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Abstract

Objective—To evaluate bronchial morphology endoscopically in rabbits and develop a valid nomenclature for the endobronchial branching pattern.

Animals—10 mature New Zealand White rabbits.

Procedures—Flexible bronchoscopy was performed in rabbits anesthetized with isoflurane via nasal mask. Airways were systematically evaluated from the larynx to the terminal branches accessible with a 2.5-mm–outer diameter flexible endoscope. Airway branching patterns were identified and assessed for variation among subjects.

Results—Airways of all rabbits were readily examined with the 2.5-mm flexible endoscope. Laryngeal structure and function were normal in each rabbit, and airway branching patterns in all rabbits evaluated were identical. At the carina, branching into left and right principal bronchi was evident. The left principal bronchus divided immediately into the left cranial and left caudal lobar bronchi. The left cranial lobe bronchus further divided into dorsal and ventral segmental bronchi. The left caudal lobe bronchus gave rise to branches originating dorsally, ventrally, and medially before continuing caudally. The right principal bronchus divided into the right cranial, right middle, and accessory lobar bronchi and continued distally as the right caudal lobar bronchus. The right cranial lobe bronchus also divided into dorsal and ventral segmental bronchi, and the right caudal lobe bronchus had branches that originated dorsally, ventrally, and medially.

Conclusions and Clinical Relevance—Definition of a standard nomenclature for airway branching in rabbits will allow precise localization of disease in clinical cases and accurate collection of airway samples in clinical and scientific evaluations.

Full access
in American Journal of Veterinary Research

Abstract

OBJECTIVE To determine effects of increasing plasma fentanyl concentrations on the minimum alveolar concentration (MAC) of isoflurane in rabbits.

ANIMALS 6 adult female New Zealand White rabbits (Oryctolagus cuniculus).

PROCEDURES Rabbits were anesthetized with isoflurane in oxygen; ventilation was controlled and body temperature maintained between 38.5° and 39.5°C. Fentanyl was administered IV by use of a computer-controlled infusion system to achieve 6 target plasma concentrations. Isoflurane MAC was determined in duplicate by use of the bracketing technique with a supramaximal electrical stimulus. Blood samples were collected for measurement of plasma fentanyl concentration at each MAC determination. The MAC values were analyzed with a repeated-measures ANOVA followed by Holm-Sidak pairwise comparisons.

RESULTS Mean ± SD plasma fentanyl concentrations were 0 ± 0 ng/mL (baseline), 1.2 ± 0.1 ng/mL, 2.2 ± 0.3 ng/mL, 4.4 ± 0.4 ng/mL, 9.2 ± 0.4 ng/mL, 17.5 ± 2.6 ng/mL, and 36.8 ± 2.4 ng/mL. Corresponding mean values for isoflurane MAC were 1.92 ± 0.16%, 1.80 ± 0.16%, 1.60 ± 0.23%, 1.46 ± 0.22%, 1.12 ± 0.19%, 0.89 ± 0.14%, and 0.70 ± 0.15%, respectively. Isoflurane MAC for plasma fentanyl concentrations ≥ 2.2 ng/mL differed significantly from the baseline value. In 3 rabbits, excessive spontaneous movement prevented MAC determination at the highest plasma fentanyl concentration.

CONCLUSIONS AND CLINICAL RELEVANCE Fentanyl reduced isoflurane MAC by approximately 60% in New Zealand White rabbits. Further studies will be needed to investigate the cardiorespiratory effects of isoflurane and fentanyl combinations in rabbits; however, fentanyl may prove to be a useful adjunct to inhalation anesthesia in this species.

Full access
in American Journal of Veterinary Research

Abstract

Objective—To determine the mineral composition of calculi, anatomic locations of the calculi, and findings of urinalysis and bacteriologic culture of urine and calculi in guinea pigs with urolithiasis.

Design—Cross-sectional study.

Animals—127 guinea pigs.

Procedures—Records of urinary calculi that had been submitted to the University of California Stone Laboratory from 1985 through 2003 were reviewed. In addition, submissions of urinary calculi for evaluation by the laboratory were prospectively solicited from 2004 through 2007. Prospectively obtained calculi were accompanied by a urine sample for urinalysis and bacteriologic culture and a completed questionnaire. All calculi were analyzed by use of polarized light microscopy and infrared spectroscopy. A subset of calculi was examined by means of x-ray diffractometry (XRD).

