Effects of constant rate infusions of dexmedetomidine or MK-467 on the minimum alveolar concentration of sevoflurane in dogs

Effects of Cannabidiol Oil on Anesthetic Requirements in Cats: MAC Determination and Serum Profiling via Nanoscale Liquid Chromatography-Tandem Mass Spectrometry

Cannabidiol (CBD), a non-psychotropic cannabinoid derived from Cannabis plants, is increasingly explored for its potential therapeutic applications in veterinary medicine. This study aimed to evaluate the impact of CBD oil on the minimum alveolar concentration of isoflurane (MACiso) in cats. Sixteen healthy cats underwent isoflurane anesthesia, and the MACiso was determined using the tail-clamping technique both at baseline and 30 min after the administration of CBD oil (2 mg/kg) via a stomach tube. CBD administration resulted in a significant 11% reduction in the MACiso, from 1.77 ± 0.14% to 1.62 ± 0.21% (p < 0.001). Following CBD administration, heart and respiratory rates were elevated at the time of MACiso determination compared to baseline whereas other physiological parameters remained unchanged. Serum biochemical analysis conducted two weeks post administration revealed a significant decrease in blood urea nitrogen (BUN) levels while one cat exhibited a mild increase in alanine aminotransferase (ALT). Proteomic analysis identified 12 CBD-associated proteins in feline serum 30 min post administration, with CBDA and THCA synthases demonstrating significant upregulation. These findings indicate that CBD oil reduces anesthetic requirements in cats without inducing significant physiological disturbances. Further research is warranted to elucidate the underlying mechanisms of CBD's anesthetic-sparing effects and its implications in veterinary anesthesia.

The Impact of Vatinoxan on the Concentrations of Medetomidine, Midazolam, and Fentanyl in Central Nervous System After Subcutaneous Co-Administration in Rats

Our aim was to investigate whether vatinoxan, a peripherally acting alpha2-adrenoceptor antagonist, would affect the concentrations of medetomidine, midazolam, and fentanyl in the central nervous system after subcutaneous co-administration. Twelve healthy male Wistar rats, aged between 13 and 15 weeks, were used in this study. The animals received one of two subcutaneously administered treatments: medetomidine 0.25 mg/kg, midazolam 2 mg/kg, and fentanyl 0.01 mg/kg (MMF) or MMF with 5 mg/kg of vatinoxan (MMF-V). 15 min later, the sedated rats were humanely euthanized with intravenous pentobarbital. Plasma and tissue, including aliquots of the cortex, thalamus, pons, and lumbar spinal cord, were harvested and analyzed for drug concentrations. The treatments were compared with Bonferroni corrected t-tests after one-way analysis of variance. The concentrations of medetomidine (144 ± 19.4 vs. 107 ± 13.1 ng/g [mean ± 95% confidence interval]) (p = 0.04) and fentanyl (2.3 ± 0.2 vs. 1.7 ± 0.3 ng/g) (p = 0.04) in the cortex were significantly higher in the rats administered MMF-V. Similarly, cortex: plasma drug concentration ratios were significantly higher for medetomidine, midazolam, and fentanyl after MMF-V (p < 0.001 for all). The results confirm that vatinoxan increases early cortical exposure to subcutaneously co-administered medetomidine and fentanyl.

Comparison Between Medetomidine and a Medetomidine-Vatinoxan Combination on Cardiorespiratory Variables in Dogs Undergoing Ovariectomy Anesthetized with Butorphanol, Propofol and Sevoflurane or Desflurane

