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.
Concentration of prostaglandins F in uterine venous plasma of anesthetized mares during the estrous cycle and early pregnancy. Prostaglandins F were quantitated by radioimmunoassay in uterine venous plasma of anesthetized mares on day 7 of estrus, days 2, 6, 10, 14 or 18 of diestrus and days 10, 14 or 18 of pregnancy. The PGF concentration was greater (P less than .01) at day 14 of diestrus than at all other days studied. The concentrations at days 10 and 18 of diestrus and at days 10, 14 and 18 of pregnancy were greater (P less than .05) than at day 7 of estrus and days 2 and 6 of diestrus. PGF concentrations at days 10 and 14 were greater (P less than .01) for diestrous than for pregnant mares.
Aspects of respiration in anaesthetized newborn foals. The arterial oxygen tension (PaO2) in clinically normal newborn foals at 1300 m above sea-level is considerably lower (less than 60 mmHg) than in similarly aged foals at lower altitudes. This figure is further reduced to less than 50 mmHg without adverse effect in newborn foals at 1300 m maintained under pentobarbitone anaesthesia for prolonged periods. Measurement of O2 dissociation curves indicates that haemoglobin becomes saturated at a lower blood O2 tension in newborn foals than adult horses.
The use of intravascular catheters for long-term studies on the mare and fetus. Methods developed for the insertion of catheters into the umbilical artery and vein and the uterine vein of the pregnancy mare are described. The technique requires careful anaesthesia and the maintenance of normal blood gas tensions, pH and arterial blood pressure. Fetal survival was variable: three mares delivered live foals and six fetuses survived more than 15 days with a maximal period of 41 days. The erythrocytes sedimentation rate (ESR) of the fetal foal was always very low at operation but subsequently increased slightly; a sudden large rise in ESR usually indicated imminent fetal deat...
Cardiopulmonary effects of positive end-expiratory pressure in anesthetized horses. The cardiopulmonary effects of 0, 5, 10, and 15 cm of H2O positive end-expiratory pressures (PEEP) were determined in anesthetized, spontaneously breathing horses, using a 4 by 4 Latin-square design with one repetition. Cardiac output, alveolar-arterial oxygen tension difference, alveolar ventilation, dead space/tidal volume ratio, and carbon dioxide elimination were not significantly altered by the procedure. As PEEP was increased, alveolar and arterial oxygen tensions, respiratory exchange ratio, and pH decreased, whereas arterial carbon dioxide tension and oxygen consumption increased. Thes...
Evaluation of xylazine as a sedative and preanesthetic agent in horses. Xylazine administered intramuscularly (IM) to horses at the dose level of 2 mg/kg was an effective sedative and preanesthetic for thiamylal sodium narcosis or thiamylal sodium and halothane anesthesia. Evaluation of response of cardiovascular, respiratory, and hepatic function did not indicate serious untoward effects, although cardiac and respiratory rate decreased, calculated vigor of left ventricular contraction decreased, calculated peripheral vascular resistance increased, and transient innocuous cardiac arrhythmias occurred. Effects of the anesthetics used on respiratory function (blood ...
Positive end-expiratory pressure in anaesthetized spontaneously breathing horses. Horses breathing spontaneously under halothane anaesthesia were subjected to expiratory resistance by the introduction of a water-trap into the expiratory limb of a circle absorber. Resistances of 10 and 20 cm H2O produced no significant increase in PaO2 (P greater than 0.05) during halothane/air and halothane/oxygen anaesthesia. The imposition of resistance was associated with an increase in PaCO2 and a significant increase in mixed venous PCO2. In three animals subjected to 20 cm H2O resistance under halothane/air anaesthesia, the cardiac output was reduced (P less than 0.01). It was conclud...
Vascular responses in the equine digit. The digital circulation was isolated in 12 ponies under pentobarbital anesthesia. Blood flow was either controlled by a pump or measured under natural perfusion. The responses to rapid changes and stoppages of blood flow indicated no evidence of autoregulation or reactive hyperemia. Local administration of acetylcholine, histamine, and prostaglandins E1 and E2 decreased prevenous resistance, whereas epinephrine and serotonin caused prevenous constriction. Large doses of epinephrine and serotonin decreased venous caliber. The effects of prostaglandins A1 and F2alpha were variable. The equine di...
Papers and articles measurement of central venous pressure in horses. Central venous pressure measurements were made in 74 horses and ponies free from clinical evidence of cardiopulmonary disease. Using the sternal manubrium as the zero reference point, the mean value obtained was 12 cm H2O (S.D. +/- 6). There was a significant correlation with body weight (r=0.6, p less than 0.001) but there was none with age, sex, breed or type. During halothane anaesthesia, using the same reference point, the mean value was 24.5 cm H2O (S.D. +/- 6) in 28 animals in right lateral recumbency, 29 cm H2O (S.D. +/- 8) in 17 animals in left lateral recumbency and -6 cm H20 (S.D. +/...
