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Abstract

Objective—To determine the hemodynamic effects of nitrous oxide in isoflurane-anesthetized cats.

Animals—12 healthy adult domestic shorthair cats.

Procedure—Cats were anesthetized by administration of isoflurane in oxygen. After instruments were inserted, end-tidal isoflurane concentration was set at 1.25 times the individual minimum alveolar concentration, and nitrous oxide was administered in a Latinsquare design at 0, 30, 50, and 70%. Each concentration was administered for 25 minutes before measurements were obtained to allow for stabilization. Heart rate; systemic and pulmonary arterial pressures; central venous pressure; pulmonary artery occlusion pressure; cardiac output; body temperature; arterial and mixed-venous pH, PCO2, PO2, and hemoglobin concentrations; PCV; and total protein and lactate concentrations were measured before and during noxious stimulation for each nitrous oxide concentration. Arterial and mixed-venous bicarbonate concentrations and oxygen saturation, cardiac index, stroke index, rate-pressure product, systemic and pulmonary vascular resistance indices, left and right ventricular stroke work indices, arterial and mixed-venous oxygen contents, oxygen delivery, oxygen consumption, oxygen extraction ratio, alveolar-to-arterial oxygen difference, and venous admixture were calculated.

Results—Arterial pressure, central venous pressure, pulmonary arterial pressure, rate-pressure product, systemic and pulmonary vascular resistance indices, arterial PCO2, and PCV increased during administration of 70% nitrous oxide. Arterial and mixed-venous pH, mixed-venous PO2, and alveolar-to-arterial oxygen difference decreased during administration of 70% nitrous oxide. Results before and during noxious stimulation were similar.

Conclusions and Clinical Relevance—Administration of 70% nitrous oxide to isoflurane-anesthetized cats resulted in improved arterial pressure, which was related to a vasoconstrictive effect. (Am J Vet Res 2003;64:273–278)

Full access
in American Journal of Veterinary Research

Abstract

Objective—To determine the thermal antinociceptive effect of various single doses of gabapentin administered orally in cats.

Animals—6 healthy adult domestic shorthair cats.

Procedures—Baseline skin temperature and baseline thermal threshold were determined via application of a thermal probe to the thorax of each cat prior to oral administration (in random order) of an empty capsule (placebo) or a capsule containing 5, 10, or 30 mg of gabapentin/kg (4 experiments/cat). After each treatment, thermal threshold was determined at intervals during an 8-hour period. Plasma gabapentin concentration was measured prior to and at 1-hour intervals after drug administration. Dose and time effects were analyzed by use of a repeated-measures ANOVA.

Results—Peak plasma gabapentin concentration increased with increasing gabapentin dose. After administration of the 5, 10, and 30 mg/kg doses, median interval until the greatest gabapentin concentration was detected was 60, 120, and 90 minutes, respectively (interval ranges were 60 to 120 minutes, 60 to 120 minutes, and 60 to 180 minutes, respectively). In the experiments involving administration of the placebo or increasing doses of gabapentin, mean ± SD baseline skin temperature and thermal threshold were 36.8 ± 1.21°C and 45.8 ± 4.4°C, 36.9 ± 1.1°C and 43.1 ± 2.4°C, 37.0 ± 0.7°C and 44.0 ± 1.5°C, and 36.1 ± 1.7°C and 43.3 ± 3.3°C, respectively. There was no significant effect of treatment on thermal threshold.

Conclusions and Clinical Relevance—At the doses evaluated, orally administered gabapentin did not affect the thermal threshold in healthy cats and therefore did not appear to provide thermal antinociception. (Am J Vet Res 2010;71:1027–1032)

Full access
in American Journal of Veterinary Research

Abstract

Objective—To determine the pharmacokinetics of gabapentin in cats after IV and oral administration.

Animals—6 healthy female adult domestic shorthair cats.

