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Abstract

Objective—To determine the anesthetic, cardiorespiratory, and metabolic effects of 4 IV anesthetic regimens in Thoroughbred horses recuperating from a brief period of maximal exercise.

Animals—6 adult Thoroughbreds.

Procedure—Horses were preconditioned by exercising them on a treadmill. Each horse ran 4 simulated races, with a minimum of 14 days between races. Races were run at a treadmill speed that caused horses to exercise at 120% of their maximal oxygen consumption. Horses ran until fatigued or for a maximum of 2 minutes. Two minutes after exercise, horses received a combination of xylazine hydrochloride (2.2 mg/kg of body weight) and acepromazine maleate (0.04 mg/kg) IV. Five minutes after exercise, horses received 1 of the following 4 IV anesthetic regimens: ketamine hydrochloride (2.2 mg/kg); ketamine (2.2 mg/kg) and diazepam (0.1 mg/kg); tiletamine hydrochloride-zolazepam hydrochloride (1 mg/kg); and guaifenesin (50 mg/kg) and thiopental sodium (5 mg/kg). Treatments were randomized. Cardiopulmonary indices were measured, and samples of blood were collected before and at specific times for 90 minutes after each race.

Results—Each regimen induced lateral recumbency. The quality of induction and anesthesia after ketamine administration was significantly worse than after other regimens, and the duration of anesthesia was significantly shorter. Time to lateral recumbency was significantly longer after ketamine or guaifenesinthiopental administration than after ketaminediazepam or tiletamine-zolazepam administration. Arterial blood pressures after guaifenesin-thiopental administration were significantly lower than after the other regimens.

Conclusions and Clinical Relevance—Anesthesia can be safely induced in sedated horses immediately after maximal exercise. Ketamine-diazepam and tiletamine- zolazepam induced good quality anesthesia with acceptable perturbations in cardiopulmonary and metabolic indices. Ketamine alone and guaifenesinthiopental regimens are not recommended. (Am J Vet Res 2000;61:1545–1552)

Full access
in American Journal of Veterinary Research

Summary

Six nontrained mares were subjected to steady-state, submaximal treadmill exercise to examine the effect of exercise on the plasma concentration of atrial natriuretic peptide (anp) in arterial, compared with mixed venous, blood. Horses ran on a treadmill up a 6° grade for 20 minutes at a speed calculated to require a power equivalent to 80% of maximal oxygen uptake (Vo 2MAX). Arterial and mixed venous blood samples were collected simultaneously from the carotid and pulmonary arteries of horses at rest and at 10 and 20 minutes of exercise. Plasma was stored at − 80 C and was later thawed; anp was extracted, and its concentration was determined by radioimmunoassay. Exercise caused significant (P < 0.05) increases in arterial and venous plasma anp concentrations. Mean ± sem arterial anp concentration increased from 25.2 ± 4.4 pg/ml at rest to 52.7 ± 5.2 pg/ml at 10 minutes of exercise and 62.5 ± 5.2 pg/ml at 20 minutes of exercise. Mean venous anp concentration increased from 24.8 ± 4.3 pg/ml at rest to 67.2 ± 14.5 pg/ml at 10 minutes of exercise and 65.3 ± 13.5 pg/ml at 20 minutes of exercise. Significant differences were not evident between arterial or mixed venous anp concentration at rest or during exercise, indicating that anp either is not metabolized in the lungs or is released from the left atrium at a rate matching that of pulmonary metabolism.

