The minimum infusion rate of alfaxalone during its co-administration with lidocaine at three different doses by constant rate infusion in goats.

OBJECTIVE: To determine the minimum infusion rate (MIR) of alfaxalone required to prevent purposeful movement in response to standardized stimulation while co-administered with lidocaine at three different doses by constant infusion rate infusion (CRI) in goats. STUDY DESIGN: Prospective, blinded, randomized crossover, experimental. ANIMALS: A total of eight healthy goats: four does and four wethers. METHODS: Anaesthetic induction was with lidocaine at 1 mg kg-1 [low dose of lidocaine (L-Lid)], 2 mg kg-1 [moderate dose (M-Lid)] or 4 mg kg-1 [high dose (H-Lid)] and alfaxalone at 2 mg kg-1. Anaesthetic maintenance was with alfaxalone initially at 9.6 mg kg-1 hour-1 combined with one of three lidocaine treatments: 3 mg kg-1 hour-1 (L-Lid), 6 mg kg-1 hour-1 (M-Lid) or 12 mg kg-1 hour-1 (H-Lid). The MIR of alfaxalone was determined by testing for responses to a stimulation in the form of clamping on a digit with a Vulsellum forceps every 30 minutes during lidocaine CRI. Basic cardiopulmonary parameters were measured. RESULTS: The alfaxalone MIRs were 8.64 (6.72-10.56), 6.72 (6.72-8.64) and 6.72 (6.72-6.72) mg kg-1 hour-1 during L-Lid, M-Lid and H-Lid, respectively, without any significant differences among treatments. Compared to the initial rate of 9.6 mg kg-1 hour-1, these reductions in MIR are equivalent to 10, 30 and 30%, respectively. Significant increases in heart rate (HR) and arterial carbon dioxide partial pressure (PaCO2) and decreases in arterial haemoglobin saturation (SaO2), arterial oxygen partial pressure (PaO2) and respiratory frequency (fR) immediately after induction were observed during all lidocaine treatments. CONCLUSIONS AND CLINICAL RELEVANCE: Lidocaine reduces the alfaxalone MIR by up to 30% with a tendency towards a plateauing in this effect at high CRIs. Immediate oxygen supplementation might be required to prevent hypoxaemia.

Antinociceptive effects of epidural magnesium sulphate alone and in combination with morphine in dogs.

OBJECTIVE: To compare the antinociceptive effects of magnesium sulphate (MgSO(4)) when administered epidurally alone and in combination with morphine. STUDY DESIGN: Experimental, randomized, 'blinded', crossover study. ANIMALS: Six healthy adult Beagle dogs. METHODS: Evaluated treatments were MgSO(4) (2.5 mg kg(-1)) alone (Mg), morphine (0.1 mg kg(-1)) alone (Mo), MgSO(4) in combination with morphine (Mm), and sterile water (0.115 mL kg(-1) ; Co) that were injected in the lumbosacral epidural space using an epidural catheter. Antinociception was measured using the von Frey mechanical threshold device applied to the carpal pads, both sides of the thorax and metatarsi. Measurements were obtained at time points: before treatment (baseline) and 0.5, 1, 2, 4, 6, 12, 18 and 24 hours after the epidural injection. Sedation, behaviour score and presence of motor deficits were assessed. Data were analyzed using a linear mixed model and Bonferroni adjustments, with significance set at p < 0.05. RESULTS: There were significant effects of treatment and time in all regions. Overall threshold values in grammes force [median (interquartile range)] when stimulation regions were combined were significantly higher in Mg [164 (135-200)], Mo [156 (129-195)] and Mm [158 (131-192)] compared to Co [145 (120-179)]. Thresholds were significantly higher compared to Co in Mg, Mo and Mm at the thorax and metatarsi, but only in Mg and Mo at the carpal pads. No motor deficits were observed at any time point. Thresholds (combined regions) were increased from baseline at one or more time points with all treatments, including control. CONCLUSION AND CLINICAL RELEVANCE: Epidural MgSO(4) produced an antinociceptive effect characterised by an increase in the mechanical thresholds of similar magnitude to that produced by epidural morphine, compared with the control group, without causing any motor deficits. No potentiation of morphine antinociception was observed. The onset and offset times of antinociception could not be clearly established. To what extent these results can be extrapolated to clinical cases requires further investigation.

