Infusion of a combination of propofol and medetomidine for long-term anesthesia in ponies

Recovery of horses from general anaesthesia: A systematic review (2000-2020) of the influence of anaesthetic protocol on recovery quality

BACKGROUND

The recovery phase after equine general anaesthesia (GA) is a time of considerable risk and therefore has been the subject of extensive research over the last 20 years. Various pharmacological interventions have been developed and studied with the objective of improving recovery quality and reducing anaesthetic-related mortality and morbidity. Nevertheless, some controversy remains regarding the influence of anaesthetic protocol choice on recovery quality from GA and its implications for recovery-related mortality and morbidity. A systematic review of the literature investigating the influence of anaesthetic protocol choice on recovery quality is currently lacking.

OBJECTIVES

To perform a detailed evaluation of the equine veterinary literature investigating the effect of anaesthetic protocol choice on equine recovery quality utilising the GRADE framework.

STUDY DESIGN

A systematic evaluation of the equine veterinary literature was performed using the GRADE framework.

METHODS

A literature search was performed and studies were assessed for eligibility by both authors utilising PRISMA guidelines. Studies meeting inclusion criteria were evaluated by both authors, categorically summarised and the quality of evidence for each sub-topic was assessed using the GRADE framework.

RESULTS

A total of 124 studies were identified which directly assessed the impact of anaesthetic protocol choice on recovery quality after GA in horses. Evaluation of the available evidence indicated that certain partial intravenous anaesthesia (PIVA) agents, cessation of intravenous lidocaine 30 minutes prior to recovery and provision of adequate analgesia improves recovery quality.

MAIN LIMITATIONS

The validity of the results of some studies may have been compromised by missing data and small sample sizes.

CONCLUSIONS

There is evidence to indicate that certain PIVA agents, cessation of intravenous lidocaine 30 minutes prior to recovery and provision of adequate analgesia improves recovery quality.

Recovery after General Anaesthesia in Adult Horses: A Structured Summary of the Literature

Simple Summary

Recovery is the most dangerous phase of general anaesthesia in horses. Numerous publications have reported about this phase, but structured reviews that try to reduce the risk of bias of narrative reviews/expert opinions, focussing on the topic are missing. Therefore, the aim of the present article was to publish the first structured review as a summary of the literature focussing on the recovery phase after general anaesthesia in horses. The objective was to summarise the available literature, taking into account the scientific evidence of the individual studies. A structured approach was followed with two experts in the field independently deciding on article inclusion and its level of scientific evidence. A total number of 444 articles, sorted by topics and classified based on their levels of evidence, were finally included into the present summary. The most important findings were summarised and discussed. The present structured review can be used as a compilation of the publications that, to date, focus on the recovery phase after general anaesthesia in adult horses. This type of review tries to minimise the risk of bias inherent to narrative reviews/expert opinions.

Abstract

Recovery remains the most dangerous phase of general anaesthesia in horses. The objective of this publication was to perform a structured literature review including levels of evidence (LoE) of each study with the keywords “recovery anaesthesia horse”, entered at once, in the search browsers PubMed and Web of Science. The two authors independently evaluated each candidate article. A final list with 444 articles was obtained on 5 April 2021, classified as: 41 “narrative reviews/expert opinions”, 16 “retrospective outcome studies”, 5 “surveys”, 59 “premedication/sedation and induction drugs”, 27 “maintenance with inhalant agents”, 55 “maintenance with total intravenous anaesthesia (TIVA)”, 3 “TIVA versus inhalants”, 56 “maintenance with partial intravenous anaesthesia (PIVA)”, 27 “other drugs used during maintenance”, 18 “drugs before/during recovery”, 18 “recovery systems”, 21 “respiratory system in recovery”, 41 “other factors”, 51 “case series/reports” and 6 “systems to score recoveries”. Of them, 167 were LoE 1, 36 LoE 2, 33 LoE 3, 110 LoE 4, 90 LoE 5 and 8 could not be classified based on the available abstract. This review can be used as an up-to-date compilation of the literature about recovery after general anaesthesia in adult horses that tried to minimise the bias inherent to narrative reviews.

A retrospective comparison of induction with thiopental/guaifenesin and propofol/ketamine in Thoroughbred racehorses anesthetized with sevoflurane and medetomidine during arthroscopic surgery

This study compares clinical characteristics between induction with thiopental/guaifenesin and propofol/ketamine in Thoroughbred racehorses anesthetized with sevoflurane and medetomidine. Clinical records of 214 horses that underwent arthroscopic surgery between 2015 and 2016 were retrospectively retrieved. Horses were premedicated with medetomidine and midazolam to sedate at the adequate level for smooth induction, and then induced with either thiopental (4.0 mg/kg) and guaifenesin (100 mg/kg) in Group TG (n=91) or propofol (1.0 mg/kg) and ketamine (1.0 mg/kg) in Group PK (n=123). Anesthesia was maintained using sevoflurane with constant rate infusion of medetomidine. Quality of induction/recovery, sevoflurane requirement, cardiovascular function and recovery characteristics were evaluated. Anesthetic induction scores (median, range) for Group TG (5, 2-5) and Group PK (5, 2-5) were not significantly different. There were no significant differences in end-tidal sevoflurane concentration (mean ± standard deviation) between Group TG and Group PK (both 2.4 ± 0.2%). Dobutamine infusion rate (µg/kg/min) required for keeping mean arterial blood pressure (MAP) above 70 mmHg in Group PK (0.43, 0.10-1.40) was significantly lower than in Group TG (0.67, 0.08-1.56). Recovery score in Group PK (5, 2-5) was significantly higher than in Group TG (4, 2-5). Both propofol/ketamine and thiopental/guaifenesin provided a smooth induction of anesthesia. Moreover, induction with propofol/ketamine resulted in lower dobutamine requirements for keeping MAP above 70 mmHg during maintenance, and better quality of recovery. Induction with propofol/ketamine would be preferable to thiopental/guaifenesin in Thoroughbred racehorses anesthetized with sevoflurane and medetomidine during arthroscopic surgery.

