Dexmedetomidine-induced pulmonary alterations in sheep

RESPONSE AND PHYSIOLOGIC OUTCOMES AFTER BUTORPHANOL, MIDAZOLAM, AND MEDETOMIDINE IMMOBILIZATION AND REVERSAL IN CAPTIVE REINDEER (RANGIFER TARANDUS)

Sedation, recovery response, and physiologic outcomes were evaluated in five captive reindeer (Rangifer tarandus) in Minnesota using a completely reversible immobilization protocol. Reindeer were immobilized with butorphanol (0.23-0.32 mg/kg), midazolam (0.23-0.32 mg/kg), and medetomidine (0.15 mg/kg) (BMM) via IM dart. Induction time (IT), recumbency time (DT), and recovery time (RT) were recorded. Temperature (T), respiratory rate (RR), pulse rate (PR), pulse oximetry (SpO2), arterial blood gas values including oxygen (PaO2), and carbon dioxide (PaCO2) tensions and lactate (Lac) were recorded preoxygen supplementation and 15 min postoxygen supplementation. Reversal was done using naltrexone (2.3-3.0 mg/kg), flumazenil (0.008-0.01 mg/kg) and atipamezole (0.62-0.78 mg/kg) (NFA) IM, limiting recumbency to 1 h. Median IT, DT, and RT were 5 min, 46 min, and 7 min, respectively. SpO2 (92 to 99%, P = 0.125), PaO2 (45.5 to 97 mmHg, P = 0.25), and PaCO2 (46.5 to 54.6 mmHg, P = 0.25) all increased, whereas Lac (3.02 to 1.93 mmol/L, P = 0.25) decreased between baseline and 15 min postoxygen supplementation, without statistical significance. BMM immobilization, and reversal with NFA provided rapid and effective immobilization and recovery, respectively. Oxygen supplementation mitigated hypoxemia in all reindeer.

Evaluation of cardiovascular effects of intramuscular medetomidine and a medetomidine-vatinoxan combination in Beagle dogs: A randomized blinded crossover laboratory study

OBJECTIVE

To compare the cardiovascular effects of a combination of medetomidine and vatinoxan (MVX) versus medetomidine (MED) alone administered intramuscularly (IM) and to determine whether heart rate (HR) can be used as a surrogate for cardiac output (CO) after the use of medetomidine with or without vatinoxan.

STUDY DESIGN

A randomized, blinded, experimental, crossover study.

ANIMALS

A group of eight healthy Beagle dogs aged 4.6 (2.3-9.4) years and weighing 12.9 (9-14.7) kg, median (range).

METHODS

Each dog was injected with 1 mg m-2 medetomidine with or without 20 mg m-2 vatinoxan IM with a washout period of 7 days. Cardiovascular data and arterial and mixed venous blood gas samples were collected at baseline, 5, 10, 15, 20, 35, 45, 60, 90 and 120 minutes after treatment administration. CO was measured at all time points via thermodilution. Differences between treatments, period and sequence were evaluated with repeated measures analysis of covariance and the relationship between HR and CO was assessed with a repeated measures analysis of variance; p values < 0.05 were deemed significant.

RESULTS

The CO was 47-96% lower after MED than after MVX (p < 0.0001). Increases in systemic, pulmonary arterial and right atrial pressures and oxygen extraction ratio were significantly higher after MED than after MVX (all p < 0.0001). HR was significantly lower after MED and the linear relationship to CO was significant (p < 0.0001).

CONCLUSIONS AND CLINICAL RELEVANCE

Overall, MED affected the cardiovascular system more negatively than MVX, and the difference in cardiovascular function between the treatments can be considered clinically relevant. HR was linearly related to CO, and decreases in HR reflected cardiac performance for dogs sedated with medetomidine with or without vatinoxan.

Effects of two alveolar recruitment manoeuvres (sustained inflation and stepwise) followed by positive end-expiratory pressure on cardiac output (measured with lithium dilution), invasive blood pressure and arterial oxygen tension in isoflurane-anaesthetised goats

