Topic:Anesthesia
Anesthesia in horses involves the administration of drugs to induce a temporary loss of sensation or consciousness, facilitating surgical procedures and other medical interventions. This complex process requires a deep understanding of equine physiology and pharmacology to ensure the safety and well-being of the animal. Anesthesia in horses can be challenging due to their size, temperament, and unique anatomical and physiological characteristics. Common anesthetic agents used in equine practice include inhalants like isoflurane and sevoflurane, as well as injectable drugs such as ketamine and xylazine. The management of anesthesia in horses also involves careful monitoring of vital signs and the use of supportive measures to prevent complications such as hypotension, hypoventilation, and post-anesthetic myopathy. This page compiles peer-reviewed research studies and scholarly articles that explore the techniques, advancements, and clinical outcomes associated with anesthesia in equine medicine.
Technique for reversible vagal blockade in the standing conscious pony. A surgical technique is described for preparation of chronic cervical vagal loops in ponies. Vagal blockade was induced by circulating methanol (-2 C) through coils which enclosed the loops. Vagal blockade increased tidal volume, heart rate, and systemic blood pressure and decreased respiratory rate. Atropine, given at a dose of 0.04 mg/kg IV, increased heart rate and systemic pressure but did not alter respiratory variables, indicating that vagal cooling caused both afferent and efferent blockade. The effects of vagal blockade were rapidly reversed when refrigerated coils were removed.
Tracheal reconstruction by resection and end-to-end anastomosis in the horse. A surgical technique for resection of a portion of the trachea followed by end-to-end anastomosis was developed on 4 clinically normal horses. The trachea healed without complications in 3 of the horses in which 3 tracheal cartilages were removed. Five tracheal cartilages were removed from the 4th horse. It had to be euthanatized because of excessive suture line tension and wound disruption, which occurred during recovery from anesthesia. Suture line tension was measured on 3 other clinically normal horses positioned in dorsal recumbency immediately after euthanasia after 3 and 5 tracheal cart...
Regional pulmonary perfusion in horses: a comparison between anaesthetised and conscious standing animals. The regional perfusion to the lungs of 14 ponies was studied using radioactively labelled microspheres injected intravenously. It was found that within half an hour of induction of anaesthesia the perfusion to the dependent lung had decreased significantly from the values in the standing animal. When anaesthesia was maintained for more than two and a half hours, however, the lung perfusions were not significantly different from the standing values when the animals were lying in lateral or supine recumbency.
Use of the portable infrared thermometer as a means of measuring limb surface temperature in the horse. Evaluation was made of the portable infrared thermometer to measure limb surface temperature in 3 horses--first standing in a stall and then placed in lateral recumbency under general anesthesia. To determine the effect of pigment, black and white targets were examined with the instrument under various clinical conditions. In each horse, thermal gradient measurements were consistent along the extremities. Mean limb surface temperatures were less than rectal temperature and greater than ambient temperature. Limb surface temperatures measured in lateral recumbency under general anesthesia were u...
Equine postanesthetic forelimb lameness: intracompartmental muscle pressure changes and biochemical patterns. Intracompartmental muscle pressures were recorded from the right and left forelimbs (extensor carpi radialis, triceps brachii) of healthy horses maintained in left lateral recumbency while under deep halothane anesthesia for 180 to 240 minutes. Cardiac output, blood pressure, blood gases, and acid-base status were monitored throughout the anesthesia, and electrolyte levels (Ca2+, P+, K+, Cl-, Na+) and enzyme activities (aspartate aminotransferase (AST), creatine phosphokinase (CPK), and blood lactate) were monitored for 7 days. Postanesthetic forelimb lameness was produced in 5 of the 6 horses...
