Objective—To evaluate degree of sedation and cardiovascular, respiratory, acid-base excess, and electrolyte variables in response to IM administration of dexmedetomidine or dexmedetomidine with atropine.
Design—Randomized crossover study.
Animals—5 healthy 1- to 2-year-old sexually intact male Treeing Walker Coonhounds.
Procedures—Dogs were instrumented with catheters placed in the dorsal pedal artery and lateral saphenous vein. All dogs received dexmedetomidine (10 μg/kg [4.5 μg/lb], IM) or dexmedetomidine with atropine (0.02 mg/kg [0.009 mg/lb], IM). Variables were measured at baseline (time 0) and 5, 15, 30, and 60 minutes after drug administration.
Results—In all dogs, lithium dilution cardiac output decreased from a mean ± SD baseline value of 5.07 ± 1.0 L/min to 2.1 ± 0.9 L/min. Cardiac output was not different between dexmedetomidine group dogs and dexmedetomidine-atropine group dogs. Mean arterial pressure increased from baseline in both groups but was significantly higher in dexmedetomidine-atropine group dogs, compared with dexmedetomidine group dogs. Heart rate in dexmedetomidine group dogs decreased from 110 ± 14.2 beats/min to 49.4 ± 10.4 beats/min by 15 minutes. No differences were seen in blood gas values, electrolyte concentration, or hemoglobin values over time or between groups. Arrhythmias were detected in dexmedetomidine-atropine group dogs and included atrioventricular block, ventricular premature contractions, and ventricular bigeminy.
Conclusions and Clinical Relevance—Administration of atropine at 0.02 mg/kg, IM, with dexmedetomidine at 10 μg/kg, IM, resulted in an increase in mean arterial blood pressure and heart rate; deleterious cardiac arrhythmias were also observed. Use of atropine with dexmedetomidine is not recommended in dogs.
To determine the effects of morphine on histamine release from 2 canine mast cell tumor (MCT) cell lines and on plasma histamine concentrations in dogs with cutaneous MCTs.
10 dogs with cutaneous MCT and 10 dogs with soft tissue sarcoma (STS).
The study consisted of 2 phases. First, 2 canine MCT cell lines were exposed to 3 pharmacologically relevant morphine concentrations, and histamine concentrations were determined by an ELISA. Second, dogs with MCT or STS received 0.5 mg of morphine/kg, IM, before surgery for tumor excision. Clinical signs, respiratory rate, heart rate, arterial blood pressure, rectal temperature, and plasma histamine concentrations were recorded before and 5, 15, 30, and 60 minutes after morphine administration but prior to surgery. Data were compared by use of a 2-way ANOVA with the Sidak multiple comparisons test.
In the first phase, canine MCT cell lines did not release histamine when exposed to pharmacologically relevant morphine concentrations. In the second phase, no differences were noted for heart rate, arterial blood pressure, and rectal temperature between MCT and STS groups. Plasma histamine concentrations did not significantly differ over time within groups and between groups.
CONCLUSIONS AND CLINICAL RELEVANCE
No significant changes in histamine concentrations were noted for both in vitro and in vivo study phases, and no hemodynamic changes were noted for the in vivo study phase. These preliminary results suggested that morphine may be used safely in some dogs with MCT.
Objective—To determine the effect of 6 plasma ketamine concentrations on the minimum alveolar concentration (MAC) of isoflurane in dogs.
Procedure—In experiment 1, the MAC of isoflurane was measured in each dog and the pharmacokinetics of ketamine were determined in isoflurane-anesthetized dogs after IV administration of a bolus (3 mg/kg) of ketamine. In experiment 2, the same dogs were anesthetized with isoflurane in oxygen. A target-controlled IV infusion device was used to administer ketamine and to achieve plasma ketamine concentrations of 0.5, 1, 2, 5, 8, and 11 μg/mL by use of parameters obtained from experiment 1. The MAC of isoflurane was determined at each plasma ketamine concentration, and blood samples were collected for ketamine and norketamine concentration determination.
Results—Actual mean ± SD plasma ketamine concentrations were 1.07 ± 0.42 μg/mL, 1.62 ± 0.98 μg/mL, 3.32 ± 0.59 μg/mL, 4.92 ± 2.64 μg/mL, 13.03 ± 10.49 μg/mL, and 22.80 ± 25.56 μg/mL for target plasma concentrations of 0.5, 1, 2, 5, 8, and 11 μg/mL, respectively. At these plasma concentrations, isoflurane MAC was reduced by 10.89% to 39.48%, 26.77% to 43.74%, 25.24% to 84.89%, 44.34% to 78.16%, 69.62% to 92.31%, and 71.97% to 95.42%, respectively. The reduction in isoflurane MAC was significant, and the response had a linear and quadratic component. Salivation, regurgitation, mydriasis, increased body temperature, and spontaneous movements were some of the adverse effects associated with the high plasma ketamine concentrations.
