Cardiac performance in cats after administration of xylazine or xylazine and glycopyrrolate: echocardiographic evaluations

Cardiac performance was evaluated in 9 healthy cats sedated with xylazine. Each cat was evaluated echocardiographically before and after the administration of xylazine or xylazine and glycopyrrolate. Each cat was echocardiographically evaluated during manual restraint only (control value), after IM administration of 0.55 mg of xylazine/kg of body weight, after IM administration of 2.2 mg of xylazine/kg, and after IM administration of 0.011 mg of glycopyrrolate/kg followed 10 minutes later by IM administration of 2.2 mg of xylazine/kg. Echocardiographic indices of cardiac performance (fractional shortening, left ventricular wall amplitude, aortic amplitude, mitral valve E point septal separation) indicated a significant decrease (P less than 0.05) in the left ventricular function and heart rate after the small (0.55 mg/kg) and large (2.2 mg/kg) dosages of xylazine. With the administration of glycopyrrolate, the bradycardia was minimized, but cardiac performance was not improved. After administration of glycopyrrolate, cardiac performance decreased, but the decrease was not significant when compared with the ventricular performance of the cats after administration of the large dosage of xylazine. Compared with control values, the reduction in left ventricular function values associated with administration of xylazine or xylazine and glycopyrrolate was independent of the heart rate. Therefore, the alpha-2 adrenergic agonist xylazine has a marked depressive effect on cardiac performance in the cat, and premedication with glycopyrrolate may not completely alleviate the undesirable bradycardia, but may actually be detrimental to the cardiovascular system.

Cardiovascular and pharmacokinetic effects of isoxsuprine in the horse

Isoxsuprine (0.6 mg/kg) administered IV to 6 standing horses produced substantial, transient decreases in systemic blood pressure, systemic vascular resistance, and stroke volume. It also produced substantial, transient increases in heart rate, cardiac output, and purposeful movement. Plasma concentrations of isoxsuprine peaked soon after the drug was administered IV and then decreased over a 12-hour period in a biexponential manner, with distribution and elimination half-lives of 14 minutes and 2.67 hours, respectively. Total body clearance and steady-state volume of distribution were calculated to be 53.8 ml/min/kg and 10.5 L/kg, respectively. When a recommended therapeutic dosage regimen (0.6 mg/kg 2 times a day, per os) was used in 4 of these horses, changes were not detected. Isoxsuprine was not detected in plasma after the drug was given orally. We conclude that 0.6 mg of isoxsuprine/kg given orally every 12 hours is not likely to produce cardiovascular changes in the resting horse and that this is probably because plasma concentrations are not high enough to do so.

Anesthetic consideration in dogs with traumatic myocarditis

The trauma patient is commonly encountered in veterinary practice. Traumatic myocarditis has often been overlooked due to its delayed onset and preoccupation with other traumatic problems. The traumatic heart is very sensitive and in itself can cause death. Often a trauma patient requires surgery and a proper anesthetic protocol must be used which does not increase the incidence of cardiac arrhythmias. A review of anesthetic management including preanesthetic medications, induction drugs and techniques and maintenance with inhalation anesthesia reveals the need for careful selection of medications. Isoflurane was shown to be beneficial in reducing the incidence of undesirable responses of these patients.

The use of atropine to control heart rate responses during detomidine sedation in horses

Detomidine is a sedative-analgesic which has a pharmacological profile similar to xylazine. There is evidence that the sedative effects are mediated through alpha-2 adrenoceptors.

Cardiopulmonary responses were determined using detomidine as the principal agent and as a preanesthetic prior to the induction of general anesthesia. Compatibility with guaifenesin, sodium thia-mylal and halothane were determined.

As in the case of xylazine, detomidine produces a slowing of heart rates. This was found to be either sinus bradycardia or heart block. There may be a corresponding increase in systolic blood pressures. The respiratory pattern is altered through the arterial blood gases and pH data supported evidence of adequate ventilation. The heart rate response to detomidine without anticholinergic treatment was transient and related to he duration of drug action.

Atropine sulfate, 0.02 mg/kg i.v. was effective in preventing or treating bradycardia or heart block from detomidine. Heart rates also increased during the administration of guaifenesin and sodium thia-mylal when given 50 min poisit-detomidine.

Arterial to end-tidal CO2 tension and alveolar dead space in halothane- or isoflurane-anesthetized ponies

The correlation between end-tidal partial pressure of CO2 (PETCO2) and arterial (PaCO2) was determined for spontaneously breathing ponies under halothane or isoflurane anesthesia. The PETCO2 was useful as a trend indicator of PaCO2 during the first 60 minutes of halothane or isoflurane anesthesia when PaCO2 values were less than 60 to 70 mm of Hg. Halothane anesthesia lasting greater than 90 minutes was associated with PaCO2 values in excess of 60 to 70 mm of Hg, a large arterial- to end-tidal PCO2 difference (PaCO2-PETCO2) and a significant increase in alveolar dead space. These effects were not seen during the same period of isoflurane anesthesia. Arterial blood gas analysis is therefore recommended during halothane anesthesia when the PETCO2 is greater than 60 to 70 mm of Hg. A decrease in alveolar capillary perfusion relative to alveolar ventilation is the most likely cause for the increase in alveolar dead space during halothane anesthesia. Based on these findings, isoflurane may be superior to halothane for prolonged anesthesia of spontaneously breathing horses.