Results—83% (43/52) of calculi from the laboratory database and 93% (70/75) of calculi that were prospectively solicited were composed of 100% calcium carbonate. Analysis via XRD confirmed that 5 of 6 calculi from a subset that had the greatest gross morphologic variation were composed of 100% calcite. Although many guinea pigs had received anti-microbials before bacteriologic cultures of urine were performed, Corynebacterium renale was isolated from 5 urine samples.

Conclusions and Clinical Relevance—Contrary to findings of other studies, urinary calculi analyzed for the present study were most commonly composed of 100% calcium carbonate, and infrared spectroscopy or XRD was necessary to differentiate this mineral from others. Treatments, including diet and husbandry practices, should be developed to help prevent development of calcium carbonate calculi in guinea pigs.

Full access
in Journal of the American Veterinary Medical Association

Abstract

Objective—To determine cytologic and microbiologic findings in bronchoalveolar lavage (BAL) fluid and SpO 2 values obtained during BAL in healthy rabbits.

Animals—9 rabbits.

Procedures—Bronchoscopic BAL of left and right caudal lobar bronchi (LB2 and RB4) was performed with 3 mL of sterile saline (0.9% NaCl) solution; SpO 2 was measured before, during, and after BAL. Percentage fluid recovered, total leukocyte counts, and differential cell counts were determined. Aerobic and anaerobic bacterial, mycoplasmal, and fungal cultures were performed from combined LB2 and RB4 samples.

Results—Mean ± SD percentage fluid volumes recovered from LB2 and RB4 were 53 ± 13% and 63 ± 13%, respectively. Mean ± SD total leukocyte counts from LB2 and RB4 were 422 ± 199 cells/μL and 378 ± 97 cells/μL, respectively. Macrophages were most frequently identified. There were no significant differences in volumes retrieved, total leukocyte counts, or differential cell percentages between LB2 and RB4. Microbial culture results were negative for 3 rabbits and positive for mixed aerobic and anaerobic bacterial growth in 6 and 2 rabbits, respectively. The SpO 2 was ≥ 95% in 7 of 9 rabbits after anesthetic induction, < 95% in 5 of 6 rabbits 1 minute after BAL, and ≥ 95% in 5 of 9 rabbits and > 90% in 4 of 9 rabbits 3 minutes after BAL.

Conclusions and Clinical Relevance—Bronchoscopic BAL with 3 mL of saline solution provided adequate fluid recovery for microbiologic and cytologic examination from the caudal lung lobes. Transient low SpO 2 was detected immediately after BAL.

Full access
in American Journal of Veterinary Research

Abstract

Objective—To determine the pharmacokinetics of butorphanol tartrate after IV and IM single-dose administration in red-tailed hawks (RTHs) and great horned owls (GHOs).

Animals—6 adult RTHs and 6 adult GHOs.

Procedures—Each bird received an injection of butorphanol (0.5 mg/kg) into either the right jugular vein (IVj) or the pectoral muscles in a crossover study (1-week interval between treatments). The GHOs also later received butorphanol (0.5 mg/kg) via injection into a medial metatarsal vein (IVm). During each 24-hour postinjection period, blood samples were collected from each bird; plasma butorphanol concentrations were determined via liquid chromatography-mass spectrometry.

Results—2- and 1-compartment models best fit the IV and IM pharmacokinetic data, respectively, in both species. Terminal half-lives of butorphanol were 0.94 ± 0.30 hours (IVj) and 0.94 ± 0.26 hours (IM) for RTHs and 1.79 ± 1.36 hours (IVj), 1.84 ± 1.56 hours (IM), and 1.19 ± 0.34 hours (IVm) for GHOs. In GHOs, area under the curve (0 to infinity) for butorphanol after IVj or IM administration exceeded values in RTHs; GHO values after IM and IVm administration were less than those after IVj administration. Plasma butorphanol clearance was significantly more rapid in the RTHs. Bioavailability of butorphanol administered IM was 97.6 ± 33.2% (RTHs) and 88.8 ± 4.8% (GHOs).

