A clinical comparison of two anaesthetic protocols using lidocaine or medetomidine in horses

OBJECTIVE: To compare the effects of two balanced anaesthetic protocols on end-tidal isoflurane (Fe'ISO), cardiopulmonary performance and quality of recovery in horses. DESIGN: Prospective blinded randomized clinical study. ANIMALS: Sixty-nine client-owned horses, American Society of Anesthesiologists category I and II, undergoing elective surgery. METHODS: The horses were premedicated with acepromazine (0.03 mg kg(-1)) IM 30-60 minutes before induction of anaesthesia and were randomly assigned to one of two treatments: in group L (37 horses) xylazine (1 mg kg(-1)) and in group M (31 horses) medetomidine (7 microg kg(-1)) was administered IV for sedation. Anaesthesia was induced 5 minutes later with ketamine (2.2 mg kg(-1)) and diazepam (0.02 mg kg(-1)) IV and maintained with isoflurane in oxygen/air (initial FIO2 0.40-0.50) and a constant rate infusion (CRI) of either lidocaine (2 mg kg(-1)/15 minutes loading dose followed by 50 microg kg(-1) minute(-1)) (group L) or medetomidine (3.5 microg kg(-1) hour(-1)) (group M). If horses showed movement or nystagmus, additional thiopental or ketamine was administered. Heart rate, mean arterial pressure (MAP), Fe'ISO and arterial blood gases were measured. Cardiac output was measured with the lithium dilution method in 10 (group L) and 11 (group M) horses every 45 minutes. Recovery was scored. RESULTS: Heart rate and the cardiac index (CI) were significantly higher in group L with changes over time. In group M, MAP was significantly higher during the first 50 minutes. Group L needed more additional ketamine and thiopental to maintain a surgical plane of anaesthesia and Fe'ISO was significantly higher from 70 minutes. Recovery was longer in group M and of better quality. The significance level was set at p < 0.05. CONCLUSIONS AND CLINICAL RELEVANCE: In group M, maintenance of stable anaesthetic depth was easier and lower Fe'ISO was required to maintain a surgical plane of anaesthesia. Recoveries were longer but of better quality. The CI was higher in group L but cardiovascular function was generally well maintained in both groups.     

Opioid-sparing effect of a medetomidine constant rate infusion during thoraco-lumbar hemilaminectomy in dogs administered a ketamine infusion

ObjectiveTo evaluate the perioperative opioid-sparing effect of a medetomidine (MED) infusion compared to a saline (SAL) infusion in otherwise healthy dogs undergoing thoraco-lumbar hemilaminectomy surgery.Study designRandomized, partially blinded, clinical study.AnimalsA total of 44 client-owned adult dogs.MethodsAll dogs were administered a 1 μg kg^–1 MED loading dose, followed by a 1.7 μg kg^–1 hour^–1 constant rate infusion (CRI) intravenously or equivalent volumes of SAL. Infusions were started 10–15 minutes before surgical incision and continued throughout the surgical procedure. All dogs were administered a standardized anaesthetic and analgesic protocol (including a ketamine CRI). Multiparametric monitoring, including invasive arterial blood pressure, was performed. A trained investigator, unaware of the treatment, performed pain scores for 4 hours postoperatively. Rescue analgesia consisted of fentanyl administered intraoperatively and methadone postoperatively. Data were tested for normality and analysed with Fisher’s exact test, Mann–Whitney U-test, analysis of variance and Kaplan–Meier survival analysis. Data are shown as median (interquartile range) and p-value was set at < 0.05.ResultsThe total dose of fentanyl was significantly lower with MED 0 (0–0.8) μg kg^–1 hour^–1 compared to SAL 3 (1.8–5.3) μg kg^–1 hour^–1 (p = 0.004). In the MED group, one dog compared to 12 dogs in the SAL group required a fentanyl CRI (p = 0.001). There were no statistically significant differences between groups regarding the total dose of methadone administered.Conclusions and clinical relevanceThe addition of a low-dose medetomidine CRI to the anaesthetic protocol decreased the need for a fentanyl CRI in otherwise healthy dogs undergoing thoraco-lumbar hemilaminectomy surgery during administration of a ketamine CRI.     