Anaesthetic, analgesic and cardiorespiratory effects of intramuscular medetomidine-ketamine combination alone or with morphine or tramadol for orchiectomy in cats.

OBJECTIVES: To compare the anaesthetic, analgesic and cardiorespiratory effects of intramuscular (IM) medetomidine and ketamine administered alone or combined with morphine or tramadol, for orchiectomy in cats. STUDY DESIGN: Randomised, blinded, prospective clinical study. ANIMALS: Thirty client-owned cats. MATERIALS AND METHODS: Cats (n = 10 in each group) received a combination of medetomidine (60 µgkg(-1) ) and ketamine (10 mg kg(-1) ) alone (MedK); combined with morphine (0.2 mg kg(-1) ) (MedKM), or combined with tramadol (2 mg kg(-1) ) (MedKT) IM. Time of induction, surgical and recovery events were recorded, and physiological parameters measured and recorded. Analgesia was evaluated with a visual analogue scale, a composite scoring system and the von Frey mechanical threshold device, every hour from three to eight hours post-drug administration injection. Data were analyzed with a linear mixed model, Kruskal-Wallis or Chi-square tests (p < 0.05). RESULTS: Median (IQR) induction and recovery times (minutes) were not significantly (p = 0.125) different between groups: 5.6 (2.7-8.0), 7.4 (5.1-9.6) and 8.0 (5.8-14.9) for induction and 128.5 (95.1-142.8), 166.4 (123.1-210.0) and 142.9 (123.4-180.2) for recovery, with MedK, MedKT and MedKM, respectively. Two cats (MedKM) required alfaxalone for endotracheal intubation. In all groups, three or four cats required additional isoflurane for surgery. Arterial oxygen tension overall (mean ± SD: 66 ± 2 mmHg) was low. Surgery resulted in increased systolic arterial blood pressure (p < 0.001), haemoglobin saturation (p < 0.001), respiratory (p = 0.003) and heart rates (p = 0.002). Pain scores did not differ significantly between groups. Von Frey responses decreased over time; changes over time varied by treatment (p < 0.001), MedK returning to baseline values more rapidly than MedKM and MedKT. No cat required rescue analgesics. CONCLUSION AND CLINICAL RELEVANCE: All three protocols can provide adequate anaesthesia and analgesia for orchiectomy in cats. However, rescue intervention to maintain surgical anaesthesia may be required in some cats. Oxygen supplementation is advised.

Effects of a constant rate infusion of magnesium sulphate in healthy dogs anaesthetized with isoflurane and undergoing ovariohysterectomy.

OBJECTIVE: To determine the effects of intravenous (IV) magnesium sulphate (MgSO(4) ) as a bolus followed by a constant rate infusion (CRI) on anaesthetic requirements, neuroendocrine stress response to surgery, haemostasis and postoperative analgesia in healthy dogs undergoing ovariohysterectomy. STUDY DESIGN: Blinded randomized clinical trial. ANIMALS: Sixteen female dogs. METHODS: After intramuscular premedication with acepromazine (0.05 mg kg(-1) ) and morphine (0.3 mg kg(-1) ), anaesthesia was induced with diazepam (0.2 mg kg(-1) ) and propofol (2 mg kg(-1) ) intravenously and maintained with isoflurane in oxygen in all dogs. Dogs were randomly assigned to two groups, M and C. Group M received MgSO(4) (50 mg kg(-1) over 15 minutes, followed by a 15 mg kg(-1) hour(-1) CRI). Group C received an equivalent bolus and CRI of lactated Ringer's solution. In addition, all dogs received lactated Ringer's solution (10 mL kg(-1) over 15 minutes followed by 10 mL kg(-1) hour(-1) ). End-tidal isoflurane and carbon dioxide tensions, cardio-respiratory variables, arterial blood gases, electrolytes, ACTH and cortisol concentrations were measured at different time points. Thromboelastography (TEG) was performed pre- and post-anaesthesia. Postoperative pain was evaluated using the short form of the Glasgow Composite Pain Scale. Data were analysed with repeated measures anova and Mann-Whitney U tests (p < 0.05). RESULTS: No statistically significant differences between groups were found in any of the measured variables. However, the alpha angle and maximal amplitude recorded by TEG in group M were significantly increased post-anaesthesia, but remained within the reference interval. One dog in Group M and two in Group C received rescue analgesia during recovery. CONCLUSIONS AND CLINICAL RELEVANCE: As used in this study, MgSO(4) failed to decrease isoflurane requirements, postoperative pain and stress hormone concentrations; however, it did not produce any cardio-respiratory or major haemostatic side effects. Administration of intravenous MgSO(4) together with an opioid during ovariohysterectomy in dogs does not seem to provide any clinical advantage.