Conclusions and Clinical Relevance—Ketamine appears to have a potential role for balanced anesthesia in dogs. (Am J Vet Res 2006;67:21–25)
Objective—To determine whether number of instrument cannulas is associated with surgical time or severity of postoperative pain in dogs undergoing laparoscopic ovariectomy.
Design—Randomized clinical trial.
Animals—18 healthy dogs.
Procedures—Dogs were randomly assigned to undergo laparoscopic ovariectomy with 1, 2, or 3 instrument cannulas. Surgical time and intraoperative and postoperative complications were recorded. Severity of pain was monitored 2, 4, 8, 12, and 24 hours after surgery by means of pain scoring with a modified Melbourne Pain Scale and palpation of surgical sites with variably sized von Frey filaments. Owner-assessed postoperative comfort was also evaluated.
Results—Surgical time was significantly longer with 1 cannula (mean ± SD, 29.7 ± 5.6 minutes) than with 2 cannulas (18.2 ± 4.4 minutes) or 3 cannulas (19.3 ± 3.4 minutes). Intraoperative complications included splenic puncture (2 dogs), pedicle hemorrhage (1 dog), and SC emphysema (1 dog); complication rates were not significantly different among groups. Total pain score was significantly lower for dogs with 2 cannulas than for dogs with 3 cannulas; total pain score for dogs with 1 cannula did not differ significantly from scores for dogs with 2 cannulas or 3 cannulas. Owner assessments of postoperative comfort and number of days pain medications were administered did not differ among groups.
Conclusions and Clinical Relevance—Results suggested that laparoscopic ovariectomy with 2 instrument cannulas, rather than with 1, resulted in shorter surgical times without increasing severity of postoperative pain.
Objective—To characterize the effects of ketamine
administration on the cardiovascular and respiratory
systems and on acid-base balance and to record
adverse effects of ketamine in isoflurane-anesthetized
Animals—6 healthy adult mongrel dogs.
Procedure—Dogs were anesthetized with isoflurane
(1.25 times the individual minimum alveolar concentration)
in oxygen, and ketamine was administered IV
to target pseudo–steady-state plasma concentrations
of 0, 0.5, 1, 2, 5, 8, and 11 µg/mL. Isoflurane concentration
was reduced to an equipotent concentration.
Cardiovascular, respiratory, and acid-base variables;
body temperature; urine production; and adverse
effects were recorded before and during noxious
stimulation. Cardiac index, stroke index, rate-pressure
product, systemic vascular resistance index, pulmonary
vascular resistance index, left ventricular
stroke work index, right ventricular stroke work index,
arterial oxygen concentration, mixed-venous oxygen
concentration, oxygen delivery, oxygen consumption,
oxygen extraction ratio, alveolar-arterial oxygen partial
pressure gradient, and venous admixture were calculated.
Plasma ketamine and norketamine concentrations
Results—Overall, ketamine administration improved
ventilation, oxygenation, hemodynamics, and oxygen
delivery in isoflurane-anesthetized dogs in a dosedependent
manner. With the addition of ketamine,
core body temperature was maintained or increased
and urine production was maintained at an acceptable
amount. However, at the higher plasma ketamine
concentrations, adverse effects such as spontaneous
movement and profuse salivation were observed.
Myoclonus and dysphoria were observed during
recovery in most dogs.
Conclusions and Clinical Relevance—Infusion of
ketamine appears to be a suitable technique for balanced
anesthesia with isoflurane in dogs. Plasma ketamine
concentrations between 2 to 3 µg/mL elicited
the most benefits with minimal adverse effects.
(Am J Vet Res 2005;66:2122–2129)
Objective—To determine fluid retention, glomerular filtration rate, and urine output in dogs anesthetized for a surgical orthopedic procedure.
Animals—23 dogs treated with a tibial plateau leveling osteotomy.
Procedures—12 dogs were used as a control group. Cardiac output was measured in 5 dogs, and 6 dogs received carprofen for at least 14 days. Dogs received oxymorphone, atropine, propofol, and isoflurane for anesthesia (duration, 4 hours). Urine and blood samples were obtained for analysis every 30 minutes. Lactated Ringer's solution was administered at 10 mL/kg/h. Urine output was measured and glomerular filtration rate was estimated. Fluid retention was measured by use of body weight, fluid balance, and bioimpedance spectroscopy.
Results—No difference was found among control, cardiac output, or carprofen groups, so data were combined. Median urine output and glomerular filtration rate were 0.46 mL/kg/h and 1.84 mL/kg/min. Dogs retained a large amount of fluids during anesthesia, as indicated by increased body weight, positive fluid balance, increased total body water volume, and increased extracellular fluid volume. The PCV, total protein concentration, and esophageal temperature decreased in a linear manner.
