Gwendolyn L. Carroll

General Anesthetic Techniques in Ruminants

Sedation, anesthesia, protection of the airway during general anesthesia, and control of pain in the perioperative period are important considerations in the management of sheep, goats, and cattle. Though ruminants are classically considered farm animals and are often intended for the production of food and fiber, these species are used extensively in research and teaching and they are increasingly important as companion animals. Whatever their use may be, anesthetic and analgesic drugs and techniques should be used to ensure minimal stress and discomfort during the perioperative period.

Recent developments in nonsteroidal antiinflammatory drugs in cats.

Pain, particularly chronic pain, is an underestimated ailment in cats. Veterinarians tend to under-diagnose and under-treat pain in this aloof and stoic species. Until recently, there was only one analgesic (i.e., butorphanol) approved in the United States for use in cats; but many analgesics, particularly opioids, have been used extra-label for this purpose. Nonsteroidal antiinflammatory drugs (NSAIDs) have been used sparingly in cats because of safety concerns, which are less of an issue with the newer agents. Meloxicam is the only NSAID labeled for use in cats in the United States, but other agents are available in this country and are labeled for use in cats in other countries.

A multisite case report on the clinical use of sevoflurane in dogs

The purpose of this report was to evaluate the clinical safety and efficacy of sevoflurane as an inhalant anesthetic in dogs. Subjective and objective data from 196 clinical cases utilizing sevoflurane as the maintenance anesthetic was collected at three sites. After preanesthetic evaluation, the attending anesthesiologist assigned the dogs to one of the following six anesthetic protocols: protocol 1, oxymorphone premedication and thiopental induction; protocol 2, oxymorphone/acetylpromazine premedication and thiopental induction; protocol 3, xylazine/butorphanol premedication and thiopental induction; protocol 4, opioid premedication and propofol induction; protocol 5, optional premedication and mask induction with sevoflurane in oxygen; and protocol 6, optional premedication and optional induction. The average quality of induction, maintenance, and recovery was good to excellent in all protocols. The three most common side effects during maintenance and recovery were hypotension, tachypnea, and apnea. Sevoflurane produces anesthesia in dogs comparable to the other inhalation anesthetics currently used (i.e., halothane and isoflurane) for diagnostic or therapeutic procedures.

Analgesics and Pain

There has been a substantial increase in the use of analgesics for pain management in the last 10 years. Traditionally, veterinarians have not been trained in the identification of or monitoring of patients that are in pain, even though an evaluation of pain is inherent in assessing improvement in many medical and surgical diseases. Until recently, the physiology and pharmacology of opioids, NSAIDs, local anesthetics, and alpha 2 agonists were taught, but the therapeutic role of these drugs was generally believed to be related to restraint, anesthesia, or control of inflammation rather than to pain management.

Dose range finding study for the efficacy of meloxicam administered prior to sodium urate-induced synovitis in cats.

OBJECTIVE To determine the lowest efficacious dose of oral meloxicam for relieving pain in cats with a sodium urate (SU)-induced acute inflammatory synovitis. STUDY DESIGN Randomized, blinded, controlled, and four-way crossover study. ANIMALS Eight surgically neutered cats (four males, four females) paired according to sex. METHODS Each pair of cats was treated with 0 (placebo), 0.025, 0.05, or 0.075 mg kg(-1) oral meloxicam once daily for 4 days prior to injection, into alternating stifles, of 1 mL of 20 mg mL(-1) SU crystals, beginning with the right stifle. Each cat received each of the four treatments, separated by at least 21 days. Analgesic efficacy was evaluated based on objective (e.g., pressure mat data total force, contact pressure, and contact area) and subjective (e.g., scores for Analgesia Scale [AS], Lameness Scale [LS], and Visual Analog Scale [VAS]) outcome measures for pain assessment. All outcome measures were recorded before and during 30 hours after SU injection. The pre-defined primary outcome measure was the area under the response-time curve (AUC(0-30) hours) of the total force of the injected limb. Data were analyzed by analysis of variance. A sequential test procedure was applied and the test sequence stopped in case of a nonsignificant result. RESULTS Meloxicam at doses of 0.05 and 0.075 mg kg(-1) day(-1) PO was significantly different from placebo for the pre-defined primary outcome measure (i.e., AUC(0-30) hours of total force). All tested meloxicam doses were lower than placebo for the subjective outcome measures (i.e., AUC(0-30) hours of AS, LS, and VAS). CONCLUSIONS AND CLINICAL RELEVANCE The lowest efficacious dose of meloxicam for relieving pain in cats with an SU-induced synovitis was 0.05 mg kg(-1) day(-1) PO according to the pre-defined primary outcome measure. However, lower doses may also be effective as seen in the subjective outcome measures.