Comparison of alfaxalone and propofol administered as total intravenous anaesthesia for ovariohysterectomy in dogs.

OBJECTIVE: To compare the anaesthetic and cardiopulmonary effects of alfaxalone with propofol when used for total intravenous anaesthesia (TIVA) during ovariohysterectomy in dogs. STUDY DESIGN: A prospective non-blinded randomized clinical study. ANIMALS: Fourteen healthy female crossbred bitches, aged 0.5-5 years and weight 16-42 kg. METHODS: Dogs were premedicated with acepromazine 0.01 mg kg(-1) and morphine 0.4 mg kg(-1). Anaesthesia was induced and maintained with either propofol or alfaxalone to effect for tracheal intubation followed by an infusion of the same agent. Dogs breathed spontaneously via a 'circle' circuit, with oxygen supplementation. Cardiopulmonary parameters (respiratory and heart rates, end-tidal carbon dioxide, tidal volume, and invasive blood pressures) were measured continuously and recorded at intervals related to the surgical procedure. Arterial blood samples were analysed for blood gas values. Quality of induction and recovery, and recovery times were determined. Non-parametric data were tested for significant differences between groups using the Mann-Whitney U-test and repeatedly measured data (normally distributed) for significant differences between and within groups by anova. RESULTS: Both propofol and alphaxalone injection and subsequent infusions resulted in smooth, rapid induction and satisfactory maintenance of anaesthesia. Doses for induction (mean ± SD) were 5.8 ± 0.30 and 1.9 ± 0.07 mg kg(-1) and for the CRIs, 0.37 ± 0.09 and 0.11 ± 0.01 mg kg(-1) per minute for propofol and alfaxalone respectively. Median (IQR) recovery times were to sternal 45 (33-69) and 60 (46-61) and to standing 74 (69-76) and 90 (85-107) for propofol and alphaxalone respectively. Recovery quality was good. Cardiopulmonary effects did not differ between groups. Hypoventilation occurred in both groups. CONCLUSIONS AND CLINICAL RELEVANCE: Following premedication with acepromazine and morphine, both propofol and alphaxalone produce good quality anaesthesia adequate for ovariohysterectomy. Hypoventilation occurs suggesting a need for ventilatory support during prolonged infusion periods with either anaesthetic agent.

Effects of propofol on isoflurane minimum alveolar concentration and cardiovascular function in mechanically ventilated goats.