Medetomidine continuous rate intravenous infusion in horses in which surgical anaesthesia is maintained with isoflurane and intravenous infusions of lidocaine and ketamine

ObjectiveTo evaluate medetomidine as a continuous rate infusion (CRI) in horses in which anaesthesia is maintained with isoflurane and CRIs of ketamine and lidocaine.Study designProspective, randomized, blinded clinical trial.AnimalsForty horses undergoing elective surgery.MethodsAfter sedation and induction, anaesthesia was maintained with isoflurane. Mechanical ventilation was employed. All horses received lidocaine (1.5 mg kg^?1 initially, then 2 mg kg^?1 hour^?1) and ketamine (2 mg kg^?1 hour^?1), both CRIs reducing to 1.5 mg kg^?1 hour^?1 after 50 minutes. Horses in group MILK received a medetomidine CRI of 3.6 μg kg^?1 hour^?1, reducing after 50 minutes to 2.75 μg kg^?1 hour^?1, and horses in group ILK an equal volume of saline. Mean arterial pressure (MAP) was maintained above 70 mmHg using dobutamine. End-tidal concentration of isoflurane (FE′ISO) was adjusted as necessary to maintain surgical anaesthesia. Group ILK received medetomidine (3 μg kg^?1) at the end of the procedure. Recovery was evaluated. Differences between groups were analysed using Mann-Whitney, Chi-Square and anova tests as relevant. Significance was taken as p < 0.05.ResultsFE′ISO required to maintain surgical anaesthesia in group MILK decreased with time, becoming significantly less than that in group ILK by 45 minutes. After 60 minutes, median (IQR) FE′ISO in MILK was 0.65 (0.4–1.0) %, and in ILK was 1 (0.62–1.2) %. Physiological parameters did not differ between groups, but group MILK required less dobutamine to support MAP. Total recovery times were similar and recovery quality good in both groups.Conclusion and clinical relevanceA CRI of medetomidine given to horses which were also receiving CRIs of lidocaine and ketamine reduced the concentration of isoflurane necessary to maintain satisfactory anaesthesia for surgery, and reduced the dobutamine required to maintain MAP. No further sedation was required to provide a calm recovery.     

Influence of a constant rate infusion of dexmedetomidine on cardiopulmonary function and recovery quality in isoflurane anaesthetized horses

ObjectiveTo investigate the influence of a dexmedetomidine constant rate infusion (CRI) in horses anaesthetized with isoflurane.Study designProspective, randomized, blinded, clinical study.AnimalsForty adult healthy horses (weight mean 491 ± SD 102 kg) undergoing elective surgery.MethodsAfter sedation [dexmedetomidine, 3.5 μg kg^?1 intravenously (IV)] and induction IV (midazolam 0.06 mg kg^?1, ketamine 2.2 mg kg^?1), anaesthesia was maintained with isoflurane in oxygen/air (FiO₂ 55–60%). Horses were ventilated and dobutamine was administered when hypoventilation [arterial partial pressure of CO₂ > 8.00 kPa (60 mmHg)] and hypotension [arterial pressure 70 mmHg] occurred respectively. During anaesthesia, horses were randomly allocated to receive a CRI of dexmedetomidine (1.75 μg kg^?1 hour^?1) (D) or saline (S). Monitoring included end-tidal isoflurane concentration, cardiopulmonary parameters, and need for dobutamine and additional ketamine. All horses received 0.875 μg kg^?1 dexmedetomidine IV for the recovery period. Age and weight of the horses, duration of anaesthesia, additional ketamine and dobutamine, cardiopulmonary data (anova), recovery scores (Wilcoxon Rank Sum Test), duration of recovery (t-test) and attempts to stand (Mann–Whitney test) were compared between groups. Significance was set at p < 0.05.ResultsHeart rate and arterial partial pressure of oxygen were significantly lower in group D compared to group S. An interaction between treatment and time was present for cardiac index, oxygen delivery index and systemic vascular resistance. End-tidal isoflurane concentration and heart rate significantly increased over time. Packed cell volume, systolic, diastolic and mean arterial pressure, arterial oxygen content, stroke volume index and systemic vascular resistance significantly decreased over time. Recovery scores were significantly better in group D, with fewer attempts to stand and significantly longer times to sternal position and first attempt to stand.Conclusions and clinical relevance A dexmedetomidine CRI produced limited cardiopulmonary effects, but significantly improved recovery quality.     

