The isoflurane sparing effect of a medetomidine constant rate infusion in horses

This clinical study analysed the anaesthetic sparing effect of a medetomidine constant rate infusion (CRI) during isoflurane anaesthesia in horses. Forty healthy horses undergoing different types of orthopaedic and soft tissue surgeries were studied in a randomized trial. Orthopaedic surgeries were primarily arthroscopies and splint bone extractions. Soft tissue surgeries were principally castrations with one ovariectomy. All horses received 0.03 mg kg^?1 acepromazine IM 1 hour prior to sedation. Group A (11 orthopaedic and nine soft tissue surgeries), was sedated with 1.1 mg kg^?1 xylazine IV, group B (13 orthopaedic and seven soft tissue surgeries) with 7 µg kg^?1 medetomidine IV. Anaesthesia was induced in both groups with 2.2 mg kg^?1 ketamine and diazepam 0.02 mg kg^?1 IV. Maintenance of anaesthesia was with isoflurane (ISO) in 100% oxygen, depth of anaesthesia was always adjusted by the first author. Group B received an additional CRI of 3.5 µg kg^?1 hour^?1 medetomidine. Respiratory rate (RR), heart rate (HR), mean arterial blood pressure (MAP), Fe ′ISO and Fe ′CO₂ were monitored with a methane insensitive monitor (Cardiocap 5, Ohmeda, Anandic, Diessenhofen) and noted every 5 minutes. Arterial blood was withdrawn for gas analysis (PaO₂, PaCO₂) 5 minutes after the induction of anaesthesia and every 30 minutes thereafter. Dobutamine (DOB) was given as a CRI to maintain mean arterial blood pressure above 70 mm Hg. Data were averaged over time (sum of measurements/number of measurements) and tested for differences between groups by unpaired t‐tests. There were no significant differences between the groups in terms of body mass (group A, 508 ± 73.7 kg; group B, 529.25 ± 78.4 kg) or duration of anaesthesia (group A, 125.5 ± 36 minutes; group B, 121.5 ± 48.4 minutes). The mean Fe ′ISO required to maintain a surgical plane of anaesthesia was significantly higher in group A (1.33 ± 0.13%) than in group B (1.07 ± 0.19%; p = 2.78 × 10^?5). Heart rate was different between the two groups (group A, 42.2 ± 8.3; group B, 32.6 ± 3.5; p = 8.8 × 10^?5). Dobutamine requirements were higher in group A (group A, 0.72 ± 0.24 μg kg^?1 minute^?1; group B, 0.53 ± 0.23 μg kg^?1 minute^?1; p = 0.023). Respiratory rate, Fe ′CO₂, PaO₂, PaCO₂ were not different between the groups. Adjustment of anaesthetic depth subjectively was easier with the medetomidine infusion and isoflurane (group B) than with isoflurane as a sole agent (group A). In group A 12 horses and in group B five horses showed purposeful movements on 27 (A) and 12 (B) occasions. They were given thiopental (group A, 0.0114 mg kg^?1 minute^?1; group B, 0.0023 mg kg^?1 minute^?1). In group A, a further 17 horses were given ketamine to deepen anaesthesia (52 occasions, 0.00426 mg kg^?1 minute^?1) whereas in group B only nine horses needed ketamine (34 occasions, 0.00179 mg kg^?1 minute^?1). An infusion of 3.5 µg kg^?1 MED during ISO anaesthesia resulted in a significantly reduced ISO requirement.     

Effect of bupivacaine on epidural analgesia produced by xylazine or medetomidine in buffaloes (Bubalus bubalis)

ObjectiveTo evaluate and compare the effect of epidural bupivacaine on analgesia produced by epidural xylazine or medetomidine in buffaloes.Study designProspective, blinded study.AnimalsTen male buffalo calves (6-8 months of age; body weight 70-90 kg) were used on two occasions to conduct a total of 20 investigations.MethodsCaudal extradural analgesia was produced in four buffalo calves each by the injection of either xylazine (0.05 mg kg^?1), medetomidine (15 μg kg^?1) or 0.5% bupivacaine (0.125 mg kg^?1), or combinations of xylazine and bupivacaine (0.05 and 0.125 mg kg^?1), or medetomidine and bupivacaine (15 μg kg^?1 and 0.125 mg kg^?1) at the first intercoccygeal extradural space. Analgesia was tested using deep pinprick stimuli.ResultsExtradural administration of xylazine or medetomidine resulted in complete analgesia of the tail, perineum, inguinal region and the upper parts of the hind limbs, which was faster in onset and longer in duration in the medetomidine group than in the xylazine group. Addition of bupivacaine increased the intensity of the analgesia produced by xylazine, but not that produced by medetomidine. All the drugs caused mild to moderate ataxia, but signs of sedation were apparent only in animals which received xylazine or medetomidine. The extradural injections of all the drugs caused significant decrease in heart rate (p = 0.024), respiratory rate (p = 0.026) and rectal temperature (p = 0.036) from the respective baseline values, but the differences between the groups were not significant.ConclusionsMedetomidine produced a longer duration of analgesia than that produced by xylazine. Bupivacaine prolonged the analgesia produced by xylazine, but the analgesia produced by the combination of medetomidine and bupivacaine was not superior to that produced by medetomidine alone.Clinical relevanceBupivacaine may be used to prolong the extradural analgesia produced by xylazine, but not that produced by medetomidine in buffaloes.     