Alveolar recruitment manoeuvres (ARM) performed during general anaesthesia improve oxygenation; however cardiovascular depression may be observed. The aim of the study was to compare the effects of sustained inflation (SI) and stepwise ARMs on cardiac output (CO), mean arterial blood pressure and arterial oxygen tension (PaO2) in ten mechanically ventilated goats anaesthetised with isoflurane. In the SI ARM, peak inspiratory presure (PIP) was increased to 30 cmH2O and sustained for 20 s. In the stepwise ARM, the PIP was increased by 5 cmH2O each minute for three minutes from 10 to 25 cmH2O. Both ARMs were followed by positive end-expiratory pressure of 5 cmH2O. Paired lithium dilution CO measurements and arterial blood samples were obtained before and after each ARM. The order of the ARM was randomised and each goat was subjected to both techniques. Data was reported as median and interquartile range (IQR). Significance was set at 0.05. The median change in CO (measured by subtracting values after and before ARM) was -0.15 L min-1 (IQR -0.51; 0.03) and - 0.90 L min-1 (IQR -1.69; -0.58) for SI and stepwise ARM respectively (p = 0.04). The median change in PaO2 was 3 kPa (IQR -2.7; 7.6) and 0.4 kPa (IQR -3.4; 5.5) for SI and stepwise ARM respectively (p = 0.03). In conclusion, SI ARM causes less impact on CO and provides a better improvement in PaO2 compared to stepwise ARM in goats.

Evaluation of the sedative and physiological effects of xylazine, detomidine, medetomidine and dexmedetomidine in goats

Background

Many α₂‐agonists are commonly used for sedation and analgesia in ruminants.

Introduction

The present study aims to compare the sedative and physiological effects of intravenous (IV) administration of xylazine, detomidine, medetomidine and dexmedetomidine in goats.

Methods

Ten healthy goats aged 6 ± 1 months and weighing 15 ± 2 kg were used in experimental, crossover Latin square, randomised and blinded study. Animals were assigned to five IV treatments: control (normal saline); xylazine (100 μg kg⁻¹); detomidine (50 μg kg⁻¹); medetomidine (20 μg kg⁻¹) and dexmedetomidine (5 μg kg⁻¹). The degree of sedation was investigated using a numerical ranking scale of 0–10. Sedation scores were compared at each time using nonparametric (Kruskal–Wallis and Mann–Whitney U) tests.

Results

Heart rate (HR), respiratory rate (RR), rectal temperature (RT), ruminal motility and capillary refill time (CRT) were performed before (baseline) and after drug administration. Animals in α₂‐adrenergic agonist treatments were sedated at 5–60 min. There were no significant differences among α₂‐adrenergic agonist treatments at 5–60 min in sedation scores. HR significantly decreased from baseline 5–90 min after α₂‐adrenergic agonists’ administration. Ruminal motility was decreased in α₂‐adrenergic agonist treatments at 5, 90 and 120 min and absent at 10–60 min. A significant decrease from baseline in RR was detected between 30 and 90 min after α₂‐adrenergic agonists’ administration. RT was unchanged in any treatment for 120 min. CRT was less than 2 s at all time points following each treatment.

Conclusions

The duration of sedation was up to 60 min after IV administration of xylazine (100 μg kg⁻¹), detomidine (50 μg kg⁻¹), medetomidine (20 μg kg⁻¹) and dexmedetomidine (5 μg kg⁻¹) in goats in this study. No significant differences were detected between xylazine, detomidine, medetomidine and dexmedetomidine in goats.

The duration of sedation was up to 60 minutes after IV administration of xylazine (100 μg kg⁻¹), detomidine (50 μg kg⁻¹), medetomidine (20 μg kg⁻¹) and dexmedetomidine (5 μg kg⁻¹) in goats. No significant differences were detected between xylazine, detomidine, medetomidine and dexmedetomidine in goats.

Effects of vatinoxan on xylazine-induced pulmonary alterations in sheep

It was hypothesized that premedication with vatinoxan, a peripheral α₂ -adrenoceptor antagonist, would mitigate xylazine-induced pulmonary alterations in sheep. Fourteen adult sheep were allotted into two equal groups and premedicated with either vatinoxan (750 µg/kg IV) or saline and sedated 10 min later with xylazine (500 µg/kg IV). Arterial oxygen saturation (SpO₂ ) was measured and respiratory rate (RR) counted at intervals. The sheep were euthanized with IV pentobarbital 10 min after xylazine administration. The severity of pulmonary parenchymal alterations was assessed and graded grossly and histologically and correlations of the morphological changes with SpO₂ evaluated. Following xylazine injection, SpO₂ was significantly higher and RR significantly lower with vatinoxan than with saline and the sheep administered vatinoxan exhibited significantly smaller quantities of tracheal foam than those receiving saline. No significant differences in macroscopic oedema scores were detected between treatments. In contrast, the vatinoxan-treated animals exhibited significantly graver microscopic interstitial alveolar oedema and haemorrhage than saline-treated animals. The histological severity scores did not correlate with changes in SpO₂ . In conclusion, xylazine induced a marked reduction in SpO₂ which was abolished by the prior administration of vatinoxan. The histologically detected alterations after pentobarbital euthanasia with vatinoxan premedication need to be studied further.

