Effects of Medetomidine Constant Rate Infusion on Sevoflurane Requirement, Cardiopulmonary Function, and Recovery Quality in Thoroughbred Racehorses Undergoing Arthroscopic Surgery

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.

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.

Clinical evaluation of constant rate infusion of alfaxalone-medetomidine combined with sevoflurane anesthesia in Thoroughbred racehorses undergoing arthroscopic surgery

Background

Alfaxalone has a number of pharmacological properties which are desirable for constant rate infusion (CRI). Previously, the co-administration of alfaxalone and medetomidine is shown to be suitable for short-term anesthesia in horses. However, the use of alfaxalone–medetomidine CRI with inhalational anesthesia under surgical procedures have not been investigated in clinical cases. The aim of the present study was to evaluate the clinical efficacy of alfaxalone–medetomidine CRI in sevoflurane-anesthetized Thoroughbred racehorses undergoing arthroscopic surgery. Sevoflurane requirement, cardiovascular function, and induction/recovery quality were compared between horses maintained with sevoflurane in combination with medetomidine CRI (3 µg/kg/h) (Group M; n = 25) and those maintained with sevoflurane in combination with alfaxalone–medetomidine CRI (0.5 mg/kg/h and 3 µg/kg/h, respectively) (Group AM; n = 25).

Results

The mean end-tidal sevoflurane concentrations were significantly lower in Group AM (1.8 ± 0.2%) than in Group M (2.4 ± 0.1%). The mean dobutamine infusion rate required for maintaining mean arterial blood pressure within the target values (60–80 mmHg) was significantly lower in Group AM (0.53 ± 0.20 µg/kg/min) than in Group M (0.85 ± 0.32 µg/kg/min). Induction and recovery scores were not significantly different between two groups. However, excitatory response during recovery were observed in five horses in Group AM. The mean plasma alfaxalone concentrations were stable throughout the maintenance period (0.77 ± 0.12 to 0.85 ± 0.13 µg/mL), and decreased significantly immediately after standing (0.32 ± 0.07 µg/mL).

Conclusions

Alfaxalone–medetomidine CRI reduced sevoflurane requirement by approximately 26% with good maintenance of cardiopulmonary function in Thoroughbred racehorses undergoing arthroscopic surgery. Sevoflurane in combination with alfaxalone–medetomidine CRI may be a clinically effective anesthetic technique for Thoroughbred racehorses. However, 20% of horses administered alfaxalone showed remarkable excitatory response during recovery. Greater attention to excitatory response may be advisable if alfaxalone is used for induction or maintenance of anesthesia. A larger study is needed to explore the clinical relevance of these findings.