Dexmedetomidine or medetomidine premedication before propofol-desflurane anaesthesia in dogs

Effect of Butorphanol-Medetomidine and Butorphanol-Dexmedetomidine on Echocardiographic Parameters during Propofol Anaesthesia in Dogs

This study compared the effects of butorphanol-medetomidine and butorphanol-dexmedetomidine combinations on echocardiographic parameters during propofol anaesthesia in dogs. The dogs were randomly divided into two groups. In the butorphanol-medetomidine (BM) group, butorphanol (0.2 mg/kg) and medetomidine (15 μg/kg) were intravenously administered; in the butorphanol-dexmedetomidine (BD) group, butorphanol (0.2 mg/kg) and dexmedetomidine (7.5 μg/kg) was used. Anaesthesia was induced with propofol and maintained with a constant-rate infusion of propofol (0.2 mg/kg/min). The echocardiographic parameters were assessed in conscious dogs (T0). Echocardiography was conducted again at 10 min post premedication (T1), followed by assessments at 30 (T2), 60 (T3), and 90 (T4) mins. The dogs were subjected to diagnostic procedures (radiography, computed tomography) under anaesthesia. A significant reduction in heart rate and cardiac output was noted in both groups at T1. There was no significant difference in the stroke volume between the BM and BD groups. The application of butorphanol-dexmedetomidine caused a significant increase in the left ventricular internal diameter in diastole and the diameter of the left atrium compared to that caused by butorphanol-medetomidine. This study documented that butorphanol-medetomidine and butorphanol-dexmedetomidine combinations caused similar reductions in heart rate and cardiac output in both groups. 'New´ valvular regurgitation occurred following their administration.

Haemodynamic effects of labetalol in isoflurane-anaesthetized dogs that received dexmedetomidine: A randomized clinical trial

OBJECTIVE

To test whether labetalol improved cardiovascular function in anaesthetized dogs injected with dexmedetomidine.

STUDY DESIGN

Prospective, randomized, blinded, clinical trial.

ANIMALS

A group of 20 healthy client-owned dogs undergoing ovariohysterectomy.

METHODS

Each dog received dexmedetomidine (5 μg kg-1) and methadone (0.2 mg kg-1) intramuscularly. General anaesthesia was induced with propofol and maintained with isoflurane in oxygen. All dogs were mechanically ventilated, and epidural anaesthesia with lidocaine was performed. Standard anaesthetic monitoring, invasive blood pressure, oesophageal Doppler and near-infrared tissue perfusion/oxygenation were applied. Peak velocity (PV), mean acceleration and stroke distance (SD) from the oesophageal Doppler were recorded. Arterial elastance (Ea) was calculated. Tissue oxygenation (rStO2) was also recorded. Prior to surgery, animals received either 0.1 mg kg-1 of labetalol intravenously (IV) over 60 seconds or the equivalent volume of saline. Data were recorded for 20 minutes. Age, weight and propofol dose were compared with a Wilcoxon rank-sum test. The effects of time, treatment and their interaction with haemodynamic and perfusion variables were analysed with mixed-effect models and Tukey's post hoc tests.

RESULTS

Significant effects of the interaction between treatment and time were observed whereby heart rate (HR) was higher in dogs given labetalol (p = 0.01), whereas arterial blood pressure and Ea were lower (p < 0.01). Similarly, PV, SD and rStO2 were higher in the labetalol group, and significant effects were detected for the interaction between treatment and time (p < 0.01).

CONCLUSIONS AND CLINICAL RELEVANCE

Labetalol at a dose of 0.1 mg kg-1 IV in dogs under general anaesthesia and administered a pre-anaesthetic medication of dexmedetomidine produced mild vasodilation (reduction of Ea), resulting in an increase in HR and left ventricular outflow. Although labetalol could be an effective option to achieve haemodynamic optimization after dexmedetomidine-induced vasoconstriction, future studies are needed to assess long-term effects.

Effect of dexmedetomidine added to retrobulbar blockade with lignocaine and bupivacaine in dogs undergoing enucleation surgery

OBJECTIVE

To investigate the effect of the addition of dexmedetomidine (BLD) to retrobulbar blockade with combined lignocaine and bupivacaine on nociception.

ANIMALS

A total of 17 eyes from 15 dogs.

METHODS

Prospective, randomized, masked clinical comparison study. Dogs undergoing unilateral enucleation were randomly assigned into two groups; a retrobulbar administration of lignocaine and bupivacaine in a 1:2 volume ratio combined with either BLD or 0.9% saline (BLS). The total volume of the intraconal injection was calculated at 0.1 mL/cm cranial length. Intraoperative parameters were recorded: heart rate (HR), respiratory rate (RR), end-tidal CO2 (EtCO2 ) arterial blood pressure (BP), and inspired isoflurane concentration (ISOinsp). Pain scores, heart rate and RR were recorded postoperatively.

RESULTS

Dogs receiving BLD (n = 8) had significantly lower intraoperative RR (p = 0.007), and significantly lower ISOinsp (p = 0.037) than dogs in the BLS group (n = 9). Postoperatively heart rate was significantly lower in the BLD group at 1 min (p = 0.025) and 1 h (p = 0.022). There were no other significant differences in intraoperative or postoperative parameters, or in postoperative pain scores (p = 0.354). Dogs receiving BLD had a higher rate of anesthetic events of bradycardia and hypertension (p = 0.027). Analgesic rescue was not needed in either group.

