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Abstract

Objective

To determine cardiorespiratory effects of a tiletamine/zolazepam-ketamine-detomidine (TZKD) combination in horses.

Animals

8 healthy adult horses.

Procedure

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 ≥ 30 minutes.

Results

All horses became recumbent within 1 minute after IV administration of TZKD. Mean ± SD duration of recumbency was 40 ± 8 minutes. All horses regained standing position after ≤ 2 attempts. Quality of anesthesia and analgesia was determined to be satisfactory in all horses. Xylazine induced decreases in respiratory rate, heart rate, cardiac output, maximum rate of increase of right ventricular pressure, and rate pressure product. The PaCO2, right atrial pressure, and peripheral vascular resistance increased, whereas blood temperature, PO2, pHa, HCO3 , PCV, total solids, Na, and K values remained unchanged. Subsequent administration of TZKD caused right atrial pressure and PaCO2 to increase and PaO2 to decrease, compared with values obtained after xylazine administration. Remaining cardiorespiratory, acid-base, hematologic, and electrolyte values did not differ from those obtained after xylazine administration.

Conclusion

IV administration of TZKD induces short-term anesthesia in horses. Potential advantages of this drug combination are the small volume of drug administered; minimal cardiorespiratory depression; quality of induction and maintenance of, and recovery from, anesthesia; and duration of drug effects. (Am J Vet Fles 1999;60:770–774)

Free access
in American Journal of Veterinary Research

Abstract

Objective

To provide quantitative assessment of forces affecting filtration of synovial fluid in response to incremental changes in arterial and venous hemodynamics.

Animals

7 clinically normal adult horses.

Procedure

Using a stationary, isolated metacarpophalangeal joint preparation, blood flow (Qacir), tissue perfusion, arterial pressure (Pacir), venous pressure (Pvcir), transsynovial fluid flow, total vascular resistance, vascular compliance, and tissue compliance were evaluated before and after arterial and venous pressure manipulations. At isogravimetric conditions, pre- and postcapillary resistance and ratios, osmotic reflection coefficient (σd), capillary pressure, net filtration pressure, and transitional microvascular pressure were determined.

Results

Synovial tissue blood flow was similar before, immediately after, and 3.5 hours after joint isolation. The σd for the joint was low, owing to the high oncotic pressure of synovial fluid at filtration-independent states. Transsynovial flow occurred in preference to lymph flow because of the high permeability of synovial tissue (low σd). Synovial fluid production and transfluid flow (synovium weight gain) increased at Pacir > 200 mm of Hg, indicating a threshold phenomenon for synovial filtration. Net filtration pressure > 6 mm of Hg is needed to effect an increase in synovial fluid flow, and pressure of approximately 11 mm of Hg is necessary to increase lymphatic flow. Vascular compliance in the joint was low, but increased markedly with Pvcir. Vascular and tissue compliance increased with increased Pacir. Vascular compliance changes caused by increased arterial pressure were minimal, compared with those caused by increased venous pressure owing to the greater elastance of arteries and the larger muscular arterial wall.

Conclusion

This isolated joint preparation permitted evaluation of codependent hemodynamic, microvascular, and transsynovial flow responses to hemodynamic manipulations. Synovial tissue permeability was markedly affected by increased vascular forces altering filtration pressures toward synovial fluid production. (Am J Vet Res 1998;59:495–503)

Free access
in American Journal of Veterinary Research

SUMMARY

The hemodynamic effects of high arterial carbon dioxide pressure (PaCO2 ) during anesthesia in horses were studied. Eight horses were anesthetized with xylazine, guaifenesin, and thiamylal, and were maintained with halothane in oxygen (end-tidal halothane concentration = 1.15%). Baseline data were collected while the horses were breathing spontaneously; then the horses were subjected to intermittent positive-pressure ventilation, and data were collected during normocapnia (PaCO2 , 35 to 45 mm of Hg), moderate hypercapnia (PaCO2 , 60 to 70 mm of Hg), and severe hypercapnia (PaCO2 , 75 to 85 mm of Hg). Hypercapnia was induced by adding carbon dioxide to the inspired gas mixture. Moderate and severe hypercapnia were associated with significant (P < 0.05) increases in aortic blood pressure, left ventricular systolic pressure, cardiac output, stroke volume, maximal rate of increase and decrease in left ventricular pressure (positive and negative dP/dtmax, respectively), and median arterial blood flow, and decreased time constant for ventricular relaxation. These hemodynamic changes were accompanied by increased plasma epinephrine and norepinephrine concentrations. Administration of the β-blocking drug, propranolol hydrochloride, markedly depressed the response to hypercapnia. This study confirmed that in horses, hypercapnia is associated with augmentation of cardiovascular function.

