to vatinoxan/saline administration until the end of anaesthesia 30 min later.

RESULTS

MAP (p < 0.0001), MPAP (p < 0.001) and MPAOP (p < 0.0001) significantly decreased from baseline after vatinoxan until the end of anaesthesia. HR increased significantly (p < 0.0001) from baseline after vatinoxan administration. However, the effect on HR subsided 3 min after vatinoxan. All variables remained constant after saline injection. There was no significant effect of vatinoxan or saline on CO.

CONCLUSION

Vatinoxan significantly reduced systemic and pulmonary artery hypertension, induced by medetomidine in wild boar.

Evaluation of intramuscular sodium nitroprusside injection to improve oxygenation in white-tailed deer (Odocoileus virginianus) anesthetized with medetomidine-alfaxalone-azaperone

OBJECTIVE

In ungulates, α₂-adrenergic agonists can decrease oxygenation possibly through alteration of pulmonary perfusion. Sodium nitroprusside can decrease pulmonary vascular resistance (PVR) and increase cardiac output (Q˙_t) through vasodilation. The objective was to determine if sodium nitroprusside would improve pulmonary perfusion and attenuate the increased alveolar-arterial (a-a) gradient resulting from medetomidine-azaperone-alfaxalone (MAA) administration.

STUDY DESIGN

Prospective, randomized, crossover study with a 2 week rest period.

ANIMALS

A group of eight adult female captive white-tailed deer (Odocoileus virginianus).

METHODS

Deer were administered MAA intramuscularly (IM), and auricular artery and pulmonary artery balloon catheters were placed. Deer spontaneously breathed air. Saline or sodium nitroprusside (0.07 mg kg^-1) were administered IM 40 minutes after MAA injection. Heart rate (HR), mean arterial pressure (MAP), mean pulmonary arterial pressure (MPAP), pulmonary artery occlusion pressure (PAOP), right atrial pressure (RAP), Q˙_t, arterial pH, PaCO₂ and PaO₂ were obtained immediately before nitroprusside injection (baseline) and 5, 10 and 15 minutes afterwards. Mixed venous blood samples were obtained at baseline and at 5 minutes. Systemic vascular resistance (SVR), PVR, intrapulmonary shunt fraction (Q˙_s/Q˙_t), a-a gradient, oxygen delivery (D˙O₂) and oxygen extraction ratio (O₂ER) were calculated. Statistical analysis was performed with repeated measures analysis of variance with correction factors. A p value < 0.05 was considered significant.

RESULTS

With nitroprusside, MAP, MPAP, PAOP, RAP, SVR and O₂ER significantly decreased and HR, Q˙_t and D˙O₂ increased compared with baseline and between treatments. There was a significant decrease in PVR and a-a gradient and increase in PaO₂ compared with baseline and saline treatment. Changes were not sustained.

CONCLUSIONS AND CLINICAL RELEVANCE

Nitroprusside temporarily changed hemodynamic variables, increased PaO₂ and decreased a-a gradient. Nitroprusside possibly led to better pulmonary perfusion of ventilated alveoli. However, IM nitroprusside at this dose is not recommended because of severe systemic hypotension and short action.