Procedures—Gabapentin was administered IV (4 mg/kg) or orally (10 mg/kg) in a crossover randomized design. Blood samples were obtained immediately before gabapentin administration and at various times up to 960 minutes after IV administration or up to 1,440 minutes after oral administration. Blood samples were immediately transferred to tubes that contained EDTA and were centrifuged at 4°C. Plasma was harvested and stored at −20°C until analysis. Plasma concentrations of gabapentin were determined by use of liquid chromatography-mass spectrometry. Gabapentin concentration-time data were fit to compartment models.

Results—A 3-compartment model with elimination from the central compartment best described the disposition of gabapentin administered IV to cats, but a 1-compartment model best described the disposition of gabapentin administered orally to cats. After IV administration, the mean ± SEM apparent volume of the central compartment, apparent volume of distribution at steady state, and clearance and the harmonic mean ± jackknife pseudo-SD for terminal half-life were 90.4 ± 11.3 mL/kg, 650 ± 14 mL/kg, 3 ± 0.2 mL/min/kg, and 170 ± 21 minutes, respectively. Mean ± SD systemic availability and harmonic mean ± jackknife pseudo-SD terminal half-life after oral administration were 88.7 ± 11.1% and 177 ± 25 minutes, respectively.

Conclusions and Clinical Relevance—The disposition of gabapentin in cats was characterized by a small volume of distribution and a low clearance.

Full access
in American Journal of Veterinary Research

Abstract

Objective—To determine the effect of 6 plasma ketamine concentrations on the minimum alveolar concentration (MAC) of isoflurane in dogs.

Animals—6 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)

Full access
in American Journal of Veterinary Research

Abstract

Objective—To determine effects of epidural administration of morphine and buprenorphine on the minimum alveolar concentration of isoflurane in cats.

Animals—6 healthy adult domestic shorthair cats.

Procedures—Cats were anesthetized with isoflurane in oxygen. Morphine (100 μg/kg diluted with saline [0.9% NaCl] solution to a volume of 0.3 mL/kg), buprenorphine (12.5 μg/kg diluted with saline solution to a volume of 0.3 mL/kg), or saline solution (0.3 mL/kg) was administered into the epidural space according to a Latin square design. The minimum alveolar concentration (MAC) of isoflurane was measured in triplicate by use of the tail clamp technique. At least 1 week was allowed between successive experiments.

Results—The MAC of isoflurane was 2.00 ± 0.18%, 2.13 ± 0.11%, and 2.03 ± 0.09% in the morphine, buprenorphine, and saline solution groups, respectively. No significant difference in MAC was detected among treatment groups.

Conclusions and Clinical Relevance—A significant effect of epidural administration of morphine or buprenorphine on the MAC of isoflurane in cats could not be detected. Further studies are needed to establish whether epidural opioid administration has other benefits when administered as a component of general anesthesia in cats.

Full access
in American Journal of Veterinary Research

Abstract

Objective—To determine the cardiopulmonary effects of increasing doses of dopamine, dobutamine, epinephrine, and phenylephrine and measure plasma concentrations of norepinephrine, epinephrine, and dopamine in cats anesthetized with isoflurane.

Animals—6 healthy adult cats.

Procedures—Each cat was anesthetized with isoflurane (1.5 X minimum alveolar concentration) on 4 occasions. Cardiopulmonary measurements were obtained after a 30-minute stabilization period; 20 minutes after the start of each infusion dose; and 30, 60, and 90 minutes after the infusion was discontinued. Cats received 5 progressively increasing infusions of epinephrine or phenylephrine (0.125, 0.25, 0.5, 1, and 2 μg/kg/min) or dobutamine or dopamine (2.5, 5, 10, 15, and 20 μg/kg/min). The order of treatment was randomly allocated.