Clinical effects of constant rate infusions of medetomidine-propofol combined with sevoflurane anesthesia in Thoroughbred racehorses undergoing arthroscopic surgery

Background

The aim of the present study was to evaluate clinical efficacy of constant rate infusions (CRIs) of medetomidine–propofol combined with sevoflurane anesthesia in Thoroughbred racehorses undergoing arthroscopic surgery. Thirty horses were sedated intravenously (IV) with medetomidine (6.0 μg/kg) and midazolam (0.02 mg/kg) and induced IV with ketamine (1.0 mg/kg) and propofol (1.0 mg/kg). These horses were randomly allocated to three groups and maintained with sevoflurane and CRI of either medetomidine (3.0 μg/kg/h) (Group M; n = 10); or medetomidine (3.0 μg/kg/h) and propofol (3.0 mg/kg/h) (Group MP3; n = 10); or medetomidine (3.0 μg/kg/h) and propofol (6.0 mg/kg/h) (Group MP6; n = 10). End-tidal sevoflurane concentration (ET_SEVO), cardiovascular parameters, plasma propofol concentration, and recovery time and quality were compared among groups. Data were analyzed by using ANOVA with Tukey’s multiple comparison test, considering P < 0.05 significant.

Results

ET_SEVO (%) was 2.4 ± 0.1 in Group M, 1.7 ± 0.2 in Group MP3, and 1.4 ± 0.2 in Group MP6; ET_SEVO declined significantly in a propofol-dose-dependent manner. The rates of dobutamine infusion (μg/kg/min) required to keep the mean arterial blood pressure over 70 mmHg were significantly lower in Group MP3 (0.20 ± 0.10) and Group MP6 (0.15 ± 0.06) than in Group M (0.37 ± 0.18). Recovery time and quality did not differ among groups. All horses in Group MP3 required only one attempt to stand, and recovery quality was excellent. Plasma propofol concentrations were stable throughout maintenance of anesthesia in Group MP3, whereas those in Group MP6 increased significantly with increasing duration of maintenance.

Conclusions

CRIs of medetomidine–propofol reduced the sevoflurane requirement for surgical anesthesia as the propofol dose increased, compared with a CRI of medetomidine alone. Additionally, the two propofol protocols provided good maintenance of cardiovascular function. CRIs of medetomidine (3.0 μg/kg/h) and propofol (3.0 mg/kg/h) resulted in excellent-quality recovery. This protocol could therefore be an especially useful additive to sevoflurane anesthesia in Thoroughbred racehorses undergoing arthroscopic surgery.

Anaesthetic responses and reflexes to propofol and its combination in swine

To determine the effectiveness of propofol alone (P), and the combination of xylazine-propofol (XP), xylazineketamine (XK), xylazine-thiopentone (XT), anaesthetic protocols were studied in randomly selected 16 healthy indigenous pigs of either sexes, age 12 to 15 months and weight ranging from 12 to 16 kg. The responses of propofol and the combinations in different stages of anaesthesia were closely monitored. Various reflex responses and muscle tenacity were also observed concurrently during the period of anaesthesia. The study found the shortest (0.29±0.02 min) induction period with XT anaesthesia and the longest (2.95±0.21 min) by XK; whereas, induction of anaesthesia with P and XP was 0.4±0.08 and 0.41±0.08 min respectively. The time required for maximum depth of anaesthesia was the shortest in P (7.50±0.65 min) than the combinations. However, the anaesthetic protocol with XP produced the highest (65.25±3.30 min) duration of anaesthesia than the shortest (10.75±1.75 min) extent with P. Moreover, time to recovery from anaesthesia was higher (83.25±2.14 min) in XT and shorter (18.50±1.32 min) in P protocol. Good muscle relaxation was observed in XP, XK and XT combinations. Palpebral, conjunctival, jaw, tail and digital reflexes were almost absent in XP and XT combinations. The study concluded that propofol itself is a safe anaesthetic for short surgical interventions and its combination with xylazine is to be recommended for prolonged surgical procedures in swine.

Evaluation of total intravenous anesthesia with propofol-guaifenesin-medetomidine and alfaxalone-guaifenesin-medetomidine in Thoroughbred horses undergoing castration

Anesthetic and cardiorespiratory effects of total intravenous anesthesia (TIVA) technique using propofol-guaifenesin-medetomidine (PGM) and alfaxalone-guaifenesin-medetomidine (AGM) were preliminarily evaluated in Thoroughbred horses undergoing castration. Twelve male Thoroughbred horses were assigned randomly into two groups. After premedication with intravenous (IV) administrations of medetomidine (5.0 µg/kg) and butorphanol (0.02 mg/kg), anesthesia was induced with guaifenesin (10 mg/kg IV), followed by either propofol (2.0 mg/kg IV) (group PGM: n=6) or alfaxalone (1.0 mg/kg IV) (group AGM: n=6). Surgical anesthesia was maintained for 60 min at a constant infusion of either propofol (3.0 mg/kg/hr) (group PGM) or alfaxalone (1.5 mg/kg/hr) (group AGM), in combination with guaifenesin (80 mg/kg/hr) and medetomidine (3.0 µg/kg/hr). Responses to surgical stimuli, cardiorespiratory values, and induction and recovery characteristics were recorded throughout anesthesia. During anesthesia induction, one horse paddled in group PGM. All horses from group AGM were maintained at adequate anesthetic depth for castration. In group PGM, 3 horses showed increased cremaster muscle tension and one showed slight movement requiring additional IV propofol to maintain surgical anesthesia. No horse exhibited apnea, although arterial oxygen tension decreased in group AGM to less than 60 mmHg. Recovery quality was good to excellent in both groups. In conclusion, TIVA using PGM and AGM infusion was available for 60 min anesthesia in Thoroughbred horses. TIVA techniques using PGM and AGM infusion provided clinically acceptable general anesthesia with mild cardiorespiratory depression. However, inspired air should be supplemented with oxygen to prevent hypoxemia during anesthesia.

