Effects of detomidine or romifidine during maintenance and recovery from isoflurane anaesthesia in horses

ObjectiveTo evaluate the effects of detomidine or romifidine on cardiovascular function, isoflurane requirements and recovery quality in horses undergoing isoflurane anaesthesia.Study designProspective, randomized, blinded, clinical study.AnimalsA total of 63 healthy horses undergoing elective surgery during general anaesthesia.MethodsHorses were randomly allocated to three groups of 21 animals each. In group R, horses were given romifidine intravenously (IV) for premedication (80 μg kg^–1), maintenance (40 μg kg^–1 hour^–1) and before recovery (20 μg kg^–1). In group D2.5, horses were given detomidine IV for premedication (15 μg kg^–1), maintenance (5 μg kg^–1 hour^–1) and before recovery (2.5 μg kg^–1). In group D5, horses were given the same doses of detomidine IV for premedication and maintenance but 5 μg kg^–1 prior to recovery. Premedication was combined with morphine IV (0.1 mg kg^–1) in all groups. Cardiovascular and blood gas variables, expired fraction of isoflurane (Fe′Iso), dobutamine or ketamine requirements, recovery times, recovery events scores (from sternal to standing position) and visual analogue scale (VAS) were compared between groups using either anova followed by Tukey, Kruskal-Wallis followed by Bonferroni or chi-square tests, as appropriate (p < 0.05).ResultsNo significant differences were observed between groups for Fe′Iso, dobutamine or ketamine requirements and recovery times. Cardiovascular and blood gas measurements remained within physiological ranges for all groups. Group D5 horses had significantly worse scores for balance and coordination (p = 0.002), overall impression (p = 0.021) and final score (p = 0.008) than group R horses and significantly worse mean scores for VAS than the other groups (p = 0.002).Conclusions and clinical relevanceDetomidine or romifidine constant rate infusion provided similar conditions for maintenance of anaesthesia. Higher doses of detomidine at the end of anaesthesia might decrease the recovery quality.     

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.     

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.     

The effects of a loading dose followed by constant rate infusion of xylazine compared with romifidine on sedation,ataxia and response to stimuli in horses

ObjectiveTo compare xylazine and romifidine constant rate infusion (CRI) protocols regarding degree of sedation, and effects on postural instability (PI), ataxia during motion (A) and reaction to different stimuli.Study designBlinded randomized experimental cross-over study.AnimalsTen adult horses.MethodsDegree of sedation was assessed by head height above ground (HHAG). Effects on PI, A and reaction to visual, tactile and acoustic stimulation were assessed by numerical rating scale (NRS) and by visual analogue scale (VAS). After baseline measurements, horses were sedated by intravenous loading doses of xylazine (1 mg kg^?1) or romifidine (80 μg kg^?1) administered over 3 minutes, immediately followed by a CRI of xylazine (0.69 mg kg^?1 hour^?1) or romifidine (30 μg kg^?1 hour^?1) which was administered for 120 minutes. Degree of sedation, PI, A and reaction to the different stimuli were measured at different time points before, during and for one hour after discontinuing drug administration. Data were analysed using two-way repeated measures anova, a Generalized Linear Model and a Wilcoxon Signed Rank Test (p < 0.05).ResultsSignificant changes over time were seen for all variables. With xylazine HHAG was significantly lower 10 minutes after the loading dose, and higher at 150 and 180 minutes (i.e. after CRI cessation) compared to romifidine. Reaction to acoustic stimulation was significantly more pronounced with xylazine. Reaction to visual stimulation was greater with xylazine at 145 and 175 minutes. PI was consistently but not significantly greater with xylazine during the first 30 minutes. Reaction to touch and A did not differ between treatments. Compared to romifidine, horses were more responsive to metallic noise with xylazine.ConclusionsTime to maximal sedation and to recovery were longer with romifidine than with xylazine.Clinical relevanceWith romifidine sufficient time should be allowed for complete sedation before manipulation.     