The aim of this study was to compare the effects of a medetomidine-vatinoxan combination versus medetomidine alone on heart rate (HR) and mean arterial pressure (MAP) in a short-term surgery in dogs. Four groups of 10 dogs were administered as follows: medetomidine and sevoflurane; medetomidine and desflurane; medetomidine-vatinoxan and sevoflurane; and medetomidine-vatinoxan and desflurane. After administration, the increase in MAP soon stopped at 102-104 mmHg in the two groups administered medetomidine-vatinoxan, compared with significantly higher values of 143-126 mmHg achieved in the two groups administered medetomidine alone. The lowest MAPs in the two medetomidine-vatinoxan groups were 46-50 mmHg, while in the medetomidine groups, they were 58-79 mmHg. From 3 min onwards after administration, in the medetomidine-vatinoxan treatments, HR remained at values very close to those of pre-administration, between 83 and 118 beats min-1, while in the medetomidine treatments, it dropped to 36-43 beats min-1 and then slowly rose to reach 71-90 beats min-1. These results encourage the use of vatinoxan in clinical settings, particularly in anesthetic protocols for dogs when bradycardia and an increase in systemic pressure should be avoided. Further clinical studies are needed to manage the short periods of hypotension, as well as the slight reduction in sedative and pain-relieving medetomidine effects found, particularly when vatinoxan is in combination with desflurane rather than sevoflurane.

Nicardipine constant rate infusion alleviates the cardiovascular effects of dexmedetomidine infusions without affecting the minimal alveolar concentration in sevoflurane-anesthetized dogs

Two randomized crossover trials evaluated the effects of nicardipine constant rate infusion (CRI) on 1) the anesthetic potency of sevoflurane and 2) the ability to attenuate dexmedetomidine-induced cardiovascular depression in anesthetized dogs. First, six healthy Beagle dogs weighing 11.7 ± 0.9 kg were allocated to one of three treatments that administered a CRI of carrier (saline) or dexmedetomidine 0.5 or 3.0 μg/kg/h following a loading dose. The minimum alveolar concentration (MAC) of sevoflurane was determined utilizing electric stimuli before and after the loading dose of nicardipine (20 μg/kg intravenously for 10 min), followed by CRI at 40 μg/kg/h with 60 min of equilibration. Subsequently, cardiovascular and blood gas variables were evaluated in another trial under sevoflurane anesthesia at the individual 1.5 MAC. After baseline measurements, the dogs were assigned to two treatments (dexmedetomidine CRI at 0.5 or 3.0 μg/kg/h following a loading dose) with sevoflurane doses adjusted to 1.5 times of MAC equivalent, and the measurements were repeated every 15 min for 120 min. After 60 min, nicardipine CRI at 40 μg/kg/h with a loading dose was added to the dexmedetomidine CRI. Dexmedetomidine infusions significantly decreased the sevoflurane MAC but nicardipine did not significantly alter the MAC either with or without dexmedetomidine CRI in dogs. Dexmedetomidine dose-dependently decreased the cardiac index and increased the systemic vascular resistance index; these effects were fully counteracted by concomitant nicardipine CRI. Nicardipine CRI can be useful for controlling the cardiovascular depression elicited by dexmedetomidine in anesthetized dogs without affecting the anesthetic potency of sevoflurane.

Sparing effect of tramadol, lidocaine, dexmedetomidine and their combination on the minimum alveolar concentration of sevoflurane in dogs

Background

Problems associated with using inhalational anaesthesia are numerous in veterinary anaesthesia practice. Decreasing the amount of used inhalational anaesthetic agents and minimising of cardiorespiratory disorders are the standard goals of anaesthetists.

Objective

This experimental study was carried out to investigate the sparing effect of intravenous tramadol, lidocaine, dexmedetomidine and their combinations on the minimum alveolar concentration (MAC) of sevoflurane in healthy Beagle dogs.

Methods

This study was conducted on six beagle dogs. Sevoflurane MAC was determined by the tail clamp method on five separate occasions. The dogs received no treatment (control; CONT), tramadol (TRM: 1.5 mg kg^-1 intravenously followed by 1.3 mg kg^-1 h^-1), lidocaine (LID: 2 mg kg^-1 intravenously followed by 3 mg kg^-1 h^-1), dexmedetomidine (DEX: 2 μg kg^-1 intravenously followed by 2 μg kg^-1 h^-1), and their combination (COMB), respectively. Cardiorespiratory variables were recorded every five minutes and immediately before the application of a noxious stimulus.

