A Comparison of Injectable Anesthetic Combinations in Horses

Six combinations of injectable anesthetic agents were administered to six adult horses in a Latin square design. The drug combinations were xylazine-ketamine, xylazine-butorphanol-ketamine, xylazine-tiletamine-zolazepam, xylazine-butorphanol-tiletamine-zolazepam, detomidine-ketamine, and detomidine-butorphanol-ketamine. Measured variables were heart rate, respiratory rate, systolic blood pressure, arterial pH (pHa), PaCO2, PaO2, recumbency time, and number of attempts necessary to stand. Quality of induction and recovery, muscle relaxation, and response to stimulus were evaluated subjectively. The horses required significantly more attempts to stand after administration of xylazine-tiletamine-zolazepam, xylazine-butorphanol-tiletamine-zolazepam, and detomidine-ketamine than after xylazine-ketamine, xylazine-butorphanol-ketamine, or detomidine-butorphanol-ketamine. Mean recumbency times varied from 23.0 minutes with xylazine-ketamine to 41.3 minutes with xylazine-butorphanol-tiletamine-zolazepam. There were significant differences in mean heart rates at minute 15, mean respiratory rates at minutes 5, 10 and 15, and mean systolic blood pressures at minute 10 of anesthesia. There were no significant differences in pHa, PaCO2 or PaO2.     

Parenteral Anticholinergics in Dogs With Normal and Elevated Intraocular Pressure

Dogs given parenteral anticholinergic drugs have been thought to be at risk for development or exacerbation of elevated intraocular pressure (IOP). In a randomized, blinded, placebo-controlled study, we evaluated the effect of intramuscular glycopyrrolate (0.01 mg/kg) on pupil diameter and IOP in unanesthetized normal dogs. Treatment with glycopyrrolate did not change pupil diameter or IOP from baseline, nor were there differences between glycopyrrolate and saline-treated (control) dogs. In addition, the authors retrospectively reviewed the medical records of 2,828 dogs undergoing general anesthesia between April 1987 and September 1990 to determine if there was an association between parenteral anticholinergic medication and postanesthetic elevation in IOP. The authors also determined the frequency of bradycardia requiring anticholinergic therapy during anesthesia in dogs with glaucoma. Of the 2,828 cases reviewed, the records of 46 dogs coded for glaucoma were examined in detail. The 46 dogs underwent 62 episodes of anesthesia, with 23 episodes including exposure to an anticholinergic drug. An increase in IOP from preanesthetic to postanesthetic measurement occurred in three dogs. One of these dogs received anticholinergic medication for bradycardia during anesthesia. The postanesthetic elevation in IOP in this dog was probably not drug related. Preanesthetic anticholinergic administration did not affect the incidence of anticholinergic administration for bradycardia during the anesthetic episode. Anticholinergic therapy during anesthesia was more frequent when the preanesthetic medication included an opiate drug. These studies do not indicate an association between parenteral anticholinergic administration and elevations in IOP.     

Pasteurella multocida isolation in a horse with retropharyngeal infection

Retropharyngeal infections in horses normally induce local painful swelling of the retropharyngeal area, which may lead to dyspnea, dysphagia, and systemic manifestations. Differential diagnosis of local painful swelling of the retropharyngeal area includes retropharyngeal lymph node infection, neoplasm, cellulitis, hematoma, guttural pouch empyema, parotiditis, and jugular thrombosis. Apart from Streptococcus equi ssp. equi, other bacteria are rarely reported as a cause of retropharyngeal abscesses. The reason for this might be a lack of specific sampling to identify the causative agent. This work deals with a case of retropharyngeal infection in an 11-year-old Standardbred stallion with acute depression, fever, tachycardia, asymmetric painful swelling in the throat area, ptyalism, and respiratory distress. Endoscopy, radiography, ultrasonography, blood analysis, and cytological examination of a puncture sample taken from the throat mass were consistent with a pyogenic to pyogranulomatous retropharyngeal inflammation. The clinical evolution was initially satisfactory in response to treatment with nonsteroidal anti-inflammatory drugs and antibiotics, but clinical signs relapsed twice, each time a few weeks after cessation of antibiotic therapy. The bacteriologic finding in this case was unusual and consisted of the isolation of a Pasteurella multocida strain that was obtained after the second relapse (ie, 79 days after initial admission), using a brain heart infusion (BHI) medium, and after two successive negative bacteriological cultures performed on day one of clinical signs and at the first relapse of clinical signs, respectively.     

