Minimum end-tidal sevoflurane concentration necessary to prevent movement during a constant rate infusion of morphine, or morphine plus dexmedetomidine in ponies

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.

Pharmacokinetics and pharmacodynamics of l-methadone in isoflurane-anaesthetized and mechanically ventilated ponies

OBJECTIVE

To evaluate the pharmacokinetics and selected pharmacodynamic effects of a commercially available l-methadone/fenpipramide combination administered to isoflurane anaesthetized ponies.

STUDY DESIGN

Prospective single-group interventional study.

ANIMALS

A group of six healthy adult research ponies (four mares, two geldings).

METHODS

Ponies were sedated with intravenous (IV) detomidine (0.02 mg kg^-1) and butorphanol (0.01 mg kg^-1) for an unrelated study. Additional IV detomidine (0.004 mg kg^-1) was administered 85 minutes later, followed by induction of anaesthesia using IV diazepam (0.05 mg kg^-1) and ketamine (2.2 mg kg^-1). Anaesthesia was maintained with isoflurane in oxygen. Baseline readings were taken after 15 minutes of stable isoflurane anaesthesia. l-Methadone (0.25 mg kg^-1) with fenpipramide (0.0125 mg kg^-1) was then administered IV. Selected cardiorespiratory variables were recorded every 10 minutes and compared to baseline using the Wilcoxon signed-rank test. Adverse events were recorded. Arterial plasma samples for analysis of plasma concentrations and pharmacokinetics of l-methadone were collected throughout anaesthesia at predetermined time points. Data are shown as mean ± standard deviation or median and interquartile range (p < 0.05).

RESULTS

Plasma concentrations of l-methadone showed a rapid initial distribution phase followed by a slower elimination phase which is best described with a two-compartment model. The terminal half-life was 44.3 ± 18.0 minutes, volume of distribution 0.43 ± 0.12 L kg^-1 and plasma clearance 7.77 ± 1.98 mL minute^-1 kg^-1. Mean arterial blood pressure increased from 85 (±16) at baseline to 100 (±26) 10 minutes after l-methadone/fenpipramide administration (p = 0.031). Heart rate remained constant. In two ponies fasciculations occurred at different time points after l-methadone administration.

CONCLUSIONS AND CLINICAL RELEVANCE

Administration of a l-methadone/fenpipramide combination to isoflurane anaesthetized ponies led to a transient increase in blood pressure without concurrent increases in heart rate. Pharmacokinetics of l-methadone were similar to those reported for conscious horses administered racemic methadone.

Plasma histamine concentrations in horses administered sodium penicillin, guaifenesin-xylazine-ketamine and isoflurane with morphine or butorphanol

OBJECTIVE

Various drugs administered to horses undergoing surgical procedures can release histamine. Histamine concentrations were evaluated in horses prepared for surgery and administered butorphanol or morphine intraoperative infusions.

STUDY DESIGN

Prospective studies with one randomized.

ANIMALS

A total of 44 client-owned horses.

METHODS

In one study, anesthesia was induced with xylazine followed by ketamine-diazepam. Anesthesia was maintained with guaifenesin-xylazine-ketamine (GXK) during surgical preparation. For surgery, isoflurane was administered with intravenous (IV) morphine (group M: 0.15 mg kg^-1 and 0.1 mg kg^-1 hour^-1; 15 horses) or butorphanol (group B: 0.05 mg kg^-1 and 0.01 mg kg^-1 hour^-1; 15 horses). Histamine and morphine concentrations were measured using enzyme-linked immunoassay before opioid injection (time 0), and after 1, 2, 5, 30, 60 and 90 minutes. In a subsequent study, plasma histamine concentrations were measured in 14 horses before drug administration (baseline), 15 minutes after IV sodium penicillin and 15 minutes after starting GXK IV infusion. Statistical comparison was performed using anova for repeated measures. Pearson correlation compared morphine and histamine concentrations. Data are presented as mean ± standard deviation. Significance was assumed when p ≤ 0.05.

RESULTS

With histamine, differences occurred between baseline (3.2 ± 2.4 ng mL^-1) and GXK (5.2 ± 7.1 ng mL^-1) and between baseline and time 0 in group B (11.9 ± 13.4 ng mL^-1) and group M (11.1 ± 12.4 ng mL^-1). No differences occurred between baseline and after penicillin or between groups M and B. Morphine concentrations were higher at 1 minute following injection (8.1 ± 5.1 ng mL^-1) than at 30 minutes (4.9 ± 3.1 ng mL^-1) and 60 minutes (4.0 ± 2.5 ng mL^-1). Histamine correlated with morphine at 2, 30 and 60 minutes.