CONCLUSIONS

The addition of BLD to retrobulbar anesthesia did not result in a detectable difference in pain scores relative to blockade with lignocaine and bupivacaine alone. Dogs receiving retrobulbar BLD had a significantly lower intraoperative RR and isoflurane requirement and an increased incidence of intraoperative bradycardia and hypertension.

Sedation Quality and Cardiorespiratory, Echocardiographic, Radiographic and Electrocardiographic Effects of Intramuscular Alfaxalone and Butorphanol in Spanish Greyhound Dogs

The quality of sedation and changes in cardiorespiratory variables after the intramuscular administration of alfaxalone and butorphanol in Spanish greyhound dogs were evaluated. Twenty-one adult dogs were included. The dogs received alfaxalone (2 mg/kg) and butorphanol (0.2 mg/kg) intramuscularly. Sedation scoring, cardiorespiratory parameters (including blood gas analysis), echocardiography, thoracic radiography and electrocardiography were performed before sedation and 30 min after drug administration. Moderate sedation was observed, and side effects, such as tremors, nystagmus and auditory hyperesthesia, were noticed. Statistically significant changes in heart rate, invasive blood pressure, pH, arterial saturation of O2 and partial pressure of O2 and CO2 were found. Echocardiographic variables, including end-diastolic volume, left ventricular diameter in diastole, aortic and pulmonic flow, diastolic transmitral flow and left atrial/aortic ratio, and electrocardiography parameters, including PQ interval and QT interval, showed statistically significant changes. In conclusion, the intramuscular administration of alfaxalone and butorphanol to healthy dogs produced moderate sedation with mild cardiorespiratory, echocardiographic and electrocardiographic changes, without alterations in cardiac size on radiographic images.

Sedative effects and changes in cardiac rhythm with intravenous premedication of medetomidine, butorphanol and ketamine in dogs

OBJECTIVE

To determine the sedative effects and characteristics of cardiac rhythm with intravenous (IV) premedication of medetomidine, butorphanol and ketamine in dogs.

STUDY DESIGN

Prospective, blinded, randomized clinical trial.

ANIMALS

A total of 116 client-owned healthy dogs undergoing elective surgery.

METHODS

Dogs were randomly allocated one of four groups: group M, medetomidine 5 μg kg^-1; group B, butorphanol 0.2 mg kg^-1; group MB, medetomidine 5 μg kg^-1 and butorphanol 0.2 mg kg^-1; or group MBK, medetomidine 5 μg kg^-1, butorphanol 0.2 mg kg^-1 and ketamine 1 mg kg^-1 IV. Sedation was assessed using a numerical descriptive scale. Heart rate (HR) and rhythm were monitored; propofol dose (mg kg^-1 IV) to allow orotracheal intubation was documented. Data were analysed using anova, accounting for multiple testing with the Tukey honest significant difference test.

RESULTS

Sedation scores varied significantly between all groups at all time points, except between groups MB and MBK at four time points. HR decreased in all groups: most in groups M and MB, least in group B. HR was initially higher in group MBK than in groups M and MB. Arrhythmias occurred in all groups: group B showed second-degree atrioventricular blocks occasionally, all other groups showed additionally ventricular escape complexes and bundle branch blocks. Dose of propofol required for orotracheal intubation was significantly higher in group B (5.0 ± 2.0 mg kg^-1) than in group M (2.6 ± 0.6 mg kg^-1). Although no difference could be demonstrated between groups MB (1.4 ± 0.6 mg kg^-1) and MBK (0.9 ± 0.8 mg kg^-1), both groups required significantly less propofol than group M.

CONCLUSION AND CLINICAL RELEVANCE

Medetomidine-based premedication protocols led to various bradyarrhythmias. Addition of subanaesthetic doses of ketamine to medetomidine-based protocols resulted in higher HRs, fewer bradyarrhythmias and fewer animals that required propofol for intubation without causing side effects in healthy dogs.

Dexmedetomidine decreases the 50% effective dose (ED50) of intravenous propofol required to prevent tracheal intubation response in Beagles

OBJECTIVE

To determine the 50% effective dose (ED50) of intravenous propofol required for successfully preventing tracheal intubation response in Beagles co-induced with dexmedetomidine.

ANIMALS

36 adult male Beagles.

PROCEDURES

The dogs were randomly assigned to either group D1, group D2, or group C (received 1 µg/kg, 2 µg/kg dexmedetomidine intravenously, or the same amount of normal saline as dexmedetomidine, 10 mL). The first dog in each group received 6 mg/kg of propofol for induction. The pump speed of propofol was 600 mL/h. The dosage varied with increments or decrements of 0.5 mg/kg based on the Dixon up-and-down method. The duration of eye-opening after propofol administration was recorded. Changes in heart rate (HR) and respiratory rate (RR) were recorded at 5 timepoints: after entering the operation room and prior to propofol administration (T1), 1 and 3 min after propofol administration (T2 and T3), 3 and 5 min after intubation (T4 and T5).

RESULTS

The required ED50 of propofol that prevented tracheal intubation response in D1, D2, and C groups were 6.4 mg/kg (95% CI, 6.1 to 6.7 mg/kg), 5.8 mg/kg (95% CI, 5.67 to 6 mg/kg), and 8.3 mg/kg (95% CI, 8 to 8.5 mg/kg), respectively. The recovery time of group D2 was significantly longer than that of groups D1 and C (P < .05). The differences in HR among the 3 groups were significant from T2 up to T5 timepoint (P < .05). The differences in RR among the 3 groups were significant at T2 and T3 timepoints (P < .05).