Detomidine-Butorphanol-Propofol for Carotid Artery Translocation and Castration or Ovariectomy in Goats

Objective—To determine the safety and efficacy of propofol, after detomidine-butorphanol premedication, for induction and anesthetic maintenance for carotid artery translocation and castration or ovariectomy in goats. Study Design—Case series. Animals—Nine 4-month-old Spanish goats (17.1 ± 2.6 kg) were used to evaluate propofol anesthesia for carotid artery translocation and castration or ovariectomy. Methods—Goats were premedicated with detomidine (10 μg/kg intramuscularly [IM]) and butorphanol (0.1 mg/kg IM) and induced with an initial bolus of propofol (3 to 4 mg/kg intravenously [IV]). If necessary for intubation, additional propofol was given in 5-mg (IV) increments. Propofol infusion (0.3 mg/kg/min IV) was used to maintain anesthesia, and oxygen was insufflated (5 L/min). The infusion rate was adjusted to maintain an acceptable anesthetic plane as determined by movement, muscle relaxation, ocular signs, response to surgery, and cardiopulmonary responses. Systolic (SAP), mean (MAP) and diastolic (DAP) arterial pressures, heart rate (HR), ECG, respiratory rate (RR), Spo₂, and rectal temperature (T) were recorded every 5 minutes postinduction; arterial blood gas samples were collected every 15 minutes. Normally distributed data are represented as mean ± SD; other data are medians (range). Results—Propofol (4.3 ± 0.9 mg/kg IV) produced smooth, rapid (15.2 ± 6 sec) sternal recumbency. Propofol infusion (0.52 ± 0.11 mg/kg/min IV) maintained anesthesia. Mean anesthesia time was 83 ± 15 minutes. Muscle relaxation was good; eye signs indicated surgical anesthesia; two goats moved before surgery began; one goat moved twice during laparotomy. Means are reported over the course of the data collection period. Means during the anesthesia for pH_a (arterial PH), P_aco₂, P_ao₂, HCO₃, and BE (base excess) ranged from 7.233 ± 0.067 to 7.319 ± 0.026, 54.1 ± 4.6 to 65.3 ± 12.0 mm Hg, 133.1 ± 45.4 to 183.8 ± 75.1 mm Hg, 26.9 ± 2.6 to 28.2 ± 2.1 mEq/L, and -0.8 ± 2.9 to 1.4 ± 2.2 mEq/L. Means over time for MAP were 53 ± 12 to 85 ± 21 mm Hg. Mean HR varied over time from 81 ± 6 to 91 ± 11 beats/minute; mean RR, from 9 ± 8 to 15 ± 5 breaths/minute; S_po₂, from 97 ± 3% to 98 ± 3%; mean T, from 36.0 ± 0.6±C to 39.1 ± 0.7±C. Over time, S_po₂ and S_ao₂ did not change significantly; HR, RR, T, and P_aco₂ decreased significantly; SAP, DAP, MAP, pH_a, P_ao₂, and BE increased significantly. HCO₃ concentrations increased significantly, peaking at 45 minutes. Recoveries were smooth and rapid; the time from the end of propofol infusion to extubation was 7.3 ± 3 minutes, to sternal was 9.2 ± 5 minutes, and to standing was 17.7 ± 4 minutes. Median number of attempts to stand was two (range of one to four). Postoperative pain was mild to moderate. Conclusions—Detomidine-butorphanol-propofol provided good anesthesia for carotid artery translocation and neutering in goats. Clinical Relevance—Detomidine-butorphanol-propofol anesthesia with oxygen insufflation may be safely used for surgical intervention in healthy goats.     

Neuromuscular Effects of Doxacurium Chloride in Isoflurane-Anesthetized Dogs

Objective—To determine the neuromuscular effects of doxacurium chloride and to construct a dose-response curve for the drug in isoflurane-anesthetized dogs. Design—Randomized, controlled trial. Animals—Six healthy, adult, mixed-breed dogs (five female, one male) weighing 24.8 ° 2.8 kg. Methods—Anesthesia was induced with isoflurane in oxygen and maintained with 1.9% to 2.3% end-tidal isoflurane concentration. Paco₂ was maintained between 35 and 45 mm Hg with mechanical ventilation. Mechanomyography was used to quantitate the evoked twitch response of the paw after supramaximal train-of-four stimulation of the superficial peroneal nerve. After baseline values were recorded, the dogs received one of three doses of doxacurium (2.0, 3.5, 4.5 μg/kg of body weight) or a saline placebo intravenously in random order. All dogs received all treatments with at least 7 days between studies. After drug administration, the degree of maximal first twitch depression compared with baseline (T,%) was recorded. Dose-response relations of doxacurium were plotted in log dose-probit format and analyzed by linear regression to determine effective dose (ED₅₀ and ED₉₀) values for doxacurium. Results—The median log dose-probit response curve showed good data correlation (r= .999) with estimates of the ED₅₀ (2.1 μg/kg) and ED₉₀ (3.5 μg/kg) for doxacurium in isoflurane-anesthetized dogs. Mean ± SD values for T₁% (first twitch tension compared with baseline) at maximal depression after drug administration, onset (time from drug administration to maximal depression of T₁%), duration (time from maximal depression of T₁% to 25% recovery of T₁%), and recovery (time from 25% to 75% recovery of T₁%) times were 92%± 4%, 40 ± 5 minutes, 108 ± 31 minutes, and 42 ± 11 minutes for dogs treated with 3.5 μg/kg of doxacurium and 94%± 7%, 41 ± 8 minutes, 111 ± 33 minutes, and 37 ± 10 minutes for dogs treated with 4.5 μg/kg of doxacurium. Conclusion and Clinical Relevance—We conclude that doxacurium is a long-acting neuromuscular blocking agent with a slow onset of action. Doxacurium can be used to provide muscle relaxation for long surgical procedures in isoflurane-anesthetized dogs. Interpatient variability, particularly of duration of drug action, may exist in the neuromuscular response to the administration of doxacurium in dogs.