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in American Journal of Veterinary Research

Summary

Six untrained mares were subjected to incremental treadmill exercise to examine exercise-induced changes in plasma renin activity (pra) and plasma aldosterone (aldo) and plasma arginine vasopressin (avp) concentrations. Plasma renin activity, aldo and avp concentrations, and heart rate (hr) were measured at each step of an incremental maximal exercise test. Mares ran up a 6° slope on a treadmill set at an initial speed of 4 m/s. Speed was increased 1 m/s each minute until hr reached a plateau. Plasma obtained was stored at − 80 C and later was thawed, extracted, and assayed for pra and aldo and avp values by use of radioimmunoassay. Exercise caused significant increase in hr from 40 ± 2 beats/min (mean ± sem) at rest to 206 ± 4 beats/min (hr max) at speed of 9 m/s. Plasma renin activity increased from 1.9 ± 1.0 ng/ml/h at rest to a peak of 5.2 ± 1.0 ng/ml/h at 9 m/s, paralleling changes in hr. Up to treadmill speed of 9 m/s, strong linear correlations were obtained between exercise intensity (and duration) and hr (r = 0.87, P < 0.05) and pra (r = 0.93, P < 0.05). Heart rate and pra reached a plateau and did not increase when speed was increased from 9 to 10 m/s. Plasma aldo concentration increased from 48 ± 16 pg/ml at rest to 191 ± 72 pg/ml at speed of 10 m/s. Linear relation was found between exercise intensity (and duration) and aldo concentration (r = 0.97, P < 0.05). Plasma avp concentration increased from 4.0 ± 3.0 pg/ml at rest to 95 ± 5.0 pg/ml at speed of 10 m/s. The relation between avp concentration and exercise intensity (and duration) appeared to be curvilinear, and was described by an exponential function (r = 0.92, P < 0.05). These data indicate that pra and aldo and avp concentrations increase in horses during progressive treadmill exercise.

Free access
in American Journal of Veterinary Research

Abstract

Objective

To determine sedative, cardiorespiratory and metabolic effects of xylazine hydrochloride, detomidine hydrochloride, and a combination of xylazine and acepromazine administered IV at twice the standard doses in Thoroughbred horses recuperating from a brief period of maximal exercise.

Animals

6 adult Thoroughbreds,

Procedure

Horses were preconditioned by exercising them on a treadmill to establish a uniform level of fitness. Each horse ran 4 simulated races, with a minimum of 14 days between races. Simulated races were run at a treadmill speed that caused horses to exercise at 120% of their maximal oxygen consumption. Horses ran until they were fatigued or for a maximum of 2 minutes. One minute after the end of exercise, horses were treated IV with xylazine (2.2 mg/kg of body weight), detomidine (0.04 mg/kg), a combination of xylazine (2.2 mg/kg) and acepromazine (0.04 mg/kg), or saline (0.9% NaCl) solution. Treatments were randomized so that each horse received each treatment once, in random order. Cardiopulmonary indices were measured, and samples of arterial and venous blood were collected immediately before and at specific times for 90 minutes after the end of each race.

Results

All sedatives produced effective sedation. The cardiopulmonary depression that was induced was qualitatively similar to that induced by administration of these sedatives to resting horses and was not severe. Sedative administration after exercise prolonged the exercise-induced increase in body temperature.

Conclusions and Clinical Relevance

Administration of xylazine, detomidine, or a combination of xylazine-acepromazine at twice the standard doses produced safe and effective sedation in horses that had just undergone a brief, intense bout of exercise. (Am J Vet Res 1999;60:1271–1279)

Free access
in American Journal of Veterinary Research

SUMMARY

Changes in clotting time (ct) and fibrinolytic actvity (fa) were evaluated in 6 mature, female horses during exercise. Two trials were performed on consecutive days, using a randomized crossover design. Each mare was assigned to either an exercise trial or a control trial on the first day, and to the alternate trial 24 hours later. Mares exercised for 20 minutes on a treadmill at an elevation of 2° and a velocity of 5 m/s. Venous blood samples were collected immediately before exercise, at 4, 8, 12, 16, and 20 minutes during exercise, and 15 minutes after cessation of exercise. Blood was placed into plain glass tubes for determination of CT, and into chilled, citrated tubes for determination of FA, plasminogen/plasmin complex activity (plg), one-stage prothrombin time (ospt), activated partial thromboplastin time (aptt), and antithrombin-III (at-III) activity. There were significant differences (P < 0.05) between the control and exercise groups for ct, fa, and plg. During exercise, clotting time decreased from 21.5 ± 1.6 minutes to 9.9 ± 1.6 minutes (mean ± sd; P < 0.05), without significant changes in ospt, aptt, or at-III. Fibrinolytic activity and plg increased (P < 0.05) during exercise. Changes in ct, fa, and plg were significant at 4 minutes of exercise, remained altered until the end of exercise, and returned to baseline values by 45 minutes of recovery. Clotting time, ospt, aptt, fa, at-III, and plg did not change (P > 0.05) during control trials.