The effects of detomidine, romifidine or acepromazine on echocardiographic measurements and cardiac function in normal horses

OBJECTIVE: To evaluate by echo- and electrocardiography the cardiac effects of sedation with detomidine hydrochloride, romifidine hydrochloride or acepromazine maleate in horses. STUDY DESIGN: An experimental study using a cross-over design without randomization. ANIMALS: Eight clinically normal Standardbred trotters. MATERIALS AND METHODS: Echocardiographic examinations (two-dimensional, guided M-mode and colour Doppler) were recorded on five different days. Heart rate (HR) and standard limb lead electrocardiograms were also obtained. Subsequently, horses were sedated with detomidine (0.01 mg kg(-1)), romifidine (0.04 mg kg(-1)) or acepromazine (0.1 mg kg(-1)) administered intravenously and all examinations repeated. RESULTS: Heart rate before treatment with the three drugs did not differ significantly (p = 0.98). Both detomidine and romifidine induced a significant decrease (p < 0.001) in HR during the first 25 minutes after sedation; while acepromazine had a varying effect on HR. For detomidine, there was a significant increase in LVIDd (left ventricular internal diameter in diastole; p = 0.034) and LVIDs (left ventricular internal diameter in systole; p < 0.001). In addition, a significant decrease was found in IVSs (the interventricular septum in systole; p < 0.001), LVFWs (the left ventricular free wall in systole; p = 0.002) and FS% (fractional shortening; p < 0.001). The frequency of pulmonary regurgitation was increased significantly (p < 0.001). Romifidine induced a significant increase in LVIDs (p < 0.001) and a significant decrease in IVSs (p < 0.001) and FS% (p = 0.002). Acepromazine had no significant effect upon any of the measured values. CONCLUSIONS: and clinical relevance The results indicate that sedation of horses with detomidine and to a lesser extent romifidine at the doses given in this study has a significant effect on heart function, echocardiographic measurements of heart dimensions and the occurrence of valvular regurgitation. Although the clinical significance of these results may be minimal, the potential effects of sedative drugs should be taken into account when echocardiographic variables are interpreted in clinical cases.     

Retrospective analysis of detomidine infusion for standing chemical restraint in 51 horses

Objective To assess the effectiveness of a detomidine infusion technique to provide standing chemical restraint in the horse. Design Retrospective study. Animals Fifty‐one adult horses aged 9.5 ± 6.9 years (range 1–23 years) and weighing 575 ± 290.3 kg. Methods Records of horses presented to our clinic over a 3‐year period in which a detomidine infusion was used to provide standing chemical restraint were reviewed. Information relating to the types of procedure performed, duration of infusion, drug dosages and adjunct drugs administered was retrieved. Results Detomidine was administered as an initial bolus loading dose (mean ± SD) of 7.5 ± 1.87 µg kg^?1. The initial infusion rate was 0.6 µg kg^?1 minute^?1, and this was halved every 15 minutes. The duration of the infusion ranged from 20 to 135 minutes. Twenty horses received additional detomidine or butorphanol during the procedure. All horses undergoing surgery received local anesthesia or epidural analgesia in addition to the detomidine infusion. A wide variety of procedures were performed in these horses. Conclusions Detomidine administered by infusion provides prolonged periods of chemical restraint in standing horses. Supplemental sedatives or analgesics may be needed in horses undergoing surgery. Clinical relevance An effective method that provides prolonged periods of chemical restraint in standing horses is described. The infusion alone did not provide sufficient analgesia for surgery and a significant proportion of animals required supplemental sedatives and analgesics.     