CLINICAL RELEVANCE

Dexmedetomidine pre-injection reduces the amount of propofol required for endotracheal intubation response in Beagles, thereby reducing the respiratory inhibition induced by propofol.

Enantiospecific pharmacokinetics of intravenous dexmedetomidine in beagles

The goal of this study was to investigate the pharmacokinetic (PK) behaviour of dexmedetomidine in dogs administered as a pure enantiomer versus as part of a racemic mixture. Eight unmedicated intact purpose‐bread beagles were included. Two intravenous treatments of either medetomidine or dexmedetomidine were administered at 10‐ to 14‐day intervals. Atipamezole or saline solution was administered intramuscularly 45 min later. Venous blood samples were collected into EDTA collection tubes, and the quantification of dexmedetomidine and levomedetomidine was performed by chiral LC–MS/MS. All dogs appeared sedated after each treatment without complication. Plasma concentrations of levomedetomidine were measured only in the racemic group and were 51.4% (51.4%–56.1%) lower than dexmedetomidine. Non‐compartmental analysis (NCA) was performed for both drugs, while dexmedetomidine data were further described using a population pharmacokinetic approach. A standard two‐compartment mammillary model with linear elimination with combined additive and multiplicative error model for residual unexplained variability was established for dexmedetomidine. An exponential model was finally retained to describe inter‐individual variability on parameters of clearance (Cl₁) and central and peripheral volumes of distribution (V₁, V₂). No effect of occurrence, levomedetomidine or atipamezole could be observed on dexmedetomidine PK parameters. Dexmedetomidine did not undergo significantly different PK when administered alone or as part of the racemic mixture in otherwise unmedicated dogs.

Effects of Sedation with Medetomidine and Dexmedetomidine on Doppler Measurements of Ovarian Artery Blood Flow in Bitches

The aim was to evaluate if medetomidine and dexmedetomidine affected arterial ovarian blood flow in dogs. The dogs were randomly assigned to two different groups. In Group 1, medetomidine (10 µg/kg) was administered intramuscularly and, in Group 2, dexmedetomidine (5 µg/kg) was used. After a preliminary exam, arterial blood pressure (BP) was measured and a duplex Doppler ultrasonographic examination of both ovarian arteries was performed. Twenty minutes after the administration of medetomidine or dexmedetomidine, BP and ovarian Doppler ultrasonography were repeated. High quality tracings of ovarian artery flow velocity were obtained in all dogs and Doppler parameters: Peak Systolic Velocity (PSV), End Diastolic Velocity (EDV) and Resistive Index (RI) were measured before and after drug administration in the left (LO) and right (RO) ovaries. PSV and EDV values decreased significantly after drug administration (p < 0.05) compared to the non-sedated values, but no differences were found between the LO and RO (p > 0.05). The RI was not affected by drugs administration in neither of the groups studied (p > 0.05). In conclusion, the administration of medetomidine or dexmedetomidine causes a decrease in blood flow velocity in the ovarian artery and may be a good choice to avoid excessive bleeding prior surgeries in which ovariectomy.

Use of intravenous lidocaine to treat dexmedetomidine-induced bradycardia in sedated and anesthetized dogs

OBJECTIVE

To assess cardiopulmonary function in sedated and anesthetized dogs administered intravenous (IV) dexmedetomidine and subsequently administered IV lidocaine to treat dexmedetomidine-induced bradycardia.

STUDY DESIGN

Prospective, randomized, crossover experimental trial.

ANIMALS

A total of six purpose-bred female Beagle dogs, weighing 9.1 ± 0.6 kg (mean ± standard deviation).

METHODS

Dogs were randomly assigned to one of three treatments: dexmedetomidine (10 μg kg^-1 IV) administered to conscious (treatments SED1 and SED2) or isoflurane-anesthetized dogs (end-tidal isoflurane concentration 1.19 ± 0.04%; treatment ISO). After 30 minutes, a lidocaine bolus (2 mg kg^-1) IV was administered in treatments SED1 and ISO, followed 20 minutes later by a second bolus (2 mg kg^-1) and a 30 minute lidocaine constant rate infusion (L-CRI) at 50 (SED1) or 100 μg kg^-1 minute^-1 (ISO). In SED2, lidocaine bolus and L-CRI (50 μg kg^-1 minute^-1) were administered 5 minutes after dexmedetomidine. Cardiopulmonary measurements were obtained after dexmedetomidine, after lidocaine bolus, during L-CRI and 30 minutes after discontinuing L-CRI. A mixed linear model was used for comparisons within treatments (p < 0.05).

RESULTS

When administered after a bolus of dexmedetomidine, lidocaine bolus and L-CRI significantly increased heart rate and cardiac index, decreased mean blood pressure, systemic vascular resistance index and oxygen extraction ratio, and did not affect stroke volume index in all treatments.

CONCLUSION AND CLINICAL RELEVANCE

Lidocaine was an effective treatment for dexmedetomidine-induced bradycardia in healthy research dogs.