Free access
in American Journal of Veterinary Research

Abstract

Objective—To compare systemic bioavailability and duration for therapeutic plasma concentrations and cardiovascular, respiratory, and analgesic effects of morphine administered per rectum, compared with IV and IM administration in dogs.

Animals—6 healthy Beagles.

Procedure—In a randomized study, each dog received the following: morphine IV (0.5 mg/kg of body weight), morphine per rectum (1, 2, and 5 mg/kg as a suppository and 2 mg/kg as a solution), and a control treatment. Intramuscular administration of morphine (1 mg/kg) was evaluated separately. Heart and respiratory rates, systolic, diastolic, and mean blood pressures, adverse effects, and plasma morphine concentrations were measured. Analgesia was defined as an increase in response threshold, compared with baseline values, to applications of noxious mechanical (pressure) and thermal (heat) stimuli. Data were evaluated, using Friedman repeated-measures ANOVA on ranks and Student-Newman-Keuls post-hoc t-tests.

Results—Significant differences were not found in cardiovascular, respiratory, or analgesia values between control and morphine groups. Overall systemic bioavailability of morphine administered per rectum was 19.6%. Plasma morphine concentration after administration of the highest dose (5 mg/kg) as a suppository was significantly higher than concentrations 60 and 360 minutes after IV and IM administration, respectively. A single route of administration did not consistently fulfill our criteria for providing analgesia.

Conclusions and Clinical Relevance—Rectal administration of morphine did not increase bioavailability above that reported for oral administration of morphine in dogs. Low bioavailability and plasma concentrations limit the clinical usefulness of morphine administered per rectum in dogs. (Am J Vet Res 2000;61:24–28)

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in American Journal of Veterinary Research

Abstract

Objective—To compare the effects of propofol and sevoflurane on the urethral pressure profile in female dogs.

Animals—10 healthy female dogs.

Procedure—Urethral pressure profilometry was performed in awake dogs, during anesthesia with sevoflurane at 1.5, 2.0, and 3.0% end-tidal concentration, and during infusion of propofol at rates of 0.4, 0.8, and 1.2 mg/kg/min. A consistent plane of anesthesia was maintained for each anesthetic protocol. Maximum urethral pressure, maximum urethral closure pressure, functional profile length, and functional area were measured.

Results—Mean maximum urethral closure pressure of awake dogs was not significantly different than that of dogs anesthetized with propofol at all infusion rates or with sevoflurane at 1.5 and 2.0% end-tidal concentration. Functional area in awake dogs was significantly higher than in anesthetized dogs. Functional area of dogs during anesthesia with sevoflurane at 3.0% end-tidal concentration was significantly lower than functional area for other anesthetic protocols. Individual differences in the magnitude of effects of propofol and sevoflurane on urethral pressures were observed.

Conclusions and Clinical Relevance—Sevoflurane is an alternative to propofol for anesthesia in female dogs undergoing urethral pressure profilometry. Use of these anesthetics at appropriate administration rates should reliably distinguish normal from abnormal maximum urethral closure pressures and functional areas. Titration of anesthetic depth is a critical component of urodynamic testing. (Am J Vet Res 2003;64:1288–1292)

Full access
in American Journal of Veterinary Research

Abstract

Objective—To compare the use of a semi-invasive vascular access port (VAP) device or noninvasive oscillometry versus invasive telemetry for blood pressure measurements in cats.

Animals—6 healthy cats.

Procedures—30 days before the study, all cats received an implanted telemeter and a VAP device. During normotension and experimentally induced hypertension, blood pressure was measured with the implanted devices and with noninvasive oscillometry at 4 time points.