Cardiopulmonary and isoflurane‐sparing effects of epidural or intravenous infusion of dexmedetomidine in cats undergoing surgery with epidural lidocaine

ObjectiveTo compare the cardiorespiratory, anesthetic-sparing effects and quality of anesthetic recovery after epidural and constant rate intravenous (IV) infusion of dexmedetomidine (DEX) in cats given a low dose of epidural lidocaine under propofol-isoflurane anesthesia and submitted to elective ovariohysterectomy.Study designRandomized, blinded clinical trial.AnimalsTwenty-one adult female cats (mean body weight: 3.1 ± 0.4 kg).MethodsCats received DEX (4 μg kg^?1, IM). Fifteen minutes later, anesthesia was induced with propofol and maintained with isoflurane. Cats were divided into three groups. In GI cats received epidural lidocaine (1 mg kg^?1, n = 7), in GII cats were given epidural lidocaine (1 mg kg^?1) + DEX (4 μg kg^?1, n = 7), and in GIII cats were given epidural lidocaine (1 mg kg^?1) + IV constant rate infusion (CRI) of DEX (0.25 μg kg^?1 minute^?1, n = 7). Variables evaluated included heart rate (HR), respiratory rate (f_R), systemic arterial pressures, rectal temperature (RT), end-tidal CO₂, end-tidal isoflurane concentration (e′ISO), arterial blood gases, and muscle tone. Anesthetic recovery was compared among groups by evaluation of times to recovery, HR, f_R, RT, and degree of analgesia. A paired t-test was used to evaluate pre-medication variables and blood gases within groups. anova was used to compare parametric data, whereas Friedman test was used to compare muscle relaxation.ResultsEpidural and CRI of DEX reduced HR during anesthesia maintenance. Mean ± SD e′ISO ranged from 0.86 ± 0.28% to 1.91 ± 0.63% in GI, from 0.70 ± 0.12% to 0.97 ± 0.20% in GII, and from 0.69 ± 0.12% to 1.17 ± 0.25% in GIII. Cats in GII and GIII had longer recovery periods than in GI.Conclusions and clinical relevanceEpidural and CRI of DEX significantly decreased isoflurane consumption and resulted in recovery of better quality and longer duration, despite bradycardia, without changes in systemic blood pressure.     

Effects of constant rate infusion of lidocaine and ketamine, with or without morphine, on isoflurane MAC in horses

REASONS FOR PERFORMING STUDY: Lidocaine and ketamine are administered to horses as a constant rate infusion (CRI) during inhalation anaesthesia to reduce anaesthetic requirements. Morphine decreases the minimum alveolar concentration (MAC) in some domestic animals; when administered as a CRI in horses, morphine does not promote haemodynamic and ventilatory changes and exerts a positive effect on recovery. Isoflurane-sparing effect of lidocaine, ketamine and morphine coadministration has been evaluated in small animals but not in horses. OBJECTIVES: To determine the reduction in isoflurane MAC produced by a CRI of lidocaine and ketamine, with or without morphine. HYPOTHESIS: Addition of morphine to a lidocaine-ketamine infusion reduces isoflurane requirement and morphine does not impair the anaesthetic recovery of horses. METHODS: Six healthy adult horses were anaesthetised 3 times with xylazine (1.1 mg/kg bwt i.v.), ketamine (3 mg/kg bwt i.v.) and isoflurane and received a CRI of lidocaine-ketamine (LK), morphine-lidocaine-ketamine (MLK) or saline (CTL). The loading doses of morphine and lidocaine were 0.15 mg/kg bwt i.v and 2 mg/kg bwt i.v. followed by a CRI at 0.1 mg/kg bwt/h and 3 mg/kg bwt/h, respectively. Ketamine was given as a CRI at 3 mg/kg bwt/h. Changes in MAC characterised the anaesthetic-sparing effect of the drug infusions under study and quality of recovery was assessed using a scoring system. Results: Mean isoflurane MAC (mean ± s.d.) in the CTL, LK and MLK groups was 1.25 ± 0.14%, 0.64 ± 0.20% and 0.59 ± 0.14%, respectively, with MAC reduction in the LK and MLK groups being 49 and 53% (P<0.001), respectively. No significant differences were observed between groups in recovery from anaesthesia. Conclusions and clinical relevance: Administration of lidocaine and ketamine via CRI decreases isoflurane requirements. Coadministration of morphine does not provide further reduction in anaesthetic requirements and does not impair recovery.     