Effect of intraluminal oxygen in intestinal strangulation obstruction in ponies. This study examined the effect of intraluminal oxygen administration on mucosal morphology following intestinal strangulation obstruction (ISO) in anesthetized ponies. The ISO was produced by ligation of the intestinal vasculature in 5 ponies for 50 minutes and 2 ponies for 90 minutes. Two ponies served as controls. Light and scanning electron microscopic examination of intestinal biopsy specimens revealed progressive mucosal degeneration following ISO in nontreated intestines, whereas high magnification scanning electron microscopic examination documented subtle evidence of microvilli disrupt...
Chemical restraint in the horse. Drugs and drug combinations currently in use for chemical restraint of the horse are discussed with a view to establishing their likely usefulness to the practising veterinary surgeon. Acepromazine maleate and xylazine hydrochloride are considered to be the most useful tranquillisers in spite of their limitations. A xylazine-methadone sequence is described for more profound chemical restraint and the possible future role of ketamine and glyceryl guaiacolate in combination with other agents to produce recumbency is discussed.
Intravenous anaesthesia in horses after xylazine premedication. The effects of combining large doses of xylazine (1.1 mg per kg intravenously) with ketamine, methohexitone and thiopentone were studied in four experimental ponies. Onset of anaesthesia was more delayed after ketamine than after the barbiturates. Assessment of smoothness of induction and recovery indicated that all three combinations were effective and acceptable. Injection of xylazine was followed by atrioventricular (A-V) block which could be prevented by the prior administration of atropine. Blood pressure was well maintained with all three combinations of drugs. Arterial oxygen tension de...
Electromagnetic measurements of metacarpal blood flow in nonanesthetized horses. Blood flow (milliliter/minute) was measured in the medial palmar artery of 12 horses, using electromagnetic flow equipment. Extraluminal flow probes were surgically placed around the artery and base-line blood flows were recorded during surgical manipulation. After horses had recovered from anesthesia, blood flows were recorded each day for 11 days. According to mean average blood flows, horses were allotted to two groups: group 1--those with predominately normal flow characteristics, and group 2--those horses with predominately abnormal flow features. Average daily mean blood flows in the med...
Alterations in horse blood cell count and biochemical values after halothane anesthesia. Quantitative changes in hematologic and serum biochemical values associated with prolonged general anesthesia produced by known alveolar doses of halothane in oxygen were determined in six young, healthy horses under laboratory conditions. In addition, 25 young equine patients anesthetized for shorter periods under clinical conditions were similarly (except hematologic values) prospectively evaluated. In normal horses, muscle- and hepatic-derived serum biochemical values were mildly increased immediately after anesthesia. Values after anesthesia remained at greater than base-line values for up...
Clinical approach to determine the contribution of the palmar and palmar metacarpal nerves to the innervation of the equine fetlock joint. To determine the sensory nerve supply of the metacarpophalangeal joint, lameness was induced in eight horses by injecting the joint with a glycerin suspension of glass micropheres. When the medial and lateral palmar nerves were anesthetized in 4 horses, there was noticeable improvement in the gait, but each horse remained lame. When the medial and lateral palmar metacarpal nerves were also anesthetized, 3 of the 4 horses became sound. To confirm the results of local anesthesia, neurectomies were performed on a second group of four horses. The lameness was alleviated only upon resection of both...
Vascular anatomy and surgical technique for bilateral adrenalectomy in the equid. The vascular anatomy of the adrenal glands and a surgical technique for bilateral adrenalectomy in the equid are described. Bilateral adrenalectomy was performed in six ponies and one horse via bilateral transcostal retroperitoneal approaches through the 18th rib during a single anesthetic period. Complications included hemorrhage from the right side only and pneumothorax which usually occurred on the right side. One pony died as a result of the surgical technique. Maintenance of adrenal function was accomplished with desoxycorticosterone pivilate and prednisolone.