Dexmedetomidine constant rate infusion for 24 hours during and after propofol or isoflurane anaesthesia in dogs

OBJECTIVE: To evaluate cardiovascular and respiratory effects and pharmacokinetics of a 24-hour intravenous constant rate infusion (CRI) of dexmedetomidine (DMED) during and after propofol (PRO) or isoflurane (ISO) anaesthesia in dogs. STUDY DESIGN: Prospective, randomized, cross-over study. ANIMALS: Ten healthy adult Beagles. METHODS: Instrumented dogs received a DMED-loading bolus (25 microg m(-2)) at time 0 followed by a 24-hour CRI (25 microg m(-2) hour(-1)), with PRO or ISO induction/maintenance of anaesthesia during the first 2 hours (PRO and ISO treatment groups, respectively). Cardiovascular, respiratory, blood gas, airway gas, serum chemistry variables and DMED plasma concentration data were collected at -15, 5, 15, 30, 45, 60, 90 and 120 minutes. A number of cardiorespiratory and tissue oxygenation variables were calculated from the above data. After the 2-hours of anaesthesia, heart and respiratory rates and electrocardiograms were recorded and DMED plasma concentrations were determined for up to 26 hours. RESULTS: Vasopressor effects and the decrease in heart rate (HR) and cardiac index induced by DMED were greater for PRO than ISO, but were within clinically acceptable ranges. Adequate oxygenation was maintained above the critical O(2) delivery level. The overall incidence of unfavourable arrhythmias was low and tended to vary inversely with HR. Mean DMED plasma concentration ranged from 0.23 to 0.47 ng mL(-1) for both groups during the 24-hour CRI with a mean elimination half-life of approximately 0.46 hour. CONCLUSION AND/CLINICAL RELEVANCE: DMED CRI resulted in typical alpha(2)-agonist induced haemodynamic changes with minimal respiratory effects, and appeared to be an efficacious adjunct during and after PRO or ISO anaesthesia in healthy dogs.     

Dexmedetomidine continuous rate infusion during isoflurane anaesthesia in canine surgical patients

OBJECTIVE: To determine the effects of three rates of dexmedetomidine (DMED) constant rate infusion (CRI) on overall tissue perfusion, isoflurane (ISO) requirements, haemodynamics and quality of recovery in canine surgical patients. STUDY DESIGN: Prospective, randomized, blinded clinical study. ANIMALS: Client-owned dogs presented for soft tissue or orthopaedic surgery. METHODS: Following intravenous (IV) pre-medication with DMED (5 microg kg(-1)) and buprenorphine (10 microg kg(-1)) and propofol induction, anaesthesia was maintained with ISO in oxygen/air supplemented with a DMED CRI (1, 2 or 3 microg kg(-1) hour(-1); groups 1, 2 and 3, respectively). Ventilation was controlled in all animals using intermittent positive pressure ventilation (IPPV). Monitoring included end-tidal (ET) gases, ECG, arterial blood pressure, body temperature and sequential arterial blood gas and lactate measurements. Quality of recovery was scored after intramuscular (IM) administration of atipamezole (ATI) (12.5 microg kg(-1)). Immediate post-operative analgesia was provided with carprofen and/or buprenorphine. An analysis of variance was conducted for repeated measurements obtained during 80 minutes after first incision. Categorical data were evaluated with Chi-square analyses. RESULTS: Arterial blood pressure remained stable and within clinically acceptable limits. Mean heart rate in group 2 was significantly lower than in group 1. The incidence of 2nd degree AV block type II was significantly higher in group 3. Mean arterial lactate concentrations remained below 2 mmol/L in all groups during the study, with a significant increase occurring during recovery compared with surgery for group 3. Mean e'ISO% was similar and <1% in all groups. Complete recovery from anaesthesia was achieved after ATI administration and was of good quality in all but three animals. CONCLUSIONS AND CLINICAL RELEVANCE: Dexmedetomidine CRI is a reliable and valuable adjunct to ISO anaesthesia in maintaining surgical anaesthesia in ASA I-II dogs. Data reported indicate adequate overall tissue perfusion and a low ISO requirement while enabling a smooth and rapid recovery following ATI. The DMED CRI of 1 microg kg(-1) hour(-1) following a loading dose of 5 microg kg(-1) produced the most favourable results.     