Cardiovascular effects following epidural injection of romifidine in isoflurane‐anaesthetized dogs

ObjectiveTo investigate the cardiovascular effects of epidural romifidine in isoflurane-anaesthetized dogs.Study designProspective, randomized, blinded experiment.AnimalsA total of six healthy adult female Beagles aged 1.25 ± 0.08 years and weighing 12.46 ± 1.48 (10.25–14.50) kg.MethodsAnaesthesia was induced with propofol (6–9 mg kg^?1) and maintained with 1.8–1.9% end-tidal isoflurane in oxygen. End-tidal CO₂ was kept between 35 and 45 mmHg (4.7–6.0 kPa) using intermittent positive pressure ventilation. Heart rate (HR), arterial blood pressure and cardiac output (CO) were monitored. Cardiac output was determined using a LiDCO monitor and the derived parameters were calculated. After baseline measurements, either 10 μg kg^?1 romifidine or saline (total volume 1 mL 4.5 kg^?1) was injected into the lumbosacral epidural space. Data were recorded for 1 hour after epidural injection. A minimum of 1 week elapsed between treatments.ResultsAfter epidural injection, the overall means (± standard deviation, SD) of HR (95 ± 20 bpm), mean arterial blood pressure (MAP) (81 ± 19 mmHg), CO (1.63 ± 0.66 L minute^?1), cardiac index (CI) (2.97 ± 1.1 L minute^?1 m^?2) and stroke volume index (SI) (1.38 ± 0.21 mL beat^?1 kg^?1) were significantly lower in the romifidine treatment compared with the overall means in the saline treatment [HR (129 ± 24 bpm), MAP (89 ± 17 mmHg), CO (3.35 ± 0.86 L minute^?1), CI (6.17 ± 1.4 L minute^?1 m^?2) and SI (2.21 ± 0.21 mL beat^?1 kg^?1)]. The overall mean of systemic vascular resistance index (SVRI) (7202 ± 2656 dynes seconds cm^?5 m^?2) after epidural romifidine injection was significantly higher than the overall mean of SVRI (3315 ± 1167 dynes seconds cm^?5 m^?2) after epidural saline injection.ConclusionEpidural romifidine in isoflurane-anaesthetized dogs caused significant cardiovascular effects similar to those reportedly produced by systemic romifidine administration.Clinical relevanceSimilar cardiovascular monitoring is required after epidural and systemically administered romifidine. Further studies are required to evaluate the analgesic effects of epidural romifidine.     

Cardiopulmonary effects of diazepam/ketamine/isoflurane or xylazine/ketamine/isoflurane in foals undergoing abdominal surgery

The purpose of this study was to evaluate the cardiopulmonary effects of anesthetic induction with diazepam/ketamine or xylazine/ketamine with subsequent maintenance of anesthesia using isoflurane in foals undergoing abdominal surgery. Seventeen foals underwent laparotomy at 7–10 days of age and a laparoscopy 7–10 days later. Foals were randomly assigned to receive xylazine (0.8 mg kg^?1)/ketamine (2 mg kg^?1) (X/K)(n = 9) or diazepam (0.2 mg kg^?1)/ketamine (2 mg kg^?1) (D/K)(n = 8) for induction of anesthesia for both procedures. In all foals, anesthesia was maintained with isoflurane in oxygen with the inspired concentration adjusted to achieve adequate depth of anesthesia as assessed by an individual blinded to the treatments. IPPV was employed throughout using a tidal volume of 10 mL kg^?1 adjusting the frequency to maintain eucapnia (PaCO₂ 35–45 mm Hg, 4.7–6.0 kPa). Cardiopulmonary variables were measured after induction of anesthesia prior to, during, and following surgery. To compare the measured cardiopulmonary variables between the two anesthetic regimes for both surgical procedures, results were analyzed using a three‐way factorial anova for repeated measures (p < 0.05). During anesthesia for laparotomy, mean CI and MAP ranged from 110 to 180 mL kg^?1 minute^?1 and 57–81 mm Hg, respectively, in the D/K foals and 98–171 mL kg^?1 minute^?1 and 50–66 mm Hg in the X/K foals. Overall, CI, HR, SAP, DAP, and MAP were significantly higher in foals in the D/K group versus the X/K group during this anesthetic period. During anesthesia for laparoscopy, mean CI and MBP ranged from 85 to 165 mL kg^?1 minute^?1 and 67–83 mm Hg, respectively, in the D/K group, and 98–171 mL kg^?1 minute^?1 and 48–67 mm Hg in the X/K group. Only HR, SAP, DAP, and MAP were significantly higher in the D/K group versus X/K group during this latter anesthetic period. There were no significant differences between groups during either surgical procedure for end‐tidal isoflurane, PaO₂, PaCO₂, or pH. In conclusion, anesthesia of foals for laparotomy and laparoscopy with diazepam/ketamine/isoflurane is associated with less hemodynamic depression than with xylazine/ketamine/isoflurane.     

Comparison of two injectable anesthetic regimes in feral cats at a large-volume spay clinic

Same‐day mass sterilization of feral cats requires rapid onset, short‐duration anesthesia. The purpose of this study was to compare our current anesthetic protocol, Telazol–ketamine–xylazine (TKX) with medetomidine–ketamine–buprenorphine (MKB). Feral female cats received either IM TKX (n = 68; 0.25 mL cat^?1; tiletamine 12.5 mg, zolazepam 12.5 mg, K 20 mg, and X 5 mg per 0.25 mL) or MKB (n = 17; M 40 µg kg^?1, K 15 mg kg^?1, and B 10 µg kg^?1). Intervals measured included time from injection to recumbency, time to surgery, duration of surgery, and time from reversal of anesthesia (TKX: yohimbine 0.50 mg cat^?1 IV; MKB: atipamezole 0.50 mg cat^?1 IM) to sternal recumbency. Following instrumentation (Vet/Ox 4403 and Vet/BP Plus 6500), physiological measurements were recorded at 5‐minute intervals, and included rectal temperature, heart rate (HR), respiratory rate (RR), SpO₂ (lingual or rectal probes), and indirect mean arterial blood pressure (MAP) (oscillometric method). Nonparametric means were compared using Mann–Whitney U‐tests. Parametric means were compared using a two‐factorial anova with Bonferroni's t‐tests. The alpha‐priori significance level was p < 0.05. Values were mean ± SD. Body weight (TKX: 2.9 ± 0.5 kg, MKB: 2.7 ± 0.7 kg), time to recumbency (TKX: 4 ± 1 minutes, MKB: 3 ± 1 minutes), time to surgery (TKX: 28 ± 7 minutes, MKB: 28 ± 5 minutes), and duration of surgery (TKX: 11 ± 7 minutes, MKB: 8 ± 5 minutes) did not differ between groups. In contrast, MKB cats required less time from reversal to sternal recumbency (TKX: 68 ± 41 minutes, MKB: 7 ± 2 minutes) and were recumbent for shorter duration (TKX: 114 ± 39 minutes, MKB: 53 ± 6 minutes). Temperature decreased during the study in both groups, but overall temperature was higher in MKB cats (38.0 ± 0.95 °C) than in TKX cats (37.5 ± 0.95 °C). RR, HR, and SpO₂ did not change during the study in either group. However, overall HR and RR were higher in TKX cats (RR: 18 ± 8 breaths minute^?1, HR: 153 ± 30 beats minute^?1) compared to MKB cats (RR: 15 ± 7 breaths minute^?1, HR: 128 ± 19 beats minute^?1). In contrast, overall SpO₂ was lower in the TKX group (90 ± 6%) compared to the MKB group (94 ± 4%). MAP was also lower in the TKX group (112 ± 29 mm Hg) compared to that in the MKB group (122 ± 20 mm Hg). However, MAP increased in the TKX group during surgery compared to pre‐surgical values, but did not change in the MKB group. The results of this study suggested that MKB might be more suitable as an anesthetic for the purpose of mass sterilization of feral female cats.     