Results—All 4 treatments increased oxygen delivery. Heart rate (HR) increased during administration of all drugs except phenylephrine, and mean arterial pressure increased during administration of all drugs except dobutamine. A progressive metabolic acidosis was detected, but whole-blood lactate concentration only increased during administration of epinephrine and dobutamine. Systemic vascular resistance index increased during administration of phenylephrine, decreased during administration of dobutamine, and remained unchanged during administration of dopamine and epinephrine. A positive inotropic effect was detected with all treatments.

Conclusions and Clinical Relevance—During anesthesia in cats, administration of dopamine, dobutamine, and epinephrine may be useful for increasing cardiac output, with dopamine having the most useful effects. Administration of phenylephrine increased cardiac and systemic vascular resistance indexes with minimal effect on HR and may be useful for increasing mean arterial pressure without increasing HR.

Full access
in American Journal of Veterinary Research

Abstract

Objective—To determine the effects of IV administration of lidocaine on thermal antinociception in conscious cats. Animals—6 cats.

Procedure—2 experiments were performed in each cat (interval of at least 2 months). In experiment 1, lidocaine pharmacokinetics were determined for each conscious cat following IV administration of a bolus of lidocaine (2 mg/kg). In experiment 2, data from experiment 1 were used to calculate appropriate doses of lidocaine that would achieve predetermined plasma lidocaine concentrations in the cats; lidocaine (or an equivalent volume of saline [0.9% NaCl] solution as the control treatment) was administered IV to target pseudo–steady-state plasma concentrations of 0, 0.5, 1, 2, 5, and 8 μg/mL. Skin temperature and thermal threshold were determined at the start of the experiment (baseline) and at each concentration. Samples of venous blood were obtained at each target concentration for plasma lidocaine concentration determination.

Results—In experiment 2, actual plasma lidocaine concentrations were 0.00 ± 0.00 μg/mL, 0.25 ± 0.18 μg/mL, 0.57 ± 0.20 μg/mL, 1.39 ± 0.13 μg/mL, 2.33 ± 0.45 μg/mL, and 4.32 ± 0.66 μg/mL for target plasma concentrations of 0, 0.5, 1, 2, 5, and 8 μg/mL, respectively. Compared with baseline values, no significant change in skin temperature or thermal threshold was detected at any lidocaine plasma concentration (or saline solution equivalent). Skin temperature or thermal threshold values did not differ between lidocaine or control treatments.

Conclusions and Clinical Relevance—Results indicated that these moderate plasma concentrations of lidocaine did not affect thermal antinociception in cats.

Full access
in American Journal of Veterinary Research

Abstract

Objective

To characterize isoflurane (ISO)-induced anesthesia in ferrets and rats.

Animals

8 ferrets (Mustela putorius furo) and 8 Sprague-Dawley rats.

Procedure

Ferrets and rats were anesthetized in a similar manner, using ISO in oxygen. Minimum alveolar concentration (MAC) was determined, using the tail-clamp method. Immediately thereafter, assessments were recorded for 0.8, 1.0, 1.5, and 2.0 MAC (order randomized) of ISO.

Results

MAC of ISO was (mean ± SEM) 1.74 ± 0.03 and 1.58 ± 0.05% for ferrets and rats, respectively. Mean arterial blood pressure (MAP) was 75.0 ± 4.3 and 107.9 ± 2.7 mm Hg at 0.8 MAC for ferrets and rats, respectively, and decreased in a parallel dose-dependent manner. Respiratory frequency decreased in rats as ISO dose increased; however, respiratory frequency increased in ferrets as ISO dose increased from 0.8 to 1.5 MAC but then decreased at 2.0 MAC. At 0.8 MAC, hypoventilation was much greater in ferrets (Paco2 = 71.4 ± 3.5 mm Hg), compared with rats (Paco2 = 57.7 ± 1.9 mm Hg). In both species, Paco2 progressively increased as anesthetic dose increased. Eyelid aperture of ferrets increased in a dose-dependent manner. Pupil diameter in ferrets and rats increased as ISO dose increased.

