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.
Doppler ultrasonography and single-fiber laser Doppler flowmetry for measurement of hind limb blood flow in anesthetized horses. To use Doppler ultrasonography and single-fiber laser Doppler flowmetry (LDF) to evaluate blood flow in the dependent and nondependent hind limbs of anesthetized horses and to evaluate changes in femoral arterial blood flow and microvascular skeletal muscle perfusion in response to administration of phenylephrine hydrochloride or dobutamine hydrochloride. Methods: 6 healthy adult horses. Methods: Horses were anesthetized and positioned in left lateral recumbency. Doppler ultrasonography was used to measure velocity and volumetric flow in the femoral vessels. Single-fiber LDF was used to measur...
Measurements of hindlimb blood flow recorded using Doppler ultrasound during administration of vasoactive agents in halothane-anesthetized horses. The purpose of the study was to determine the ability of Doppler ultrasound to detect changes in femoral blood flow during pharmacologic manipulation of arterial blood pressure. Doppler ultrasonography was performed in the femoral vessels of six halothane-anesthetized horses before and during administration of phenylephrine HCI and sodium nitroprusside. The time-averaged mean velocity and volumetric flow were calculated. The contour of the velocity waveform was assessed, and the early diastolic deceleration slope (EDDS) and pulsatility index (PI) were calculated. Administration of phenylephrin...
Assessment of muscle oxygenation in the horse by near infrared spectroscopy. This study examined the ability of near infrared spectroscopy (NIRS) to noninvasively determine changes to muscle oxygenation in the resting horse. Five horses had (NIRS) performed over extremity muscle while under general anaesthesia, first with 8 min limb ischaemia, then systemic hypoxaemia for 5 min. A second group of 6 awake horses had NIRS performed over extremity muscle while being administered hypoxic gas (F(I)O2 0.10) for 5 min, and after return to steady state, limb ischaemia was induced for an additional 5 min. In the anaesthetised horses' ischaemia induced marked and significant mus...
Effects of pre-exercise frusemide administration and post exercise anaesthesia on cardiopulmonary and acid-base parameters and blood and plasma volumes in horses exercised supramaximally to fatigue. Six horses were randomly assigned to receive either frusemide (F) (0.5 mg/kg i.v.) or an equivalent volume of saline (S) i.v., 4 h prior to treadmill exercise. Horses were instrumented to enable measurement of heart rate (HR), systolic (SAP), mean (MAP), and diastolic (DAP) carotid arterial pressures, pulmonary artery pressure (PAP), central venous pressure (CVP), pulmonary arterial temperature (TEMP), blood gases, and cardiac output (CO). Plasma (PV) and blood volumes (BV) were measured using 2 injections of Evan's Blue dye. Baseline parameters were recorded while the horse stood quietly. Hor...
Effect of frusemide and hypertonic saline on electrolytes during post exercise anaesthesia. This study evaluated the effects of pre-exercise frusemide administration and hypertonic saline (H) infusion during anaesthesia on arterial pH, blood gases and electrolytes in 6 Thoroughbred horses anaesthetised immediately post exercise. Horses received either frusemide (F) (0.5 mg/kg, i.v.) or a saline placebo (P) injection 4 h prior to treadmill exercise. Exercise consisted of a 3 min warm-up at 40% VO2max followed by exercise to fatigue. Detomidine (40 micrograms/kg, i.v.) was given within 5 min of stopping and followed 5 min later by zolazepam-tiletamine (1.25 mg/kg, i.v.) to induce anaes...
Sedation and antisedation as tools in equine lameness examination. A kinematic study was performed to establish the locomotion pattern of horses under detomidine sedation and the effects of antagonization for possible use during lameness examinations in uncooperative horses. The kinematics of 17 Warmblood horses (9 sound, 8 lame with chronic forelimb lameness) were recorded on 2 days using a high-speed video system while trotting (3.9 m/s) on a treadmill. On each day a control measurement was carried out prior to sedation with detomidine (10 micrograms/kg bwt) and repeated recordings at 15, 25, 35, 45 and 60 min after sedation. On the second day, sedation was...
Nerve block and intra-articular anaesthesia of the forelimb in the sound horse. Nerve blocks and intra-articular anaesthesia are used extensively as routine methods in lameness evaluation. The method is based on the assumption that the technique itself does not change the movement pattern. The aim of this study was to carry out a quantitative kinematic study to confirm or reject the hypothesis that high palmar digital nerve block (HPDN) and intra-articular fetlock joint anaesthesia (IAF) influence significantly the movement pattern of the horse. Seven Standardbred horses trotting at 4.5 m/s were recorded at 240 Hz on a treadmill before and after anaesthesia by use of a Pr...
