Comparison between the effects of postanesthetic xylazine and dexmedetomidine on characteristics of recovery from sevoflurane anesthesia in horses

Objective

To compare postanesthetic xylazine and dexmedetomidine on recovery characteristics from sevoflurane anesthesia in horses.

Cardiopulmonary effects of dexmedetomidine and ketamine infusions with either propofol infusion or isoflurane for anesthesia in horses

ObjectiveTo examine the cardiopulmonary effects of two anesthetic protocols for dorsally recumbent horses undergoing carpal arthroscopy.Study designProspective, randomized, crossover study.AnimalsSix horses weighing 488.3 ± 29.1 kg.MethodsHorses were sedated with intravenous (IV) xylazine and pulmonary artery balloon and right atrial catheters inserted. More xylazine was administered prior to anesthetic induction with ketamine and propofol IV. Anesthesia was maintained for 60 minutes (or until surgery was complete) using either propofol IV infusion or isoflurane to effect. All horses were administered dexmedetomidine and ketamine infusions IV, and IV butorphanol. The endotracheal tube was attached to a large animal circle system and the lungs were ventilated with oxygen to maintain end-tidal CO₂ 40 ± 5 mmHg. Measurements of cardiac output, heart rate, pulmonary arterial and right atrial pressures, and body temperature were made under xylazine sedation. These, arterial and venous blood gas analyses were repeated 10, 30 and 60 minutes after induction. Systemic arterial blood pressures, expired and inspired gas concentrations were measured at 10, 20, 30, 40, 50 and 60 minutes after induction. Horses were recovered from anesthesia with IV romifidine. Times to extubation, sternal recumbency and standing were recorded. Data were analyzed using one and two-way anovas for repeated measures and paired t-tests. Significance was taken at p=0.05.ResultsPulmonary arterial and right atrial pressures, and body temperature decreased from pre-induction values in both groups. PaO₂ and arterial pH were lower in propofol-anesthetized horses compared to isoflurane-anesthetized horses. The lowest PaO₂ values (70–80 mmHg) occurred 10 minutes after induction in two propofol-anesthetized horses. Cardiac output decreased in isoflurane-anesthetized horses 10 minutes after induction. End-tidal isoflurane concentration ranged 0.5%–1.3%.Conclusion and clinical relevanceBoth anesthetic protocols were suitable for arthroscopy. Administration of oxygen and ability to ventilate lungs is necessary for propofol-based anesthesia.     

Recovery from desflurane anesthesia in horses with and without post-anesthetic xylazine

The objective of this study was to compare recovery from desflurane anesthesia in horses with or without post-anesthetic xylazine. Six adult horses were anesthetized on 2 occasions, 14 d apart using a prospective, randomized crossover design. Horses were sedated with xylazine, induced to lateral recumbency with ketamine and diazepam, and anesthesia was maintained with desflurane. One of 2 treatments was administered intravenously at the end of anesthesia: xylazine [0.2 mg/kg body weight (BW)] or an equivalent volume of saline. Recovery parameters were recorded and assessed by 2 blinded observers. A Wilcoxon signed-rank test was used to analyze recovery data. Heart rate, arterial blood pressures, and arterial blood gas data were analyzed using 2-way analysis of variance (ANOVA) for repeated measures. Values of P < 0.05 were considered significant. Duration of anesthesia was not different between groups. Administration of xylazine at the end of desflurane anesthesia was associated with significantly longer times to first movement, endotracheal tube removal, first attempt to achieve sternal recumbency, sternal recumbency, first attempt to stand, and standing. Number of attempts to stand and quality of recovery scores were not different between groups. Administering xylazine after desflurane anesthesia resulted in longer recovery times. Recovery scores were not significantly different between groups.     