Evaluation of the sedative,analgesic, clinicophysiological and haematological effects of intravenous detomidine,detomidine‐butorphanol,romifidine and romifidine‐butorphanol in standing donkeys

The aim of this investigation was to determine and evaluate the sedative, analgesic, clinicophysiological and haematological effects of intravenous (i.v.) injection of detomidine, detomidine‐butorphanol, romifidine and romifidine‐butorphanol. Six standing donkeys were used. Each donkey received 4 i.v. treatments and the order of treatment was randomised with a one‐week interval between each treatment. We found that i.v. injection of a combination of detomidine‐butorphanol or romifidine‐butorphanol produced potent neuroleptanalgesic effects thus providing better, safe and effective sedation with complete analgesia in standing donkeys compared with injection of detomidine or romifidine alone. The changes and reduction in pulse rate were within acceptable limits. The changes in clinicophysiological, haematological and biochemical values were mild and transient in these clinically healthy donkeys.     

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.     

RESEARCH PAPER: Romifidine as a constant rate infusion in isoflurane anaesthetized horses: a clinical study

Objective To evaluate the effects of a constant rate infusion (CRI) of romifidine on the requirement of isoflurane, cardiovascular performance and recovery in anaesthetized horses undergoing arthroscopic surgery. Study design Randomized blinded prospective clinical trial. Animals Thirty horses scheduled for routine arthroscopy. Methods After premedication (acepromazine 0.02 mg kg^?1, romifidine 80 μg kg^?1, methadone 0.1 mg kg^?1) and induction (midazolam 0.06 mg kg^?1 ketamine 2.2 mg kg^?1), anaesthesia was maintained with isoflurane in oxygen. Horses were assigned randomly to receive a CRI of saline (group S) or 40 μg kg^?1 hour^?1 romifidine (group R). The influences of time and treatment on anaesthetic and cardiovascular parameters were evaluated using an analysis of variance. Body weight (t‐test), duration of anaesthesia (t‐test) and recovery score (Wilcoxon Rank Sum Test) were compared between groups. Significance was set at p < 0.05. Results All but one horse were positioned in the dorsal recumbent position and ventilated from the start of anaesthesia. End tidal isoflurane concentrations were similar in both groups at similar time points and over the whole anaesthetic period. Cardiac output was significantly lower in horses of the R group, but there were no significant differences between groups in cardiac index, body weight or age. All other cardiovascular parameters were similar in both groups. Quality of recovery did not differ significantly between groups, but more horses in group R stood without ataxia at the first attempt. One horse from group S had a problematic recovery. Conclusions and clinical relevance No inhalation anaesthetic sparing effect or side effects were observed by using a 40 μg kg^?1 hour^?1 romifidine CRI in isoflurane anaesthetized horses under clinical conditions. Cardiovascular performance remained acceptable. Further studies are needed to identify the effective dose of romifidine that will induce an inhalation anaesthetic sparing effect in anaesthetized horses.     

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.     

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.     

Effect of a constant rate infusion of lidocaine on the quality of recovery from sevoflurane or isoflurane general anaesthesia in horses

REASONS FOR PERFORMING STUDY: Lidocaine constant rate infusions (CRIs) are common as an intraoperative adjunct to general anaesthesia, but their influence on quality of recovery has not been thoroughly determined. OBJECTIVES: To determine the effects of an intraoperative i.v. CRI of lidocaine on the quality of recovery from isoflurane or sevoflurane anaesthesia in horses undergoing various surgical procedures, using a modified recovery score system. HYPOTHESIS: The administration of intraoperative lidocaine CRI decreases the quality of recovery in horses. METHODS: Lidocaine (2 mg/kg bwt bolus followed by 50 microg/kg bwt/min) or saline was administered for the duration of surgery or until 30 mins before the end of surgery under isoflurane (n = 27) and sevoflurane (n = 27). RESULTS: Horses receiving lidocaine until the end of surgery had a significantly higher degree of ataxia and a tendency towards significance for a lower quality of recovery. There was no correlation between lidocaine plasma concentrations at recovery and the quality of recovery. CONCLUSIONS: Intraoperative CRI of lidocaine affects the degree of ataxia and may decrease the quality of recovery. POTENTIAL RELEVANCE: Discontinuing lidocaine CRI 30 mins before the end of surgery is recommended to reduce ataxia during the recovery period.     