Results

The COMB treatment had the greatest sevoflurane MAC-sparing effect (67.4 ± 13.9%) compared with the other treatments (5.1 ± 25.3, 12.7 ± 14.3, and 40.3 ± 15.1% for TRM, LID, and DEX treatment, respectively). The cardiopulmonary variables remained within the clinically acceptable range following COMB treatment, although the mean arterial pressure was higher and accompanied by bradycardia.

Conclusions

Tramadol-lidocaine-dexmedetomidine co-infusion produced a remarkable sevoflurane MAC-sparing effect in clinically healthy beagle dogs and could result in the alleviation of cardiorespiratory depression caused by sevoflurane. Cardiorespiratory variables should be monitored carefully to avoid undesirable side effects induced by dexmedetomidine.

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.

Combined effects of dexmedetomidine and vatinoxan infusions on minimum alveolar concentration and cardiopulmonary function in sevoflurane-anesthetized dogs

OBJECTIVE

To evaluate the effects of combined infusions of vatinoxan and dexmedetomidine on inhalant anesthetic requirement and cardiopulmonary function in dogs.

STUDY DESIGN

Prospective experimental study.

METHODS

A total of six Beagle dogs were anesthetized to determine sevoflurane minimum alveolar concentration (MAC) prior to and after an intravenous (IV) dose (loading, then continuous infusion) of dexmedetomidine (4.5 μg kg^-1 hour^-1) and after two IV doses of vatinoxan in sequence (90 and 180 μg kg^-1 hour^-1). Blood was collected for plasma dexmedetomidine and vatinoxan concentrations. During a separate anesthesia, cardiac output (CO) was measured under equivalent MAC conditions of sevoflurane and dexmedetomidine, and then with each added dose of vatinoxan. For each treatment, cardiovascular variables were measured with spontaneous and controlled ventilation. Repeated measures analyses were performed for each response variable; for all analyses, p < 0.05 was considered significant.

RESULTS

Dexmedetomidine reduced sevoflurane MAC by 67% (0.64 ± 0.1%), mean ± standard deviation in dogs. The addition of vatinoxan attenuated this to 57% (0.81 ± 0.1%) and 43% (1.1 ± 0.1%) with low and high doses, respectively, and caused a reduction in plasma dexmedetomidine concentrations. Heart rate and CO decreased while systemic vascular resistance increased with dexmedetomidine regardless of ventilation mode. The co-administration of vatinoxan dose-dependently modified these effects such that cardiovascular variables approached baseline.

CONCLUSIONS AND CLINICAL RELEVANCE

IV infusions of 90 and 180 μg kg^-1 hour^-1 of vatinoxan combined with 4.5 μg kg^-1 hour^-1 dexmedetomidine provide a meaningful reduction in sevoflurane requirement in dogs. Although sevoflurane MAC-sparing properties of dexmedetomidine in dogs are attenuated by vatinoxan, the cardiovascular function is improved. Doses of vatinoxan >180 μg kg^-1 hour^-1 might improve cardiovascular function further in combination with this dose of dexmedetomidine, but beneficial effects on anesthesia plane and recovery quality may be lost.

Inhibition and facilitation of nociceptively evoked muscular activity by fentanyl or dexmedetomidine in isoflurane-anaesthetized pigs

OBJECTIVE

To investigate motor and cardiovascular responses to dexmedetomidine or fentanyl in isoflurane-anaesthetized pigs.

STUDY DESIGN

Experimental, balanced, block randomized, two-group design.

ANIMALS

A group of 16 crossbred pigs, 55 ± 8 days (mean ± standard deviation) old.