Application of α2 -adrenergic agonists combined with anesthetics and their implication in pulmonary intravascular macrophages-insulted pulmonary edema and hypoxemia in ruminants

Alpha₂ -adrenergic agonists have been implicated in the development of pulmonary edema (PE) and sustained hypoxemia that lead to life-threatening pulmonary distress in ruminants, especially with sensitive and compromised animals. Recently, there is limited understanding of exact mechanism underlying pulmonary alterations associated with α₂ -adrenergic agonist administration. Ruminants have a rich population of pulmonary intravascular macrophages (PIMs) in the pulmonary circulation, which may be involved in the development of pulmonary alveolo-capillary barrier damage. Hence, the central thesis of this review is overviewing the literatures regarding the systemic use of α₂ -adrenergic agonists in domestic ruminants, focusing on their pulmonary side effects, especially on the influence of PIMs on the lung. At this moment, further studies are needed to provide a clear emphasis and better understanding of the potential role of PIMs in the lung pathophysiology associated with α₂ -adrenergic agonists. These preliminary studies would be potentially to develop future medications and intervention targets that may be helpful to alleviate or prevent the critical striking pulmonary effects, and thereby improving the safety of α₂ -agonist application in ruminants.

Case Report: Subclinical Verminous Pneumonia and High Ambient Temperatures Had Severe Impact on the Anesthesia of Semi-domesticated Eurasian Tundra Reindeer (Rangifer tarandus tarandus) With Medetomidine-Ketamine

Semidomesticated Eurasian tundra reindeer (Rangifer tarandus tarandus, n = 21) were scheduled twice for chemical immobilization with medetomidine–ketamine as part of a scientific experiment in June 2014. During the first round of immobilizations, seven animals developed severe respiratory depression (RD). Three individuals died, and 4 recovered. The ambient temperature during the 2 days of immobilization (June 3 and 4) was high (mean 13.9–17.6°C) compared to the normal mean temperature for these 2 days (7–8°C) based on statistical records. During the second round of immobilizations, using the same anesthetic protocol for the remaining animals as in the first round but conducted under cooler conditions (mean 6.6°C for the period June 9–18), no signs of RD were observed. Clinical and pathological investigations indicated that the animals suffered from circulatory changes possibly caused by high ambient temperatures and granulomatous interstitial pneumonia due to Elaphostrongylus rangiferi larvae. These conditions, together with the cardiovascular effects of medetomidine, were likely causes of RD and the fatal outcome. We conclude that chemical immobilization of reindeer with medetomidine–ketamine should be avoided in May–June due to the potential risk when animals partly in winter coats encounter rising ambient temperatures and usually have parasites developing in their airways.

EVALUATION OF TWO MEDETOMIDINE-AZAPERONE-ALFAXALONE COMBINATIONS IN CAPTIVE ROCKY MOUNTAIN ELK (CERVUS ELAPHUS NELSONI)

Alfaxalone has been successfully used intramuscularly (im) combined with medetomidine and azaperone for immobilization of small ungulates. An experimental 40 mg/ml alfaxalone solution (RD0387) was recently formulated for reduced injection volume. The objective of this study was to assess the efficacy and cardiopulmonary effects of high-concentration alfaxalone combined with medetomidine and azaperone for the intramuscular immobilization of captive Rocky Mountain elk (Cervus elaphus nelsoni). Seven adult female elk were used in a crossover design in which they were administered alfaxalone 1 mg/kg, medetomidine 0.05 mg/kg, and azaperone 0.1 mg/kg or alfaxalone 0.5 mg/kg, medetomidine 0.1 mg/kg, and azaperone 0.1 mg/kg im approximately 3 wk apart. Drugs were delivered to each elk in a chute by hand injection. Once recumbent, elk were placed in sternal recumbency for a period of 30 min, during which time level of sedation, response to minor procedures, heart rate, respiratory rate, rectal temperature, oxygen saturation, and direct arterial blood pressures were recorded every 5 min. Arterial blood gases were performed every 15 min. At 30 min, elk were administered atipamezole 0.25 or 0.5 mg/kg im and recovery quality and times were recorded. Statistical comparisons were made by t test, Wilcoxon signed rank test, and repeated measures analysis (significance level P < 0.05). Both drug combinations provided effective immobilization for 30 min, with induction and recovery time and quality similar to other medetomidine-based combinations used in elk. Cardiopulmonary effects included bradycardia, hypertension, and hypoxemia that resolved with oxygen supplementation. The average injection volume in the low-dose alfaxalone combination was approximately 5 ml. These combinations provided deep sedation and the ability to perform minor procedures in captive elk, with acceptable cardiopulmonary parameters as long as supplemental oxygen was provided.