Effect of Medetomidine, Dexmedetomidine, and Their Reversal with Atipamezole on the Nociceptive Withdrawal Reflex in Beagles

The objectives were: (1) to compare the antinociceptive activity of dexmedetomidine and medetomidine, and (2) to investigate its modulation by atipamezole. This prospective, randomized, blinded experimental trial was carried out on eight beagles. During the first session, dogs received either medetomidine (MED) (0.02 mg kg-1 intravenously (IV)] or dexmedetomidine (DEX) [0.01 mg kg-1 IV), followed by either atipamezole (ATI) (0.1 mg kg-1) or an equivalent volume of saline (SAL) administered intramuscularly 45 min later. The opposite treatments were administered in a second session 10-14 days later. The nociceptive withdrawal reflex (NWR) threshold was determined using a continuous tracking approach. Sedation was scored (0 to 21) every 10 min. Both drugs (MED and DEX) increased the NWR thresholds significantly up to 5.0 (3.7-5.9) and 4.4 (3.9-4.8) times the baseline (p = 0.547), at seven (3-11) and six (4-9) minutes (p = 0.938), respectively. Sedation scores were not different between MED and DEX during the first 45 min (15 (12-17), p = 0.67). Atipamezole antagonized sedation within 25 (15-25) minutes (p = 0.008) and antinociception within five (3-6) minutes (p = 0.008). Following atipamezole, additional analgesics may be needed to maintain pain relief.

Comparison of sedation in dogs: methadone or butorphanol in combination with dexmedetomidine intravenously

OBJECTIVE

Opioids can be combined with alpha-2-adrenoreceptor agonists to sedate dogs for radiography. The study investigated the sedative effects of methadone or butorphanol in combination with dexmedetomidine in dogs undergoing stifle radiography.

STUDY DESIGN

Prospective, blinded, randomized, clinical trial.

ANIMALS

A total of 52 healthy dogs requiring sedation for stifle radiography were enrolled.

METHODS

Dogs were assessed for body condition [body condition score (BCS)], temperament and pain using the short-form composite measure pain scale (CMPS-SF). Dogs were randomized to be administered methadone 0.2 mg kg^-1 (group M) or butorphanol 0.2 mg kg^-1 (group B) in combination with dexmedetomidine 2 μg kg^-1 intravenously (IV). Sedation was assessed using a numerical descriptive score, from 0 (no sedation) to 11 (greatest sedation), before administration and at 5, 10, 15 and 20 minutes by one blinded assessor. Onset signs of sedation, pulse rate and respiratory rates were recorded. Positioning for radiography was attempted at 5 minutes. If positioning was not possible at 10 minutes, dexmedetomidine 2 μg kg^-1 was administered IV, with the dog recorded as failed sedation and withdrawn from further analysis. Following normality testing, data were assessed using Student t test, Mann-Whitney test, two-way analysis of variance and Fisher's exact test for failed sedations. Results are reported as mean ± standard deviation. Statistical significance was set at p < 0.05.

RESULTS

Groups were similar for sex, age, weight, BCS, temperament and CMPS-SF. The onset of sedation was faster in group B than in group M (p = 0.048). Sedation scores were higher in group B at 10 minutes compared to group M (p = 0.003). Failed sedation occurred in 12 dogs in group M and two in group B (p = 0.002). Pulse rates were lower in group B at 5 and 10 minutes (p = 0.002).

CONCLUSION AND CLINICAL RELEVANCE

IV butorphanol provides more effective sedation at 10 minutes than methadone, in combination with dexmedetomidine.

Effect of dexmedetomidine on the minimum infusion rate of propofol preventing movement in dogs

OBJECTIVE

To determine the effect of dexmedetomidine on induction dose and minimum infusion rate of propofol preventing movement (MIR_NM).

STUDY DESIGN

Randomized crossover, unmasked, experimental design.

ANIMALS

Three male and three female healthy Beagle dogs weighing 10.2 ± 2.8 kg.

METHODS

Dogs were studied on three occasions at weekly intervals. Premedications were 0.9% saline (treatment P) or dexmedetomidine (1 μg kg^-1, treatment PLD; 2 μg kg^-1, treatment PHD) intravenously. Anesthesia was induced with propofol (2 mg kg^-1 and then 1 mg kg^-1 every 15 seconds) until intubation. Anesthesia was maintained for 90 minutes in P with propofol (0.5 mg kg^-1 minute^-1) and saline, in PLD with propofol (0.35 mg kg^-1 minute^-1) and dexmedetomidine (1 μg kg^-1 hour^-1), and in PHD with propofol (0.3 mg kg^-1 minute^-1) and dexmedetomidine (2 μg kg^-1 hour^-1). The stimulus (50 V, 50 Hz, 10 ms) was applied to the antebrachium, and propofol infusion was increased or decreased by 0.025 mg kg^-1 minute^-1 based on a positive or negative response, respectively. Data were analyzed using a mixed-model anova and presented as mean ± standard error.

RESULTS

Propofol induction doses were 8.68 ± 0.57 (P), 6.13 ± 0.67 (PLD) and 4.78 ± 0.39 (PHD) mg kg^-1 and differed among treatments (p < 0.05). Propofol MIR_NM values were 0.68 ± 0.13, 0.49 ± 0.16 and 0.26 ± 0.05 mg kg^-1 minute^-1 for P, PLD and PHD, respectively. Propofol MIR_NM decreased 59% in PHD (p < 0.05). Plasma propofol concentrations were 14.04 ± 2.30 (P), 11.30 ± 4.30 (PLD) and 7.96 ± 0.72 (PHD) μg mL^-1 and dexmedetomidine concentrations were 0.68 ± 0.12 (PLD) and 0.89 ± 0.08 (PHD) ng mL^-1 at MIR_NM determination.