METHODS

Deltoid electromyography (EMG) was recorded during isoflurane anaesthesia. Electrical stimulation using 5, 10, 20 and 40 mA of the distal right thoracic limb elicited a nociceptive withdrawal reflex (NWR), quantified by the area under the curve (AUC) for the simulation intensity versus EMG amplitude response curve. Latency to movement evoked by clamping a claw for maximum 60 seconds was noted. Arterial blood pressure and pulse rate were recorded. Data were sampled at baseline and during dexmedetomidine 0.25, 0.5, 1.0, 2.0, 4.0 and 8.0 μg kg^-1 hour^-1 or fentanyl 5, 10, 20, 40, 80 and 160 μg kg^-1 hour^-1 infusions. The influence of infusion rate on NWR AUC and spontaneous EMG was analysed using a mixed model, with p < 5%.

RESULTS

NWR AUC increased at fentanyl 5 μg kg^-1 hour^-1 but decreased at fentanyl 40, 80 and 160 μg kg^-1 hour^-1 and dexmedetomidine 4.0 and 8.0 μg kg^-1 hour^-1. All pigs at fentanyl 80 μg kg^-1 hour^-1, and three pigs at dexmedetomidine 8.0 μg kg^-1 hour^-1 had mechanical latencies greater than 60 seconds. Spontaneous EMG activity increased accompanied by visually evident 'shivering' at fentanyl 5, 10 and 20 μg kg^-1 hour^-1 but decreased at dexmedetomidine 2, 4 and 8 μg kg^-1 hour^-1. Clinically relevant effects of increasing infusion rates on blood pressure or pulse rate were not observed.

CONCLUSION AND CLINICAL RELEVANCE

If anaesthetic plane or antinociception is evaluated in pigs, response to claw clamping and NWR will not necessarily give uniform results when comparing drugs. If only one method is used, results should be interpreted cautiously.

Investigation of the effects of vatinoxan on somatic and visceral antinociceptive efficacy of medetomidine in dogs

OBJECTIVE

To determine whether concurrent vatinoxan administration affects the antinociceptive efficacy of medetomidine in dogs at doses that provide circulating dexmedetomidine concentrations similar to those produced by medetomidine alone.

ANIMALS

8 healthy Beagles.

PROCEDURES

Dogs received 3 IV treatments in a randomized crossover-design trial with a 2-week washout period between experiments (medetomidine [20 μg/kg], medetomidine [20 μg/kg] and vatinoxan [400 μg/kg], and medetomidine [40 μg/kg] and vatinoxan [800 μg/kg]; M20, M20V400, and M40V800, respectively). Sedation, visceral and somatic nociception, and plasma drug concentrations were assessed. Somatic and visceral nociception measurements and sedation scores were compared among treatments and over time. Sedation, visceral antinociception, and somatic antinociception effects of M20V400 and M40V800 were analyzed for noninferiority to effects of M20, and plasma drug concentration data were assessed for equivalence between treatments.

RESULTS

Plasma dexmedetomidine concentrations after administration of M20 and M40V800 were equivalent. Sedation scores, visceral nociception measurements, and somatic nociception measurements did not differ significantly among treatments within time points. Overall sedative effects of M20V400 and M40V800 and visceral antinociceptive effects of M40V800 were noninferior to those produced by M20. Somatic antinociception effects of M20V400 at 10 minutes and M40V800 at 10 and 55 minutes after injection were noninferior to those produced by M20.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggested coadministration with vatinoxan did not substantially diminish visceral antinociceptive effects of medetomidine when plasma dexmedetomidine concentrations were equivalent to those produced by medetomidine alone. For somatic antinociception, noninferiority of treatments was detected at some time points.

Effects of intramuscular vatinoxan (MK-467), co-administered with medetomidine and butorphanol, on cardiopulmonary and anaesthetic effects of intravenous ketamine in dogs

OBJECTIVE

To investigate the impact of intramuscular (IM) co-administration of the peripheral α₂-adrenoceptor agonist vatinoxan (MK-467) with medetomidine and butorphanol prior to intravenous (IV) ketamine on the cardiopulmonary and anaesthetic effects in dogs, followed by atipamezole reversal.

STUDY DESIGN

Randomized, masked crossover study.

ANIMALS

A total of eight purpose-bred Beagle dogs aged 3 years.

