Clinical assessment of anesthesia with isoflurane and medetomidine in 300 equidae

Abstract

SummaryA new anesthetic protocol for horses was evaluated in 300 clinical patients. Particular attention was paid to cardiopulmonary function and recovery, as poor recoveries and bad cardiovascular function represent the main causes for the high mortality rate associated with equine anesthesia. 300 equidae of mixed breed, mean age of 8 years and mean weight of 486 kg were anaesthetised. Horses were premedicated with acepromazine IM. Following sedation with medetomidine IV, anaesthesia was induced with ketamine and diazepam IV. Anesthesia was maintained with isoflurane in oxygen and constant rate infusion of medetomidine. Horses were allowed to breathe spontaneously, unless apnea necessitated artificial ventilation. Heart rates, respiratory rates, arterial blood pressure, and composition of inhaled and exhaled gases were monitored continuously. Arterial blood gases were measured regularly. Incremental boli of ketamine or thiopentone were noted. Morphine and medetomidine were administered for recovery. Recovery time was recorded and recovery quality was scored on a 1-5 scale (1=best, 5= worst). Mean duration of anaesthesia was 149 minutes. Hypotension or hypoxemia occurred in a small number of horses. Both resolved when either additional fluids and sympathomimetics or a higher concentration of inspiratory oxygen was administered. 146 horses received supplemental ketamine and 29 thiopentone respectively. Recovery was scored excellent or good in 299 horses, poor in one horse. Mean duration of recovery was 50 minutes. Results suggest that the described anesthetic protocol is suitable to maintain anesthesia in horses for various procedures of considerable duration. Cardiopulmonary function was well maintained and recoveries were of exceptionally good quality. Keywords: Horse, anaesthesia, medetomidine, cardiopulmonary functionKlinische Anwendung von Isofluran/Medetomidin-Anästhesie bei 300 Equiden Die Mortaliätsrate in der Pferdeanästhesie ist mit 1 % sehr hoch. Im Vergleich dazu liegt sie in der Kleintieranästhesie bei lediglich 0.15 % und in der Humananästhesie bei 0.002 %. Die drei häufigsten perioperativen Todesursachen beim Pferd sind Herzkreislaufstillstand zu Beginn der Anästhesie, sowie Frakturen und Myopathien während der Aufwachphase. Für längere operative Eingriffe sind heutzutage Inhalationsanästhetika Mittel der Wahl. Diese führen zu einer Beeinträchtigung der Kreislauffunktion und dadurch zu einer verminderten muskulären Durchblutung. Dies fördert die Entstehung oben genannter Myopathien. Eine neue Möglichkeit Pferde sicherer zu anästhesieren bietet der kombinierte Einsatz von Inhalationsanästhetika und Analgetika oder Sedativa. Ein Sedativum mit hervorragenden analgetischen Eigenschaften ist Medetomidin, der zurzeit potenteste und spezifischste α 2 -Agonist. Medetomidin kann aufgrund seiner pharmakokinetischen Eigenschaften beim Pferd während einer Inhalationsanästhesie kontinuierlich infundiert werden. Dies resultiert in einer Verminderung des Bedarfes an Inhalationsanästhetika, stabiler Herzkreislauff...

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

“…In contrast, in group D, 6 out of 7 laterally recumbent horses needed mechanical ventilation, suggesting that an infusion of DEX may reduce respiratory drive in isoflurane anaesthetized horses. A previous study with medetomidine in isoflurane anaesthetized horses (Kalchofner et al. 2006) reported that only three out 300 horses needed mechanical ventilation.…”

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

“…Blinded clinical studies appear not to be good options to detect reductions in inhalants, especially when depth of anaesthesia is evaluated subjectively, according to clinical signs. This is of extreme importance in horses with infusions of α 2 ‐agonists, in which a “lighter” appearance, compared with traditional inhalant protocols, is common (Kalchofner et al., ). No isoflurane concentration reductions were demonstrated after romifidine (Devisscher, Schauvliege, Dewulf, & Gasthuys, ), detomidine (Schauvliege et al., ) and dexmedetomidine (Marcilla et al., ).…”

The cardiovascular status of isoflurane-anaesthetized horses with and without dexmedetomidine constant rate infusion evaluated at equivalent depths of anaesthesia

“…Previous studies evaluating depth of anaesthesia have suggested that horses receiving α 2 ‐agonists during surgery seem to be more lightly anaesthetized based on traditional ocular parameters (Kalchofner et al. ; Ringer et al. ; Marcilla et al.…”