The recovery of horses from inhalant anesthesia: a comparison of halothane and isoflurane. Recovery is one of the more precarious phases of equine general anesthesia. The quality and rate of recovery of horses from halothane and isoflurane anesthesia were compared to determine differences in the characteristics of emergence from these commonly used inhalant anesthetics. Methods: Prospective, randomized blinded clinical trial. Methods: A total of 96 Thoroughbred and 3 Standardbred racehorses admitted for elective distal forelimb arthroscopy. Methods: All horses were premedicated with intravenous xylazine, induced with guaifenesin and ketamine, and maintained on a large animal circle ...
Effects of analgesia of the distal interphalangeal joint or palmar digital nerves on lameness caused by solar pain in horses. To determine if pain of the dorsal margin of the sole in horses can be attenuated by anesthesia of either the distal interphalangeal (DIP) joint or the palmar digital (PD) nerves. Methods: A unilateral forelimb lameness was induced by creating solar pain. Response to administration of local anesthetic or saline solution into the DIP joint and to administration of local anesthetic around the PD nerves was evaluated. Methods: Six horses. Methods: Lameness was induced by creating pressure on the dorsal margin of the sole by screwing set-screws into a nut welded to the inside of each branch of a s...
Effects of inhaled nitric oxide 10 ppm in spontaneously breathing horses anaesthetized with halothane. Inhaled nitric oxide, a selective pulmonary vasodilator, is known to improve arterial oxygenation after cardiopulmonary bypass and during acute respiratory distress syndrome in humans. During general anaesthesia with spontaneous ventilation, healthy adult horses develop large alveolar-arterial oxygen tension differences. In this study, we have determined the effects of inhaled nitric oxide (10 parts per million (ppm)) on venous admixture and pulmonary haemodynamics in horses anaesthetized with halothane. Seven adult horses were studied twice in random sequence. After premedication with romifid...
Inhaled carbon monoxide concentration during halothane or isoflurane anesthesia in horses. The purpose of this study was to assess carbon monoxide (CO) exposure during equine anesthesia with either halothane (H) or isoflurane (I) delivered in a circle rebreathing system. Methods: Prospective clinical investigation. Methods: Fifty client-owned horses. Methods: Horses were randomly assigned for anesthetic maintenance with H (n = 26) or I (n = 24). Two large animal anesthetic machines were used and assigned to a single agent for 2-4 weeks at a time. Machines were disassembled and soda lime changed prior to switching anesthetic agents. Inhalant anesthetic concentration and CO concentrat...
High intraosseous pressure as a cause of lameness in a horse with a degloving injury of the metatarsus. A 6-year-old Paint mare undergoing treatment for a degloving injury of the right metatarsus developed a non-weight-bearing lameness 19 days after admission. Diagnostic nerve blocks localized the source of pain to the area between the tarsus and the metatarsophalangeal joint. Radiography of the metatarsus and metatarsophalangeal joint, arthrocentesis of the metatarsophalangeal joint, and ultrasonography of the flexor tendons, flexor tendon sheath, and suspensory ligament failed to identify the cause of the lameness. The horse was anesthetized and intraosseous pressure was measured in the left a...
Anatomic, radiographic and physiologic comparisons of the internal carotid and maxillary artery in the horse. The anatomy of the internal carotid and maxillary arteries was examined using angiography, subtraction angiography and arterial cast preparations in three horses. Subtraction angiography was superior to angiography in demonstrating the anatomy of the occipital, external ophthalmic, ethmoidal and palatine arteries. In three horses manipulation of the internal carotid and occipital arteries during angiography resulted in vasospasm which prevented filling of these vessels with contrast. Direct arterial blood pressure measurements of the maxillary artery impinging on the guttural pouches was measu...
Hemodynamic effects of ionized calcium in horses anesthetized with halothane or isoflurane. To evaluate the effects of halothane and isoflurane on cardiovascular function and serum total and ionized calcium concentrations in horses, and to determine whether administration of calcium gluconate would attenuate these effects. Methods: 6 clinically normal adult Thoroughbreds. Methods: Catheters were inserted for measurement of arterial blood pressures, pulmonary arterial blood pressures, right ventricular pressure (for determination of myocardial contractility), right atrial pressure, and cardiac output and for collection of arterial blood samples. Anesthesia was then induced with xylazi...