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.

Comparison of the efficacy of two ventilatory strategies in improving arterial oxygen tension and content in anaesthetized sheep

OBJECTIVE

To compare F-shunt and oxygen content indices in sheep ventilated with a positive end-expiratory pressure (PEEP) of 5 cmH₂O alone or preceded by a stepwise alveolar recruitment manoeuvre (ARM).

STUDY DESIGN

Randomized crossover design.

ANIMALS

A total of six nonpregnant Brogna ewes weighing 34-47 kg, undergoing thoracolumbar magnetic resonance scan.

METHODS

In medetomidine-sedated sheep, anaesthesia was induced with propofol and maintained with isoflurane 1.1% ± 0.1% and an inspired oxygen fraction (FiO₂) of 0.4. Animals were placed in left lateral recumbency and, after 10 minutes of spontaneous breathing, mechanically ventilated with 5 cmH₂O of PEEP with (group ARM) or without (group PEEP) a stepwise recruitment manoeuvre. Maintaining a fixed driving pressure of 15 cmH₂O, PEEP was increased from 0 to 20 cmH₂O every 3 minutes in 5 cmH₂O increments. In each sheep, arterial blood samples were collected to measure arterial gases and to calculate F-shunt, PaO₂/alveolar oxygen partial pressure (PAO₂) and PaO₂/FIO₂ during spontaneous breathing before mechanical ventilation (T₀), after 20 minutes of ventilation (T₂₀) and during spontaneous breathing at extubation (T_ext).

RESULTS

Both ventilatory strategies improved the arterial oxygen content although four animals in group PEEP showed oxygen content compatible with hypoxia compared with group ARM. F-shunt values were not statistically different at any time point in sheep that underwent only PEEP ventilation while they decreased at T₂₀ and T_ext compared with T₀ in group ARM. At extubation F-shunt was statistically lower in sheep that underwent an ARM. Mechanical ventilation improved PaO₂/PAO₂ and PaO₂/FIO₂ but they did not differ between groups.

CONCLUSIONS

and clinical relevance The stepwise ARM evaluated in this study improved oxygenation indices and decreased F-shunt. This effect was maintained at extubation compared with sheep that were ventilated with only PEEP 5 cmH₂O.

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.

Clinical effects of epidurally administered dexmedetomidine with or without lidocaine in sheep

BACKGROUND

The aims of this study were evaluate cardiopulmonary, sedative and antinociceptive effects of dexmedetomidine-lidocaine combination via lumbosacral epidural injection in sheep.

METHODS

Six Santa Inês breed sheep, 16±6 months old and weighing 42.2 ± 5.7 kg were used. Sheep were subjected to epidural anaesthesia with three treatments: L, lidocaine (1.2 mg/kg), D, dexmedetomidine (2.5 μg/kg) or DL, dexmedetomidine plus lidocaine (2.5 μg/kg + 1.2 mg/kg). Drugs were injected via pre-placed lumbosacral epidural catheters. Cardiopulmonary, arterial blood gases, electrolytes, degree of sedation and antinociceptive aspects were measured before drug administration (T0) and then at 15, 30, 60 and 120 min after drug injection (T15-T120) in all treatments and at T0 to T240 in DL.

RESULTS

There were significantly increases in PaCO₂ at times T60 and T120 in D, and at T30-T120 in DL, compared to baseline. The antinociceptive effects were observed up to 240 min in DL and 60 min in L, and were more intense in DL. Treatment D provided analgesia only in the perineal region, and only at T15.

CONCLUSION

The combination of DEX with lidocaine produced similar cardiopulmonary changes compared with either drug alone, but with greater and more prolonged antinociceptive effects.

Comparative evaluation of sedative and clinical effects of dexmedetomidine and xylazine in dromedary calves (Camelus dromedarius)

OBJECTIVE

To compare the sedative and clinical effects of intravenous (IV) administration of dexmedetomidine and xylazine in dromedary calves.