METHODS

Each dog was instrumented and administered two treatments 2 weeks apart: medetomidine (20 μg kg^-1) and butorphanol (100 μg kg^-1) premedication with vatinoxan (500 μg kg^-1; treatment MVB) or without vatinoxan (treatment MB) IM 20 minutes before IV ketamine (4 mg kg^-1). Atipamezole (100 μg kg^-1) was administered IM 60 minutes after ketamine. Heart rate (HR), mean arterial (MAP) and central venous (CVP) pressures and cardiac output (CO) were measured; cardiac (CI) and systemic vascular resistance (SVRI) indices were calculated before and 10 minutes after MVB or MB, and 10, 25, 40, 55, 70 and 100 minutes after ketamine. Data were analysed with repeated measures analysis of covariance models. A p-value <0.05 was considered statistically significant. Sedation, induction, intubation and recovery scores were assessed.

RESULTS

At most time points, HR and CI were significantly higher, and SVRI and CVP significantly lower with MVB than with MB. With both treatments, SVRI and MAP decreased after ketamine, whereas HR and CI increased. MAP was significantly lower with MVB than with MB; mild hypotension (57-59 mmHg) was recorded in two dogs with MVB prior to atipamezole administration. Sedation, induction, intubation and recovery scores were not different between treatments, but intolerance to the endotracheal tube was observed earlier with MVB.

CONCLUSIONS AND CLINICAL RELEVANCE

Haemodynamic performance was improved by vatinoxan co-administration with medetomidine-butorphanol, before and after ketamine administration. However, vatinoxan was associated with mild hypotension after ketamine with the dose used in this study. Vatinoxan shortened the duration of anaesthesia.

Effects of constant rate infusions of dexmedetomidine, remifentanil and their combination on minimum alveolar concentration of sevoflurane in dogs

OBJECTIVE

To evaluate the effects of constant rate infusions (CRIs) of dexmedetomidine and remifentanil alone and their combination on minimum alveolar concentration (MAC) of sevoflurane in dogs.

STUDY DESIGN

Randomized crossover experimental study.

ANIMALS

A total of six (three males, three females) healthy, adult neutered Beagle dogs weighing 12.6 ± 1.4 kg.

METHODS

Anesthesia was induced with sevoflurane in oxygen until endotracheal intubation was possible and anesthesia maintained with sevoflurane using positive-pressure ventilation. Each dog was anesthetized five times and was administered each of the following treatments: saline (1 mL kg^-1 hour^-1) or dexmedetomidine at 0.1, 0.5, 1.0 or 5.0 μg kg^-1 loading dose intravenously over 10 minutes followed by CRI at 0.1, 0.5, 1.0 or 5.0 μg kg^-1 hour^-1, respectively. Following 60 minutes of CRI, sevoflurane MAC was determined in duplicate using an electrical stimulus (50 V, 50 Hz, 10 ms). Then, CRI of successively increasing doses of remifentanil (0.15, 0.60 and 2.40 μg kg^-1 minute^-1) was added to each treatment. MAC was also determined after 30 minutes equilibration at each remifentanil dose. Isobolographic analysis determined interaction from the predicted doses required for a 50% MAC reduction (ED₅₀) with remifentanil, dexmedetomidine and remifentanil combined with dexmedetomidine, with the exception of dexmedetomidine 5.0 μg kg^-1 hour^-1, obtained using log-linear regression analysis.

RESULTS

The sevoflurane MAC decreased dose-dependently with increasing infusion rates of dexmedetomidine and remifentanil. Remifentanil ED₅₀ values were lower when combined with dexmedetomidine than those obtained during saline-remifentanil. Synergistic interactions between dexmedetomidine and remifentanil for MAC reduction occurred with dexmedetomidine at 0.5 and 1.0 μg kg^-1 hour^-1.

CONCLUSIONS AND CLINICAL RELEVANCE

Combined CRIs of dexmedetomidine and remifentanil synergistically resulted in sevoflurane MAC reduction. The combination of dexmedetomidine and remifentanil effectively reduced the requirement of sevoflurane during anesthesia in dogs.