CONCLUSIONS AND CLINICAL RELEVANCE

GXK increased histamine concentration, but concentrations were similar with morphine and butorphanol.

Epidural administration of opioid analgesics improves quality of recovery in horses anaesthetised for treatment of hindlimb synovial sepsis

BACKGROUND

Opioid epidural analgesia has been shown to provide effective analgesia in horses. There is a lack of evidence regarding the effect of opioid epidural analgesia on quality of recovery in horses.

OBJECTIVES

Identify whether opioid epidural analgesia influences quality of recovery in horses undergoing general anaesthesia required for management of hindlimb synovial sepsis.

STUDY DESIGN

Single-centre retrospective cross-sectional study.

METHODS

Data were obtained from the clinical records of horses which had undergone arthroscopic or tenoscopic surgery for management of hindlimb synovial sepsis over a 9-year period in a referral hospital population. Multivariable logistic regression analysis was used to identify the perioperative factors that impact on quality of recovery.

RESULTS

Records from 149 horses, undergoing 170 general anaesthetics were included. Multivariable logistic regression analysis showed that opioid epidural analgesia (OR 3.0, 95% CI 1.2 to 7.2, P = .02) was associated with good quality of recovery, whereas Cob breeds (OR 0.16, 95% CI 0.06 to 0.46, P = .001), age (in years) (OR 0.90, 95% CI 0.83 to 0.97, P = .004) increasing intraoperative dosages (in mg/kg) of thiopental (OR 0.64, 95% CI 0.46 to 0.90, P = .01) or ketamine (OR 0.42, 95% CI 0.18 to 0.98, P = .04) were associated with poor quality of recovery.

MAIN LIMITATIONS

Certain variables that may influence quality of recovery, such as patient temperament and hindlimb orthopaedic co-morbidities were not recorded. The clinical prediction model obtained is only applicable to the specific facilities, population and perianaesthetic management practiced at our institution.

CONCLUSIONS

Opioid epidural analgesia is significantly associated with good quality of recovery in horses undergoing general anaesthesia required for management of hindlimb synovial sepsis. Other risk factors, such as increasing age, cob breed, use of higher intraoperative dosages (in mg/kg) of ketamine and/or thiopental, were associated with poor quality of recovery.

BEVA primary care clinical guidelines: Analgesia

Primary care guidelines provide a reference point to guide clinicians based on a systematic review of the literature, contextualised by expert clinical opinion. These guidelines develop a modification of the GRADE framework for assessment of research evidence (vetGRADE) and applied this to a range of clinical scenarios regarding use of analgesic agents. Key guidelines produced by the panel included recommendations that horses undergoing routine castration should receive intratesticular local anaesthesia irrespective of methods adopted and that horses should receive NSAIDs prior to surgery (overall certainty levels high). Butorphanol and buprenorphine should not be considered appropriate as sole analgesic for such procedures (high certainty). The panel recommend the continuation of analgesia for 3 days following castration (moderate certainty) and conclude that phenylbutazone provided superior analgesia to meloxicam and firocoxib for hoof pain/laminitis (moderate certainty), but that enhanced efficacy has not been demonstrated for joint pain. In horses with colic, flunixin and firocoxib are considered to provide more effective analgesia than meloxicam or phenylbutazone (moderate certainty). Given the risk of adverse events of all classes of analgesic, these agents should be used only under the control of a veterinary surgeon who has fully evaluated a horse and developed a therapeutic, analgesic plan that includes ongoing monitoring for such adverse events such as the development of right dorsal colitis with all classes of NSAID and spontaneous locomotor activity and potentially ileus with opiates. Finally, the panel call for the development of a single properly validated composite pain score for horses to allow accurate comparisons between medications in a robust manner.

Plasma concentrations at two dexmedetomidine constant rate infusions in isoflurane anaesthetized horses: a clinical study

OBJECTIVE

To determine dexmedetomidine plasma concentrations at two infusion rates in isoflurane anaesthetized horses and compare cardiovascular effects and anaesthetic recovery between treatments.

STUDY DESIGN

Prospective, randomized, masked clinical study.

ANIMALS

Healthy, adult, client-owned, non-food producing horses presented for castration.

METHODS

Premedication consisted of acepromazine, romifidine and morphine, and anaesthesia was induced with ketamine and midazolam. The horses were randomized to receive dexmedetomidine 0.5 μg kg^-1 hour^-1 (treatment DL, n = 7) or 1.75 μg kg^-1 hour^-1 (treatment DH, n = 7) for 90 minutes of isoflurane anaesthesia at an end-tidal concentration of 1.2%. Venous plasma concentrations were determined with liquid chromatography-electrospray-ionization-tandem mass spectrometry. Jugular venous and arterial blood was sampled for blood gas analysis at the start and end of the infusion. Changes in cardiovascular variables from the start to the end of the infusion, and recovery parameters were statistically compared between treatments.