Effects of gastric distention-volvulus on coronary blood flow and myocardial oxygen consumption in the dog

Gastric distention-volvulus (GDV; at 50 mm of Hg gastric inflation pressure) was experimentally induced in 8 dogs anesthetized using pentobarbital. Hemodynamic indices including heart rate, mean arterial pressure, cardiac output, and coronary blood flow (4 dogs) were measured during a 20-minute period of GDV and for 10 minutes after decompression. Arterial and coronary venous oxygen tensions were also measured for calculation of myocardial oxygen extraction (7 dogs) and myocardial oxygen consumption (4 dogs). Dogs were monitored for 72 hours postoperatively for the occurrence of arrhythmias, then were euthanatized for gross and histologic examination of the heart. Experimental GDV resulted in significant (P less than 0.05) decreases in cardiac output (89%), mean arterial pressure (45%), and coronary blood flow (50%) compared with control values. Myocardial oxygen extraction increased (30%) and overall myocardial oxygen consumption decreased (50%), compared with control values. Evidence of subendocardial necrosis was seen in 6 dogs, 4 of which had developed ventricular arrhythmias 8 to 24 hours postoperatively.

Anesthetic waste gases in veterinary medicine: analysis of the problem and suggested guidelines for reducing personnel exposures

Anesthetic waste gases are a concern to veterinarians and their personnel. Investigations have shown that many of the anesthetic units used in veterinary medicine have leaks that contribute to operating room contamination. Many others do not have appropriate scavanging attachments to remove escaping gases. Personnel were frequently observed carelessly using equipment or handling anesthetic agents in a manner contributing to excessive exposure. Proper maintenance of equipment and careful use of gaseous anesthetic agents can significantly reduce waste gas levels and exposure of personnel.

Cardiopulmonary resuscitation in the horse

Depression of the cardiopulmonary system of the horse during anesthesia is not an uncommon event. In many situations simple approaches for improving the function of the horse are necessary to avoid loss of life. This study has been completed utilizing an anesthetic approach frequently used in horses and a cardioresuscitative technique which can be utilized by the practicing veterinarian. Severe depression to arrest were produced experimentally and each animal was resuscitated through support of ventilation and circulation.

Anesthesia for small animal pediatric and geriatric patients. I. Anesthesia for small animal pediatric patients

Anesthetic management of the pediatric patient is a challenge which can give rise to a most rewarding anesthetic management if one takes into consideration the normal physiological function of the pediatric patient. One should choose the appropriate medications which may safely be administered to an animal of this age. Control of anesthesia through the use of appropriate anesthetic equipment and the use of appropriate monitoring will aid safe management. The selection of adjunct medications can achieve control of complications and aid ultimate uncomplicated recovery.

Anesthesia for small animal geriatric patient

The decreased adaptability normally associated with aging animals is described. Anesthetic evaluation and management of these alterations can be successfully completed if wide variations in organ functions are not required of the patient by the surgeon or anesthetist.

General anesthesia in pleasure horses

Anesthetic management of the pleasure horse consists of the appropriate selection and administration of pre-anesthetic medications including anticholinergics, tranquilizers and narcotics followed by appropriate techniques of anesthetic induction. The anesthetic induction must vary somewhat for the pleasure horse practice since many of the procedures are completed on farms and ranches. As a result the inducing of anesthesia will frequently be with the same agent which will be used to maintain anesthesia. Noticeably will be the reduction and duration of anesthesia and surgical time. The induction of anesthesia will predominately be with ultra-short barbiturates alone or in combination with muscle relaxants or combinations of tranquilizers and dissociative anesthetics. Supplemental injections of intravenous agents or halothane, methoxyflurane or enflurane may be used to maintain anesthesia. Recoveries can be expected to vary according to the duration of anesthesia and the selection of agents that have been used. Anesthetic complications predominately consist of cardiopulmonary responses and those associated with recovery.

Preanesthetic evaluation and management of malignant hyperthermia in the pig experimental model

Fifty-three swine from the University of Missouri Sinclair Medical Research Farm were used in experimentation to determine their susceptibility to malignant hyperthermia, to determine appropriate anesthetic agents for susceptible swine and to investigate appropriate pharmaceutical agents which could protect against the development of malignant hyperthermia. The screening technics used were successful in determining susceptible animals to MH and the anesthesia studies indicated that dissociative anesthetics had less tendency to trigger MH than did halothane and pancuronium was shown to have greater safety as a muscle relaxant than succinylcholine in this group of pigs. Pigs pretreated with reserpine had less tendency to develop symptoms of MH and some were completely protected. The principle undesirable effect was the development of hypotension if sufficient reserpine was used to provide total protection.