Cardiovascular effects of total intravenous anesthesia using ketamine-medetomidine-propofol (KMP-TIVA) in horses undergoing surgery

Cardiovascular effects of total intravenous anesthesia using ketamine-medetomidine-propofol drug combination (KMP-TIVA) were determined in 5 Thoroughbred horses undergoing surgery. The horses were anesthetized with intravenous administration (IV) of ketamine (2.5 mg/kg) and midazolam (0.04 mg/kg) following premedication with medetomidne (5 µg/kg, IV) and artificially ventilated. Surgical anesthesia was maintained by controlling propofol infusion rate (initially 0.20 mg/kg/min following an IV loading dose of 0.5 mg/kg) and constant rate infusions of ketamine (1 mg/kg/hr) and medetomidine (1.25 µg/kg/hr). The horses were anesthetized for 175 ± 14 min (range from 160 to 197 min). Propofol infusion rates ranged from 0.13 to 0.17 mg/kg/min, and plasma concentration (Cpl) of propofol ranged from 11.4 to 13.3 µg/ml during surgery. Cardiovascular measurements during surgery remained within clinically acceptable ranges in the horses (heart rate: 33 to 37 beats/min, mean arterial blood pressure: 111 to 119 mmHg, cardiac index: 48 to 53 ml/kg/min, stroke volume: 650 to 800 ml/beat and systemic vascular resistance: 311 to 398 dynes/sec/cm(5)). The propofol Cpl declined rapidly after the cessation of propofol infusion and was significantly lower at 10 min (4.5 ± 1.5 µg/ml), extubation (4.0 ± 1.2 µg/ml) and standing (2.4 ± 0.9 µg/ml) compared with the Cpl at the end of propofol administration (11.4 ± 2.7 µg/ml). All the horses recovered uneventfully and stood at 74 ± 28 min after the cessation of anesthesia. KMP-TIVA provided satisfactory quality and control of anesthesia with minimum cardiovascular depression in horses undergoing surgery.

Effects of a constant rate infusion of medetomidine-propofol on isoflurane minimum alveolar concentrations in horses

The aim of this investigation was to determine the isoflurane-sparing effect and impact on arterial blood pressure and anaesthetic recovery of a constant rate infusion of medetomidine-propofol in horses. In a prospective, crossover, randomised study, six healthy horses (mean ± SD age, 13.7 ± 7.7 years; weight, 433 ± 51 kg) were anaesthetised twice with isoflurane and were randomly assigned to receive one of two treatments on each occasion, at least 2 weeks apart. The first treatment was saline (CTL group) and the second a medetomidine-propofol infusion (MP group; 1.25 µg/kg/h medetomidine and 3 mg/kg/h propofol). The isoflurane minimum alveolar concentration (MAC) was determined and the reduction in anaesthetic requirements was calculated. Cardiopulmonary data were recorded at different intervals during the procedure and anaesthetic recovery was blindly assessed using three independent scales. The MAC in the MP group (0.43 ± 0.08%) was 65% lower than in the CTL group (1.23 ± 0.10%). The MP group had a higher mean arterial blood pressure and required less dobutamine than the CTL group. The recovery quality in both groups was considered fair or good and an improvement was observed using the Donaldson scale in the MP group. The administration of a medetomidine-propofol constant rate infusion reduced anaesthetic isoflurane requirements to a clinically significant extent and improved stability of arterial blood pressure together with a good quality recovery. This regime could be useful for providing balanced anaesthesia in horses.

Clinical evaluation of alfaxalone to induce and maintain anaesthesia in cats undergoing neutering procedures

This study looked at the use and efficacy of alfaxalone for total intravenous anaesthesia (TIVA) in cats. Following intramuscular medetomidine (20 μg/kg) and morphine (0.3 mg/kg) premedication, anaesthesia was induced and maintained with intravenous alfaxalone. Patients were breathing 100% oxygen. Heart rate (HR), respiratory rate (RR), end-tidal carbon dioxide, oxygen saturation of haemoglobin and indirect arterial blood pressure via Doppler (DAP) were recorded every 5 mins. Thirty-four cats (10 males and 24 females), between the age of 6 and 18 months, and weighing between 1.8 and 5.3 kg, and undergoing neutering procedures were included in this study. The results are presented as median (min, max) values. The time to first spontaneous movement (TS) was >30 mins in 19 cats, of which 12 received atipamezole for reversal of the effects of medetomidine. The TS was 53 (43, 130) mins in these 12 cats and 50 (40, 72) mins in the other seven cats. The body temperature in those 19 cats was significantly lower than the other cats ( P = 0.05). The alfaxalone induction dose and maintenance infusion rate were1.7 (0.7, 3.0) mg/kg and 0.18 (0.06, 0.25) mg/kg/min, respectively. The HR, RR and DAP were 145 (68, 235) beats/min, 17 (5, 40) breaths/min and 110 (58, 210) mmHg, respectively. Apnoea was not observed in any cat. In conclusion, alfaxalone TIVA in combination with medetomidine and morphine premedication was effective in feral and domestic cats for the performance of neutering surgery; low body temperature might have resulted in longer recoveries in some cats.

Evaluation of the clinical efficacy of two partial intravenous anesthetic protocols, compared with isoflurane alone, to maintain general anesthesia in horses

OBJECTIVE

To compare the ability of 2 partial IV anesthesia (PIVA) techniques to maintain anesthesia, compared with isoflurane alone, in horses.

ANIMALS

45 horses.

PROCEDURES

Client-owned horses requiring general anesthesia for a variety of procedures of at least 1 hour's duration were randomly allocated to 3 groups (n = 15/group) that differed for the maintenance protocol. Anesthesia was maintained with isoflurane with a starting end-tidal isoflurane concentration of 1.3% (isoflurane group) or a concentration of 1% supplemented with an adjustable continuous infusion of guaifenesin-ketamine (IGK group) or romifidine-ketamine (IRK group). A predefined scoring system was used to assess anesthetic depth and to adjust anesthetic delivery. The need for rescue anesthetics and recovery quality were compared.

RESULTS

A mean ± SD end-tidal isoflurane concentration of 1.36 ± 0.16% was necessary to maintain a surgical plane of anesthesia in the isoflurane group. Mean infusion rates of 5.0 ± 1.3 μL/kg/min and 5.1 ± 0.8 μL/kg/min were necessary to maintain a surgical plane of anesthesia in the IRK and IGK groups, respectively. A lower need for ketamine as a rescue anesthetic was observed in the IGK group, compared with the isoflurane group. Higher blood pressure and lower heart rates were found at selected time points for the IRK group, compared with the IGK and isoflurane groups.