RESULTS

Fourteen male horses, 2-6 years old, 325-536 kg were included. Mean ± standard deviation dexmedetomidine plasma concentrations at 30, 60 and 90 minutes with treatment DL were 0.22 ± 0.05, 0.29 ± 0.07 and 0.33 ± 0.08 ng mL^-1, and with treatment DH were 0.65 ± 0.11, 0.89 ± 0.10 and 1.01 ± 0.10 ng mL^-1. The 95% confidence interval for change minute^-1 in dexmedetomidine plasma concentrations between 75 and 90 minutes was 0-1% for both treatments. With treatment DH, the heart rate decreased significantly more from the beginning to the end of the infusion compared to DL (p = 0.043). No other significant differences were found between treatments in cardiovascular or recovery parameters.

CONCLUSIONS AND CLINICAL RELEVANCE

Infusion of dexmedetomidine in isoflurane anaesthetized horses resulted in plasma concentrations with low variation at both infusion rates, approaching stable levels after 75 minutes of infusion. No differences of clinical importance were found when comparing cardiovascular variables and quality of recovery between treatments.

Is there a place for dexmedetomidine in equine anaesthesia and analgesia? A systematic review (2005-2017)

The objective of this review was to perform a literature compilation of all the equine publications that used dexmedetomidine as the first article on this topic was published, in 2005. We also aimed to answer the question whether the use of dexmedetomidine can currently be justified. For that, we compiled information from databases, such as PubMed, Google Scholar and Web of Science and the proceedings of the last veterinary anaesthesiology meetings. Dexmedetomidine is an attractive drug to be used in horses, mainly due to its pharmacokinetic profile and pharmacodynamics that favour its use as intravenous constant rate infusion (CRI). Nowadays, its clinical use is popular for sedation in prolonged standing procedures and during partial intravenous anaesthesia (PIVA) and total intravenous anaesthesia (TIVA). However, legal requirements for its use should be taken into account.

Endogenous Opiates and Behavior: 2015

This paper is the thirty-eighth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2015 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia, stress and social status, tolerance and dependence, learning and memory, eating and drinking, drug abuse and alcohol, sexual activity and hormones, pregnancy, development and endocrinology, mental illness and mood, seizures and neurologic disorders, electrical-related activity and neurophysiology, general activity and locomotion, gastrointestinal, renal and hepatic functions, cardiovascular responses, respiration and thermoregulation, and immunological responses.

Antinociceptive effects of three escalating dexmedetomidine and lignocaine constant rate infusions in conscious horses

Dexmedetomidine and lignocaine IV are used clinically to provide analgesia in horses. The aims of this study were to investigate the antinociceptive effects, plasma concentrations and sedative effects of 2, 4 and 6 µg/kg/h dexmedetomidine IV, with a bolus of 0.96 µg/kg preceding each continuous rate infusion (CRI), and 20, 40 and 60 µg/kg/min lignocaine IV, with a bolus of 550 µg/kg preceding each CRI, in 10 Swiss Warmblood horses. Electrically elicited nociceptive withdrawal reflexes were evaluated by deltoid muscle electromyography. Nociceptive threshold and tolerance were determined by electromyography and behaviour following single and repeated stimulation. Plasma concentrations of drugs were determined by liquid chromatography and mass spectrometry. Sedation was scored on a visual analogue scale. Dexmedetomidine increased nociceptive threshold to single and repeated stimulation for all CRIs, except at 2 µg/kg/h, where no increase in single stimulation nociceptive threshold was observed. Dexmedetomidine increased nociceptive tolerance to single and repeated stimulation at all CRIs. There was large individual variability in dexmedetomidine plasma concentrations and levels of sedation; the median plasma concentration providing antinociceptive effects to all recorded parameters was 0.15 ng/mL, with a range from <0.02 ng/mL (below the lower limit of quantification) to 0.25 ng/mL. Lignocaine increased nociceptive threshold and tolerance to single and repeated stimulation at CRIs of 40 and 60 µg/kg/min, corresponding to plasma lignocaine concentrations >600 ng/mL. Only nociceptive tolerance to repeated stimulation increased at 20 µg/kg/min lignocaine. Lignocaine at 40 µg/kg/min and dexmedetomidine at 4 µg/kg/h were the lowest CRIs resulting in consistent antinociception. Lignocaine did not induce significant sedation.