CONCLUSIONS AND CLINICAL RELEVANCE

Dexmedetomidine (1 and 2 μg kg^-1) decreased propofol induction dose. Dexmedetomidine (2 μg kg^-1 hour^-1) resulted in a significant decrease in propofol MIR_NM.

A comparison of cardiopulmonary effects and anaesthetic requirements of two dexmedetomidine continuous rate infusions in alfaxalone-anaesthetized Greyhounds

OBJECTIVE

To determine the effects of two dexmedetomidine continuous rate infusions on the minimum infusion rate of alfaxalone for total intravenous anaesthesia (TIVA), and subsequent haemodynamic and recovery effects in Greyhounds undergoing laparoscopic ovariohysterectomy.

STUDY DESIGN

Prospective, randomized and blinded clinical study.

ANIMALS

Twenty-four female Greyhounds.

METHODS

Dogs were premedicated with dexmedetomidine 3 μg kg^-1 and methadone 0.3 mg kg^-1 intramuscularly. Anaesthesia was induced with IV alfaxalone to effect and maintained with a TIVA mixture of alfaxalone in combination with two different doses of dexmedetomidine (0.5 μg kg^-1 hour^-1 or 1 μg kg^-1 hour^-1; groups DEX0.5 and DEX1, respectively). The alfaxalone starting dose rate was 0.07 mg kg^-1 minute^-1 and was adjusted (± 0.02 mg kg^-1 minute^-1) every 5 minutes to maintain a suitable depth of anaesthesia. A rescue alfaxalone bolus (0.5 mg kg^-1 IV) was administered if dogs moved or swallowed. The number of rescue boluses was recorded. Heart rate, arterial blood pressure and arterial blood gas were monitored. Qualities of sedation, induction and recovery were scored. Differences between groups were tested for statistical significance using a Student's t test or Mann-Whitney U test as appropriate.

RESULTS

There were no differences between groups in sedation, induction and recovery quality, the median (range) induction dose of alfaxalone [DEX0.5: 2.2 (1.9-2.5) mg kg^-1; DEX1: 1.8 (1.2-2.9) mg kg^-1], total dose of alfaxalone rescue boluses [DEX0.5: 21.0 (12.5-38.8) mg; DEX1: 22.5 (15.5-30.6) mg] or rate of alfaxalone (DEX0.5: 0.12±0.04 mg kg^-1 minute^-1; DEX1: 0.12±0.03 mg kg^-1 minute^-1).

CONCLUSIONS AND CLINICAL RELEVANCE

Co-administration of dexmedetomidine 1 μg kg^-1 hour^-1 failed to reduce the dose rate of alfaxalone compared with dexmedetomidine 0.5 μg kg^-1 hour^-1 in Greyhounds undergoing laparoscopic ovariohysterectomy. The authors recommend an alfaxalone starting dose rate of 0.1 mg kg^-1 minute^-1. Recovery quality was good in the majority of dogs.

Cardiorespiratory and anaesthetic effects of two continuous rate infusions of dexmedetomidine in alfaxalone anaesthetized dogs

Six Beagles were used in this prospective randomised crossover experimental study. Dexmedetomidine was administered at 0, 1 or 2 μg/kg IV for group C, LDA and HDA, respectively. Animals were induced and maintained with alfaxalone at 0.07 mg/kg/min with a CRI dexmedetomidine dose of 0, 0.5 or 1 μg/kg/h for group C, LDA and HDA, respectively. Cardiorespiratory variables, arterial blood gases and depth of anaesthesia were recorded. The recovery times and quality of recovery were scored. Group HDA produced a greater increase in the depth of anaesthesia than LDA. However, with both protocols, CI was halved compared to normal values in dogs. The use of oxygen before and during the anaesthetic maintenance is advisable, mainly if dexmedetomidine is going to be use as a pre-medicant and maintenance agent. The quality of recovery was better in groups receiving dexmedetomidine, without causing an increase in recovery time.

Effects of chemical restraint on electroretinograms recorded sequentially in awake, sedated, and anesthetized dogs

OBJECTIVE

To quantitatively and qualitatively compare electroretinography (ERG) recordings in awake, sedated, and anesthetized dogs.

ANIMALS

Six 6-month-old Beagles.

PROCEDURES

A brief ERG protocol for dogs was used. Following 1-minute and subsequent 5-minute dark adaptation, mixed rod-cone responses were recorded bilaterally with a handheld multispecies ERG device with dogs in each of 3 states of consciousness: awake, sedated (dexmedetomidine and butorphanol), and anesthetized (atropine and hydromorphone, followed by propofol and midazolam and anesthetic maintenance with isoflurane). Low- and high-frequency noise levels were quantified via Fourier analysis, and the effect of consciousness state on signal amplitude, implicit time, and noise was analyzed via repeated-measures ANOVA. In addition, 13 veterinary ophthalmologists who were unaware of the dogs' consciousness states subjectively graded the ERG recording quality, and scores for each tracing were compared.

RESULTS

ERG amplitudes were highest in awake dogs and lowest in anesthetized dogs. Implicit times were shortest in awake dogs and longest in anesthetized dogs. Differences in b-wave amplitudes and a-wave implicit times were significant. Neither low- nor high-frequency noise levels differed significantly among consciousness states. Furthermore, no significant differences were identified among observers' scores assigned to ERG tracings.

CONCLUSIONS AND CLINICAL RELEVANCE

Anesthesia and sedation resulted in significant attenuation and delay of ERG responses in dogs. Chemical restraint of dogs had no consistently significant effect on low- or high-frequency noise levels or on observer perception of signal quality.