A clinical study on the effect in horses during medetomidine-isoflurane anaesthesia, of butorphanol constant rate infusion on isoflurane requirements, on cardiopulmonary function and on recovery characteristics

ObjectiveTo test if the addition of butorphanol by constant rate infusion (CRI) to medetomidine–isoflurane anaesthesia reduced isoflurane requirements, and influenced cardiopulmonary function and/or recovery characteristics.Study designProspective blinded randomised clinical trial.Animals61 horses undergoing elective surgery.MethodsHorses were sedated with intravenous (IV) medetomidine (7 μg kg^?1); anaesthesia was induced with IV ketamine (2.2 mg kg^?1) and diazepam (0.02 mg kg^?1) and maintained with isoflurane and a CRI of medetomidine (3.5 μg kg^?1 hour^?1). Group MB (n = 31) received butorphanol CRI (25 μg kg^?1 IV bolus then 25 μg kg^?1 hour^?1); Group M (n = 30) an equal volume of saline. Artificial ventilation maintained end-tidal CO₂ in the normal range. Horses received lactated Ringer’s solution 5 mL kg^?1 hour^?1, dobutamine <1.25 μg kg^?1 minute^?1 and colloids if required. Inspired and exhaled gases, heart rate and mean arterial blood pressure (MAP) were monitored continuously; pH and arterial blood gases were measured every 30 minutes. Recovery was timed and scored. Data were analyzed using two way repeated measures anova, independent t-tests or Mann–Whitney Rank Sum test (p < 0.05).ResultsThere was no difference between groups with respect to anaesthesia duration, end-tidal isoflurane (MB: mean 1.06 ± SD 0.11, M: 1.05 ± 0.1%), MAP (MB: 88 ± 9, M: 87 ± 7 mmHg), heart rate (MB: 33 ± 6, M: 35 ± 8 beats minute^?1), pH, PaO₂ (MB: 19.2 ± 6.6, M: 18.2 ± 6.6 kPa) or PaCO_2. Recovery times and quality did not differ between groups, but the time to extubation was significantly longer in group MB (26.9 ± 10.9 minutes) than in group M (20.4 ± 9.4 minutes).Conclusion and clinical relevanceButorphanol CRI at the dose used does not decrease isoflurane requirements in horses anaesthetised with medetomidine–isoflurane and has no influence on cardiopulmonary function or recovery.     

Cardiorespiratory effects of a cardioselective muscarinic antagonist in anesthetized horses

Treatment of bradycardia in horses has been historically ignored because of the motility depressant effects of nonselective antimuscarinics. This study evaluated the cardiopulmonary effects of a cardioselective (M2) muscarinic antagonist, methoctramine (MET), in anesthetized horses. In a previous in vitro study, we determined that supraphysiological doses of MET were necessary to inhibit acetylcholine‐induced longitudinal jejunal smooth muscle contractions in this species. Six adult horses were allocated to two treatments in a randomized complete block design. Anesthesia was induced with xylazine/ketamine, and maintained with halothane (1% end‐tidal) and a constant infusion of xylazine (1 mg kg^?1 hour^?1) under mechanical ventilation. Invasive hemodynamic variables were monitored at baseline (approximately 45 minutes after induction) and for 120 minutes after MET or saline (control) had been injected. MET was titrated at 10‐minute intervals (10 µg kg^?1 IV) until the heart rate (HR) increased at least 30% above the baseline, or a maximum cumulative dose of 30 µg kg^?1 had been injected. A person blinded to the treatment evaluated recovery scores and monitored intestinal auscultation until 24 hours after the end of anesthesia using previously published methods. Cardiovascular parameters were analyzed by anova followed by a Dunnet's test, and nonparametrical data were analyzed by a Mann–Whitney U‐test (p < 0.05). Values were mean ± SEM unless otherwise stated. MET significantly increased HR from baseline to 120 minutes post‐injection (from 29 ± 1 to 36 ± 2 beats minute^?1 at 20 minutes). Thermodilution cardiac output (CO) and mean arterial pressure (MAP) were increased from baseline to 75 minutes post‐MET injection (from 13.9 ± 0.8 to 19.4 ± 2.0 L minute^?1 for CO at 20 minutes, and from 82 ± 3 to 103 ± 5 mm Hg for MAP at 20 minutes). Recovery characteristics and bowel auscultation scores did not differ among the groups. The return to at least 75% of the maximum auscultation score occurred at 10 (8–18) hours [median (range)] for controls and at 9 (8–12) hours for MET. It was concluded that MET increased HR and improved hemodynamic function during halothane/xylazine anesthesia with no apparent effect on return to full‐bowel motility, as assessed by auscultation. Accordingly, M2 muscarinic antagonists might be represented as a safer alternative to treat intraoperative bradycardia in horse.     