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.     

Preliminary investigation of concurrent administration of phenylbutazone and romifidine in healthy horses

ObjectiveTo characterize the cardiorespiratory and electrocardiographic effects of the combined administration of phenylbutazone and romifidine.Study designProspective four-period, four-treatment, blinded, randomized, crossover trial.AnimalsFive, healthy, mixed breed horses.MethodsPrior to treatment administration, a catheter was introduced into the intra-thoracic cranial vena cava via the jugular vein and a subcutaneously located carotid artery was catheterised. All treatments were administered intravenously (IV) and consisted of saline placebo (PLC), phenylbutazone (PBZ, 4.4 mg kg^?1) romifidine (ROM, 80 μg kg^?1) and a combination of phenylbutazone (4.4 mg kg^?1) and romifidine (80 μg kg^?1). There was at least a 1 week washout period between treatments. Heart rate (HR), respiratory rate (f_R), systolic (SAP), diastolic (DAP) and mean (MAP) arterial pressures and central venous pressure (CVP) were recorded for baseline (prior to drug administration) and at 5 minute intervals thereafter for 30 minutes. Electrocardiographic abnormalities were recorded. Data were analyzed by anova.ResultsFor the cardiovascular variables there were no statistically significant (p > 0.05) differences between horses treated with ROM and PBZ_ROM. Statistically significant (p < 0.05) differences only occurred between treatments with romifidine (ROM and PBZ_ROM) and without romifidine (PLC and PBZ). Within treatments, for ROM, changes over time were statistically significant (p < 0.05) for HR, SAP, DAP, MAP and CVP. For PBZ_ROM, changes over time were statistically significant (p < 0.05) for CVP. Sino-atrial and atrio-ventricular blocks occurred in horses treated with ROM and PBZ_ROM.Conclusions and clinical relevanceThe combined IV administration of phenylbutazone and romifidine had no statistically significant effect on cardiorespiratory variables. These limited data suggest no evidence why both agents should not be included in a preoperative medication protocol for healthy horses but do not exclude the possibility of interactions occurring in a larger population.     

Pharmacokinetics of detomidine and its metabolites following intravenous and intramuscular administration in horses

Reasons for performing study: Detomidine is commonly used i.v. for sedation and analgesia in horses, but the pharmacokinetics and metabolism of this drug have not been well described. Objectives: To describe the pharmacokinetics of detomidine and its metabolites, 3‐hydroxy‐detomidine (OH‐detomidine) and detomidine 3‐carboxylic acid (COOH‐detomidine), after i.v. and i.m. administration of a single dose to horses. Methods: Eight horses were used in a balanced crossover design study. In Phase 1, 4 horses received a single dose of i.v. detomidine, administered 30 μg/kg bwt and 4 a single dose i.m. 30 üg/kg bwt. In Phase 2, treatments were reversed. Plasma detomidine, OH‐detomidine and COOH‐detomidine were measured at predetermined time points using liquid chromatography‐mass spectrometry. Results: Following i.v. administration, detomidine was distributed rapidly and eliminated with a half‐life (t_1/2(el)) of approximately 30 min. Following i.m. administration, detomidine was distributed and eliminated with t_1/2(el) of approximately one hour. Following, i.v. administration, detomidine clearance had a mean, median and range of 12.41, 11.66 and 10.10–18.37 ml/min/kg bwt, respectively. Detomidine had a volume of distribution with the mean, median and range for i.v. administration of 470, 478 and 215–687 ml/kg bwt, respectively. OH‐detomidine was detected sooner than COOH‐detomidine; however, COOH‐detomidine had a much greater area under the curve. Conclusions and potential relevance: These pharmacokinetic parameters provide information necessary for determination of peak plasma concentrations and clearance of detomidine in mature horses. The results suggest that, when a longer duration of plasma concentration is warranted, the i.m. route should be considered.     

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.