STUDY DESIGN

Experimental, crossover, randomized, blinded study.

ANIMALS

A total of seven healthy male dromedary calves aged 14 ± 2 weeks and weighing 95 ± 5.5 kg.

METHODS

Calves were assigned three IV treatments: treatment XYL, xylazine (0.2 mg kg^-1); treatment DEX, dexmedetomidine (5 μg kg^-1); and control treatment, normal saline (0.01 mL kg^-1). Sedation scores, heart rate (HR), respiratory rate (f_R), rectal temperature (RT) and ruminal motility were recorded before (baseline) and after drug administration. Sedation signs were scored using a 4-point scale. One-way anova and Mann-Whitney U tests were used for data analysis.

RESULTS

Calves in treatments XYL and DEX were sedated at 5-60 minutes. Sedation had waned in XYL calves, but not DEX calves, at 60 minutes (p = 0.037). Sedation was not present in calves of any treatment at 90 minutes. HR decreased from baseline in XYL and DEX at 5-90 minutes after drug administration and was lower in DEX than XYL at 5 minutes (p = 0.017). HR was lower in DEX (p = 0.001) and XYL (p = 0.013) than in control treatment at 90 minutes. f_R decreased from baseline in XYL and DEX at 5-60 minutes after drug administration and was lower in DEX than XYL at 5 minutes (p = 0.013). RT was unchanged in any treatment over 120 minutes. Ruminal motility was decreased in XYL at 5, 90 and 120 minutes and absent at 10-60 minutes. Motility was decreased in DEX at 5, 10 and 120 minutes and was absent at 15-90 minutes.

CONCLUSION AND CLINICAL RELEVANCE

The duration of sedation from dexmedetomidine (5 μg kg^-1) and xylazine (0.2 mg kg^-1) was similar in dromedary calves.

Cardiopulmonary effects of vatinoxan in sevoflurane-anaesthetised sheep receiving dexmedetomidine

The effects of pre-treatment with vatinoxan (MK-467) on dexmedetomidine-induced cardiopulmonary alterations were investigated in sheep. In a crossover study design with a 20-day washout, seven sheep were anaesthetised with sevoflurane in oxygen and air. The sheep were ventilated with the pressure-limited volume-controlled mode and a positive end-expiratory pressure of 5cmH₂O. Peak inspiratory pressure (PIP) was set at 25cmH₂O. The sheep received either 150μg/kg vatinoxan HCl (VAT+DEX) or saline intravenously (IV) 10min before IV dexmedetomidine HCl (3μg/kg, DEX). Cardiopulmonary variables were measured before treatments (baseline), 3min after vatinoxan or saline, and 5, 15 and 25min after dexmedetomidine. Computed tomography (CT) of lung parenchyma was performed at baseline, 2min before dexmedetomidine, and 10, 20 and 30min after DEX. Bronchoalveolar lavage (BAL) was performed after the last CT scan and shortly before sheep recovered from anaesthesia. After VAT, cardiac output significantly increased from baseline. DEX alone significantly decreased partial arterial oxygen tension, total dynamic compliance and tidal volume, whereas PIP was significantly increased. With VAT+DEX, these changes were minimal. No significant changes were detected in haemodynamics from baseline after DEX. With VAT+DEX, mean arterial pressure and systemic vascular resistance were significantly decreased from baseline, although hypotension was not detected. On CT, lung density was significantly increased with DEX as compared to baseline. No visual abnormalities were detected in bronchoscopy and no differences were detected in the BAL fluid after either treatment. The pre-administration of vatinoxan alleviates dexmedetomidine-induced bronchoconstriction, oedema and hypoxaemia in sevoflurane-anaesthetised sheep.

Adverse reactions of α2-adrenoceptor agonists in cats reported in 2003-2013 in Finland

OBJECTIVE

To describe suspected adverse drug reactions in cats associated with use of α₂-adrenoceptor agonists.

STUDY DESIGN

Retrospective study.

ANIMALS

A total of 90 cats.

METHODS

Data were collected from reports on adverse reactions to veterinary medicines sent to the Finnish Medicines Agency during 2003-2013. All reports of suspected adverse reactions associated with use of α₂-adrenoceptor agonists in cats were included. Probable pulmonary oedema was diagnosed based on post mortem or radiological examination, or presence of frothy or excess fluid from the nostrils or trachea. If only dyspnoea and crackles on auscultation were reported, possible pulmonary oedema was presumed.

