To compare efficacy and duration of desensitization of oral structures with a lidocaine-bupivacaine mixture administered via a lateral percutaneous or modified infraorbital approach.
6 healthy adult hound-type female dogs.
In this crossover study, dogs were randomized for side (left or right) and maxillary nerve approach (lateral percutaneous or infraorbital), with a 2-week washout period. Dogs were anesthetized, and a 2-mL mixture of 2% lidocaine and 0.5% bupivacaine (50:50 [vol/vol]) was administered with a 22-gauge, 4.5-cm-long catheter inserted through the infraorbital canal (infraorbital approach) or with a shielded stimulating needle to the maxillary nerve (percutaneous approach). Reflex-evoked motor potentials were measured for the maxillary canine tooth, fourth premolar tooth, second molar tooth, and hard palate mucosa ipsilateral to the injected mixture and for the contralateral maxillary canine tooth (control) at three 10-minute intervals before injection (baseline) and at predetermined times after injection for up to 6.7 hours. For each oral structure, the proportion of dogs with desensitization (efficacy) and time to onset and duration of desensitization were compared between approaches.
The proportion of dogs with successful nerve blockade did not significantly differ between infraorbital and percutaneous approaches and among the 4 oral structures. Time to onset of desensitization did not differ between approaches, but duration was significantly longer with the infraorbital approach.
CONCLUSIONS AND CLINICAL RELEVANCE
A modified infraorbital approach with the lidocaine-bupivacaine mixture had similar effects to a lateral percutaneous approach but provided a longer duration of desensitization. Neither approach was universally successful at desensitizing all oral structures.
Objective—To quantitate dose- and time-related
anesthetic-sparing effects of xylazine hydrochloride
(XYL) during isoflurane-induced anesthesia in horses
and to characterize selected physiologic responses of
anesthetized horses to administration of XYL.
Animals—6 healthy adult horses.
Procedure—Horses were anesthetized 2 times to
determine the minimum alveolar concentration (MAC)
of isoflurane in O2 and to characterize the anestheticsparing
effect (MAC reduction) after IV administration
of XYL (0.5 and 1 mg/kg of body weight, random
order). Selected measures of cardiopulmonary function,
blood glucose concentrations, and urinary output
also were measured during the anesthetic studies.
Results—Isoflurane MAC (mean ± SEM) was
reduced by 24.8 ± 0.5 and 34.2 ± 1.9% at 42 ± 7 and
67 ± 10 minutes, respectively, after administration of
XYL at 0.5 and 1 mg/kg. Amount of MAC reduction by
XYL was dose- and time-dependent. Overall, cardiovascular
and respiratory values varied little among
treatments. Administration of XYL increased blood
glucose concentration; the magnitude of change was
dose- and time-dependent. Urine volume increased
but not significantly.
Conclusions and Clinical Relevance—Administration
of XYL reduced the anesthetic requirement
for isoflurane in horses. The magnitude of the
decrease is dose- and time-dependent. Administration
of XYL increases blood glucose concentration
in anesthetized horses in a dose-related manner.
(Am J Vet Res 2000;61:1225–1231)
Objective—To develop a clinically applicable technique for recording cord dorsum potentials (CDPs) following stimulation of the radial and ulnar nerves and establish reference values for radial and ulnar sensory nerve conduction velocities (SNCVs) in the wings of ducks.
Animals—8 clinically normal adult female mallard ducks (Anas platyrhynchos).
Procedures—Radial and ulnar compound nerve action potentials (CNAPs) and CDPs were recorded following distal sensory nerve stimulation. The CDPs were recorded from the interarcuate space between the last cervical vertebra and the first thoracic vertebra. Surgical dissection and transection of the brachial plexus in 1 anesthetized duck were performed to identify nerve root location and confirm functional loss of nerve conduction assessed by loss of the CDP.
Results—Radial and ulnar CNAPs and CDPs were consistently recorded in all birds. Median radial SNCV was 38.3 m/s (range, 36.0 to 49.0 m/s), and ulnar SNCV was 35.3 m/s (range, 28.0 to 40.0 m/s). Surgical transection of the brachial plexus resulted in complete loss of the CDP.
Conclusions and Clinical Relevance—Measurement of radial and ulnar SNCV or CDP is feasible in isoflurane-anesthetized mallard ducks. The CDP accurately reflects sensory nerve conduction through the brachial plexus. Assessment of brachial plexus function in mallard ducks via evaluations of SNCVs and CDPs may have application for diagnosis of traumatic injuries to the brachial plexus, evaluation of neuropathies associated with exposure to toxic chemicals, and assessment of the efficacy of interventions such as brachial plexus nerve blockade.