Conclusions and Clinical Relevance—In RTHs and GHOs, butorphanol was rapidly absorbed and distributed via all routes of administration; the drug's rapid terminal half-life indicated that published dosing intervals for birds may be inadequate in RTHs and GHOs.

Full access
in American Journal of Veterinary Research

Abstract

Objective—To determine the median effective dose (ED50; equivalent to the minimum alveolar concentration [MAC]) of isoflurane, sevoflurane, and desflurane for anesthesia in iguanas.

Animals—6 healthy adult green iguanas.

Procedure—In unmedicated iguanas, anesthesia was induced and maintained with each of the 3 volatile drugs administered on separate days according to a Latin square design. Iguanas were endotracheally intubated, mechanically ventilated, and instrumented for cardiovascular and respiratory measurements. During each period of anesthesia, MAC was determined in triplicate. The mean value of 2 consecutive expired anesthetic concentrations, 1 that just permitted and 1 that just prevented gross purposeful movement in response to supramaximal electrical stimulus, and that were not different by more than 15%, was deemed the MAC.

Results—Mean ± SD values for the third MAC determination for isoflurane, sevoflurane, and desflurane were 1.8 ± 0.3%, 3.1 ± 1.0%, and 8.9 ± 2.1% of atmospheric pressure, respectively. The MAC for all inhaled agents was, on average, 22% greater for the first measurement than for the third measurement.

Conclusions and Clinical Relevance—Over time, MACs decreased for all 3 agents. Final MAC measurements were similar to values reported for other species. The decrease in MACs over time may be at least partly explained by limitations of anesthetic uptake and distribution imposed by the reptilian cardiorespiratory system. Hence, for a constant end-tidal anesthetic concentration in an iguana, the plane of anesthesia may deepen over time, which could contribute to increased morbidity during prolonged procedures.

Full access
in American Journal of Veterinary Research

Abstract

OBJECTIVE

Describe the pharmacokinetics of grapiprant administered orally with food to red-tailed hawks (RTHAs; Buteo jamaicensis) and compare the results with previously described grapiprant pharmacokinetics administered without food in this species.

ANIMALS

6 healthy adult RTHA (3 males, 3 females) under human care.

PROCEDURES

A single dose of grapiprant (30 mg/kg) was given orally to RTHAs, followed by force-feeding. Blood samples were obtained at 14 time points for 120 hours postgrapiprant administration. Plasma concentrations of grapiprant were measured via tandem liquid chromatography-mass spectrometry. Nonparametric superimposition using pharmacokinetic modeling software used plasma concentrations to calculate simulations of grapiprant plasma concentrations for 30 mg/kg administered orally with food every 12 hours.

RESULTS

The arithmetic mean maximum plasma concentration was 405.8 ng/mL, time to maximum plasma concentration was 16 hours, and harmonic mean terminal half-life was 15.6 hours. Simulations determined 30 mg/kg every 12 hours could attain minimum effective concentrations (> 164 ng/mL) reported in dogs for a sustained period of approximately 20 hours.

CLINICAL RELEVANCE

Grapiprant plasma concentrations were achieved above the canine therapeutic concentrations within 16 hours postmedication. Mean concentrations were maintained for approximately 20 hours. Simulations support a dosing frequency of 12-hour intervals with food reaching minimum effective concentrations established for canines, although it is unknown whether these plasma concentrations are therapeutic for birds. Bioaccumulation was not noted on simulations secondary to increased grapiprant administration. Further research including multidose assessments at this current dose with food, in vitro pharmacological characterization, and pharmacodynamic studies in this species are warranted.

Open access
in American Journal of Veterinary Research

Abstract

OBJECTIVE To evaluate effects of administration of a 4.7-mg deslorelin acetate implant on egg laying in healthy cockatiels (Nymphicus hollandicus).

ANIMALS 52 cockatiels.

PROCEDURES 26 breeding pairs (a female and its respective male in each pair) were selected on the basis of their history of egg laying. Female birds were sedated and received a 4.7-mg deslorelin acetate implant (n = 13) or placebo implant (13) in the subcutaneous tissues between the scapulae. Male and female birds of each breeding pair were placed in separate but adjacent cages. Birds were exposed to 16 hours of light and 8 hours of darkness. A nest box was placed in cages of female birds to stimulate reproductive activity. Egg production and quality were monitored daily for 365 days.