CONCLUSIONS AND CLINICAL RELEVANCE

Both PIVA protocols were satisfactory to maintain smooth and stable surgical anesthesia in horses. The present study supports previous findings in which PIVA has isoflurane-sparing effects. Furthermore, PIVA did not impair recovery quality.

Real time monitoring of propofol blood concentration in ponies anaesthetized with propofol and ketamine

This study examined the pharmacokinetics of propofol by infusion in ponies using an analyser for the rapid measurement of propofol concentrations. The analyser (Pelorus 1000; Sphere Medical Ltd., Cambridge, UK) has a measurement cycle of approximately five minutes. Ten Welsh-cross ponies (weighing 135-300 kg) undergoing minor procedures were studied after premedication with acepromazine 0.03 mg/kg and detomidine 0.015 mg/kg. Anaesthesia was induced with ketamine 2 mg/kg and diazepam 0.03 mg/kg, and maintained with an infusion of propofol at an initial rate of 0.16 mg/kg/min for the first thirty minutes, after a bolus of 0.3 mg/kg; and ketamine by infusion (20-40 μg/kg/min). Blood samples (<2 mL) were collected prior to, during and after the infusion, and on assuming standing position. Anaesthesia was uneventful; with the duration of infusion 31-89 min. Blood propofol concentrations during the infusion ranged between 1.52 and 7.65 μg/mL; pseudo-steady state concentrations 3.64-6.78 μg/mL, and concentrations on assuming standing position 0.75-1.40 μg/mL. Propofol clearance and volume of distribution were 31.4 (SD 6.1) mL/min/kg and 220.7 (132.0) mL/kg, respectively. The propofol analyser allows titration of propofol to a given concentration; and may be useful for anaesthesia in animals where kinetics are unknown; in disease states; and where intercurrent therapies affect propofol disposition.

Minimum infusion rates and recovery times from different durations of continuous infusion of fospropofol, a prodrug of propofol, in rabbits: a comparison with propofol emulsion

OBJECTIVE

To explore, in rabbits, the minimum infusion rates (MIR) required and recovery time from long duration (≤ 8 hours) continuous infusion of fospropofol disodium, a novel water-soluble prodrug of propofol, and compare it with propofol.

STUDY DESIGN

Prospective, randomized, blinded experimental trial.

ANIMALS

Ninety-six adult laboratory rabbits, mean ± SD weight 2.20 ± 0.15 kg.

METHODS

Stage 1. 16 rabbits were assigned to receive fospropofol disodium or propofol to measure MIR, using an up-and-down method with response to tail-clamping stimulus (TCS). Stage 2. Eighty rabbits were allocated to group F (fospropofol disodium) or group P (propofol), and further subdivided (n = 10 in each subgroup) according to infusion time (2, 4, 6 or 8 hours), to groups F(2h), F(4h), F(6h), F(8h) and P(2h), P(4h), P(6h), P(8h). Fospropofol or propofol were infused, and tail clamping applied to maintain the same depth of anaesthesia until infusion was completed. Times to recover righting reflex (RR), to respond to TCS, and total recovery to different durations of continuous infusion of two anaesthetic drugs were noted. Respiratory and pulse rates and oxygen saturation were analyzed. The plasma concentrations of fospropofol disodium, the active metabolite propofol (propofol(F) ) and propofol emulsion were measured with respect to loss and recovery of RR and TCS.

RESULTS

MIR of fospropofol disodium was 2.0 mg kg(-1) minute(-1) , and MIR of propofol was 0.9 mg kg(-1) minute(-1) . Times in minutes to total recovery from anaesthesia in groups F and P were as follows, F(2h) 15 ± 3; F(4h) 26 ± 4; F(6h) 52 ± 6; F(8h) 84 ± 10; and P(2h) 10 ± 1; P(4h) 19 ± 7; P(6h) 36 ± 7; P(8h) 48 ± 5.

CONCLUSIONS AND CLINICAL RELEVANCE

After continuous intravenous infusion in rabbits (≤ 8 hours), fospropofol disodium and propofol both show an extension of recovery time with increasing infusion time, fospropofol disodium showing a significantly greater prolongation compared to propofol emulsion when infusion time increases to 6 and 8 hours.

Evaluation of cardiovascular, respiratory and biochemical effects, and anesthetic induction and recovery behavior in horses anesthetized with a 5% micellar microemulsion propofol formulation

OBJECTIVE

To characterize cardiovascular, respiratory and biochemical effects and recovery behavior associated with a 3-hour continuous infusion of a micellar microemulsion propofol formulation in horses.

STUDY DESIGN

Prospective experimental trial.

ANIMALS

Six healthy adult horses, 9 +/- 2 years old and weighing 557 +/- 14 kg.

METHODS

All horses received xylazine (1 mg kg(-1), IV) 5 minutes prior to anesthetic induction. Each horse was anesthetized on two occasions with a 5% micellar microemulsion propofol formulation (2 mg kg(-1), IV); first as a single bolus (phase I) and then as a 3-hour continuous infusion (phase II). Propofol pharmacokinetics were obtained from phase I and used to determine the starting infusion rates in phase II. Anesthetic induction and recovery characteristics were quantitatively and qualitatively assessed. Cardiovascular, respiratory and biochemical parameters were monitored during anesthesia and recovery.

RESULTS

Induction quality varied, ranging from good to poor. Standing and overall recovery quality scores were consistently excellent in phase I but more variability was observed among horses in phase II. Heart rate (HR) and mean arterial pressure (MAP) were adequately maintained but marked hypoventilation developed. There were only minimal changes in blood biochemical analytes following anesthesia.

CONCLUSIONS AND CLINICAL RELEVANCE

The micellar microemulsion propofol formulation, administered as a 3-hour continuous infusion, showed similar results compared to those previously described with a commercially available propofol preparation. However, based on present findings, use of propofol as a primary anesthetic in horses for prolonged periods of anesthesia requires further study to determine the limits of safety and clinical applicability.