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.     

Comparison of the effects of an intravenous lidocaine infusion combined with 1% isoflurane versus 2% isoflurane alone on selected cardiovascular variables and recovery characteristics during equine general anaesthesia

Objectives

To compare the effects of a lidocaine constant rate infusion (CRI) combined with 1% isoflurane versus those of 2% isoflurane alone on cardiovascular variables in anaesthetized horses, and to estimate the sample size required to detect a difference in recovery quality.

Development of a romifidine constant rate infusion with or without butorphanol for standing sedation of horses

ObjectiveTo determine constant rate infusion (CRI) protocols for romifidine (R) and romifidine combined with butorphanol (RB) resulting in constant sedation and romifidine plasma concentrations.Study designBlinded randomized crossover study.AnimalsTen adult research horses.MethodsPart I: After determining normal height of head above ground (HHAG = 100%), loading doses of romifidine (80 μg kg^?1) with butorphanol (RB: 18 μg kg^?1) or saline (R) were given intravenously (IV). Immediately afterwards, a butorphanol (RB: 25 μg kg^?1 hour^?1) or saline (R) CRI was administered for 2 hours. The HHAG was used as marker of sedation depth. Sedation was maintained for 2 hours by additional romifidine (20 μg kg^?1) whenever HHAG > 50%. The dose rate of romifidine (μg kg^?1 hour^?1) required to maintain sedation was calculated for both treatments. Part II: After loading doses, the romifidine CRIs derived from part I were administered in parallel to butorphanol (RB) or saline (R). Sedation and ataxia were evaluated periodically. Romifidine plasma concentrations were measured by HPLC-MS-MS at 0, 5, 10, 15, 30, 45, 60, 90, 105, and 120 minutes. Data were analyzed using paired t-test, Fisher's exact test, Wilcoxon signed rank test, and two-way anova for repeated measures (p < 0.05).ResultsThere was no significant difference in romifidine requirements (R: 30; RB: 29 μg kg^?1 hour^?1). CRI protocols leading to constant sedation were developed. Time to first additional romifidine bolus was significantly longer in RB (mean ± SD, R: 38.5 ± 13.6; RB: 50.5 ± 11.7 minutes). Constant plasma concentrations of romifidine were achieved during the second hour of CRI. Ataxia was greater when butorphanol was added.ConclusionRomifidine bolus, followed by CRI, provided constant sedation assessed by HHAG. Butorphanol was ineffective in reducing romifidine requirements in unstimulated horses, but prolonged the sedation caused by the initial romifidine bolus.Clinical relevanceBoth protocols need to be tested under clinical conditions.     

Development of a xylazine constant rate infusion with or without butorphanol for standing sedation of horses

ObjectiveTo elaborate constant rate infusion (CRI) protocols for xylazine (X) and xylazine/butorphanol (XB) which will result in constant sedation and steady xylazine plasma concentrations.Study designBlinded randomized experimental study.AnimalsTen adult research horses.MethodsPart I: After normal height of head above ground (HHAG = 100%) was determined, a loading dose of xylazine (1 mg kg^?1) with butorphanol (XB: 18 μg kg^?1) or saline (X: equal volume) was given slowly intravenously (IV). Immediately afterwards, a CRI of butorphanol (XB: 25 μg kg^?1 hour^?1) or saline (X) was administered for 2 hours. The HHAG was used as a marker of depth of sedation. Sedation was maintained for 2 hours by additional boluses of xylazine (0.3 mg kg^?1) whenever HHAG >50%. The dose of xylazine (mg kg^?1 hour^?1) required to maintain sedation was calculated for both groups. Part II: After the initial loading dose, the calculated xylazine infusion rates were administered in parallel to butorphanol (XB) or saline (X) and sedation evaluated. Xylazine plasma concentrations were measured by HPLC-MS-MS at time points 0, 5, 30, 45, 60, 90, and 120 minutes. Data were analyzed using paired t-test, Wilcoxon signed rank test and a 2-way anova for repeated measures (p < 0.05).ResultsThere was no significant difference in xylazine requirements (X: 0.69, XB: 0.65 mg kg^?1 hour^?1) between groups. With treatment X, a CRI leading to prolonged sedation was developed. With XB, five horses (part I: two, part II: three) fell down and during part II four horses appeared insufficiently sedated. Xylazine plasma concentrations were constant after 45 minutes in both groups.ConclusionXylazine bolus, followed by CRI, provided constant sedation. Additional butorphanol was ineffective in reducing xylazine requirements and increased ataxia and apparent early recovery from sedation in unstimulated horses.Clinical relevanceData were obtained on unstimulated healthy horses and extrapolation to clinical conditions requires caution.     