RESULTS

Pulmonary oedema was suspected in 61 cases. Of these cats, 37 were categorised as probable and 24 as possible pulmonary oedema. The first clinical signs had been noted between 1 minute and 2 days (median, 15 minutes) after α₂-adrenoceptor agonist administration. Many cats probably had no intravenous overhydration when the first clinical signs were detected, as either they presumably had no intravenous cannula or the signs appeared before, during or immediately after cannulation. Of the 61 cats, 43 survived, 14 died and for four the outcome was not clearly stated.

CONCLUSIONS AND CLINICAL RELEVANCE

Pulmonary oedema is a perilous condition that may appear within minutes of an intramuscular administration of sedative or anaesthetic agent in cats. The symptoms were not caused by intravenous overhydration, at least in cats having no venous cannula when the first clinical signs were detected.

Sedative and cardiorespiratory effects of detomidine constant rate infusion in sheep

The use of sheep in experiments is widespread and is increasing worldwide, and so is the need to develop species-specific anaesthetic techniques to ensure animal safety. Previous studies have mentioned several protocols involving the administration of alpha-2 adrenergic agonists in sheep; however, assessment of the efficacy and safety of these infusion techniques is still relatively new. Thus, the aim of the present study is to assess the effectiveness of detomidine constant rate infusion (CRI) in sheep by measuring the cardiovascular and respiratory parameters, blood gas variables and sedation scores. Eight adult female Santa Inês sheep received 20 µg/kg of detomidine hydrochloride intravenously as a bolus loading dose, followed by an infusion rate of 60 µg/kg/h. The heart rates and respiratory rates changed continuously during the CRI period. No arrhythmias were observed. The reduction in arterial partial pressure of oxygen (PaO₂) was not significant, but one animal showed signs of hypoxaemia (minimum PaO₂ of 66.9 mmHg). The arterial partial pressure of carbon dioxide (PaCO₂) increased, but the animals did not become hypercapnic. The bicarbonate (HCO^3-), pH and base excess (BE) tended towards metabolic alkalosis. The cardiac output (CO), stroke volume (SV), cardiac index (CI) and ejection fraction (EF%) showed no significant changes. The fractional shortening (FS%) decreased slightly, starting at T_45min. Sedation scores varied between 3 (0/10) after sedation and during recovery and 7 (0/10) during CRI. We concluded that administering detomidine at an infusion rate of 60 µg/kg/h in Santa Inês sheep is a simple technique that produces satisfactory sedation for minimally invasive procedures.

Dexmedetomidine enhances human lung fluid clearance through improving alveolar sodium transport

Accumulating evidence shows that dexmedetomidine can attenuate lung edema with acute lung injury in experimental mouse and rat models, but the mechanisms of dexmedetomidine on human alveolar fluid transport are still unknown. We measured the effects of dexmedetomidine on alveolar fluid clearance in human lung lobes ex vivo. Moreover, we measured the regulation of transepithelial Na⁺ transport by dexmedetomidine in H441 cells by electrophysiological technique and Western blot method. Our results showed that intratracheal instillation of dexmedetomidine markedly increased the reabsorption of 5% bovine serum albumin instillate (19.8 ± 1.4%, P < 0.01 vs. Control, n = 5). Further studies suggested that dexmedetomidine increased amiloride-sensitive short-circuit currents in permeabilized H441 monolayers and whole cell amiloride-sensitive Na⁺ currents in a dose-dependent fashion. Real-time PCR and Western blot results showed that dexmedetomidine could enhance the mRNA and protein expression of α-ENaC subunit, while inhibiting the phosphorylation of ERK_1/2 . These data demonstrate that dexmedetomidine could improve human lung fluid clearance and lung epithelial Na⁺ channel activity, and these effects may be mediated through the enhancement of α-ENaC expression and inhibition of ERK_1/2 pathway.

Anesthetic techniques influence the induction of pulmonary capillary hemorrhage during diagnostic ultrasound scanning in rats

OBJECTIVES

Pulmonary capillary hemorrhage can be induced by diagnostic ultrasound (US) during direct pulmonary US scanning in rats. The influence of specific anesthetic techniques on this bioeffect was examined.