A comparison of four systems for scoring recovery quality after general anaesthesia in horses

REASON FOR PERFORMING STUDY

The recovery quality scoring systems (RQSSs) in current use have not been critically reviewed for reliability.

OBJECTIVE

To examine reliability (reproducibility) of 4 RQSSs when applied to a ranked series.

METHODS

A DVD incorporating the recordings of 9 horses recovering from general anaesthesia was evaluated by final year students over 5 days. On Day 1, each evaluator ranked recoveries from 1-9 (1 = best). Over the following 4 days, each evaluator scored the same recoveries using 4 different RQSSs (3 of them in common usage and previously published) applied in random order. The scores from each RQSS were ranked and plotted against the Day 1 ranking of each evaluator to establish the extent of agreement using generalisability theory. The same 9 recoveries were also ranked by 12 experienced equine anaesthetists and the Spearman Rank Correlation coefficient calculated to determine the agreement between experienced and inexperienced evaluators.

RESULTS

The recoveries were evaluated by 117 students. All 4 RQSSs were equally reliable with low (<4%) interobserver variability. The main (80%) source of total variation arose from differences between horses. The overall ranking within each RQSS was strongly correlated with Day 1 ranking. There was strong correlation (r = 0.983) between the students' ranking and that established by experienced anaesthetists. Interobserver reliability was similar with all 4 RQSSs.

CONCLUSION

All 4 RQSSs studied were similarly reliable.

POTENTIAL RELEVANCE

The selection of a universally acceptable RQSS from amongst the 4 examined can be based on criteria other than reliability, e.g. ease of use. This will facilitate wider scale multi-centre studies in recovery quality after anaesthesia in horses.

Evaluation of bispectral index (BIS) as an indicator of central nervous system depression in horses anesthetized with propofol

The bispectral index (BIS) was evaluated as an indicator of central nervous system (CNS) depression in horses anesthetized with propofol. Five non-premedicated horses were anesthetized with 7 mg/kg, IV propofol and the minimum infusion rate (MIR) of propofol required to maintain anesthesia was determined during intermittent positive pressure ventilation in each horse. The BIS was determined 20 min later and after stabilization at 2.0 MIR, 1.5 MIR, and 1.0 MIR. The BIS was also recorded after the cessation of propofol infusion when the horses regained spontaneous breathing and swallowing reflex. The MIR and plasma concentration (Cp) of propofol were 0.20 +/- 0.03 mg/kg/min and 17.5 +/- 4.0 microg/ml, respectively. The BIS value and Cp were 59 +/- 13 and 26.7 +/- 8.6 microg/ml at 2.0 MIR, 63 +/- 9 and 22.9 +/- 9.7 microg/ml at 1.5 MIR, 64 +/- 13 and 20.1 +/- 5.9 microg/ml at 1.0 MIR, 64 +/- 24 and 13.0 +/- 2.8 microg/ml at return of spontaneous breathing, and 91 +/- 4 and 11.0 +/- 3.4 microg/ml when the swallowing reflex returned, respectively. The BIS value was significantly less in anesthetized horses compared to horses once swallowing returned (p=0.025). The BIS value was significantly correlated with the propofol Cp (r=-0.625, p=0.001). There was not a significant difference in the BIS values during the MIR multiples of propofol. The BIS was a useful indicator of awakening but did not indicate the degree of CNS depression during propofol-anesthesia in horses.

Cardiopulmonary effects and pharmacokinetics of i.v. dexmedetomidine in ponies

REASONS FOR PERFORMING STUDY

Currently available sedatives depress cardiopulmonary function considerably; therefore, it is important to search for new, less depressive sedatives. The study was performed to assess duration and intensity of cardiopulmonary side effects of a new sedative, dexmedetomidine (DEX), in horses.

OBJECTIVES

To study pharmacokinetics and cardiopulmonary effects of i.v. DEX.

METHODS

Pharmacokinetics of 3.5 microg/kg bwt i.v. DEX were studied in a group of 8 mature (mean age 4.4 years) and 6 old ponies (mean age 20 years). Cardiopulmonary data were recorded in mature ponies before and 5, 10, 20, 30, 45 and 60 mins after administration of DEX 3.5 microg/kg bwt i.v. Data were analysed using ANOVA for repeated measures, and where appropriate Dunnett's t test was used to detect differences from resting values (P < 0.05).

RESULTS

Within 2 h after DEX administration, plasma levels were beyond limits of quantification (0.05 ng/ml). Mean values for kinetic parameters for mature and old ponies were: Cmax (ng/ml) 4.6 and 3.8, t 1/2 (min) 19.8 and 28.9 and AUC (ng.min/ml) 34.5 and 44.3, respectively. Heart rate, central venous pressure, pulmonary artery pressure and pulmonary capillary wedge pressure did not change significantly compared to presedation values throughout the 60 min observation period. Compared to presedation values, stroke volume and mixed venous PO2 were reduced for the first 5 mins, paralleled by an increase in systemic and pulmonary vascular resistance. Cardiac index was reduced for the first 10 mins, arterial blood pressures at 20, 30 and 45 mins and respiratory rate throughout the 60 min observation period, but no change in arterial PO2 or PCO2 occurred.

CONCLUSIONS

DEX administration i.v. causes similar cardiopulmonary changes to those caused by other alpha-2 adrenoceptor agonists, but of very short duration. DEX is redistributed particularly rapidly.

POTENTIAL RELEVANCE

DEX might be safer for sedation of horses because of its very short-lasting cardiopulmonary side effects. For long duration sedation, its kinetics favour its use as a continuous infusion.

Complications in equine anesthesia

General anesthesia of horses entails considerable risk of morbidity and mortality. A large-scale, multicenter study reported that the death rate from non-colic-related anesthetics was 0.9%, while the perianesthetic mortality rate at a single, busy equine surgical practice was somewhat more favorable, at 0.12%. While any perianesthetic death is devastating, mortality figures alone do not reflect the overall morbidity of equine anesthesia in terms of nonterminal events or injuries related to recovery. In some circumstances, recognition of perianesthetic complications may allow appropriate intervention to prevent the complication from worsening or progressing to mortality. This article describes some of the complications that may occur during and after general anesthesia of horses, and suggests ways to prevent or mitigate them.