Complications common to ventricular assist device support are rare with 90 days of DeBakey VAD® support in calves

The DeBakey VAD® is a miniaturized, electromagnetically driven axial flow pump intended for long-term ventricular assist. Safety and performance data from six calves implanted with the complete DeBakey VAD® system are reported elsewhere; here we describe complications and necropsy findings for these same six animals, all of which survived 90 days. The study was conducted according to a uniform protocol, which included anticoagulation and antibiotic prophylaxis. Clinical complications tracked included bleeding, cardiovascular abnormalities (e.g., arrhythmias, tachycardia unrelated to pain, bradycardia), hemolysis, hepatic dysfunction, renal dysfunction, thromboembolism (neurologic or peripheral), or infection. Each adverse event was retrospectively categorized with regard to severity (mild, moderate, severe) and relationship to device. Clinical findings were confirmed by necropsy. There was no evidence of systemic infection, thromboembolism, hemolysis, or renal or hepatic dysfunction in these six animals during the study period. A single adverse event was noted in each of two of the calves. Both events were considered mild according to the predefined criteria. Bleeding related to the surgical implantation procedure and requiring reoperation occurred in one animal. The other animal had evidence of a superficial infection at the exit site of the cables on the left lateral thoracic wall; the infection did not extend into the thoracic cavity. Chronic, healed small renal infarct scars were present in several animals. Mild valvular endocardiosis was observed in two calves and mild fibroelastosis was present in the endocardium at the site of the inflow cannula in three calves; however, these lesions were not considered clinically significant. No other gross or histologic abnormalities were noted at necropsy. In conclusion, calves implanted with the complete DeBakey VAD® for 90 days demonstrated few complications and had no significant necropsy findings. Complications common to ventricular assist device (VAD) support (i.e., hemolysis, infection, bleeding, thromboembolism) were rare during long-term support (90 days) with the DeBakey VAD.

A pilot study: sodium urate synovitis as an acute model of inflammatory response using objective and subjective criteria to evaluate arthritic pain in cats.

Sodium urate (SU) synovitis was evaluated as a model for feline arthritic pain using a placebo- and positive-controlled (meloxicam) randomized blinded controlled single crossover design. Monosodium urate crystals [20 mg (1 mL) rod-shaped] were injected into alternate stifles of trained anesthetized cats (n = 3) with a 28 day washout. During the first trial phase, two cats received meloxicam (0.1 mg/kg, PO), a nonsteroidal anti-inflammatory drug (NSAID), for three days before and on the day of SU injection; the third cat received placebo. Treatments and stifles were switched for the second trial. Total force, contact pressure and area of the fore and hind limbs were measured using a pressure mat one day and 0.5 h before, and 2, 4, 6, 8, 10, 24, and 30 h post-SU injection. Skin temperature, joint circumference, analgesia, lameness, and visual analogue scale (VAS) pain scores, were measured at the same times. Comparisons were made for each time and for areas under the curve (AUC) using original and change from baseline; P < 0.05 was significant. Significant differences in force mat data and subjective data were found for the hind limb data (total force and total contact pressure at 6, 10, and 30 h; analgesia and VAS for pain at 4 h; lameness at 10, 24, and 30 h) and for AUC(0)-->(24h) and AUC(0)-->(30 h) (total force, total contact pressure, and mean lameness score) and for differences from BL AUC(0)-->(10h) (total contact area) and AUC(0)-->(24h) (total contact area and mean lameness score) and AUC(0)-->(30 h) (total force, total contact area, and mean lameness). No cats required rescue analgesia. Injection of 1 mL of monosodium urate into the stifle of a cat causes moderate transitory pain and was suitable for assessing analgesic efficacy of an NSAID with a pressure mat and subjective criteria.

