Sedative effect of intramuscular medetomidine with and without vatinoxan (MK-467), and its reversal with atipamezole in sheep

The impact of vatinoxan on medetomidine-ketamine-midazolam immobilization in Patagonian maras (Dolichotis patagonum)

OBJECTIVE

To compare cardiovascular and ventilatory effects, immobilization quality and effects on tissue perfusion of a medetomidine-ketamine-midazolam combination with or without vatinoxan (MK-467), a peripherally acting α₂-adrenoceptor antagonist.

STUDY DESIGN

Randomized, blinded, crossover study.

ANIMALS

A group of nine healthy Patagonian maras (Dolichotis patagonum).

METHODS

Maras were immobilized twice with: 1) medetomidine hydrochloride (0.1 mg kg^-1) + ketamine (5 mg kg^-1) + midazolam (0.1 mg kg^-1) (MKM) + saline or 2) MKM + vatinoxan hydrochloride (0.8 mg kg^-1), administered intramuscularly. Drugs were mixed in the same syringe. At 20, 30 and 40 minutes after injection, invasive blood pressure, heart rate, respiration rate, end-tidal CO₂, haemoglobin oxygen saturation, and muscle oxygenation were measured, arteriovenous oxygen content difference was calculated. Muscle tone, jaw tone, spontaneous blinking and palpebral reflex were evaluated. Times to initial effect, recumbency, initial arousal and control of the head were recorded. Paired t test, Wilcoxon matched-pairs signed rank test and analysis of variance were used to compare protocols; (p < 0.05).

RESULTS

Vatinoxan significantly reduced systolic (p = 0.0002), mean (MAP; p < 0.0001) and diastolic (p < 0.0001) arterial blood pressures between 20 and 40 minutes. MAPs at 30 minutes (mean ± standard deviation) with MKM and MKM + vatinoxan were 105 ± 12 and 71 ± 14 mmHg, respectively. Without vatinoxan, four animals were hypertensive (MAP > 120 mmHg), whereas with vatinoxan, four animals were hypotensive (MAP < 60 mmHg). Muscle and jaw tone were significantly more frequently present with MKM (both p = 0.039). Other measurements did not significantly differ between protocols.

CONCLUSIONS AND CLINICAL RELEVANCE

In Patagonian maras, vatinoxan attenuated the increase in blood pressure induced by medetomidine. Muscle and jaw tone were more frequently present with MKM, indicating that quality of immobilization with vatinoxan was more profound.

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.

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

OBJECTIVE

To determine the effect of intravenous vatinoxan administration on bradycardia, hypertension and level of anaesthesia induced by medetomidine-tiletamine-zolazepam in red deer (Cervus elaphus).

STUDY DESIGN AND ANIMALS

A total of 10 healthy red deer were included in a randomised, controlled, experimental, crossover study.

METHODS

Deer were administered a combination of 0.1 mg kg^-1 medetomidine hydrochloride and 2.5 mg kg^-1 tiletamine-zolazepam intramuscularly, followed by 0.1 mg kg^-1 vatinoxan hydrochloride or equivalent volume of saline intravenously (IV) 35 minutes after anaesthetic induction. Heart rate (HR), mean arterial blood pressure (MAP), respiration rate (f_R), end-tidal CO₂ (Pe'CO₂), arterial oxygen saturation (SpO₂), rectal temperature (RT) and level of anaesthesia were assessed before saline/vatinoxan administration (baseline) and at intervals for 25 minutes thereafter. Differences within treatments (change from baseline) and between treatments were analysed with linear mixed effect models (p < 0.05).

RESULTS

Maximal (81 ± 10 beats minute^-1) HR occurred 90 seconds after vatinoxan injection and remained significantly above baseline (42 ± 4 beats minute^-1) for 15 minutes. MAP significantly decreased from baseline (122 ± 10 mmHg) to a minimum MAP of 83 ± 6 mmHg 60 seconds after vatinoxan and remained below baseline until end of anaesthesia. HR remained unchanged from baseline (43 ± 5 beats minute^-1) with the saline treatment, whereas MAP decreased significantly (112 ± 16 mmHg) from baseline after 20 minutes. Pe'CO₂, f_R and SpO₂ showed no significant differences between treatments, whereas RT decreased significantly 25 minutes after vatinoxan. Level of anaesthesia was not significantly influenced by vatinoxan.

CONCLUSIONS AND CLINICAL RELEVANCE

Vatinoxan reversed hypertension and bradycardia induced by medetomidine without causing hypotension or affecting the level of anaesthesia in red deer. However, the effect on HR subsided 15 minutes after vatinoxan IV administration. Vatinoxan has the potential to reduce anaesthetic side effects in non-domestic ruminants immobilised with medetomidine-tiletamine-zolazepam.