Effects of xylazine hydrochloride during isoflurane-induced anesthesia in horses

OBJECTIVE: To quantitate dose- and time-related anesthetic-sparing effects of xylazine hydrochloride (XYL) during isoflurane-induced anesthesia in horses and to characterize selected physiologic responses of anesthetized horses to administration of XYL. ANIMALS: 6 healthy adult horses. PROCEDURE: Horses were anesthetized 2 times to determine the minimum alveolar concentration (MAC) of isoflurane in O2 and to characterize the anesthetic-sparing effect (MAC reduction) after IV administration of XYL (0.5 and 1 mg/kg of body weight, random order). Selected measures of cardiopulmonary function, blood glucose concentrations, and urinary output also were measured during the anesthetic studies. RESULTS: Isoflurane MAC (mean +/- SEM) was reduced by 24.8 +/- 0.5 and 34.2 +/- 1.9% at 42 +/- 7 and 67 +/- 10 minutes, respectively, after administration of XYL at 0.5 and 1 mg/kg. Amount of MAC reduction by XYL was dose- and time-dependent. Overall, cardiovascular and respiratory values varied little among treatments. Administration of XYL increased blood glucose concentration; the magnitude of change was dose- and time-dependent. Urine volume increased but not significantly. CONCLUSIONS AND CLINICAL RELEVANCE: Administration of XYL reduced the anesthetic requirement for isoflurane in horses. The magnitude of the decrease is dose- and time-dependent. Administration of XYL increases blood glucose concentration in anesthetized horses in a dose-related manner.     

Cardiovascular effects of xylazine and detomidine in horses

The cardiovascular effects of xylazine and detomidine in horses were studied. Six horses were given each of the following 5 treatments, at 1-week intervals: xylazine, 1.1 mg/kg, IV; xylazine, 2.2 mg/kg, IM; detomidine, 0.01 mg/kg, IV; detomidine, 0.02 mg/kg, IV; and detomidine, 0.04 mg/kg, IM. All treatments resulted in significantly decreased heart rate, increased incidence of atrioventricular block, and decreased cardiac output and cardiac index; cardiac output and cardiac index were lowest following IV administration of 0.02 mg of detomidine/kg. Mean arterial pressure was significantly reduced for various periods with all treatments; however, IV administration of 0.02 mg of detomidine/kg caused hypertension initially. Systemic vascular resistance was increased by all treatments. Indices of ventricular contractility and relaxation, +dP/dt and -dP/dt, were significantly depressed by all treatments. Significant changes were not detected in stroke volume or ejection fraction. The PCV was significantly reduced by all treatments. Respiratory rate was significantly decreased with all treatments, but arterial carbon dioxide tension did not change. Arterial oxygen tension was significantly decreased briefly with the 3 IV treatments only.     

Comparison of recoveries from halothane vs isoflurane anesthesia in horses.

Recovery from isoflurane anesthesia was shorter, with no difference in quality, compared with halothane anesthesia in 2 groups of horses. In 1 group, 12 horses scheduled for elective arthroscopy were randomly assigned to receive halothane or isoflurane for maintenance of anesthesia during surgery. In the other group, 6 horses received anesthesia only, on 2 occasions, with halothane on 1 occasion, and isoflurane on the other. Difference in the quality of recovery was not seen between isoflurane and halothane anesthesia in either group. In the group that had surgery, recovery to sternal position was significantly shorter when isoflurane was used. In the group not treated surgically, recovery to sternal and standing positions was significantly shorter with isoflurane.     

Cardiopulmonary effects of an infusion of remifentanil or morphine in horses anesthetized with isoflurane and dexmedetomidine