METHODS

Ketamine plus xylazine has been used previously. In this study, the influence of intraperitoneal injections of ketamine and pentobarbital, inhalational isoflurane, and the supplemental use of xylazine with ketamine and isoflurane was tested. A diagnostic US machine with a 7.6-MHz linear array was used to image the right lung of anesthetized rats in a warmed water bath at different mechanical index (MI) settings. Pulmonary capillary hemorrhage was assessed by measuring comet tail artifacts in the image and by morphometry of the hemorrhagic areas on excised lungs.

RESULTS

Pulmonary capillary hemorrhage was greatest for pentobarbital, lower for inhalational isoflurane, and lowest for ketamine anesthesia, with occurrence thresholds at MIs of about 0.44, 0.8, and 0.8, respectively. Addition of xylazine produced a substantial increase in hemorrhage and a significant proportion of hemorrhage occurrence for ketamine at an MI of 0.7 (P < .01) and for isoflurane at an MI of 0.52 (P < .01).

CONCLUSIONS

Ketamine plus xylazine and pentobarbital yield lower thresholds than ketamine or isoflurane alone by nearly a factor of 2 in MI. These results suggest that the choice of the anesthetic agent substantially modifies the relative risks of pulmonary capillary hemorrhage from pulmonary US.

Optimal management of the critically ill: anaesthesia, monitoring, data capture, and point-of-care technological practices in ovine models of critical care

Animal models of critical illness are vital in biomedical research. They provide possibilities for the investigation of pathophysiological processes that may not otherwise be possible in humans. In order to be clinically applicable, the model should simulate the critical care situation realistically, including anaesthesia, monitoring, sampling, utilising appropriate personnel skill mix, and therapeutic interventions. There are limited data documenting the constitution of ideal technologically advanced large animal critical care practices and all the processes of the animal model. In this paper, we describe the procedure of animal preparation, anaesthesia induction and maintenance, physiologic monitoring, data capture, point-of-care technology, and animal aftercare that has been successfully used to study several novel ovine models of critical illness. The relevant investigations are on respiratory failure due to smoke inhalation, transfusion related acute lung injury, endotoxin-induced proteogenomic alterations, haemorrhagic shock, septic shock, brain death, cerebral microcirculation, and artificial heart studies. We have demonstrated the functionality of monitoring practices during anaesthesia required to provide a platform for undertaking systematic investigations in complex ovine models of critical illness.

Proteogenomics of selective susceptibility to endotoxin using circulating acute phase biomarkers and bioassay development in sheep: a review

Scientists have injected endotoxin into animals to investigate and understand various pathologies and novel therapies for several decades. Recent observations have shown that there is selective susceptibility to Escherichia coli lipopolysaccharide (LPS) endotoxin in sheep, despite having similar breed characteristics. The reason behind this difference is unknown, and has prompted studies aiming to explain the variation by proteogenomic characterisation of circulating acute phase biomarkers. It is hypothesised that genetic trait, biochemical, immunological and inflammation marker patterns contribute in defining and predicting mammalian response to LPS. This review discusses the effects of endotoxin and host responses, genetic basis of innate defences, activation of the acute phase response (APR) following experimental LPS challenge, and the current approaches employed in detecting novel biomarkers including acute phase proteins (APP) and micro-ribonucleic acids (miRNAs) in serum or plasma. miRNAs are novel targets for elucidating molecular mechanisms of disease because of their differential expression during pathological, and in healthy states. Changes in miRNA profiles during a disease challenge may be reflected in plasma. Studies show that gel-based two-dimensional electrophoresis (2-DE) coupled with either matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF MS) or liquid chromatography–mass spectrometry (LC-MS/MS) are currently the most used methods for proteome characterisation. Further evidence suggests that proteomic investigations are preferentially shifting from 2-DE to non-gel based LC-MS/MS coupled with data extraction by sequential window acquisition of all theoretical fragment-ion spectra (SWATH) approaches that are able to identify a wider range of proteins. Enzyme-linked immunosorbent assay (ELISA), quantitative real-time polymerase chain reaction (qRT-PCR), and most recently proteomic methods have been used to quantify low abundance proteins such as cytokines. qRT-PCR and next generation sequencing (NGS) are used for the characterisation of miRNA. Proteogenomic approaches for detecting APP and novel miRNA profiling are essential in understanding the selective resistance to endotoxin in sheep. The results of these methods could help in understanding similar pathology in humans. It might also be helpful in the development of physiological and diagnostic screening assays for determining experimental inclusion and endpoints, and in clinical trials in future.