Evaluation of cardiovascular effects of total intravenous anesthesia with propofol or a combination of ketamine-medetomidine-propofol in horses

OBJECTIVE

To evaluate the cardiovascular effects of total IV anesthesia with propofol (P-TIVA) or ketamine-medetomidine-propofol (KMP-TIVA) in horses.

ANIMALS

5 Thoroughbreds.

PROCEDURES

Horses were anesthetized twice for 4 hours, once with P-TIVA and once with KMP-TIVA. Horses were medicated with medetomidine (0.005 mg/kg, IV) and anesthetized with ketamine (2.5 mg/kg, IV) and midazolam (0.04 mg/kg, IV). After receiving a loading dose of propofol (0.5 mg/kg, IV), anesthesia was maintained with a constant rate infusion of propofol (0.22 mg/kg/min) for P-TIVA or with a constant rate infusion of propofol (0.14 mg/kg/min), ketamine (1 mg/kg/h), and medetomidine (0.00125 mg/kg/h) for KMP-TIVA. Ventilation was artificially controlled throughout anesthesia. Cardiovascular measurements were determined before medication and every 30 minutes during anesthesia, and recovery from anesthesia was scored.

RESULTS

Cardiovascular function was maintained within acceptable limits during P-TIVA and KMP-TIVA. Heart rate ranged from 30 to 40 beats/min, and mean arterial blood pressure was > 90 mm Hg in all horses during anesthesia. Heart rate was lower in horses anesthetized with KMP-TIVA, compared with P-TIVA. Cardiac index decreased significantly, reaching minimum values (65% of baseline values) at 90 minutes during KMP-TIVA, whereas cardiac index was maintained between 80% and 90% of baseline values during P-TIVA. Stroke volume and systemic vascular resistance were similarly maintained during both methods of anesthesia. With P-TIVA, some spontaneous limb movements occurred, whereas with KMP-TIVA, no movements were observed.

CONCLUSIONS AND CLINICAL RELEVANCE

Cardiovascular measurements remained within acceptable values in artificially ventilated horses during P-TIVA or KMP-TIVA. Decreased cardiac output associated with KMP-TIVA was primarily the result of decreases in heart rate.

Evaluation of total intravenous anesthesia with propofol or ketamine-medetomidine-propofol combination in horses

Objective-To compare the anesthetic and cardiorespiratory effects of total IV anesthesia with propofol (P-TIVA) or a ketamine-medetomidine-propofol combination (KMP-TIVA) in horses. Design-Randomized experimental trial. Animals-12 horses. Procedure-Horses received medetomidine (0.005 mg/kg [0.002 mg/lb], IV). Anesthesia was induced with midazolam (0.04 mg/kg [0.018 mg/lb], IV) and ketamine (2.5 mg/kg [1.14 mg/lb], IV). All horses received a loading dose of propofol (0.5 mg/kg [0.23 mg/lb], IV), and 6 horses underwent P-TIVA (propofol infusion). Six horses underwent KMP-TIVA (ketamine [1 mg/kg/h {0.45 mg/lb/h}] and medetomidine [0.00125 mg/kg/h {0.0006 mg/lb/h}] infusion; the rate of propofol infusion was adjusted to maintain anesthesia). Arterial blood pressure and heart rate were monitored. Qualities of anesthetic induction, transition to TIVA, and maintenance of and recovery from anesthesia were evaluated. Results-Administration of KMP IV provided satisfactory anesthesia in horses. Compared with the P-TIVA group, the propofol infusion rate was significantly less in horses undergoing KMP-TIVA (0.14 +/- 0.02 mg/kg/min [0.064 +/- 0.009 mg/lb/min] vs 0.22 +/- 0.03 mg/kg/min [0.1 +/- 0.014 mg/lb/min]). In the KMP-TIVA and P-TIVA groups, anesthesia time was 115 +/- 17 minutes and 112 +/- 11 minutes, respectively, and heart rate and arterial blood pressure were maintained within acceptable limits. There was no significant difference in time to standing after cessation of anesthesia between groups. Recovery from KMP-TIVA and P-TIVA was considered good and satisfactory, respectively. Conclusions and Clinical Relevance-In horses, KMP-TIVA and P-TIVA provided clinically useful anesthesia; the ketamine-medetomidine infusion provided a sparing effect on propofol requirement for maintaining anesthesia.

The influence of butorphanol dose on characteristics of xylazine-butorphanol-propofol anesthesia in horses at altitude

OBJECTIVE

To characterize behavioral and physiological responses to short-term, unsupplemented intravenous (IV) anesthesia in healthy horses at high altitude (2240 m), and to test the hypothesis that the dose of butorphanol modifies the response of the horse to propofol anesthesia following xylazine pre-medication.

STUDY DESIGN

Randomized prospective butorphanol dose cross-over experimental design. Animals Eight healthy horses, 13 +/- 6 (mean +/- SD) years of age, and weighing 523 +/- 26 kg.

METHODS

Each horse was anesthetized three times with at least 3 weeks between each anesthesia. After collecting pre-drug data, xylazine (0.5 mg kg(-1)) was given IV. Five minutes later butorphanol was given IV according to a randomized order of three doses: 0.025, 0.05 and 0.075 mg kg(-1). Five minutes later, anesthesia was induced with propofol, 2 mg kg(-1) IV. Data on heart rate (HR) and respiratory rate (f(r)), mean arterial blood pressure, P(a)O(2), P(a)CO(2) and pH(a) were collected before, during and for 60 minutes following anesthesia, and quality of induction and recovery was scored.

RESULTS

The pre-drug values for the three butorphanol groups did not differ. The combined pre-drug values from the 24 studies were HR, 33 +/- 7 beats minute(-1); f(r), 11 +/- 3 breaths minute(-1); P(a)O(2), 67 +/- 7 mmHg; P(a)CO(2), 36 +/- 4 mmHg; and pH(a), 7.42 +/- 0.04. Five minutes after anesthetic induction P(a)O(2) decreased and P(a)CO(2) increased 14.5 +/- 7.7 and 5.1 +/- 4.9 mmHg, respectively, but returned to pre-drug levels within 15 minutes of anesthetic recovery. There were no significant butorphanol dose-related differences in physiological results, anesthetic induction and recovery quality scores or recovery time.