ObjectiveTo examine the cardiopulmonary effects of infusions of remifentanil or morphine, and their influence on recovery of horses anesthetized with isoflurane and dexmedetomidine.Study designRandomized crossover study with 7-day rest periods.AnimalsSix adult horses (507 ± 61 kg).MethodsAfter the horses were sedated with xylazine, anaesthesia was induced with ketamine and diazepam, and maintained with isoflurane. After approximately 60 minutes, a dexmedetomidine infusion was started (0.25 μg kg^?1 then 1.0 μg^?1 kg^?1 hour^?1) in combination with either saline (group S), morphine (0.15 mg kg^?1 then 0.1 mg kg^?1 hour^?1; group M), or remifentanil (6.0 μg kg^?1 hour^?1; group R) for 60 minutes. Mean arterial pressure, heart rate, end-tidal carbon dioxide tension, and end-tidal isoflurane concentration were recorded every 5 minutes. Core body temperature, cardiac output, right ventricular and arterial blood-gas values were measured every 15 minutes. Cardiac index, systemic vascular resistance (SVR), intrapulmonary shunt fraction, alveolar dead space, oxygen delivery and extraction ratio were calculated. Recoveries were videotaped and scored by two observers blinded to the treatment. Data were analyzed using repeated measures anova followed by Dunnett’s or Bonferroni’s significant difference test. Recovery scores were analyzed using a Kruskal–Wallis test.ResultsNo significant differences were found among groups. Compared to baseline, heart rate decreased and SVR increased significantly in all groups, and cardiac index significantly decreased in groups S and M. Hemoglobin concentration, oxygen content and oxygen delivery significantly decreased in all groups. The oxygen extraction ratio significantly increased in groups M and R. Lactate concentration significantly increased in group S. Recovery scores were similar among groups.Conclusions and clinical relevanceDexmedetomidine alone or in combination with remifentanil or morphine infusions was infused for 60 minutes without adverse effects in the 6 healthy isoflurane-anesthetized horses in this study.     

Evaluation of xylazine and ketamine for total intravenous anesthesia in horses

OBJECTIVE: To evaluate the use of xylazine and ketamine for total i.v. anesthesia in horses. ANIMALS: 8 horses. PROCEDURE: Anesthetic induction was performed on 4 occasions in each horse with xylazine (0.75 mg/kg, i.v.), guaifenesin (75 mg/kg, i.v.), and ketamine (2 mg/kg, i.v.). Intravenous infusions of xylazine and ketamine were then started by use of 1 of 6 treatments as follows for which 35, 90, 120, and 150 represent infusion dosages (microg/kg/min) and X and K represent xylazine and ketamine, respectively: X35 + K90 with 100% inspired oxygen (O2), X35 + K120-(O2), X35 + K150-(O2), X70 + K90-(O2), K150-(O2), and X35 + K120 with a 21% fraction of inspired oxygen (ie, air). Cardiopulmonary measurements were performed. Response to a noxious electrical stimulus was observed at 20, 40, and 60 minutes after induction. Times to achieve sternal recumbency and standing were recorded. Quality of sedation, induction, and recovery to sternal recumbency and standing were subjectively evaluated. RESULTS: Heart rate and cardiac index were higher and total peripheral resistance lower in K150-(O2) and X35 + K120-air groups. The mean arterial pressure was highest in the X35 + K120-air group and lowest in the K150-(O2) group (125 +/- 6 vs 85 +/- 8 at 20 minutes, respectively). Mean Pa(O2) was lowest in the X35 + K120-air group. Times to sternal recumbency and standing were shortest for horses receiving K150-(O2) (23 +/- 6 minutes and 33 +/- 8 minutes, respectively) and longest for those receiving X70 + K90-(O2) (58 +/- 28 minutes and 69 +/- 27 minutes, respectively). CONCLUSIONS AND CLINICAL RELEVANCE: Infusions of xylazine and ketamine may be used with oxygen supplementation to maintain 60 minutes of anesthesia in healthy adult horses.     