Physiologic and serum biochemistry values in free-ranging Hoffmann's two-toed (Choloepus hoffmanni) and brown-throated three-toed (Bradypus variegatus) sloths immobilized using dexmedetomidine and ketamine

Dexmedetomidine, a highly selective alpha-2 adrenergic agonist and dextrorotary enantiomer of medetomidine, was combined with ketamine and used to immobilize 14 free-ranging Choloepus hoffmanni (Hoffmann's two-toed sloths) and 11 Bradypus variegatus (brown-throated three-toed sloths) in Upala, Costa Rica. Following intramuscular injection of ketamine (2.1 mg/kg) and dexmedetomidine (11 microg/kg), heart rate, respiratory rate, and indirect systolic blood pressure were measured every 5 min for a total of 25 min. An iStat (CG8+) was used to evaluate serum biochemical and hematologic values during anesthesia. After 30 min of anesthesia, atipamezole (0.13 mg/kg) was administered intramuscularly, which resulted in rapid and smooth recoveries. Mean heart rate and respiratory rate remained unchanged in both C. hoffmanni and B. variegatus over time. Progressive decreases in mean indirect systolic blood pressure were documented in both species. Results of this study suggest a combination of dexmedetomidne and ketamine is a safe and effective anesthetic protocol for use in free-ranging C. hoffmanni and B. variegatus. Similar to other alpha-2 adrenergic agonist-based immobilization protocols, close monitoring of cardiovascular and respiratory parameters are recommended. This study also provides serum biochemical and hematologic data in free-ranging C. hoffmanni and B. variegatus.

A comparison of medetomidine and its active enantiomer dexmedetomidine when administered with ketamine in mice

Background

Medetomidine-ketamine (MK) and dexmedetomidine-ketamine (DK) are widely used to provide general anaesthesia in laboratory animals, but have not been compared directly in many of these species, including rodents. This study aimed to compare the onset and depth of anaesthesia, and changes in vital signs, after intraperitoneal (IP) or subcutaneous (SC) administration of ketamine (75 mg kg^-1) combined with medetomidine (1 mg kg^-1) or dexmedetomidine (0.5 mg kg^-1) using a randomised semi-crossover design with ≥ 48 hours between treatments in 10 male and 10 female mice. Each mouse was anaesthetised twice using the same administration route (IP or SC): once with each drug-ketamine combination. Anaesthetised mice were monitored on a heating pad without supplemental oxygen for 89 minutes; atipamezole was administered for reversal. The times that the righting reflex was lost post-injection and returned post-reversal were analysed using general linear models. Tail-pinch and pedal reflexes were examined using binomial generalized linear models. Pulse rate (PR), respiratory rate (fr), and arterial haemoglobin saturation (S_pO₂) were compared using generalized additive mixed models.

Results

There were no significant differences among treatments for the times taken for loss and return of the righting reflex, or response of the tail-pinch reflex. The pedal withdrawal reflex was abolished more frequently with MK than DK over time (P = 0.021). The response of PR and S_pO₂ were similar among treatments, but fr was significantly higher with MK than DK (P ≤ 0.0005). Markedly low S_pO₂ concentrations occurred within 5 minutes post-injection (83.8 ± 6.7%) in all treatment groups and were most severe after 89 minutes lapsed (66.7 ± 7.5%). No statistical differences were detected in regards to administration route (P ≤ 0.94).

Conclusions

This study failed to demonstrate clinical advantages of the enantiomer dexmedetomidine over medetomidine when combined with ketamine to produce general anaesthesia in mice. At the doses administered, deep surgical anaesthesia was not consistently produced with either combination; therefore, anaesthetic depth must be assessed before performing surgical procedures. Supplemental oxygen should always be provided during anaesthesia to prevent hypoxaemia.

Two doses of dexmedetomidine in combination with buprenorphine for premedication in dogs; a comparison with acepromazine and buprenorphine

OBJECTIVE

To assess as premedicants, the sedative, cardiorespiratory and propofol-sparing effects in dogs of dexmedetomidine and buprenorphine compared to acepromazine and buprenorphine.

STUDY DESIGN

Prospective, randomised, blinded clinical study.

ANIMALS

Sixty healthy dogs (ASA grades I/II). Mean (SD) body mass 28.0 ± 9.1 kg, and mean age 3.4 ± 2.3 years.

METHODS

  Dogs were allocated randomly to receive 15 μg kg(-1) buprenorphine combined with either 30 μg kg(-1) acepromazine (group 1), 62.5 μg m(-2) dexmedetomidine (group 2), or 125 μg m(-2) dexmedetomidine (group 3) intramuscularly. After 30 minutes, anaesthesia was induced using a propofol target controlled infusion. Heart rate, respiratory rate, and oscillometric arterial blood pressure were recorded prior to induction, at endotracheal intubation and at 3 and 5 minutes post-intubation. Induction quality and pre-induction sedation were scored on 4 point scales. Propofol target required for endotracheal intubation was recorded. Data were analysed using Chi-squared tests, Kruskal-Wallis, one way and general linear model ANOVA (p<0.05).