The effect of low dose rocuronium bromide on eyeball position, muscle relaxation, and ventilation in dogs

A central eyeball position is often required during sedation or anaesthesia to facilitate examination of the eye. However, use of neuromuscular blockade to produce a central eye position may result in depressed ventilation. This study evaluated the eyeball position, muscle relaxation and changes in ventilation during general anaesthesia after the IV administration of 0.1 mg kg^?1 rocuronium. With client consent, 12 dogs of different breeds, body mass 27.2 ± 11.8 kg, aged 5.6 ± 2.8 years (mean ± SD) were anaesthetized for ocular examination. Pre‐anaesthetic medication was 0.01 mg kg^?1 medetomidine and 0.2 mg kg^?1 butorphanol IV. Anaesthesia was induced with propofol to effect and maintained with 10 mg kg^?1 hour^?1 propofol by infusion. The dogs were placed in left lateral recumbency, their trachea intubated and connected to a circle breathing system (Fi O₂ = 1.0). All dogs breathed spontaneously. The superficial peroneal nerve of the right hind leg was stimulated every 15 seconds with a train‐of‐four (TOF) stimulation pattern and neuromuscular function was assessed with an acceleromyograph (TOF‐Guard). Adequacy of ventilation was measured with the Ventrak 1550. After 10 minutes of anaesthesia to allow stabilisation of baseline values, 0.1 mg kg^?1 rocuronium was administered IV. Minute volume (Vm ), tidal volume (Vt ), respiratory rate (RR), Pe ′CO₂ and maximal depression of T1 and TOF ratio were measured. Data were analysed using a paired t‐test. The changes in the eyeball position were recorded. A total of 100 ± 33 seconds after the injection of rocuronium, T1 was maximally depressed to 62 ± 21% and the TOF ratio to 42 ± 18% of baseline values. Both variables returned to baseline after 366 ± 132 seconds (T1) and 478 ± 111 seconds (TOF). There was no significant reduction in Vm (2.32 ± 1.1 L minute^?1), Vt (124.1 ± 69.3 mL) and RR (10 ± 3.8 breaths minute^?1) and no increase in Pe ′CO₂ (6.5 ± 2.1 kPa (48.8 ± 16.1 mm Hg)) throughout the procedure. The eyeball rotated to a central position 35 ± 7 seconds after rocuronium IV and remained there for a minimum of 20 ± 7 minutes in all dogs. We conclude that rocuronium at a dose of 0.1 mg kg^?1 can be administered to dogs IV with minimal changes in ventilatory variables. The eyeball is fixed in a central position for at least 20 minutes, which greatly facilitates clinical examination.     

Endothelin receptor subtype A blockade does not affect the haemodynamic recovery from haemorrhage during xenon/remifentanil or isoflurane/remifentanil anaesthesia in dogs

ObjectiveTo test the compensatory role of endothelin-1 when acute blood loss is superimposed on anaesthesia, by characterizing the effect of systemic endothelin receptor subtype A (ET_A) blockade on the haemodynamic and hormonal responses to haemorrhage in dogs anaesthetized with xenon/remifentanil (X/R) or isoflurane/remifentanil (I/R).Study designProspective experimental randomized controlled study.AnimalsSix female Beagle dogs, 13.4 ± 1.3 kg.MethodsAnimals were anaesthetized with remifentanil 0.5 μg kg^?1 minute^?1 plus either 0.8% isoflurane (I/R) or 63% xenon (X/R), with and without (Control) the systemic intravenous endothelin receptor subtype A antagonist atrasentan (four groups, n = 6 each). After 60 minutes of baseline anaesthesia, the dogs were bled (20 mL kg^?1) over 5 minutes and hypovolemia was maintained for 1 hour. Continuous haemodynamic monitoring was performed via femoral and pulmonary artery catheters; vasoactive hormones were measured before and after haemorrhage.ResultsIn Controls, systemic vascular resistance (SVR), vasopressin and catecholamine plasma concentrations were higher with X/R than with I/R anaesthesia at pre-haemorrhage baseline. The peak increase after haemorrhage was higher during X/R than during I/R anaesthesia (SVR 7420 ± 867 versus 5423 ± 547 dyne seconds cm^?5; vasopressin 104 ± 23 versus 44 ± 6 pg mL^?1; epinephrine 2956 ± 310 versus 177 ± 99 pg mL^?1; norepinephrine 862 ± 117 versus 195 ± 33 pg mL^?1, p < 0.05). Haemorrhage reduced central venous pressure from 3 ± 1 to 1 ± 1 cmH₂O (I/R, ns) and from 8 ± 1 to 5 ± 1 cmH₂O (X/R, p < 0.05), but did not reduce mean arterial pressure, nor cardiac output. Atrasentan did not alter the haemodynamic and hormonal response to haemorrhage during either anaesthetic protocol.Conclusions and clinical relevanceSelective ET_A receptor blockade with atrasentan did not impair the haemodynamic and hormonal compensation of acute haemorrhage during X/R or I/R anaesthesia in dogs.     

Cardiovascular effects of epidural administration of methadone, ropivacaine 0.75% and their combination in isoflurane anaesthetized dogs

ObjectiveTo compare the cardiovascular effects of four epidural treatments in isoflurane anaesthetised dogs.Study designProspective, randomized. experimental study.AnimalsSix female, neutered Beagle dogs (13.3 ± 1.0 kg), aged 3.6 ± 0.1 years.MethodsAnaesthesia was induced with propofol (8.3 ± 1.1 mg kg^?1) and maintained with isoflurane in a mixture of oxygen and air [inspiratory fraction of oxygen (FiO₂) = 40%], using intermittent positive pressure ventilation. Using a cross-over model, NaCl 0.9% (P); methadone 1% 0.1 mg kg^?1 (M); ropivacaine 0.75% 1.65 mg kg^?1 (R) or methadone 1% 0.1 mg kg^?1 + ropivacaine 0.75% 1.65 mg kg^?1 (RM) in equal volumes (0.23 mL kg^?1) using NaCl 0.9%, was administered epidurally at the level of the lumbosacral space. Treatment P was administered to five dogs only. Cardiovascular and respiratory variables, blood gases, and oesophageal temperature were recorded at T-15 and for 60 minutes after epidural injection (T0).ResultsMean overall heart rate (HR in beats minute^?1) was significantly lower after treatment M (119 ± 16) (p = 0.0019), R (110 ± 18) (p < 0.0001) and RM (109 ± 13) (p < 0.0001), compared to treatment P (135 ± 21). Additionally, a significant difference in HR between treatments RM and M was found (p = 0.04). After both ropivacaine treatments, systemic arterial pressures (sAP) were significantly lower compared to other treatments. No significant overall differences between treatments were present for central venous pressure, cardiac output, stroke volume, systemic vascular resistance, oxygen delivery and arterial oxygen content (CaO₂). Heart rate and sAP significantly increased after treatment P and M compared to baseline (T-15). With all treatments significant reductions from baseline were observed in oesophageal temperature, packed cell volume and CaO₂. A transient unilateral Horner’s syndrome occurred in one dog after treatment R.Conclusions and clinical relevanceClinically important low sAPs were observed after the ropivacaine epidural treatments in isoflurane anaesthetised dogs. Systemic arterial pressures were clinically acceptable when using epidural methadone.     