A comparison of two different ketamine and diazepam combinations with an alphaxalone and medetomidine combination for induction of anaesthesia in sheep

AIMS

To investigate the perceived adverse effects of a particular batch of ketamine during induction of anaesthesia in sheep and to assess if any adverse effects would make intubation more difficult for the veterinary students.

METHODS

Thirty adult sheep (mean bodyweight 74.5 (SD 9.4) kg) were randomly assigned to one of six groups of five sheep. Sheep in Groups A and B received I/V 0.5 mg/kg diazepam and 10 mg/kg ketamine (Ketamine Injection; Parnell Laboratories NZ Ltd, of the suspect batch); those in Groups C and D received I/V 0.5 mg/kg diazepam and 10 mg/kg ketamine (Ketalar; Hospira NZ Ltd.), and those in Groups E and F received I/V 2 μg/kg medetomidine and 2 mg/kg alphaxalone. In Groups A, C and E, intubation was by an experienced anaesthetist, and in Groups B, D and F intubation was by a veterinary student. Time from injection to successful intubation, the ease of intubation, saturation of haemoglobin with oxygen (SpO₂) and partial pressure of oxygen in arterial blood (PaO₂) were measured before the sheep were connected to an anaesthetic machine and allowed to breath oxygen. Times to extubation, holding its head up and standing, maximum and minimum heart rates, respiratory rates, maximal end tidal CO₂, and the quality of recovery were then recorded.

RESULTS

There were no measurable differences in outcomes between sheep in Groups A and B compared with C and D. Time to intubation was slightly shorter for the experienced anaesthetist than the student, but the difference was not significant. The sheep in Groups E and F took less time to recover than those in Groups A-D (p<0.05), but there were no significant differences between the groups in either the ease of induction or quality of recovery. Most sheep in Groups E and F showed minor excitatory effects, mainly at induction, which did not interfere with induction. Respiratory rates were lower in Groups E and F than Groups A-D (p<0.01), but SpO₂ was higher in Groups E and F than A and B (p<0.05).

CONCLUSIONS

The clinical impression that the batch of Parnell ketamine produced unexpected effects was shown to be incorrect. All the combinations produced anaesthesia that allowed intubation by the veterinary student.

CLINICAL RELEVANCE

All the drug combinations produced satisfactory anaesthesia in sheep, but the alphaxaloneand medetomidine combination resulted in faster recovery.

Evaluation of medetomidine-ketamine-butorphanol anesthesia with atipamezole-naltrexone antagonism in captive male guanacos (Lama guanicoe)

Seven captive adult male guanacos (Lama guanicoe) weighing 112.0 +/- 10.9 kg (mean +/- standard deviation) were anesthetized with a combination of medetomidine (90.0 +/- 8.8 microg/kg), ketamine (2.7 +/- 0.3 mg/kg), and butorphanol (0.3 +/- 0.03 mg/kg) administered intramuscularly to evaluate its anesthetic and cardiopulmonary effects. Inductions were smooth and rapid, with a mean time to initial effect of 3 +/- 1.5 min and a mean time to recumbency of 5.1 +/- 3.1 min. Anesthesia was predictable, smooth, and characterized by excellent muscle relaxation. Spontaneous ventilation was maintained throughout anesthesia in all animals. Marked bradycardia ranging from 24 to 52 beats/min was noted across all time points for all individuals. Median heart rates decreased during the procedures, but median heart rate, temperature, respiratory rate, and end-tidal carbon dioxide values over the 20 min monitoring period were not significantly different. Mean arterial partial pressure of oxygen (PaO2) on initial sampling was 65.9 +/- 14.8 mm Hg, with six of seven animals exhibiting hypoxemia (PaO2 <80 mm Hg). After oxygen supplementation for 20 min, mean PaO2 values showed statistically significant increases to a mean value of 127.7 +/- 32.4 mm Hg (P = 0.0014). Mean arterial partial pressure of carbon dioxide (PaCO2) showed a significant increase over the monitoring period (P = 0.0004), and mild hypoventilation (PaCO2 >45 mm Hg) was noted in four animals. Mean total duration of procedure time was 23.3 +/- 3.3 min. All guanacos received 0.45 +/- 0.04 mg/kg atipamezole and 2.7 +/- 0.25 mg/kg naltrexone administered intramuscularly for anesthetic antagonism. Recoveries were smooth and uncomplicated. Mean time to sternal recumbency after antagonist administration was 7.7 +/- 4.5 min, and time to successful standing was 12.9 +/- 5.0 min, with all animals standing on first attempt.