Detection and comparison of nitric oxide in clinically normal horses and those with naturally acquired small intestinal strangulation obstruction. The purpose of this study was to determine whether nitric oxide (NO) is present in clinically normal horses under basal conditions and if it increases secondary to naturally acquired small intestinal strangulation obstruction. Thirty-one horses were used; 20 horses with naturally acquired small intestinal strangulation obstruction and 11 clinically normal horses with no signs of gastrointestinal tract disease. Jugular venous blood, abdominal fluid, and urine were collected for NO quantification. Plasma, abdominal fluid, and urine were stored at -70 degrees C until analyzed for NO using a chemi...
Evaluation of iodophor skin preparation techniques and factors influencing drainage from ventral midline incisions in horses. To document natural bacterial flora on the ventral aspect of the equine abdomen, to compare 2 preparation techniques, and to identify potential risk factors that may contribute to incisional drainage. Methods: Prospective study. Methods: 53 horses undergoing exploratory celiotomy. Methods: Group-1 horses (n = 26) were prepared with povidone-iodine and alcohol. Group-2 horses (27) were prepared with a film-forming iodophor complex. Numbers of bacterial colony-forming units (CFU) were measured before and after surgical scrub, following skin closure, and after recovery from general anesthesia. Sw...
Predictors of arterial oxygen tension in anesthetized horses: 1,610 cases (1992-1994). To identify factors associated with various arterial partial pressures of oxygen (Pao2) in anesthetized horses. Methods: Retrospective study. Methods: 1,450 horses anesthetized a total of 1,610 times with isoflurane or halothane. Methods: Anesthesia records, particularly results of blood gas analyses, were reviewed, and horses were grouped on the basis of lowest Pao2. Results: For horses with lowest Pao2 < 120 mm Hg, those with low pulse pressure, that underwent anesthesia on an emergency basis, or that were males were more likely to have Pao2 < 80 mm Hg. For horses with lowest Pao2 <...
Lameness associated with the bicipital bursa in an Arab stallion. Severe, chronic lameness in the left forelimb of a five-year-old Arab stallion was localised to the bicipital bursa by local anaesthesia and gamma scintigraphy. Radiographic and ultrasonographic examinations of the proximal humeral tubercles and bicipital bursa revealed new bone production in the region of the intertubercular grooves and irregularities in the density of the soft tissues of the bicipital tendon and bursa. An endoscopic examination of the bicipital bursa with a standard arthroscope under general anaesthesia was a useful diagnostic procedure. The stallion was euthanased, and mark...
Effects of ketamine on the equine electroencephalogram during anesthesia with halothane in oxygen. To investigate the effects of ketamine on the electroencephalogram (EEG) of the horse. Methods: Prospective experimental study. Methods: Eight Welsh mountain pony geldings weighing between 280 and 330 kg, 5 to 9 years old. Methods: During halothane anesthesia at an end-tidal halothane concentration between 0.75 and 0.85%, the EEG frequency power spectrum and the auditory evoked potential were recorded while an infusion of ketamine was given. Ketamine 200 mg was infused over 5 minutes in 8 ponies. The effects of ketamine on the EEG were recorded continuously during the infusion and for a furthe...
Effects of glucose infusion on the endocrine, metabolic and cardiorespiratory responses to halothane anaesthesia of ponies. Glucose was infused intravenously into six ponies during halothane anaesthesia, to evaluate its effect on their endocrine response to anaesthesia. The ponies were premedicated with acepromazine, and anaesthesia was induced with thiopentone and maintained with halothane in oxygen for two hours. Glucose was infused to maintain the plasma glucose concentration above 20 mmol/litre. Anaesthesia was associated with hypothermia, a decrease in haematocrit, hypotension, hyperoxaemia, respiratory acidosis and an increase in the plasma concentrations of lactate and arginine vasopressin. The concentration...
Equine castration: review of anatomy, approaches, techniques and complications in normal, cryptorchid and monorchid horses. Complications associated with equine castration are the most common cause of malpractice claims against equine practitioners in North America. An understanding of the embryological development and surgical anatomy is essential to differentiate abnormal from normal structures and to minimise complications. Castration of the normal horse can be performed using sedation and regional anaesthesia while the horse is standing, or under general anaesthesia when it is recumbent. Castration of cryptorchid horses is best performed under general anaesthesia at a surgical facility. Techniques for castratio...
Pharmacokinetics of medetomidine in ponies and elaboration of a medetomidine infusion regime which provides a constant level of sedation. The pharmacokinetics of intravenous (i.v.) medetomidine (7 mcg kg(-1)) were best described by a two-compartment model in five ponies. Total body clearance was 4 (SD 0.60) 1 kg h,(-1)t(1/2alpha)7. 6 (0.91) minutes and t(1/2beta)51.3 (13.09) minutes. In one pony the one-compartmental model was best fit, and total body clearance was 4. 2 l kg h(-1)and t(1/2)was 11 minutes. Medetomidine plasma levels had fallen below the limits of quantification (0.05 ng ml(-1)) within 4 hours. Medetomidine 5 mcg kg(-1)i.v. followed by an infusion of 3.5 mcg kg h(-1)for two hours provided a constant level of sedat...