CONCLUSIONS AND CLINICAL RELEVANCE

Dose of butorphanol did not markedly influence study results. Notably, low P(a)O(2) values related to geographic location of study and general anesthesia indicates a narrow margin of error for hypoxemia-related complications in anesthetized horses breathing unsupplemented air at high altitude.

Cardiovascular Effects of Continuous Propofol Infusion in Horses

We examined the influence of propofol infusion on cardiovascular system at the rate of 0.14, 0.20 and 0.30 mg/kg/min in six adult Thoroughbred horses. The cardiovascular parameters were heart rate (HR), mean arterial pressure (MAP), mean right atrial pressure (MRAP), stroke volume (SV), cardiac output (CO), systemic vascular resistance (SVR), pre-ejection period (PEP) and ejection time (ET). In order to keep the ventilation conditions constantly, intermittent positive pressure ventilation was performed, and the partial arterial CO(2) pressure was maintained at 45 to 55 mmHg during maintenance anesthesia. SV showed a significant dose-dependent decrease however, CO did not show significant change. SVR decreased significantly at higher dose. PEP was prolonged and PEP/ET increased significantly at the highest dose. From these results, it became clear that SV decreases dose-dependently due to decrease of cardiac contractility during anesthesia with continuous propofol infusion in horses. On the other hand, since MAP and CO did not show significant changes, total intravenous anesthesia with propofol was suggested to be suitable for long-term anesthesia in horses.

Total intravenous anaesthesia in horses using medetomidine and propofol

OBJECTIVE

To examine the clinical suitability of medetomidine-propofol infusions for total intravenous anaesthesia in horses.

ANIMALS

Fifty client-owned horses of mixed breed, age [mean +/- SD (range)] 6.6 +/- 4.4 (0.04-18) years, mass 478 +/- 168.3 (80-700) kg presented for a range of operations requiring general anaesthesia.

MATERIALS AND METHODS

Pre-anaesthetic medication was intravenous (IV) medetomidine 7 mug kg(-1). Anaesthesia was induced with IV ketamine (2 mg kg(-1)) and diazepam (0.02 mg kg(-1)). After endotracheal intubation, O2 was delivered (FiO2 > 0.85). Positive pressure ventilation was initiated if breath-holding in excess of 1 minute occurred. Anaesthesia was maintained with a constant rate medetomidine infusion (3.5 microg kg(-1) hour(-1)) and propofol infused IV to effect (initial dose 0.1 mg kg(-1) minute(-1)). Heart (HR) respiratory (fr) and propofol administration rates, and systemic arterial blood pressures were recorded at 5-minute intervals. Arterial blood gas (O2 and CO2) tensions and pH values were recorded every 15 minutes. Ten minutes after ending medetomidine-propofol infusion, medetomidine (2 microg kg(-1); IV) was given. Cardiopulmonary data were analysed using descriptive statistical techniques.

RESULTS

Thirty-three orthopaedic, seven integumentary and 10 elective abdominal operations were performed. Cardiopulmonary data, presented as range of mean individual (and absolute individual minimum and maximum values) were: HR: 28.0-39.2 (16-88) beats minute(-1); mean arterial blood pressure: 74.0-132.5 (42-189) mmHg; PaO2: 22.1-42.9 (4.9-67.8) kPa; [166-322 (37-508) mmHg], PaCO2: 6.7-8.1 (4.2-11.8) kPa [50-61 (32-88) mmHg] and pH 7.35-7.39 (7.15-7.48). Positive pressure ventilation was required in 23 horses. In three horses, HR values below 20 beats minute(-1) were treated with 20 microg kg(-1) atropine (IV). Mean propofol infusion rates were 98-108 microg kg(-1) minute(-1). During anaesthesia, movement occurring in 14 horses was controlled with thiopental. Duration of anaesthesia was 111.6 +/- 41.4 (46-225) minutes. Recovery in all horses was uneventful and completed within 42.2 +/- 19.8 (12-98) minutes.

CONCLUSIONS AND CLINICAL RELEVANCE

Medetomidine-propofol infusion produces adequate conditions for a range of surgical procedures. Cardiovascular function was adequate, as no pressor agents were required. Positive pressure ventilation was required in 23 horses.

The Minimum Infusion Rate (MIR) of Propofol for Total Intravenous Anesthesia after Premedication with Xylazine in Horses

To investigate an adequate infusion rate of propofol for total intravenous anesthesia (TIVA) in horses, the minimum infusion rate (MIR) comparable to the minimum alveolar anesthetic concentration (MAC) of inhalation anesthetic was determined under constant ventilation condition by intermittent positive pressure ventilation (IPPV). In addition, arterial propofol concentration was measured to determine the concentration corresponding to the MIR (concentration preventing reaction to stimulus in 50% of population, Cp(50)). Further, 95% effective dose (ED(95)) was estimated as infusion rate for acquiring adequate anesthetic depth. Anesthetic depth was judged by the gross purposeful movement response to painful stimulus. MIR and Cp(50) were 0.10 +/- 0.02 mg/kg/min and 5.3 +/- 1.4 microg/ml, respectively. ED(95) was estimated as 0.14 mg/kg/min (1.4MIR).

Use of a combination of propofol and fentanyl, alfentanil, or sufentanil for total intravenous anesthesia in cats

OBJECTIVE

To determine the cardiorespiratory effects of an i.v. infusion of propofol alone or in association with fentanyl, alfentanil, or sufentanil in cats and, for each combination, the minimal infusion rate of propofol that would inhibit a response to noxious stimuli.

DESIGN

Randomized crossover study.

ANIMALS

6 cats.

PROCEDURE

Cats were anesthetized 4 times in random order. After i.v. administration of fentanyl, alfentanil, sufentanil, or saline (0.9% NaCl) solution, anesthesia was induced with propofol (7 mg/kg 13.2 mg/lb], i.v.) and maintained for 90 minutes with a continuous infusion of propofol in conjunction with fentanyl (0.1 microg/kg/min [0.045 microg/lb/min]), alfentanil (0.5 microg/kg/min [0.23 microg/lb/min]), sufentanil (0.01 microg/kg/min [0.004 microg/lb/min]), or saline solution (0.08 mL/kg/min [0.036 mL/lb/min]).