Results—Compared with invasive telemetry, VAP had a correlation coefficient from 0.8487 to 0.9972, and noninvasive oscillometry had a correlation coefficient from 0.7478 to 0.9689.

Conclusions and Clinical Relevance—Use of the VAP device and noninvasive oscillometry had a high degree of correlation with invasive telemetry as the gold standard for blood pressure measurement. Use of a VAP device resulted in a slightly higher degree of correlation, compared with noninvasive oscillometry.

Full access
in American Journal of Veterinary Research

Abstract

Objective—To determine the effect of IV administration of crystalloid (lactated Ringer's solution [LRS]) or colloid (hetastarch) fluid on isoflurane-induced hypotension in dogs.

Animals—6 healthy Beagles.

Procedures—On 3 occasions, each dog was anesthetized with propofol and isoflurane and instrumented with a thermodilution catheter (pulmonary artery). Following baseline assessments of hemodynamic variables, end-tidal isoflurane concentration was increased to achieve systolic arterial blood pressure (SABP) of 80 mm Hg. At that time (0 minutes), 1 of 3 IV treatments (no fluid, LRS [80 mL/kg/h], or hetastarch [80 mL/kg/h]) was initiated. Fluid administration continued until SABP was within 10% of baseline or to a maximum volume of 80 mL/kg (LRS) or 40 mL/kg (hetastarch). Hemodynamic variables were measured at intervals (0 through 120 minutes and additionally at 150 and 180 minutes in LRS- or hetastarch-treated dogs). Several clinicopathologic variables including total protein concentration, PCV, colloid osmotic pressure, and viscosity of blood were assessed at baseline and intervals thereafter (0 through 120 minutes).

Results—Administration of 80 mL of LRS/kg did not increase SABP in any dog, whereas administration of ≤ 40 mL of hetastarch/kg increased SABP in 4 of 6 dogs. Fluid administration increased cardiac index and decreased systemic vascular resistance. Compared with hetastarch treatment, administration of LRS decreased blood viscosity. Treatment with LRS decreased PCV and total protein concentration, whereas treatment with hetastarch increased colloid osmotic pressure.

Conclusions and Clinical Relevance—Results indicated that IV administration of hetastarch rather than LRS is recommended for the treatment of isoflurane-induced hypotension in dogs.

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in American Journal of Veterinary Research

Abstract

Objective—To evaluate the accuracy of a commercial ultrasonographic cardiac output (CO) monitoring system (UCOMS) in anesthetized Beagles as assessed by comparison with thermodilution CO (TDCO).

Animals—8 healthy anesthetized Beagles.

Procedures—Simultaneous UCOMS and TDCO measurements of CO were obtained during 4 hemodynamic states: baseline anesthesia (0.5% to 1.5% isoflurane), a higher depth of anesthesia (2% to 3.5% isoflurane) to yield a ≥ 15% reduction in systolic arterial blood pressure, IV infusion of colloidal solution to a mean right atrial pressure of ≥ 15 mm Hg, and IV infusion of dobutamine at 5 μg/kg/min. Measurements were obtained at 2 probe positions: the subxiphoid region and the right thoracic inlet. Correlation and agreement of results between methods were determined via linear regression analysis and Bland-Altman plots.

Results—A significant positive correlation was detected between UCOMS andTDCO measurements obtained at the subxiphoid (R = 0.86) and thoracic inlet (R = 0.83) positions. Bland-Altman plots revealed minimal bias between methods (bias ± SD, −0.03 ± 0.73 L/min and −0.20 ± 0.80 L/min for subxiphoid and thoracic inlet measurements, respectively). However, the percentage error associated with UCOMS measurements made at the 2 positions was > 45%.

Conclusions and Clinical Relevance—When compared with the results of TDCO, CO measured with the UCOMS exceeded commonly accepted limits of error in healthy dogs. The UCOMS was, however, able to track changes in CO across hemodynamic states. Additional research is needed to assess the usefulness of the UCOMS for monitoring CO in critically ill dogs.

Full access
in American Journal of Veterinary Research