The effects of pre-anesthetic administration of xylazine on the cardiovascular responses to dobutamine in halothane anaesthetized horses

Studies evaluating the effects of dobutamine in horses do not consistently report increases in cardiac output despite increases in arterial blood pressure. The concurrent administration of the α₂ agonist clonidine, in people, inhibited the chronotropic effects of dobutamine and increased left ventricular stroke work ( Zimpfer et al. 1982 ). Our study was performed to determine if pre‐medication with an α₂ agonist affects the response to dobutamine in anaesthetized horses. Eleven horses were anaesthetized on four separate occasions for one of four randomly assigned treatments; (I) no xylazine, no dobutamine (II) xylazine, no dobutamine (III) no xylazine, dobutamine, and (IV) xylazine, dobutamine. Horses received 0.02 mg kg^?1 of butorphanol IV 10 minutes prior to anesthetic induction. Two minutes prior to induction, groups II and IV received 0.5 mg kg^?1 of IV xylazine. Anaesthesia was induced with 6–7 mg kg^?1 of thiopental and maintained with halothane. End‐tidal halothane concentrations were maintained between 1.1 and 1.2% in groups I and III, and 0.9–1.0% for groups II and IV. Heart rate, cardiac output, right atrial pressure, and systolic (SAP), diastolic (DAP) and mean (MAP) arterial pressure were recorded 30 minutes after beginning halothane anaesthesia (T10). Cardiac output was estimated using Lithium dilution ( Linton et al. 2000 ). Baseline measurements were repeated twice, at 5‐minute intervals (T5 and T0). At time 0 (T0), an IV infusion of either saline (100 mL hour^?1) or dobutamine (0.001 mg kg^?1 minute^?1) was started and data recorded at 5‐minute intervals for 30 minutes (T5 – T30). Stroke volume and systemic vascular resistance (SVR) were calculated. Data were analysed using repeated measures anova (p < 0.01 significant) and Newman–Keuls for multiple comparisons. Cardiac output and stroke volume increased over time in groups III and IV. Cardiac index was higher in groups III and IV than in groups I and II from T10 until completion of the study. Estimates of cardiac index at T30 for groups I–IV were 45 ± 9, 46 ± 11, 71 ± 11, and 78 ± 19 mL kg^?1 minute^?1, respectively (mean ± SD). Stroke index was higher in groups III and IV than in groups I and II from T15 to T30. Values for stroke index at T30 for groups I–IV were 0.98 ± 0.19, 1.11 ± 0.18, 1.46 ± 0.21, 1.74 ± 0.33 mL kg^?1. Heart rate decreased from T10–T30 in groups I and II. Heart rate was greater in groups I and III than in groups II and IV at T5 and T0. Values for heart rate at T0 for groups I–IV were 48 ± 5, 42 ± 5, 50 ± 4, 43 ± 4 beats minute^?1. Systolic arterial pressure, DAP and MAP were higher in groups III and IV than in groups I and II from T5 to T30. There were no differences in SVR between groups. Dobutamine at 0.001 mg kg^?1 minute^?1 increased cardiac output, blood pressure, and stroke volume. Premedication with xylazine at 0.5 mg kg^?1 did not appear to affect the response to dobutamine.     

Hyoscine‐N‐butylbromide premedication on cardiovascular variables of horses sedated with medetomidine

ObjectiveTo evaluate the effects of intravenous (IV) or intramuscular (IM) hyoscine premedication on physiologic variables following IV administration of medetomidine in horses.Study designRandomized, crossover experimental study.AnimalsEight healthy crossbred horses weighing 330 ± 39 kg and aged 7 ± 4 years.MethodsBaseline measurements of heart rate (HR), cardiac index (CI), respiratory rate, systemic vascular resistance (SVR), percentage of patients with second degree atrioventricular (2^oAV) block, mean arterial pressure (MAP), pH, and arterial partial pressures of carbon dioxide (PaCO₂) and oxygen (PaO₂) were obtained 5 minutes before administration of IV hyoscine (0.14 mg kg^?1; group HIV), IM hyoscine (0.3 mg kg^?1; group HIM), or an equal volume of physiologic saline IV (group C). Five minutes later, medetomidine (7.5 μg kg^?1) was administered IV and measurements were recorded at various time points for 130 minutes.ResultsMedetomidine induced bradycardia, 2^oAV blocks and increased SVR immediately after administration, without significant changes in CI or MAP in C. Hyoscine administration induced tachycardia and hypertension, and decreased the percentage of 2^oAV blocks induced by medetomidine. Peak HR and MAP were higher in HIV than HIM at 88 ± 18 beats minute^?1 and 241 ± 37 mmHg versus 65 ± 16 beats minute^?1 and 192 ± 38 mmHg, respectively. CI was increased significantly in HIV (p ≤ 0.05). Respiratory rate decreased significantly in all groups during the recording period. pH, PaCO₂ and PaO₂ were not significantly changed by administration of medetomidine with or without hyoscine.Conclusion and clinical relevanceHyoscine administered IV or IM before medetomidine in horses resulted in tachycardia and hypertension under the conditions of this study. The significance of these changes, and responses to other dose rates, requires further investigation.     