Alternatives to Opioid Analgesia in Small Animal Anesthesia: Alpha-2 Agonists

Alpha-2 agonists have potent analgesic effects, in addition to their sedative actions. Alpha-2 agonists provide analgesia through any of several routes of administration, including parenteral, oral, epidural or intrathecal and intraarticular, because of spinal and supraspinal actions. Systemic doses are short acting, whereas local administration at the site of action result in longer analgesic effects. The potent cardiovascular and respiratory effects of alpha-2 agonists should be considered when used as analgesics.

Concentrations of medetomidine enantiomers and vatinoxan, an α2-adrenoceptor antagonist, in plasma and central nervous tissue after intravenous coadministration in dogs

OBJECTIVE

To quantify the peripheral selectivity of vatinoxan (L-659,066, MK-467) in dogs by comparing the concentrations of vatinoxan, dexmedetomidine and levomedetomidine in plasma and central nervous system (CNS) tissue after intravenous (IV) coadministration of vatinoxan and medetomidine.

STUDY DESIGN

Experimental, observational study.

ANIMALS

A group of six healthy, purpose-bred Beagle dogs (four females and two males) aged 6.5 ± 0.1 years (mean ± standard deviation).

METHODS

All dogs were administered a combination of medetomidine (40 μg kg^-1) and vatinoxan (800 μg kg^-1) as IV bolus. After 20 minutes, the dogs were euthanized with an IV overdose of pentobarbital (140 mg kg^-1) and both venous plasma and CNS tissues (brain, cervical and lumbar spinal cord) were harvested. Concentrations of dexmedetomidine, levomedetomidine and vatinoxan in all samples were quantified by liquid chromatography-tandem mass spectrometry and data were analyzed with nonparametric tests with post hoc corrections where appropriate.

RESULTS

All dogs became deeply sedated after the treatment. The CNS-to-plasma ratio of vatinoxan concentration was approximately 1:50, whereas the concentrations of dexmedetomidine and levomedetomidine in the CNS were three- to seven-fold of those in plasma.

CONCLUSIONS AND CLINICAL RELEVANCE

With the doses studied, these results confirm the peripheral selectivity of vatinoxan in dogs, when coadministered IV with medetomidine. Thus, it is likely that vatinoxan preferentially antagonizes α₂-adrenoceptors outside the CNS.

Effects of dexmedetomidine, with or without vatinoxan (MK-467), on minimum alveolar concentration of isoflurane in cats

OBJECTIVE

To characterize the effects of dexmedetomidine, with or without vatinoxan, on the minimum alveolar concentration of isoflurane (MACISO) in cats.

STUDY DESIGN

Randomized crossover experimental study.

ANIMALS

A group of six adult healthy male neutered cats.

METHODS

Cats were anesthetized with isoflurane in oxygen and instrumented. Dexmedetomidine was administered using a target-controlled infusion system to achieve 10 target plasma concentrations ranging from 0 to 40 ng mL-1. Additionally, vatinoxan or an equivalent volume of saline was administered using a target-controlled infusion system to achieve a target plasma concentration of 4 μg mL-1. Pulse rate (PR), respiratory rate, systolic arterial pressure (SAP), hemoglobin oxygen saturation, body temperature, end-tidal partial pressure of carbon dioxide and drug concentrations were measured. MACISO was determined at each target plasma dexmedetomidine concentration using the bracketing method and the tail clamp technique. Pharmacodynamic models were fitted to the plasma dexmedetomidine concentration-MACISO. Pharmacodynamic parameters were tested for equivalence, and if rejected, for difference.

RESULTS

Dexmedetomidine alone decreased MACISO in a plasma concentration-dependent manner. Maximum reduction was 77 ± 4%; the dexmedetomidine concentration producing 50% of the maximum decrease (IC50) was 0.77 ng mL-1. Vatinoxan increased MACISO in the absence of dexmedetomidine, decreased the potency of dexmedetomidine for its MACISO-reducing effect (IC50 = 12 ng mL-1) and lessened the maximum MACISO reduction (60 ± 14%). PR decreased less and SAP increased less when dexmedetomidine was administered with vatinoxan compared with saline.