OBJECTIVE: To evaluate the effects of propofol, on isoflurane minimum alveolar concentration (MAC) and cardiovascular function in mechanically ventilated goats. STUDY DESIGN: Prospective, randomized, crossover experimental study. ANIMALS: Six goats, three does and three wethers. METHODS: General anaesthesia was induced with isoflurane in oxygen. Following endotracheal intubation, anaesthesia was maintained with isoflurane in oxygen. Intermittent positive pressure ventilation was applied. Baseline isoflurane MAC was determined, the noxious stimulus used being clamping a claw. The goats then received, on separate occasions, three propofol treatments intravenously: bolus of 0.5 mg kg(-1) followed by a constant rate infusion (CRI) of 0.05 mg kg(-1) minute(-1) (treatment LPROP); bolus of 1.0 mg kg(-1) followed by a CRI of 0.1 mg kg(-1) minute(-1) (treatment MPROP), bolus of 2.0 mg kg(-1) followed by a CRI of 0.2 mg kg(-1) minute(-1) (treatment HPROP). Isoflurane MAC was re-determined following propofol treatments. Plasma propofol concentrations at the time of MAC confirmation were measured. Cardiopulmonary parameters were monitored throughout the anaesthetic period. Quality of recovery was scored. The Friedman test was used to test for differences between isoflurane MACs. Medians of repeatedly measured cardiovascular parameters were tested for differences between and within treatments using repeated anova by ranks (p<0.05 for statistical significance). RESULTS: Isoflurane MAC [median (interquartile range)] was 1.37 (1.36-1.37) vol%. Propofol CRI significantly reduced the isoflurane MAC, to 1.15 (1.08-1.15), 0.90 (0.87-0.93) and 0.55 (0.49-0.58) vol% following LPROP, MPROP and HPROP treatment, respectively. Increasing plasma propofol concentrations strongly correlated (Spearman rank correlation) with decrease in MAC (Rho=0.91). Cardiovascular function was not affected significantly by propofol treatment. Quality of recovery was satisfactory. CONCLUSIONS AND CLINICAL RELEVANCE: In goats, propofol reduces isoflurane MAC in a dose-dependent manner with minimal cardiovascular effects.

Total intravenous anaesthesia (TIVA) with propofol-fentanyl and propofol-midazolam combinations in spontaneously-breathing goats.

OBJECTIVE: To compare the efficacy and cardiopulmonary effects of propofol and fentanyl, with propofol and midazolam for total intravenous anaesthesia. STUDY DESIGN: Prospective, randomized, crossover experimental study. ANIMALS: Six goats; three does and three wethers. METHODS: Goats received either fentanyl 0.02 mg kg(-1) (treatment FP) or midazolam 0.3 mg kg(-1) (treatment MP) intravenously. One minute later anaesthesia was induced with propofol, then maintained by constant rate infusion of propofol 12.0 mg kg(-1) hour(-1) and fentanyl 0.02 mg kg(-1) hour(-1) (treatment FP) or propofol 12.0 mg kg(-1) hour(-1) and midazolam 0.3 mg kg(-1) hour(-1) (treatment MP) for 90 minutes. Response to noxious stimulus was tested every 10 minutes and propofol dose adjusted to prevent purposeful movement. Cardiopulmonary parameters were measured continuously, and arterial blood-gas analysis performed intermittently. Recovery was timed and quality scored. Results are presented as median (IQR). RESULTS: Differences in the propofol induction dose [4.00 (3.96-4.01) and 3.97 (3.91-4.00) mg kg(-1) for treatments FP and MP, respectively] were not significant. Quality of induction in both groups was smooth. The median propofol dose for maintenance was less (p = 0.004) with treatment FP (12.0 mg kg(-1) hour(-1) than MP (18.0 mg kg(-1) hour(-1). Cardiopulmonary function was well maintained with both treatments. Recovery times in minutes from the end of anaesthetic infusion for treatments FP and MP respectively were; to extubation 3.0 (3.0-3.0) and 4.5 (3.3-5.0); to sternal position, 4.5 (3.3-5.0) and 5.0 (5.0-6.5) and to standing 13.0 (10.3-15.0) and 15.0 (11.3-17.3). Quality of recovery was acceptable in both groups, but abnormal behavioural signs were observed after treatment FP. CONCLUSIONS AND CLINICAL RELEVANCE: Total intravenous anaesthesia with propofol and fentanyl or propofol and midazolam, at the doses studied, in spontaneously-breathing, oxygen-supplemented goats is practicable. Recovery from the fentanyl-propofol combination is not always smooth.