Comparison of lidocaine, xylazine, and lidocaine−xylazine for caudal epidural analgesia in cattle

Objective To directly compare the time to onset and duration of analgesia produced by a lidocaine/xylazine combination with that produced by lidocaine and xylazine administered alone in the caudal epidural space of dairy cattle. Design Prospective randomized experimental study. Animals Nine adult (> 4 years of age) dairy cows (520–613 kg). Methods Caudal epidural analgesia was produced in all cows with 2% lidocaine (0.22 mg kg^?1; 5.5 mL 500 kg^?1), 10% xylazine (0.05 mg kg^?1 diluted to 5.5 mL 500 kg^?1 with sterile water), and 2% lidocaine/10% xylazine (0.22 mg kg^?1/0.05 mg kg^?1; total volume of 5.7 mL 500 kg^?1), at no earlier than weekly intervals in a Latin square design. Time to onset, duration and cranial spread of analgesia were recorded, as were degree of sedation, ataxia and ptyalism. Results No significant difference (p > 0.05) was noted for time (mean ± SEM) of onset of analgesia between lidocaine (4.8 ± 1.0 minutes) and the lidocaine/xylazine combination (5.1 ± 0.9 minutes) but onset of analgesia following xylazine was significantly longer (11.7 ± 1.0 minutes) than either of the other two treatments. Lidocaine/xylazine (302.8 ± 11.0 minutes) produced analgesia of significantly longer duration than that of xylazine (252.9 ± 18.9 minutes) and both the lidocaine/xylazine combination and xylazine alone produced analgesia of significantly longer duration than that produced by lidocaine (81.8 ± 11.8 minutes). In all cattle, xylazine, administered either alone or with lidocaine, induced mild to moderate sedation and ataxia and cutaneous analgesia from the coccyx to T13. Mild ataxia was also present in those cattle receiving lidocaine alone. Conclusion The combination of xylazine and lidocaine produces analgesia of quicker onset and longer duration than xylazine administered alone and of longer duration than lidocaine administered alone. Clinical relevance Utilizing this combination, long‐duration obstetrical and surgical procedures could commence relatively soon after epidural injection and could be completed without re‐administration of anesthetic agents.     

Antinociceptive effect of intrathecally applied alpha2 agonists (xylazine and detomidine) in sheep and the response to atipamezole

This study evaluated the antinociceptive and physiologic effects of xylazine (X) and detomidine (D) administered intrathecally (IT) at the lumbosacral space, before and after the injection of atipamezole (A) IV. The study was approved by the National Animal Protection Authorities. Five adult healthy female sheep were anaesthetized with propofol on four occasions to inject the following treatments IT: groups 1 and 2, 0.05 mg kg^?1 X (2 mg mL^?1 saline) IT; groups 3 and 4, 0.01 mg kg^?1 D (0.5 mg mL^?1 saline) IT ( Waterman et al. 1988 ). Nociceptive threshold (TH) was tested by applying pulsed and stepwise enhanced direct current ( Ludbrook et al. 1995 ) at one hind leg pastern and noting the current at the moment of foot lift. Maximum current applied was 40 mA. Baseline TH was measured twice before anaesthesia and every 10 minutes when the sheep regained consciousness. Atipamezole was given IV immediately after reaching maximum analgesic action of X and D as defined by two equal or decreasing TH values and measurements were continued for 90 minutes. The dose of A for groups 1 and 3 was 0.005 mg kg^?1 (0.25 mg mL^?1 saline) IV, and for groups 2 and 4 was 0.0025 mg kg^?1 A (0.25 mg mL^?1 saline) IV. Heart rate (HR), mean direct arterial pressure (MAP), PaO₂ and PaCO₂ were measured. The differences between measurements recorded before and after treatment were analysed using a paired t‐test for the drug effects and a nonparametric Wilcoxon's rank sum test for the comparison between groups. A p‐value < 0.05 was considered significant. All sheep were able to stand before A IV. Threshold baseline value was 4.5 ± 1.7 (mean ± SD) mA for all animals. Xylazine caused a significantly higher TH rise (35.2 ± 1.8 mA), faster onset (21.1 ± 16.0 minutes) and longer duration of the TH enhancement (104.1 ± 8.6 minutes) than D (TH: 16.3 ± 7.8 mA, onset: 49.5 ± 28.4 minutes, duration: 59.3 ± 27.3 minutes). A significant increase in PaCO₂ was observed in the X and D treated animals, 0.39 ± 0.21 kPa (2.9 ± 1.6 mm Hg) and 0.39 ± 0.29 kPa (2.9 ± 2.2 mm Hg), respectively. Heart rate was significantly decreased by ?21 ± 17 beats minute^?1 for X animals and ?13 ± 13 beats minute^?1 for D. Mean arterial pressure (?9 ± 13 mm Hg for X and ?1 ± 11 mm Hg for D animals) and PaO₂ 0.65 ± 1.32 kPa (4.9 ± 9.9 mm Hg) for X and 1.45 ± 4.19 kPa (10.9 ± 31.4 mm Hg) for D animals) did not change significantly. The nociceptive threshold was not affected by A in any group. Threshold values of all X treated animals before A was 39.3 ± 1.4 mA and after was 37.2 ± 6.3 (group 1) and 40 ± 0 (group 2). Threshold values of all D treated animals before A was 21.0 ± 8.3 and after was 19.4 ± 7.3 (group 3) and 24.8 ± 8.0 (group 4). At the dosages administered intrathecally in this study, X and to a lower degree D induce antinociception without major physiologic changes. Atipamezole up to 0.005 mg kg^?1 IV does not affect the resulting antinociception as assessed by electrical stimulation.     

Sedative effects of hydromorphone or oxymorphone with or without acepromazine in dogs

Hydromorphone is an agonist opioid with potency approximately five times that of morphine and half that of oxymorphone. The purpose of this study was to compare hydromorphone with oxymorphone, with or without acepromazine, for sedation in dogs, and to measure plasma histamine before and after drug administration. Ten dogs received IM hydromorphone (H; 0.2 mg kg^?1), oxymorphone (O; 0.1 mg kg^?1), hydromorphone with acepromazine (H; 0.2 mg kg^?1, A; 0.05 mg kg^?1) or oxymorphone with acepromazine (O; 0.1 mg kg^?1, A; 0.05 mg kg^?1) in a randomized Latin‐square design. Sedation score, heart rate, respiratory rate, blood pressure, and SpO₂ were recorded at baseline and every 5 minutes after drug administration up to 25 minutes. Plasma histamine was measured at baseline and at 25 minutes post‐drug administration. Data were analyzed with repeated measures anova . Mean ± SD body weight was 21.62 ± 1.54 kg. Mean ± SD age was 1.07 ± 0.19 years. Sedation score was significantly greater for OA after 5 minutes than O alone (4.1 ± 3.5 versus 1.9 ± 1.5) and for HA after 15 minutes than H alone (8.6 ± 2.9 versus 5.9 ± 2.5). There was no significant difference in sedation between H and O at any time point. There was no significant difference between groups at any time with respect to heart rate, respiratory rate, blood pressure or SpO₂. Mean ± SD plasma histamine (nM ml^?1) for all groups was 1.72 ± 2.69 at baseline and 1.13 ± 1.18 at 25 minutes. There was no significant change in plasma histamine concentration in any group. Hydromorphone is effective for sedation in dogs and does not cause measurable increase in histamine. Sedation with hydromorphone is enhanced by acepromazine.     