RESULTS Deslorelin acetate implants significantly suppressed egg laying in cockatiels, compared with effects for the placebo implants. Eleven of 13 placeboimplanted birds laid eggs between 12 and 42 days after implantation. None of the deslorelin-implanted birds laid eggs within 180 days after implantation, and only 5 of 13 deslorelin-implanted birds laid an egg during the study period (first egg laid between 192 and 230 days after implantation). No differences in egg quality or number of eggs per clutch were observed between the 2 groups.

CONCLUSIONS AND CLINICAL RELEVANCE Insertion of a 4.7-mg deslorelin acetate implant suppressed egg laying in healthy cockatiels for at least 180 days. Studies are necessary to evaluate effects of a deslorelin acetate implant in other avian species or in association with reproductive disorders.

Full access
in American Journal of Veterinary Research

Abstract

OBJECTIVE To determine the pharmacokinetics and adverse effects following SC administration of ceftiofur crystalline free acid (CCFA) in New Zealand White rabbits.

ANIMALS 6 adult sexually intact female New Zealand White rabbits.

PROCEDURES Each rabbit was administered 40 mg of CCFA/kg SC. A blood sample was obtained immediately before (0 minutes), at 5 and 30 minutes after, and at 1, 1.5, 2, 3, 4, 8, 12, 24, 48, 72, 95, 120, 144, and 168 hours after administration, and plasma concentrations of ceftiofur free acid equivalents (CFAE) were measured. Pharmacokinetic parameters were calculated. For each rabbit, body weight, food consumption, fecal output, and injection site were monitored. Minimum inhibitory concentrations of ceftiofur for 293 bacterial isolates from rabbit clinical samples were determined.

RESULTS Mean ± SD peak plasma concentration of CFAE and time to maximum plasma concentration were 33.13 ± 10.15 μg/mL and 1.75 ± 0.42 hours, respectively. The mean terminal half-life of CFAE was 42.6 ± 5.2 hours. Plasma CFAE concentration was > 4 μg/mL for approximately 24 hours and > 1 μg/mL for at least 72 hours after CCFA administration. An apparently nonpainful subcutaneous nodule developed at the injection site in 3 of 6 rabbits.

CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that CCFA (40 mg/kg) could be administered SC every 24 to 72 hours to New Zealand White rabbits to treat infections with ceftiofur-susceptible bacteria. Single-dose administration of CCFA resulted in minimal adverse effects. Additional studies are needed to evaluate the effects of repeated CCFA administration in New Zealand White rabbits.

Full access
in American Journal of Veterinary Research

Abstract

OBJECTIVE

To determine the pharmacokinetics and adverse effects of maropitant citrate after IV and SC administration to New Zealand White rabbits (Oryctolagus cuniculus).

ANIMALS

11 sexually intact (3 males and 8 females) adult rabbits.

PROCEDURES

Each rabbit received maropitant citrate (1 mg/kg) IV or SC. Blood samples were collected at 9 (SC) or 10 (IV) time points over 48 hours. After a 2-week washout period, rabbits received maropitant by the alternate administration route. Pharmacokinetic parameters were calculated. Body weight, food and water consumption, injection site, mentation, and urine and fecal output were monitored.

RESULTS

Mean ± SD maximum concentration after SC administration was 14.4 ± 10.9 ng/mL and was detected at 1.25 ± 0.89 hours. Terminal half-life after IV and SC administration was 10.4 ± 1.6 hours and 13.1 ± 2.44 hours, respectively. Bioavailability after SC administration was 58.9 ± 13.3%. Plasma concentration at 24 hours was 2.87 ± 1.69 ng/mL after IV administration and 3.4 ± 1.2 ng/mL after SC administration. Four rabbits developed local dermal reactions at the injection site after SC injection. Increased fecal production was detected on the day of treatment and 1 day after treatment.

CONCLUSIONS AND CLINICAL RELEVANCE

Plasma concentrations of rabbits 24 hours after SC and IV administration of maropitant citrate (1 mg/kg) were similar to those of dogs at 24 hours. Reactions at the SC injection site were the most common adverse effect detected. Increased fecal output may suggest an effect on gastrointestinal motility. Additional pharmacodynamic and multidose studies are needed.

Full access
in American Journal of Veterinary Research