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.

Effect of detomidine or romifidine constant rate infusion on plasma lactate concentration and inhalant requirements during isoflurane anaesthesia in horses

Objective

Influence of detomidine or romifidine constant rate infusion (CRI) on plasma lactate concentration and isoflurane requirements in horses undergoing elective surgery.

Comparison of intraoperative cardiorespiratory and behavioral responses to medetomidine combined with tramadol or butorphanol during standing laparoscopic ovariectomy in horses

The purpose of this study was to assess the cardiorespiratory and behavioral responses to the combination of medetomidine and tramadol (M-T) or butorphanol (M-B) in standing laparoscopic ovariectomy in horses. One ovary was removed under M-T and the contralateral ovary was removed under M-B with at least 4 weeks between operations at random. Horses were sedated using intravenous medetomidine (5 µg/kg) followed by tramadol (1 mg/kg) or butorphanol (10 µg/kg) after 5 min. Sedation was maintained through the repeated injection of medetomidine (1 µg/kg) and tramadol (0.4 mg/kg) or medetomidine (1 µg/kg) and butorphanol (4 µg/kg) every 15 min. Cardiorespiratory function and behavioral responses, including, sedation, ataxia, and analgesia, were assessed during the surgery. There were no significant differences in cardiorespiratory values and sedation and analgesia scores between M-T and M-B. Ataxia scores were significantly lower in M-T than in M-B. This result suggests that M-T could maintain smooth and stable standing surgery with minimal cardiorespiratory changes in horses.     

Evaluation of a romifidine constant rate infusion protocol with or without butorphanol for dentistry and ophthalmologic procedures in standing horses

ObjectiveTo compare the clinical usefulness of constant rate infusion (CRI) protocols of romifidine with or without butorphanol for sedation of horses.Study designProspective ‘blinded’ controlled trial using block randomization.AnimalsForty healthy Freiberger stallions.MethodsThe horses received either intravenous (IV) romifidine (loading dose: 80 μg kg^?1; infusion: 30 μg kg^?1 hour^?1) (treatment R, n = 20) or romifidine combined with butorphanol (romifidine loading: 80 μg kg^?1; infusion: 29 μg kg^?1 hour^?1, and butorphanol loading: 18 μg kg^?1; infusion: 25 μg kg^?1 hour^?1) (treatment RB, n = 20). Twenty-one horses underwent dentistry and ophthalmic procedures, while 19 horses underwent only ophthalmologic procedure and buccal examination. During the procedure, physiologic parameters and occurrence of head/muzzle shaking or twitching and forward movement were recorded. Whenever sedation was insufficient, additional romifidine (20 μg kg^?1) was administered IV. Recovery time was evaluated by assessing head height above ground. At the end of the procedure, overall quality of sedation for the procedure was scored by the dentist and anaesthetist using a visual analogue scale. Statistical analyses used two-way anova or linear mixed models as relevant.ResultsSedation quality scores as assessed by the anaesthetist were R: median 7.55, range: 4.9–9.0 cm, RB: 8.8, 4.7–10.0 cm, and by the dentist R: 6.6, 3.0–8.2 cm, RB: 7.9, 6.6–8.8 cm. Horses receiving RB showed clinically more effective sedation as demonstrated by fewer poor scores and a tendency to reduced additional drug requirements. More horses showed forward movement and head shaking in treatment RB than treatment R. Three horses (two RB, one R) had symptoms of colic following sedation.Conclusions and clinical relevanceThe described protocols provide effective sedation under clinical conditions but for dentistry procedures, the addition of butorphanol is advantageous.