Techniques for evaluation of right ventricular relaxation rate in horses and effects of inhalant anesthetics with and without intravenous administration of calcium gluconate. To determine the most repeatable method for evaluating right ventricular relaxation rate in horses and to determine and compare effects of isoflurane or halothane with and without the added influence of intravenously administered calcium gluconate on right ventricular relaxation rates in horses. Methods: 6 Thoroughbred horses from 2 to 4 years old. Methods: 6 models (2 for monoexponential decay with zero asymptote, 3 for monoexponential decay with variable asymptote, and 1 for biexponential decay) for determining right ventricular relaxation rate were assessed in conscious and anesthetized hor...
Laparoscopically assisted resection of umbilical structures in foals. A technique for laparoscopically assisted resection of umbilical structures in foals was developed. Eleven foals ranging from 8 to 42 days old underwent this procedure. Results of bacteriologic culture of umbilical structures were positive in 7 foals. Mean duration of anesthesia was 99 minutes, of which the initial 20 to 25 minutes were typically devoted to positioning and preparation of the foal for surgery. Major complications did not develop in any foal. Minor complications, such as slippage of the endoscopic ligating clip or laceration of the bladder during dissection, were dealt with succ...
Anesthesia of horses with a combination of detomidine, zolazepam, tiletamine, and isoflurane immediately after strenuous treadmill exercise. To evaluate effects of strenuous exercise in adult horses immediately before anesthesia and to determine whether prior exercise affects anesthesia induction, recovery, or both. Methods: 6 healthy Thoroughbreds in good condition and trained to run on a treadmill, each horse serving as its own control. Methods: Horses ran on a treadmill until fatigued, then were sedated immediately with detomidine hydrochloride and anesthetized with a zolazepam hydrochloride-tiletamine combination. Anesthesia was maintained with isoflurane in oxygen for another 90 minutes. Blood samples were taken before, during...
Cardiorespiratory effects of a tiletamine/zolazepam-ketamine-detomidine combination in horses. To determine cardiorespiratory effects of a tiletamine/zolazepam-ketamine-detomidine (TZKD) combination in horses. Methods: 8 healthy adult horses. Methods: Horses were instrumented for measurement of cardiorespiratory, acid-base, and electrolyte values. Each horse was given xylazine (0.44 mg/kg of body weight, IV) 10 to 15 minutes prior to induction of recumbency by administration of the TZKD combination. Cardiorespiratory, acid-base, and electrolyte values were measured at 5-minute intervals for > or =30 minutes. Results: All horses became recumbent within 1 minute after IV administration of...
Detomidine-propofol anesthesia for abdominal surgery in horses. To evaluate propofol for induction and maintenance of anesthesia, after detomidine premedication, in horses undergoing abdominal surgery for creation of an experimental intestinal adhesion model. Methods: Prospective study. Methods: Twelve horses (424 +/- 81 kg) from 1 to 20 years of age (5 females, 7 males). Methods: Horses were premedicated with detomidine (0.015 mg/kg i.v.) 20 to 25 minutes before induction, and a propofol bolus (2 mg/kg i.v.) was administered for induction. Propofol infusion (0.2 mg/kg/min i.v.) was used to maintain anesthesia. The infusion rate was adjusted to maintain an...
Alpha 2 agonists and antagonists. The alpha 2 agonists can produce reliable dose-dependent sedation and analgesia in most species. Nevertheless, they can also produce significant physiological adverse side effects depending on dose, rate, route of administration, and the concurrent use of other CNS depressants. For this reason, it may be best to use a low dose of an alpha 2 agonist as a preanesthetic agent. The alpha 2 agonists are best suited for young, healthy, exercise-tolerant patients. The combining of low doses of alpha 2, opioid, and benzodiazepine agonists results in a synergistic CNS depressant response while minimizi...
Comparison of peripheral and core temperatures in anesthetized horses. To examine temporal patterns of rectal, nasal, groin, and skin temperatures measured in adult horses undergoing general anesthesia and to determine accuracy and precision of temperatures at these sites, compared with core temperature. Methods: 5 healthy adult horses. Methods: Induction, maintenance of, and recovery from general anesthesia were performed in an air-conditioned surgical suite. Room temperature and relative humidity were approximately 21 C and 40%, respectively. Anesthesia was maintained for 2.5 hours, and body temperatures were measured and recorded every 5 minutes. Mean values w...