Free access
in American Journal of Veterinary Research

SUMMARY

Programmed electrical stimulation techniques were used to evaluate the effects of halothane and isoflurane on induction of atrial fibrillation in anesthetized dogs. Experiments were performed in 16 dogs anesthetized with α-chloralose. Critically timed premature stimuli were applied to the right atrial appendage and Bachmann bundle to determine the atrial fibrillation threshold, defined as the minimal current required to induce rapid, irregular atrial electrical activity of at least 8 seconds' duration, Atrial fibrillation thresholds were determined at baseline (0.0% inhalational anesthetic), 0.5 minimal alveolar concentration (mac), and 1.0 mac of halothane (n = 8) and isoflurane (n = 8).

In the absence of inhalation anesthetic, it was significantly (P < 0.01) easier to induce atrial fibrillation at the Bachmann bundle vs the right atrial appendage. Atrial fibrillation threshold at the Bachmann bundle was not affected by increasing concentrations of halothane, but was increased by 1.0 mac of isoflurane (P < 0.05). It was concluded that at 1.0 mac isoflurane, but not halothane, has antifibrillatory effects in atrial tissue.

Free access
in American Journal of Veterinary Research

SUMMARY

The cardiopulmonary effects of 4 positions (standing, right lateral, left lateral, and dorsal recumbency) were evaluated in conscious cattle in which no sedatives or anesthetic drugs were given. Each position was maintained for 30 minutes, during which time there were no significant changes in heart rate, respiratory rate, mean arterial blood pressure, arterial pH, PaCO2 , arterial base excess, or venous blood gas values. Significant decreases in PaO2 developed when cattle were in lateral positions and dorsal recumbency. Cardiac index was unchanged in all positions, except in dorsal recumbency at 30 minutes, when it was significantly decreased.

Free access
in American Journal of Veterinary Research

SUMMARY

Eight adult female cattle (6 Holstein, 1 Jersey, 1 Brown Swiss) were used to determine the antagonistic effects of tolazoline, an α2-adrenoceptor antagonist, on xylazine-induced (via caudal epidural administration) depression of cns, respiratory, and cardiovascular activity and rumen motility. A 2% solution of xylazine HCl was injected into the epidural space at the first coccygeal interspace, using a dosage of 0.05 mg/kg of body weight, diluted to a 5-ml volume with sterile water, and administered at a rate of approximately 1 ml/30 s. Eight minutes after xylazine injection, either tolazoline (0.3 mg/kg) or saline solution (4 ml) was administered iv. All 8 cattle were treated, using both regimens in a random sequence; at least 1 week elapsed between treatments. Epidurally administered xylazine induced caudal analgesia (S3 to coccyx), as evaluated by no response to superficial and deep muscular pinprick, and induced sedation, cardiopulmonary depression, and inhibition of rumen motility, but all cattle remained standing. Tolazoline effectively reversed xylazine-induced rumen hypomotility, and partially antagonized xylazine-induced cardiopulmonary depression without affecting sedation and desirable local (S3 to coccyx) analgesic effects.

Free access
in American Journal of Veterinary Research

Abstract

Objective—To determine the effects of perzinfotel, butorphanol, and their combination on the minimal alveolar concentration (MAC) of isoflurane in cats.

Animals—7 healthy sexually intact cats (4 males and 3 females), aged 12 to 17 months and weighing 2.8 to 4.6 kg.

Procedures—In a crossover design, saline (0.9% NaCl) solution, perzinfotel (2.5 to 15 mg/kg; IV, IM, and SC), butorphanol tartrate (0.2 mg/kg, IM), or a combination of 5 mg of perzinfotel/kg and 2 mg of butorphanol tartrate/kg (both IM) was administered to 6 cats before 7 separate episodes of anesthesia with isoflurane in oxygen. Heart rate, arterial blood pressure, bispectral index (BIS), and inspiration and expiration concentrations of isoflurane were continuously monitored. The isoflurane MAC was determined twice during anesthesia.

Results—IV, IM, and SC administration of perzinfotel at 2.5 to 15 mg/kg resulted in a significant decrease in mean isoflurane MAC by 43.3% to 68.0%. The BIS significantly increased after perzinfotel administration via the same routes at 2.5 to 15 mg/kg and after perzinfotelbutorphanol administration IM. Blood pressure was significantly higher after perzinfotel was administered at 5 mg/kg, IM; 10 mg/kg, IV; and 10 mg/kg, SC than after saline solution administration.