Closure of ductus arteriosus determined by cardiac catheterization and angiography in newborn foals. The physiologic closure of the ductus areteriosus was determined in 4 foals less than 16 hours old. The common carotid artery was catheterized, using local anesthesia and tranquilization, and contrast medium was injected into the ascending aorta. Radiographs were made of heart and great vessels during and after the injection to visualize the pathway of injected contrast medium.
Influence of induced hypermagnesemia and hypocalcemia on neuromuscular blocking property of oxytetracycline in the horse. The neurally evoked contractile response of the upper lip muscles of horses anesthetized with halothane was used to evaluate the neuromuscular blocking property of oxytetracycline which was administered intravenously at total dose rate of 21 to 28 mg/kg. This dose rate did not alter the contractile response which had a mean control value (and standard error; SE) of 1.76 plus or minus 0.22 kg. Arterial blood pressure was not affected by these dose rates. Neuromuscular blocking effect of the antibiotic occurred when it was administered during partial neuromuscular blockade which had been induced...
The use of ultrasonic energy to vaporize anaesthetic liquids. Ultrasonic energy, provided by a commercially available water vaporizer, was used to vaporize methoxyflurane, halothane, and chloroform. The vaporizer was placed directly in the respiratory line, and the anaesthetic liquid was vaporized one drop at a time. Anaesthesia was maintained for periods up to 6 hr in horses, ponies, calves, sheep, dogs, and one pig. This method of vaporizing liquids is applicable to a wide variety of anaesthetics. It is easily controlled, and the same vaporizer can be used with a wide range of sizes of subjects. The vaporizer can be placed directly in the respiratory c...
Static pulmonary compliance in ponies. Static pulmonary and total compliance during expiration was measured in fifteen healthy anesthetized ponies. Mean body weight of the ponies was 140.6 kg and ranged from 83.6 to 211.4 kg. For the fifteen ponies, mean values and SD were: total compliance (Ct), 168.7 plus or minus 47.2 ml/CMH2O, and mean pulmonary compliance (Cl), 368.4 plus or minus 90.3 ml/cmH2O. Both Ct and Cl were significantly dependent on body weight, calculated surface area, height at the withers, and circumference about the chest. Repeatability of compliance measurement from day to day was confirmed by measuring complianc...
Post-operative management of equine abdominal patients. Adequate post-operative management of equine abdominal patients is as necessary to patient survival as the most heroic corrective surgery. Post-operative management must begin during the anaesthesia recovery phase to insure adequate oxygen supply, ventilation, and minimize any abdominal discomfort. The animal's physiological status must be constantly monitored to detect and determine the degree of abnormalities concerning serum electrolytes, fluid balance, and acid-base abnormalities. The most commonly observed serum electrolyte imbalance is hypokalaemia. Replacement potassium is usually suppl...
Monitoring and evaluating the physiological changes in the horse with acute abdominal disease. Initial examination and therapy, and the avoidance of maltreatment are emphasized. Gastric decompression is of prime importance, after which no compound should be administered via stomach tube. Where large amounts of high starch grains are fed, primary acute gastric dilatation must be differentiated from that secondary to small bowel dilatation, by immediate gastric intubation and irrigation of the cardia with lidocaine. If cessation of pain and improvement of peristalsis and general attitude follow, the former state may be assumed. If pain persists and peristalsis does not improve markedly, o...
The indirect measurement of arterial blood pressure in the horse. An accurate modified auscultatory technique for the indirect measurement of arterial pressure in the horse is described. Limitations of the method were sensitivity to external motion in nervous, conscious horses, and the failure to detect Korotkoff sounds in shocked, anaesthetized surgical cases. The apparatus required for the method is expensive and is probably impractical for routine monitoring during anaesthesia.
Ventilation and cardiovascular studies during mechanical control of ventilation in horses. Eleven out of 12 horses were underventilating while breathing spontaneously during halothane anaesthesia with high arterial carbon dioxide tensions. In addition, large alveolar to arterial oxygen tension gradients were found to be present. Mechanically, controlled ventilation with an intermittent positive pressure of 20-30 cm H2O reduced arterial carbon dioxide levels to normal. The alveolar to arterial oxygen gradients did not increase and in some cases decreased. These (A - a) Po2 gradients were due mainly to true shunt of the order of 30 per cent and not to ventilation perfusion inequality....
Cardiac output in the conscious and anaesthetised horse. Cardiac output in the horse was measured before and at predetermined times during 2-hour periods of thiopentone-halothane and thiopentone-diethyl ether anaesthesia. Left ventricular stroke volume was decreased to a similar extent during anaesthesia with each volatile agent, but a greater reduction in cardiac output occurred during halothane anaesthesia. This finding reflected the differing effects of halothane and ether on heart rate, a slight bradycardia occurring with the former agent while ether produced a small degree of tachycardia. The latter effect was attributed to enhanced sympathoadr...