CONCLUSION AND CLINICAL RELEVANCE

Vatinoxan altered the effect of dexmedetomidine on MACISO. A high plasma dexmedetomidine concentration in the presence of vatinoxan resulted in a large decrease in MACISO, with attenuation of dexmedetomidine-induced cardiovascular effects. The vatinoxan-dexmedetomidine combination may provide clinical benefits in isoflurane-anesthetized cats.

Effect of α2-adrenoceptor antagonism on the minimum alveolar concentration of isoflurane in cats

OBJECTIVE

To characterize the effect of α₂-adrenoceptor antagonism on the minimum alveolar concentration of isoflurane (MAC_ISO) in cats.

STUDY DESIGN

Prospective experimental study.

ANIMALS

A group of five healthy adult male neutered cats.

METHODS

Cats were anesthetized with isoflurane in oxygen and instrumented. MAC_ISO was determined in duplicate in five cats, before and during administration of atipamezole (250 μg kg^-1 followed by 250 μg kg^-1 hour^-1) using the bracketing technique and tail clamping. Estimates of MAC_ISO obtained before and during administration of atipamezole were compared using a two-tailed paired t test.

RESULTS

MAC_ISO during atipamezole administration (mean ± standard deviation 2.73% ± 0.07%) was significantly larger than before atipamezole administration (1.95% ± 0.13%; p < 0.0001).

CONCLUSION AND CLINICAL RELEVANCE

The role of α₂-adrenoceptors in inhaled anesthetic-induced immobility may be larger than previously thought. Antagonism of an α₂-adrenoceptor agonist during inhalation anesthesia may result in an increase in MAC disproportionate to the MAC reduction induced by the agonist.

Cardiac troponin I in dogs anaesthetized with propofol and sevoflurane: the influence of medetomidine premedication and inspired oxygen fraction

OBJECTIVE

To investigate changes in serum cardiac troponin I (cTnI) concentrations in dogs in which medetomidine was used for sedation or for premedication prior to anaesthesia with propofol and sevoflurane.

STUDY DESIGN

Prospective clinical study.

ANIMALS

A total of 66 client-owned dogs.

METHODS

The dogs were sedated with medetomidine (0.04 mg kg^-1) intravenously (IV) (group M; n = 20) and left to breath room air or anaesthetized with propofol (6.5 ± 0.76 mg kg^-1 IV) and sevoflurane (4.5% vaporizer setting) in oxygen (group P + S; n = 20) or with medetomidine (0.04 mg kg^-1 IV), propofol (1.92 ± 0.63 mg kg^-1) and sevoflurane (3% vaporizer setting) in oxygen (group M + P + S; n = 26), respectively. After 35 minutes, medetomidine was antagonized with atipamezole (0.1 mg kg^-1 intramuscularly). Blood samples for serum cTnI determination were taken before sedation or anaesthesia, 6 and 12 hours and 4 days thereafter. Serum cTnI concentrations were measured with the Architect STAT Troponin-I assay.

RESULTS

Before sedation or anaesthesia, cTnI concentrations were above the detection limit in 22 out of 66 (33%) of dogs. Compared to basal values, cTnI concentrations significantly increased at 6 and 12 hours in all groups and at day 4 in group M. There were no differences in cTnI concentration between groups at baseline, at 6 hours and at 4 days. At 12 hours, cTnI concentrations were significantly higher in groups M and P + S, respectively, compared to group M + P + S.

CONCLUSIONS AND CLINICAL RELEVANCE

Oxygenation during anaesthesia and reduction of propofol and sevoflurane dose due to the sparing effects of medetomidine might have played a role in alleviation of myocardial hypoxic injury as indicated by the less severe and short-lived increase of cTnI in the M + P + S group.