RESULTS

Minimal infusion rate of propofol required to prevent a response to a noxious stimulus was higher when cats received saline solution. After 70 minutes, minimal infusion rate of propofol was significantly higher with fentanyl than with sufentanil. Decreases in heart rate, systolic blood pressure, rectal temperature, and respiratory rate were detected with all treatments. Oxygen saturation did not change significantly, but end-tidal partial pressure of carbon dioxide increased with all treatments. There were no significant differences in recovery times or sedation and recovery scores among treatments.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggest that infusion of propofol in combination with fentanyl, alfentanil, or sufentanil results in satisfactory anesthesia in cats.

Medetomidine-ketamine anaesthesia induction followed by medetomidine-propofol in ponies: infusion rates and cardiopulmonary side effects

REASONS FOR PERFORMING STUDY

To search for long-term total i.v. anaesthesia techniques as a potential alternative to inhalation anaesthesia.

OBJECTIVES

To determine cardiopulmonary effects and anaesthesia quality of medetomidine-ketamine anaesthesia induction followed by 4 h of medetomidine-propofol anaesthesia in 6 ponies.

METHODS

Sedation consisted of 7 microg/kg bwt medetomidine i.v. followed after 10 min by 2 mg/kg bwt i.v. ketamine. Anaesthesia was maintained for 4 h with 3.5 microg/kg bwt/h medetomidine and propofol at minimum infusion dose rates determined by application of supramaximal electrical pain stimuli. Ventilation was spontaneous (F(I)O2 > 0.9). Cardiopulmonary measurements were always taken before electrical stimulation, 15 mins after anaesthesia induction and at 25 min intervals.

RESULTS

Anaesthesia induction was excellent and movements after pain stimuli were subsequently gentle. Mean propofol infusion rates were 0.89-0.1 mg/kg bwt/min. No changes in cardiopulmonary variables occured over time. Range of mean values recorded was: respiratory rate 13.0-15.8 breaths/min; PaO2 29.1-37.9 kPa; PaCO2 6.2-6.9 kPa; heart rate 31.2-40.8 beats/min; mean arterial pressure 90.0-120.8 mmHg; cardiac index 44.1-59.8 ml/kg bwt/min; mean pulmonary arterial pressure 11.8-16.4 mmHg. Recovery to standing was an average of 31.1 mins and ponies stood within one or 2 attempts.

CONCLUSIONS

In this paper, ketamine anaesthesia induction avoided the problems encountered previously with propofol. Cardiovascular function was remarkably stable. Hypoxaemia did not occur but, despite F(I)O2 of > 0.9, minimal PaO2 in one pony after 4 h anaesthesia was 8.5 kPa.

POTENTIAL RELEVANCE

The described regime might offer a good, practicable alternative to inhalation anaesthesia and has potential for reducing the fatality rate in horses.

Effects of Propofol-Sevoflurane Anesthesia on the Maternal and Fetal Hemodynamics Blood Gases, and Uterine Activity in Pregnant Goats

To determine the effects of propofol and sevoflurane on hemodynamics, acid-base balance and uterine activity in pregnant animals, a prospective experimental study was designed by use of ten pregnant goats. Propofol was intravenously administered at a bolus dose of 5 mg/kg and then infused a rate of 0.3 mg/kg/min for 5 min. Following the induction, the animals were incrementally inhaled 2.7 and 4.1% of end-tidal concentration of sevoflurane each for 30 min, and then recovered. The maternal and fetal heart rate (HR), arterial blood pressure (BP) and acid-base balance, the intrauterine pressure (IUP), and the uterine blood flow (UBF) were measured. Following the pre-anesthetic data, the parameters were measured 7 times throughout the anesthetic and recovering periods. The propofol infusion induced 1.37 times of HR increase and produced decrease in PO(2) and a relevant metabolic acidemia in the mother, with no effect in the fetus. Sevoflurane reduced BP in the fetus from 30 (2.7%) to 60 (4.1%) min of inhalation. The uterine contractions disappeared throughout sevoflurane inhalation, and then recurred within 15 min after the cessation of sevoflurane. Propofol injection increases HR, and induces a moderate hypoxemia and metabolic acidemia associated with the suppressed ventilation for pregnant goats, with less effect on the fetal hemodinamics. Sevoflurane causes minimal change in maternal hemodynamics, but induces significant hypotension in the fetus and reduction of uterine activity. These data may be useful in making anesthetic choices combined with analgesia for Caesarian section in goats.

Cardiopulmonary effects of prolonged anesthesia via propofol-medetomidine infusion in ponies

OBJECTIVE

To determine cardiopulmonary effects of total IV anesthesia with propofol and medetomidine in ponies and effect of atipamezole on recovery.

ANIMALS

10 ponies.

PROCEDURE

After sedation was induced by IV administration of medetomidine (7 microg/kg of body weight), anesthesia was induced by IV administration of propofol 12 mg/kg) and maintained for 4 hours with infusions of medetomidine (3.5 microg/kg per hour) and propofol 10.07 to 0.11 mg/kg per minute). Spontaneous respiration was supplemented with oxygen. Cardiopulmonary measurements and blood concentrations of propofol were determined during anesthesia. Five ponies received atipamezole (60 microg/kg) during recovery.

RESULTS

During anesthesia, mean cardiac index and heart rate increased significantly until 150 minutes, then decreased until cessation of anesthesia. Mean arterial pressure and systemic vascular resistance index increased significantly between 150 minutes and 4 hours. In 4 ponies, PaO2 decreased to < 60 mm Hg. Mean blood propofol concentrations from 20 minutes after induction onwards ranged from 2.3 to 3.5 microg/ml. Recoveries were without complications and were complete within 28 minutes with atipamezole administration and 39 minutes without atipamezole administration.

CONCLUSIONS AND CLINICAL RELEVANCE

During total IV anesthesia of long duration with medetomidine-propofol, cardiovascular function is comparable to or better than under inhalation anesthesia. This technique may prove suitable in equids in which prompt recovery is essential; however, in some animals severe hypoxia may develop and oxygen supplementation may be necessary.