RESULTS

Age was significantly lower in group 1 (1.0 (1.0-3.8) years) than group 2 (5.0 (2.0-7.0) years), (median, (IQR)). There were no significant differences in sedation or quality of induction between groups. After premedication, heart rate was significantly lower and arterial blood pressures higher in groups 2 and 3 than group 1, but there was no significant difference between groups 2 and 3. Propofol targets were significantly lower in group 3 (1.5 (1.0-2.5) μg mL(-1) ) than group 1 (2.5 (2.0-3.0) μg mL(-1) ); no significant differences existed between group 2 (2.0 (1.5-2.5) μg mL(-1) ) and the other groups (median, (interquartile range)).

CONCLUSIONS AND CLINICAL RELEVANCE

When administered with buprenorphine, at these doses, dexmedetomidine had no advantages in terms of sedation and induction quality over acepromazine. Both doses of dexmedetomidine produced characteristic cardiovascular and respiratory effects of a similar magnitude.

Anestesia epidural com associação medetomidina e lidocaína, em gatos pré-medicados com acepromazina e midazolam

Avaliaram-se os efeitos anestésicos promovidos pela associação medetomidina e lidocaína por via epidural, em gatos pré-tratados com acepromazina e midazolam. Foram utilizados 10 gatos adultos, machos e fêmeas, hígidos e com média de peso de 2,5±0,6kg, distribuídos em dois grupos (GM e GL) de igual número (n=5). Administraram-se, como medicação pré-anestésica, acepromazina, 0,2mg/kg, e midazolam, 0,5mg/kg, via intramuscular, e 20 minutos depois, nos animais do GM, por via epidural, lidocaína, 4,4mg/kg, associada à medetomidina, 0,02mg/kg. Os gatos do GL receberam lidocaína, 4,4mg/kg, associada à solução de NaCl a 0,9%. As avaliações ocorreram antes da pré-anestesia (MPA), 20 minutos após a MPA e antes da anestesia epidural, e aos 10, 20, 30 e 40 minutos após a anestesia epidural, respectivamente, T-20, T0, T10, T20, T30 e T40. Foram avaliados: frequência cardíaca (FC) e respiratória (FR), temperatura do corpo, saturação de oxiemoglobina, analgesia, miorrelaxamento e período de recuperação. No GM, a FC diminuiu em T20, T30 e T40 em relação ao T-20 e T10 e foi mais baixa que a FC do GL em T20, T30 e T40, respectivamente, 86, 91 e 88 bat/min e 194, 205 e 177 bat/min. A FR variou entre o T-20 e os outros momentos de avaliação nos animais do GL. Nas variáveis eletrocardiográficas, houve diferenças entre T20, T30 e T40 e T-20 e T0, valores de 235, 238 e 240ms e 156 e 161ms, respectivamente, somente no GM. Este grupo diferiu do GL nas avaliações em T20, T30 e T40, valores de 147, 132 e 150ms para os gatos do GL. Oitenta por cento dos gatos tiveram analgesia intensa, e em todos os animais ocorreu relaxamento da mandíbula e da língua. O tempo de recuperação foi de 40 e 15min no GM e no GL, respectivamente. Concluiu-se que a associação lidocaína com medetomidina promoveu plano anestésico estável com grau de anestesia e recuperação anestésica de boa qualidade.

Metabolic stability and determination of cytochrome P450 isoenzymes' contribution to the metabolism of medetomidine in dog liver microsomes

Medetomidine is a potent and selective alpha2-adrenergic agonist. The activation of alpha2-adrenergic receptor mediates a variety of effects including sedation, analgesia, relief of anxiety, vasoconstriction and bradycardia. However, our main interest is the sedative effects of medetomidine when used as a premedicant prior surgery in companion animals, especially in dogs. Recently, data suggested that following intravenous infusion at six dosing regiments non-linear pharmacokinetics was observed. Major causes of non-linear pharmacokinetics are the elimination of the drug not following a simple first-order kinetics and/or the elimination half-life changing due to saturation of an enzyme system. The goal of this study was to establish the metabolic stability and determine the metabolic pathway of medetomidine in dog liver microsomes. Consequently, Michaelis-Menten parameters (V(max), K(m)), T(1/2) and CL(i) were determined. The incubations were performed in a microcentrifuge tube and containing various concentrations of medetomidine (10-5000 nM), 1 mg/mL of microsomal proteins suspended in 0.1 M phosphate buffer, pH 7.4. Microsomal suspensions were preincubated with NADPH (1 mM) for 5 min at 37 degrees C prior to fortification with medetomidine. Samples were taken at various time points for kinetic information and the initial velocity (v(i)) was determined after 10 min incubation. The reaction was stopped by the addition of an internal standard solution (100 ng/mL of dextrometorphan in acetone). Medetomidine concentrations were determined using a selective and sensitive HPLC-ESI/MS/MS method. Using non-linear regression, we determined a K(m) value of 577 nM, indicating relatively low threshold enzyme saturation consistent with previous in vivo observation. The metabolic stability was determined at a concentration of 100 nm (<<K(m)) and the observed T(1/2) was 90 min with a CL(i) of 0.008 mL/min indicating moderately low clearance in dog liver microsomes, also consistent with previous in vivo data. Moreover, results suggest that principally medetomidine is metabolized by the CYP3A with a small contribution from CYP2D and CYP2E. The participation of CYP3A is an important discovery since medetomidine is used as a premedicant in combination with fentanyl, ketamine and/or midazolam. These findings combined with a low K(m) value may indicate that medetomidine can competitively inhibit the metabolism of these drugs and consequently significantly impair metabolic clearance.