Conclusions and Clinical Relevance—Dogs anesthetized for a tibial plateau leveling osteotomy retained a large amount of fluids, had low urinary output, and had decreased PCV, total protein concentration, and esophageal temperature. Evaluation of urine output alone in anesthetized dogs may not be an adequate indicator of fluid balance.
Objective—To determine whether withholding of food affects autonomic nervous system balance by analysis of heart rate (HR), HR variability (HRV), and frequency of second-degree atrioventricular block in horses.
Animals—5 healthy Thoroughbreds.
Procedures—For two 24-hour periods in a crossover study, food was withheld from horses or horses were maintained on their regular feeding schedule (control conditions) in their stalls and Holter monitor ECG recordings were obtained. The ECGs were analyzed by use of fast-Fourier transformation, and power spectrum densities were calculated for low-frequency (0.01 to 0.07 Hz) and high-frequency (0.07 to 0.6 Hz) variations in HR. Serum cortisol and plasma ACTH, norepinephrine, and glucose concentrations were measured at predetermined time points.
Results—Withholding of food resulted in significantly lower HR and more frequent second-degree atrioventricular block (the frequency of which was inversely related to the HR), compared with findings for control conditions. Circadian rhythms were similar during food-withholding and control conditions; peak HR was detected from 7:00 pm to 8:00 pm, and the lowest HR was detected in the early morning. During food-withholding conditions, the low-frequency and high-frequency components of HRV were significantly higher, and the low-frequency-to-high-frequency ratio was lower than during control conditions. Serum cortisol concentration was higher and plasma glucose concentration was lower at 6:00 pm in horses when food was withheld, compared with findings during control conditions.
Conclusions and Clinical Relevance—Indices of HRV seemed to be sensitive to changes in autonomic nervous activity and may be useful as clinical indices of the neuroendocrine response to stressors in horses.
Objective—To compare anesthesia-related events associated with IV administration of 2 novel micellar microemulsion preparations (1% and 5%) and a commercially available formulation (1%) of propofol in horses.
Animals—9 healthy horses.
Procedures—On 3 occasions, each horse was anesthetized with 1 of the 3 propofol formulations (1% or 5% microemulsion or 1% commercial preparation). All horses received xylazine (1 mg/kg, IV), and anesthesia was induced with propofol (2 mg/kg, IV). Induction and recovery events were quantitatively and qualitatively assessed. Venous blood samples were obtained before and at intervals following anesthesia for quantification of clinicopathologic variables.
Results—Compared with the commercial formulation, the quality of anesthesia induction in horses was slightly better with the micellar microemulsion formulas. In contrast, recovery characteristics were qualitatively and quantitatively indistinguishable among treatment groups (eg, time to stand after anesthesia was 34.3 ± 7.3 minutes, 34.1 ± 8.8 minutes, and 39.0 ± 7.6 minutes in horses treated with the commercial formulation, 1% microemulsion, and 5% microemulsion, respectively). During recovery from anesthesia, all horses stood on the first attempt and walked within 5 minutes of standing. No clinically relevant changes in hematologic and serum biochemical analytes were detected during a 3-day period following anesthesia.
Conclusions and Clinical Relevance—Results suggest that the micellar microemulsion preparation of propofol (1% or 5%) has similar anesthetic effects in horses, compared with the commercially available lipid propofol formulation. Additionally, the micellar microemulsion preparation is anticipated to have comparatively low production costs and can be manufactured in various concentrations.
Objective—To evaluate the effects of morphine administration for 6 days on gastrointestinal tract function in healthy adult horses.
Procedures—Horses were randomly allocated into 2 groups in a crossover study. Horses in the treatment group received morphine sulfate at a dosage of 0.5 mg/kg, IV, every 12 hours for 6 days. Horses in the control group received saline (0.9% NaCl) solution at a dosage of 10 mL, IV, every 12 hours for 6 days. Variables assessed included defecation frequency, weight of feces produced, intestinal transit time (evaluated by use of barium-filled spheres and radiographic detection in feces), fecal moisture content, borborygmus score, and signs of CNS excitement and colic.
Results—Administration of morphine resulted in gastrointestinal tract dysfunction for 6 hours after each injection. During those 6 hours, mean ± SD defecation frequency decreased from 3.1 ± 1 bowel movements in control horses to 0.9 ± 0.5 bowel movements in treated horses, weight of feces decreased from 4.1 ± 0.7 kg to 1.1 ± 0.7 kg, fecal moisture content decreased from 76 ± 2.7% to 73.5 ± 2.9%, and borborygmus score decreased from 13.2 ± 2.9 to 6.3 ± 3.9. Mean gastrointestinal transit time was also increased, compared with transit times in control horses.
Conclusions and Clinical Relevance—Morphine administered at 0.5 mg/kg twice daily decreased propulsive motility and moisture content in the gastrointestinal tract lumen. These effects may predispose treated horses to development of ileus and constipation.