Comparative cardiovascular, analgesic, and sedative effects of medetomidine, medetomidine–hydromorphone, and medetomidine–butorphanol in dogs

The purpose of this study was to determine the cardiovascular, analgesic, and sedative effects of IV medetomidine (M, 20 µg kg^?1), medetomidine–hydromorphone (MH, 20 µg kg^?1 ? 0.1 mg kg^?1), and medetomidine–butorphanol (MB, 20 µg kg^?1 ? 0.2 mg kg^?1) in dogs. Using a randomized cross‐over design and allowing 1 week between treatments, six healthy, mixed‐breed dogs (five males and one female) weighing 20 ± 3 kg, were induced to anesthesia by face‐mask administration of 2.9% ET sevoflurane to facilitate instrumentation prior to administration of the treatment combinations. Dogs were intubated and instrumented to enable measurement of heart rate (HR), systolic arterial pressure (SAP), mean arterial pressure (MAP), diastolic arterial pressure (DAP), mean pulmonary arterial pressure (PAP), pulmonary arterial occlusion pressure (PAOP), central venous pressure (CVP), pulmonary arterial temperature (TEMP), and cardiac output via thermodilution using 5 mL of 5% dextrose, and recording the average of the three replicate measurements. Cardiac index (CI) and systemic (SVR) and pulmonary vascular resistances were calculated. After instrumentation was completed, administration of sevoflurane was discontinued, and the dogs were allowed to recover for 30 minutes prior to administration of the treatment drugs. After collection of the baseline samples for blood gas analysis and recording the baseline cardiovascular variables, the test agents were administered IV over 10 seconds and the CV variables recorded at 5, 10, 15, 30, 45, and 60 minutes post‐injection. In addition, arterial blood was sampled for blood gas analysis at 15 and 45 minutes following injection. Intensity and duration of analgesia (assessed by toe‐pinch response using a hemostat) and level of sedation were evaluated at the above time points and at 75 and 90 minutes post‐injection. Data were analyzed using anova for repeated measures with posthoc differences between means identified using Bonferroni's method (p < 0.05). Administration of M, MH, or MB was associated with increases in SAP, MAP, DAP, PAP, PAOP, CVP, SVR, and TEMP and with decreases in HR and CI. No differences in CV variables between treatment groups were identified at any time. PaO₂ increased over time in all groups and was significantly higher when MH was compared with M. At 45 minutes, PaO₂ tended to decrease over time and was significantly lower when MH and MB were compared with M at 15 minutes. Analgesia scores for MH and MB were significantly higher compared with M through 45 minutes, while analgesia scores for MH were significantly higher compared with M through 90 minutes. Sedation scores were higher for MH and MB compared with M throughout 90 minutes. Durations of lateral recumbency were 108 ± 10.8, 172 ± 15.5, and 145 ± 9.9 minutes for M, MH, and MB, respectively. We conclude that MH and MB are associated with improved analgesia and sedation and have similar CV effects when compared with M.     

Comparison of three anaesthetic protocols in Bennett’s wallabies (Macropus rufogriseus)

ObjectiveInvestigate physiological and sedative/anaesthetic effects of xylazine, medetomidine or dexmedetomidine combined with ketamine in free-ranging Bennett's wallabies.Study designProspective clinical trial.AnimalsTwenty-six adult free-ranging Bennett's wallabies.MethodsAnimals were darted intramuscularly with one of three treatments: xylazine and ketamine, 2.0 and 15.0 mg kg^?1, respectively (XK): medetomidine and ketamine 0.1 and 5.0 mg kg^?1 (MK) and dexmedetomidine and ketamine 0.05 and 5.0 mg kg^?1 (DMK). Body weights were estimated. If the animal was still laterally recumbent after 45 minutes of anaesthesia, then an alpha-2 adrenoceptor antagonist, atipamezole, was administered (XK: 0.4 mg kg^?1, MK: 5 mg kg^?1, DMK: 2.5 mg kg^?1). Heart rate (HR) and respiratory rate (f_R) were recorded at 5-minute intervals and temperature at 10-minute intervals. Venous blood was taken 30 minutes after initial injection. Statistical analysis utilized anova. p < 0.05 was considered significant.ResultsAnimals became recumbent rapidly in all groups. XK animals had muscle twitches, responded to external stimuli, and three animals required additional dosing; this was not observed in the MK and DMK groups. HR (mean ± SD beats minute^?1) in XK (81 ± 4) was significantly higher than MK (74 ± 2) and DMK (67 ± 4). There were no differences in f_R, temperature, blood-gas and biochemical values between groups. More animals in MK (9/10) and DMK (5/6) needed antagonism of anaesthesia compared with XK (1/10). There were no adverse effects after anaesthesia.Conclusion and clinical relevanceCardio-respiratory effects were similar in all groups. There were fewer muscle twitches and reactions to external stimuli in MK and DMK. Duration of anaesthesia was shorter in XK; most animals in MK and DMK needed atipamezole to assist recovery. All three treatments provided satisfactory sedation/anaesthesia and are suitable for use in Bennett's wallabies.     