Conclusions and Clinical Relevance—Perzinfotel administration decreased the isoflurane MAC and increased several BIS and blood pressure values in anesthetized cats. Administration of perzinfotel prior to isoflurane anesthesia may improve anesthetic safety by reducing inhalant anesthetic requirements and improving cardiovascular function during anesthesia. (Am J Vet Res 2010;71:1270–1276)

Full access
in American Journal of Veterinary Research

Objective

To test the hypothesis that small volumes of hypertonic saline-dextran (HSD) solution can be used to effectively resuscitate dogs in shock induced by gastric dilatation-volvulus (GDV). and, compared with administration of large volumes of lactated Ringer's solution (LRS), can be used to limit the overall volume of fluid needed for resuscitation.

Design

Prospective, clinical study.

Animals

15 dogs with GDV-induced shock.

Procedure

Initially, HSD solution (5 ml/kg of body weight) or LRS (60 to 90 ml/kg) was administered. All dogs then received a maintenance administration (20 ml/kg/h) of LRS. Cardiorespiratory, blood gas, and serum biochemical analyses were performed over a 4-hour period after initiation of treatment.

Results

Systolic arterial and central venous pressures and plasma volume increased more rapidly in dogs in the HSD + LRS group. The cumulative dose of fluids administered to dogs in the HSD + LRS group was significantly less than that administered to dogs in the LRS group. Serum sodium and chloride concentrations and osmolality increased significantly in dogs in the HSD + LRS group, but not in dogs in the LRS group. Ventricular arrhythmias were detected in both groups of dogs, but did not appear to be induced by either form of fluid therapy.

Clinical Implications

Administration of HSD rapidly restored cardiorespiratory function and induced resuscitation equivalent to administration of large volumes of LRS. Use of HSD solutions to treat dogs in GDV-induced shock may be more efficient than use of isotonic fluids. Administration of HSD solution was not associated with noticeable complications.

Free access
in Journal of the American Veterinary Medical Association

Abstract

Objective—To determine the effects of IV administration of enalaprilat on cardiorespiratory and hematologic variables as well as inhibition of angiotensin converting enzyme (ACE) activity in exercising horses.

Animals—6 adult horses.

Procedure—Horses were trained by running on a treadmill for 5 weeks. Training was continued throughout the study period, and each horse also ran 2 simulated races at 120% of maximum oxygen consumption. Three horses were randomly selected to receive treatment 1 (saline [0.9% NaCl] solution), and the remaining 3 horses received treatment 2 (enalaprilat; 0.5 mg/kg of body weight, IV) before each simulated race. Treatment groups were reversed for the second simulated race. Cardiorespiratory and hematologic data were obtained before, during, and throughout the 1-hour period after each simulated race. Inhibition of ACE activity was determined during and after each race in each horse.

Results—Exercise resulted in significant increases in all hemodynamic variables and respiratory rate. The pH and PO2 of arterial blood decreased during simulated races, whereas PCO2 remained unchanged. Systemic and pulmonary blood pressure measurements and arterial pH, PO2, and PCO2 returned to baseline values by 60 minutes after simulated races. Enalaprilat inhibited ACE activity to < 25% of baseline activity without changing cardiorespiratory or blood gas values, compared with horses administered saline solution.

Conclusions and Clinical Relevance—Enalaprilat administration almost completely inhibited ACE activity in horses without changing the hemodynamic responses to intense exercise and is unlikely to be of value in preventing exercise-induced pulmonary hemorrhage. (Am J Vet Res 2001;62:1008–1013)

Full access
in American Journal of Veterinary Research

Abstract

Objective—To measure QT interval duration and QT dispersion in Boxers and to determine whether QT variables correlate with indices of disease severity in Boxers with familial ventricular arrhythmias, including the number of ventricular premature complexes per day, arrhythmia grade, and fractional shortening.

Animals—25 Boxers were evaluated by ECG and echocardiography.

Procedure—The QT interval duration was measured from 12-lead ECG and corrected for heart rate (QTc), using Fridericia's formula. The QT and QTc were calculated for each lead, from which QT and QTc dispersion were determined. Echocardiography and 24-hour ambulatory ECG were performed to evaluate for familial ventricular arrhythmias. Total number of ventricular premature complexes, arrhythmia grade, and fractional shortening were determined and used as indices of disease severity.

Results—There was no correlation between any QT variable and total number of ventricular premature complexes, arrhythmia grade, or fractional shortening. No difference between QT dispersion and QTc dispersion was identified, and correction for heart rate did not affect the results.

Conclusions and Clinical Relevance—QT interval duration and dispersion did not correlate with indices of disease severity for familial ventricular arrhythmias. Heart rate correction of the QT interval did not appear to be necessary for QT dispersion calculation in this group of dogs. QT dispersion does not appear to be a useful noninvasive diagnostic tool in the evaluation of familial ventricular arrhythmias of Boxers. Identification of affected individuals at risk for sudden death remains a challenge in the management of this disease. (Am J Vet Res 2001;62:1481–1485)

Full access
in American Journal of Veterinary Research