Conclusions and Clinical Relevance

The MAP and Paco2 in ferrets and rats and eyelid aperture in ferrets consistently and predictably changed in response to changes in anesthetic dose of ISO. Magnitude of respiratory depression was greater in ferrets than rats. Changes in MAP and Paco2 in ferrets and rats and eyelid aperture in ferrets are consistent guides to changes in depth of ISO-induced anesthesia. (Am J Vet Res 1999;60:1577–1583)

Free access
in American Journal of Veterinary Research

Abstract

Objective

To characterize variables used to monitor rabbits during inhalation anesthesia.

Animals

8 male New Zealand White rabbits.

Procedure

Rabbits were similarly anesthetized with halothane (HAL) or isoflurane (ISO) in a crossover study; half received HAL followed by ISO, and the protocol was reversed for the remaining rabbits. After induction, minimum alveolar concentration (MAC) was determined for each agent, using the tail-clamp method, and variables were recorded at 0.8, 1.0, 1.5, and 2.0 MAC (order randomized).

Results

Mean ± sem mac was 1.42 ± 0.05 and 2.07 ± 0.09% for hal and iso, respectively. Directly measured auricular mean arterial blood pressure was 52.8 ± 5.6 and 54.8 ± 6.1 mm Hg at 0.8 mac for hal and iso, respectively, and decreased from these values in a parallel dose-dependent manner. Respiratory frequency remained constant (range, 69 to 78 breaths/min) over the range of hal doses but incrementally decreased from a mean of 53 (at 0.8 mac) to 32 breaths/min (at 2.0 mac) for iso. The Paco2 was similar at 0.8 mac for hal and iso and progressively increased with increasing doses of both agents; Paco2 at 2.0 mac for iso was significantly greater than that at 2.0 mac for hal (79.8 ± 13.7 vs 54.9 ± 4.0 mm Hg, respectively). Eyelid aperture consistently increased in a dose-dependent manner for both anesthetics.

Conclusions

Arterial blood pressure, Paco2, and eyelid aperture consistently and predictably changed in rabbits in response to changes in anesthetic doses. The magnitude of respiratory depression was greater for iso than for hal. (Am J Vet Res 1999;60:1189–1195)

Free access
in American Journal of Veterinary Research

Objective

To describe 7 cases of acute postoperative azotemia in dogs and to examine by use of a case-control study the possible association between this complication and administration of nafcillin.

Design

Retrospective and case-control study.

Animals

7 case dogs and 28 matched control dogs.

Procedure

Cases of acute renal failure or acute renal insufficiency were identified by retrospective study of records of dogs treated between July 1, 1992, and Feb 28, 1995, and from information received from a practitioner. A random sample of records of dogs undergoing invasive procedures between Dec 1, 1992, and Nov 30, 1993, was examined to determine the prevalence of nafcillin use. Each case dog was matched with 4 control dogs, and data were subjected to logistic regression analysis, employing exact conditional inference on the parameter estimates.

Results

Case dogs were between 1 and 9 years old and weighed between 21 and 60 kg. Preoperatively, none of the dogs had a history of renal disease, and BUN concentrations, hematocrit, and plasma protein concentrations were within reference ranges. Postoperatively, each dog became azotemic and had clinical signs consistent with uremia. Hyponatremia was recorded in 6 case dogs. One dog did not respond to treatment and was euthanatized. Two dogs had persistent isosthenuria, and 4 dogs recovered. Nafcillin was used in approximately 502 of 2,184 (23%) dogs that underwent invasive procedures between Dec 1, 1992, and Nov 30, 1993. The use of nafcillin ceased on Nov 30, 1993, and no further cases were recorded in the following 15 months. In the case-control study, the only factor that was significantly associated with the occurrence of acute postoperative azotemia was administration of nafcillin.

Clinical Implications

Intraoperative use of nafcillin may be associated with development of acute postoperative azotemia in dogs. (J Am Vet Med Assoc 1996; 208:1043–1047)

Free access
in Journal of the American Veterinary Medical Association