Evaluation of medetomidine-ketamine and dexmedetomidine-ketamine in Chinese water deer (Hydropotes inermis)

ObjectiveTo investigate physiological and sedative/immobilization effects of medetomidine or dexmedetomidine combined with ketamine in free-ranging Chinese water deer (CWD).Study designProspective clinical trial.Animals10 free-ranging adult Chinese water deer (11.0 ± 2.6 kg).MethodsAnimals were darted intramuscularly with 0.08 ± 0.004 mg kg^?1 medetomidine and 3.2 ± 0.2 mg kg^?1 ketamine (MK) or 0.04 ± 0.01 mg kg^?1 dexmedetomidine and 2.9 ± 0.1 mg kg^?1 ketamine (DMK) If the animal was still laterally recumbent after 60 minutes of immobilization, atipamezole was administered intravenously (MK: 0.4 ± 0.02 mg kg^?1, DMK: 0.2 ± 0.03 mg kg^?1). Heart rate (HR) respiratory rate (f_R) and temperature were recorded at 5-minute intervals. Arterial blood was taken 15 and 45 minutes after initial injection. Statistical analysis was performed using Student’s t-test or anova. p < 0.05 was considered significant.ResultsAnimals became recumbent rapidly in both groups. Most had involuntary ear twitches, but there was no response to external stimuli. There were no statistical differences in mean HR (MK: 75 ± 14 beats minute^?1; DMK: 85 ± 21 beats minute^?1), f_R (MK: 51 ± 35 breaths minute^?1; DMK; 36 ± 9 breaths minute^?1), temperature (MK: 38.1 ± 0.7 °C; DMK: 38.4 ± 0.5 °C), blood gas values (MK: PaO₂ 63 ± 6 mmHg, PaCO₂ 49.6 ± 2.6 mmHg, HCO₃^? 30.8 ± 4.5 mmol L^?1; DMK: PaO₂ 77 ± 35 mmHg, PaCO₂ 45.9 ± 11.5 mmHg, HCO₃^? 31.0 ± 4.5 mmol L^?1) and biochemical values between groups but temperature decreased in both groups. All animals needed antagonism of immobilization after 60 minutes. Recovery was quick and uneventful. There were no adverse effects after recovery.Conclusion and clinical relevanceBoth anaesthetic protocols provided satisfactory immobilisation. There was no clear preference for either protocol and both appear suitable for CWD.     

The use of pulsed electromagnetic field (PEMF) therapy to provide post-operative analgesia in the dog

Buprenorphine is an effective analgesic when administered epidurally to humans. The purpose of this study was to compare epidural buprenorphine (B; n = 10) with epidural morphine (M; n = 10) for post‐operative analgesia in dogs undergoing cranial cruciate ligament repair. All dogs were premedicated with acepromazine (0.1 mg kg^?1 IM), induced with propofol (4–6 mg kg^?1 IV) and maintained with halothane in oxygen. Dogs were randomly assigned to receive B (0.004 mg kg^?1) or M (0.1 mg kg^?1) in the lumbosacral epidural space in a total volume of 0.2 mL kg^?1. End‐tidal halothane and CO₂ and temperature were recorded every 15 minutes until extubation (t = 0). A numerical rating pain score (SPS) was recorded at t = 0, 1, 2, 4, 6, 10 and 24 hours by a blinded observer. Dogs received rescue morphine (1.0 mg kg^?1 IM) if indicated by SPS and the time of rescue analgesic administration was recorded. Observable side‐effects such as urinary retention, sedation or pruritus were recorded. Data were analyzed with repeated measures anova . Mean ± SD body weight (kg) and age (yrs) for B dogs was 34.2 ± 10.8 and 5.5 ± 2.8; for M dogs these values were 36.6 ± 13.5 and 5.9 ± 3.3. Mean ± SD SPS for B dogs at t = 0, 1, 2, 4, 6, 10 and 24 hours were 1.2 ± 0.75, 3.2 ± 2.0, 4.5 ± 4.3, 4.6 ± 3.4, 4.7 ± 3.0, 5.0 ± 4.9 and 5.1 ± 3.5. For M dogs these values were 1.7 ± 0.5, 2.6 ± 2.0, 3.7 ± 0.75, 4.2 ± 2.2, 4.1 ± 3.0, 3.1 ± 2.1 and 3.9 ± 1.9. There were no significant differences between B and M with respect to SPS, times or frequency of rescue morphine administration, end‐tidal halothane and CO₂, or esophageal temperature. Fifty per cent of dogs in both groups required rescue morphine. Buprenorphine is as effective as morphine for epidural analgesia in healthy dogs undergoing hindlimb orthopedic surgery.     

The effect of epidural injection speed on epidural pressure and distribution of solution in anesthetized dogs

ObjectiveTo determine the effect of injection speed on epidural pressure (EP), injection pressure (IP), epidural distribution (ED) of solution, and extent of sensory blockade (SB) during lumbosacral epidural anesthesia in dogs.Study designProspective experimental trial.AnimalsTen healthy adult Beagle dogs weighing 8.7 ± 1.6 kg.MethodsGeneral anesthesia was induced with propofol administered intravenously and maintained with isoflurane. Keeping the dogs in sternal recumbency, two spinal needles connected to electrical pressure transducers were inserted into the L6-L7 and the L7-S1 intervertebral epidural spaces for EP and IP measurements, respectively. Bupivacaine 0.5% diluted in iohexol was administered epidurally to each dog via spinal needle at L7-S1 intervertebral space, at two rates of injection (1 and 2 mL minute^?1 groups), with a 1-week washout period. Epidural distribution was verified with computed tomography, and SB was evaluated after arousal by pinching the skin with a mosquito hemostatic forceps over the vertebral dermatomes. The results were analyzed according to each injection speed, using paired t- and Wilcoxon signed-rank tests.ResultsMean ± SD of baseline EP and IP values were 2.1 ± 6.1 and 2.6 ± 7.1 mmHg, respectively. Significant differences were observed between 1 and 2 mL minute^?1 groups for peak EP (23.1 ± 8.5 and 35.0 ± 14.5 mmHg, p = 0.047) and peak IP (68.5 ± 10.7 and 144.7 ± 32.6 mmHg, p <0.001). However, the median (range) of the ED, 11.5 (4–22) and 12 (5–21) vertebrae, and SB, 3.5 (0–20) and 1 (0–20) dermatomes, values of the two groups were not related to injection speed.Conclusions and clinical relevanceThe EP profile during injection was measured by separating the injection and pressure monitoring lines. The increase in epidural injection speed increased the EP, but not the ED or the SB in dogs.