Hemodynamics and bispectral index (BIS) of dogs anesthetized with midazolam and ketamine associated with medetomidine or dexmedetomidine and submitted to ovariohysterectomy

PURPOSE: To evaluate hemodynamics and bispectral index (BIS) in bitches anesthetized with ketamine and midazolam in combination with dexmedetomidine or medetomidine and submitted to ovariohysterectomy. METHODS: Twenty bitches pretreated with levomedetomidine and buprenorphine were anesthetized with 5 mg.kg-1 ketamine and 0.2 mg.kg-1 midazolam i.v. Continuous infusion of 0.4 mg.kg-1.h-1 midazolam and 20 mg.kg-1.h-1 ketamine was initiated in combination with DEX (n=10): 20 µg.kg-1.h-1 dexmedetomidine or MED (n=10): 30 µg.kg-1.h-1 medetomidine over 30 minutes. A pharmacokinetic study provided dexmedetomidine plasma concentration, set to be 3.0 ng.mL-1. RESULTS: BIS decreased in both groups (P<0.05), but it was lower in DEX (P<0.05) as compared to MED. No differences were found in hemodynamic parameters (heart rate, systolic, diastolic and mean arterial pressure) between groups (P>0.05), but heart rate decreased in both groups, as compared to control values (P<0.05). Respiratory rate decreased (P<0.05) and expired end tidal CO2 increased progressively (P<0.05) and similarly in both groups. Anesthetic recovery period was similar between groups (P<0.05) with no adverse effects. CONCLUSION: Continuous administration of dexmedetomidine with calculated plasma concentration equal to 3 ng.mL-1 in combination with midazolam and ketamine provides suitable anesthesia for spay surgery in bitches, hemodynamic stability and calm awakening with no adverse effects.

Analgesia for the critically ill dog or cat: an update

Acute pain reliably accompanies severe illness and injury, and when sufficiently severe, it can complicate the recovery of critically ill patients. Because acute pain is closely tied to the neurologic process of nociception, pharmacologic therapy is often essential and effective. This update focuses on two methods of treatment of acute pain-local anesthetic infusion and continuous intravenous infusion of multimodal agents-that can be layered on top of standard care with other drugs.

Does pethidine affect the cardiovascular and sedative effects of dexmedetomidine in dogs?

OBJECTIVES

To investigate pethidine's effects on sedation and cardiovascular variables in dogs premedicated with dexmedetomidine.

METHODS

Sixty American Society of Anesthesiologists (ASA) I dogs were presented for routine neutering. Heart rate was measured at admission. Dogs were randomly assigned to one of the five groups to decide premedication; group D5+P (dexmedetomidine 5 microg/kg plus pethidine 5 mg/kg), D10+P (dexmedetomidine 10 microg/kg plus pethidine 5 mg/kg) with three control groups, D5 (dexmedetomidine 5 microg/kg), D10 (dexmedetomidine 10 microg/kg) or P (pethidine 5 mg/kg). Heart rate was measured at 3, 5, 10 and 20 minutes after preanaesthetic medication. Simple descriptive scores for sedation were assigned after 20 minutes. Anaesthesia was induced using propofol and maintained using isoflurane in oxygen. Heart rate was recorded throughout anaesthesia.

RESULTS

Sedation scores after preanaesthetic medication were significantly higher (P<0.001) in groups D5+P and D10+P compared with the other three groups. D5+P and D10+P groups tended to have lower heart rates in dogs at all time points after premedication compared with groups containing only pethidine or dexmedetomidine at the relevant dose.

CLINICAL SIGNIFICANCE

Greater sedation is achieved using combinations of dexmedetomidine and pethidine compared with each drug alone. Pethidine does not attenuate the alpha-2 adrenergic-induced bradycardia.

Effect of medetomidine infusion on the anaesthetic requirements of desflurane in dogs

The objective of this paper was to evaluate the effect of constant rate infusion of medetomidine on the anaesthetic requirements of desflurane in dogs. For this, six healthy dogs were studied. Measurements for baseline were taken in the awake, unsedated dogs, then each dog received intravenously (i.v.) three anaesthetic protocols: M (no medetomidine infusion), M0.5 (infusion of medetomidine at 0.5 microg/kg/h, i.v.) or M1 (infusion of medetomidine at 1 microg/kg/h, i.v.). All dogs were sedated with medetomidine (2 microg/kg, i.v.) and measurements repeated in 10 min. Induction of anaesthesia was delivered with propofol (3 mg/kg, i.v.) and maintained with desflurane for 90 min to achieve a defined surgical plane of anaesthesia in all cases. After tracheal intubation infusion of medetomidine was initiated and maintained until the end of anaesthesia. Cardiovascular, respiratory, arterial pH (pHa) and arterial blood gas tensions (PaO(2), PaCO(2)) variables were measured during the procedure. End tidal desflurane concentration (EtDES) was recorded throughout anaesthesia. Time to extubation, time to sternal recumbency and time to standing were also noted. Heart rate and respiratory rate were significantly decreased during sedation in all protocols compared to baseline values. Mean heart rate, mean arterial pressure, systolic arterial pressure, diastolic arterial pressure, respiratory rate, tidal volume, arterial oxygen saturation, end-tidal CO(2), pHa, PaO(2), and PaCO(2) during anaesthesia were similar for all protocols. EtDES for M (8.6 +/- 0.8%) was statistically higher than for M0.5 (7.6 +/- 0.5%) and M1 (7.3 +/- 0.7%) protocols. Infusion of medetomidine reduces desflurane concentration required to maintain anaesthesia in dogs.