Pharmacokinetics and selected behavioral responses to butorphanol and its metabolites in goats following intravenous and intramuscular administration

OBJECTIVE To evaluate disposition of a single dose of butorphanol in goats after intravenous (IV) and intramuscular (IM) administration and to relate behavioral changes after butorphanol administration with plasma concentrations. DESIGN Randomized experimental study. ANIMALS Six healthy 3-year-old neutered goats (one male and five female) weighing 46.5 ± 10.5 kg (mean ± D). METHODS Goats were given IV and IM butorphanol (0.1 mg kg-1) using a randomized cross-over design with a 1-week interval between treatments. Heparinized blood samples were collected at fixed intervals for subsequent determination of plasma butorphanol concentrations using an enzyme linked immunosorbent assay (ELISA). Pharmacokinetic values (volume of distribution at steady state [VdSS], systemic clearance [ClTB], extrapolated peak plasma concentration [C0] or estimated peak plasma concentration [CMAX], time to estimated peak plasma concentration [TMAX], distribution and elimination half-lives [t1/2], and bioavailability) were calculated. Behavior was subjectively scored. A two-tailed paired t-test was used to compare the elimination half-lives after IV and IM administration. Behavioral scores are reported as median (range). A Friedman Rank Sums test adjusted for ties was used to analyze the behavioral scores. A logit model was used to determine the effect of time and concentration on behavior. A value of p < 0.05 was considered significant. RESULTS Volume of distribution at steady state after IV administration of butorphanol was 1.27 ± 0.73 L kg-1, and ClTB was 0.0096 ± 0.0024 L kg-1 minute-1. Extrapolated C0 of butorphanol after IV administration was 146.5 ± 49.8 ng mL-1. Estimated CMAX after IM administration of butorphanol was 54.98 ± 14.60 ng mL-1, and TMAX was 16.2 ± 5.2 minutes; bioavailability was 82 ± 41%. Elimination half-life of butorphanol was 1.87 ± 1.49 and 2.75 ± 1.93 hours for IV and IM administration, respectively. Goats became hyperactive after butorphanol administration within the first 5 minutes after administration. Behavioral scores for goats were significantly different from baseline at 15 minutes after IV administration and at 15 and 30 minutes after IM administration. Both time and plasma butorphanol concentration were predictors of behavior. Behavioral scores of all goats had returned to baseline by 120 minutes after IV administration and by 240 minutes after IM administration. Conclusions and Clinical Relevance  The dose of butorphanol (0.1 mg kg-1, IV or IM) being used clinically to treat postoperative pain in goats has an elimination half-life of 1.87 and 2.75 hours, respectively. Nonpainful goats become transiently excited after IV and IM administration of butorphanol. Clinical trials to validate the efficacy of butorphanol as an analgesic in goats are needed.

Repeated injectable anesthesia in six horses for cobalt therapy

Little information exists about repeated injectable anesthesia in horses, therefore our purpose is to report the anesthetic method we used to facilitate clinical treatment. Between 1992 and 1999, we anesthetized 6 horses 12 times each at 2^3 day intervals, to allow cobalt therapy (CO) of their tumors. One horse received an additional 10 treatments (T). The ¢ve mares and one gelding (3 QH, 1 Paint, 1TB, 1grade) had a mean age of 927 years (mean 2 SD) and mean weight of 505254 kg. Horses were anesthetized with xylazine (X, 1.020.08mg kgÿ1) and tiletamine-zolazepam (TZ, 1.020.08mg kgÿ1) given IV. Butorphanol (B, 0.02620.01) was given with X, 12 times in one horse and11 times in two horses. A portable multifunction monitor was used to provide ECG, hemoglobin saturation and NIBP. Additional drugs (X, B or ketamine) were required to maintain immobility during transport from the CO room or when horses were repositioned for bilateralT (¢ve horses). No horse required additional drugs after the fourth T. Heart rates were always within normal range (30^45 beats minÿ1) and mean arterial blood pressures were elevated (85^140mmHg). Mean maintenance time (T plus transport time) was 3026minutes, while recovery time (when placed in recovery stall to standing) was 46216 minutes. Oxygen was nasally insu¥ated at 15 Lminÿ1 during T and in recovery. Recoveries were generally good and improved over the course of T. All horses lost weight duringT; meanweight loss was 27222 kg. Horses appeared to acclimatize to transport and treatment, as judged by the fact that lower X doses (10% decrease) or no additional drugs were required during treatment or transport after the ¢rst 3^4 treatments. In conclusion, all horses tolerated repeated anesthesia with injectable agents without apparent adverse side e¡ects.