Pharmacokinetics and clinical effects of pirfenidone administered intravenously in horses

OBJECTIVE: To characterize the plasma pharmacokinetics and clinical effects of pirfenidone administered IV in healthy horses. ANIMALS: 6 adult horses. PROCEDURES: A 15 mg/kg dose of pirfenidone was administered IV over 5 minutes. Physical variables were recorded and blood samples collected prior to infusion; 2.5 minutes after beginning infusion; at the end of infusion; and at 3, 6, 9, 12, 15, 20, 25, 30, 40, 50, 60, 75, and 90 minutes and 2, 2.5, 3, 4, 6, 8, 12, and 24 hours after completion of infusion. Plasma concentrations of pirfenidone and its metabolites were determined. RESULTS: Mild clinical effects, including tachycardia and muscle fasciculations, were observed during drug administration but stopped at the end of the infusion. Pirfenidone and 2 metabolites, hydroxypirfenidone and carboxypirfenidone, were detected by the end of the 5-minute infusion. Mean peak plasma concentration of pirfenidone was 182.5 micromol/L, detected at the end of the infusion. Mean peak plasma concentrations of hydroxypirfenidone and carboxypirfenidone were 1.07 and 3.4 micromol/L, respectively, at 40 minutes after infusion. No parent drug or metabolites were detected at 24 hours. Distribution of pirfenidone best fit a 2-compartment model, and the drug had mean +/- SEM elimination half-life of 86.0 +/- 4.7 minutes, mean body clearance of 6.54 +/- 0.45 mL/kg/min, and apparent volume of distribution at steady state of 0.791 +/- 0.056 L/kg. CONCLUSIONS AND CLINICAL RELEVANCE: Intravenous administration of pirfenidone was tolerated with transient adverse affects during infusion, and drug clearance was rapid.     

The cardiovascular effects of dexmedetomidine given by continuous infusion during isoflurane anesthesia in dogs

In a previous study we showed that the MAC of isoflurane was decreased by 18 ± 12% and 59 ± 7% by constant rate infusions of dexmedetomidine at 0.5 and 3 μg kg^–1 hour^–1. The purpose of this study was to document the cardiovascular changes associated with these infusions of dexmedetomidine at 1.3 MAC isoflurane/ dexmedetomidine. Dogs were anesthetized with isoflurane in oxygen given by mask. A cephalic venous catheter, a dorsal pedal arterial catheter and a balloon tipped, Swan–Ganz, pulmonary arterial catheter were placed percutaneously. After instrumentation the dogs were maintained at 1.3 MAC isoflurane for 60 minutes. At this time a set of measurements was made including, heart rate, respiratory rate, core body temperature, pulmonary and systemic arterial blood pressures (SAP, MAP, DAP, CVP, SPAP, MPAP, DPAP and PAOP), cardiac output and arterial and mixed venous blood samples were collected for the measurement of blood gases, pH, hemoglobin concentration, PCV and total protein. Calculated variables included base excess (BE), (HCO₃^?), cardiac index, systemic and pulmonary vascular resistance indices, oxygen delivery, oxygen consumption, oxygen utilization ratio and shunt fraction. After these measurements to dogs were randomly assigned to receive a loading dose of 0.5 or 3 μg kg^–1 of dexmedetomidine given over 6 minutes followed by an infusion of 0.5 (LD) or 3 μg kg^–1 hour^–1 (HD), respectively. The concentration of isoflurane was reduced by the above percentages, respectively, to maintain 1.3 MAC. Full sets of measurements were repeated at 10, 30, 60, 90, 120, 150 and 180 minutes after the start of the loading dose. Measured and calculated variables were compared with baseline using an anova and a post‐hoc Tukey's test. Significance was set at p = 0.05 and results are given as mean ± SD. The initial concentration of isoflurane was 1.73 ± 0.02% and was reduced to 1.41 ± 0.02 and 0.72 ± 0.09% for the LD and HD, respectively. Heart rate decreased with both doses but no other parameter changed significantly with the LD. With the HD there were significant changes in SAP, MAP, DAP, CVP, MPAP, PAOP, CI, SVRI, PCV, DO₂ and shunt fraction. The LD appeared to have minimal effect on the cardiopulmonary values measured, whereas the HD caused typical changes expected with an alpha‐2 agonist.     

Clinical comparison of dexmedetomidine and medetomidine for isoflurane balanced anaesthesia in horses

Objective

To compare the effects of two balanced anaesthetic protocols (isoflurane–dexmedetomidine versus medetomidine) on sedation, cardiopulmonary function and recovery in horses.