Comparison of circulatory and respiratory effects of isoflurane and halothane anesthesia in horses. Circulatory and respiratory effects of alveolar concentrations of 1.31, 1.97, and 2.62 vol% of isoflurane in oxygen were studied in eight young, healthy horses during spontaneous and controlled ventilation. These isoflurane concentrations were equivalent, respectively, to 1.0, 1.5, and 2.0 times the minimal alveolar concentration of isoflurane, which prevents movement in horses in response to a standard pain stimulus. Results of the isoflurane studies were compared with similarly derived findings in these same horses during equipotent halothane in oxygen anesthesia. Isoflurane, similar to halo...
Biochemical effects of succinylcholine chloride in mechanically ventilated horses anesthetized with halothane in oxygen. Succinylcholine chloride administered to horses anesthetized with halothane in oxygen and mechanically ventilated, caused slight but statistically insignificant (P less than 0.01) increases in creatine phosphokinase, lactic dehydrogenase, and aspartate aminotransferase activity. The increases in these enzymes have been explained on the basis of muscle damage resulting from succinylcholine chloride induced muscle fasciculations and by hypoperfusion of tissues due to depression of the cardiovascular system caused by general anesthesia. These changes were not clinically apparent based upon the ab...
Evaluation of concentrated solutions of guaifenesin for equine anesthesia. The pH, osmolality, stability, and bacteriostatic characteristics of 5%, 10%, and 15% solutions of guaifenesin were studied. In vitro and in vivo experiments were done to determine the hemolytic potential of the more concentrated solutions on equine blood, as compared with the recommended 5% solution. The primary objective was to determine whether more concentrated solutions could be used clinically. The secondary objective was to determine the optimal diluent (water, 0.9% saline, or 5% dextrose). It was concluded that a 10% solution of guaifenesin made in sterile distilled water was most suit...
Evaluation of the demand valve for resuscitation of horses. Arterial blood gas values, rate of pulmonary nitrogen washout, respiratory rate, arterial blood pressure, heart rate, and cardiac output were determined during ventilation of six anesthetized horses, with a demand valve. The horses were allowed to ventilate spontaneously, or intermittent positive pressure ventilation was utilized. When compared with spontaneous ventilation, intermittent positive pressure ventilation caused a significant increase in the rate of pulmonary nitrogen washout and a significant decrease of arterial carbon dioxide. It was concluded that intermittent positive pressure ...
[Incarcerated scrotal hernia in a gelding (author’s transl)]. The clinical examination, anaesthesia and surgery in a gelding with an incarcerated scrotal hernia are described. The results of examination of the blood at regular intervals are shown in a table. Surgery was performed without enterectomy. The postoperation course was uneventful. It is concluded that the possibility of scrotal hernia should be borne in mind, even in geldings with colic. The incarcerated portion of the small intestine is usually found to be the jejuno-ileal junction. The anaesthesiological and surgical features of equine scrotal hernia are discussed.
Enflurane anesthesia in the pony: a comparative study between enflurane and halothane. Enflurane, a new volatile anesthetic agent, was compared with halothane as components of a commonly used clinical anesthetic regime in the pony. Enflurane provides satisfactory general anesthesia when administered at a maintenance concentration of approximately 1.5-2.5%, in combination with a 1:1 nitrous oxide-oxygen mixture. With both agents cardiac rhythm and pulse were stable, however significant arterial hypotension occurred, especially during and following induction, being anesthetic concentration dependent. Hypoventilation was induced by both agents, there being no significant quantitati...
Postural effects on lung volumes and asynchronous ventilation in anesthetized horses. Quasi-static pressure-volume curves and single-breath nitrogen washouts were performed simultaneously on eight anesthetized horses (average body wt = 485 kg) in left lateral, right lateral, prone, and supine postures (sequence randomized). The shift from prone to lateral or supine posture decreased expiratory reserve volume (ERV), vital capacity (VC), residual volume (RV), functional residual capacity (FRC), and total lung capacity (TLC); RV and FRC expressed as %TLC were unchanged, suggesting that in the lateral and supine postures a significant portion of the lung volume was not recruited by...