Objective—To determine the antinociceptive effects of epidural administration of morphine or buprenorphine in cats by use of a thermal threshold model.
Animals—6 healthy adult cats.
Procedures—Baseline thermal threshold was determined in duplicate. Cats were anesthetized with isoflurane in oxygen. Morphine (100 μg/kg diluted with saline [0.9% NaCl] solution to a total volume of 0.3 mL/kg), buprenorphine (12.5 μg/kg diluted with saline solution to a total 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. Thermal threshold was determined at various times up to 24 hours after epidural injection.
Results—Epidural administration of saline solution did not affect thermal threshold. Thermal threshold was significantly higher after epidural administration of morphine and buprenorphine, compared with the effect of saline solution, from 1 to 16 hours and 1 to 10 hours, respectively. Maximum (cutout) temperature was reached without the cat reacting in 0, 74, and 11 occasions in the saline solution, morphine, and buprenorphine groups, respectively.
Conclusions and Clinical Relevance—Epidural administration of morphine and buprenorphine induced thermal antinociception in cats. At the doses used in this study, the effect of morphine lasted longer and was more intense than that of buprenorphine.
OBJECTIVE To determine the locomotor response to the administration of fentanyl in horses with and without the G57C polymorphism of the μ-opioid receptor.
ANIMALS 20 horses of various breeds and ages (10 horses heterozygous for the G57C polymorphism and 10 age-, breed-, and sex-matched horses that did not have the G57C polymorphism).
PROCEDURES The number of steps each horse took was counted over consecutive 2-minute periods for 20 minutes to determine a baseline value. The horse then received a bolus of fentanyl (20 μg/kg, IV), and the number of steps was again counted during consecutive 2-minute periods for 60 minutes. The mean baseline value was subtracted from each 2-minute period after fentanyl administration; step counts with negative values were assigned a value of 0. Data were analyzed by use of a repeated-measures ANOVA.
RESULTS Data for 19 of 20 horses (10 horses with the G57C polymorphism and 9 control horses without the G57C polymorphism) were included in the analysis. Horses with the G57C polymorphism had a significant increase in locomotor activity, compared with results for horses without the polymorphism. There was a significant group-by-time interaction.
CONCLUSIONS AND CLINICAL RELEVANCE Horses heterozygous for the G57C polymorphism of the μ-opioid receptor had an increased locomotor response to fentanyl administration, compared with the response for horses without this polymorphism. The clinical impact of this finding should be investigated.
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.
Objective—To evaluate the effect of pneumoperitoneum on cardiorespiratory variables and working space during experimental induction of 3 intra-abdominal pressures (IAPs) in cats.
Animals—6 healthy young adult neutered male domestic shorthair cats.
Procedures—All cats were anesthetized through use of a standardized protocol. A catheter was placed in the right femoral artery for blood pressure and blood gas monitoring. A thermodilution catheter was placed in the right jugular vein via fluoroscopic guidance. Cardiopulmonary variables were measured before (baseline) and 2 and 30 minutes after initiation of pneumoperitoneum at IAPs of 4, 8, and 15 mm Hg; these were created through the use of a mechanical insufflator. At each IAP, abdominal dimensions (height, width, and circumference) were measured at a standardized location.
Results—At 4 mm Hg and 8 mm Hg IAP, no clinically important changes were identified in cardiorespiratory values. Heart rate, cardiac index, and stroke volume index remained unchanged throughout the study at all IAPs. Mean arterial blood pressure began to increase at 8 mm Hg and was significantly higher, compared with baseline, at both time points at 15 mm Hg. At 15 mm Hg, Paco2 was significantly higher and cats were more acidotic than at baseline. Working space was subjectively greater at 8 mm Hg than at 4 mm Hg IAP; however, at 15 mm Hg, no clinically important enlargement of the working space was identified, compared with at 8 mm Hg.
Conclusions and Clinical Relevance—Values of cardiopulmonary variables were largely unchanged by induction of pneumoperitoneum in healthy cats up to an IAP of 8 mm Hg, and no clinically important increases in working space were evident at an IAP of 15 versus 8 mm Hg. These findings provide little justification for use of IAPs > 8 mm Hg in healthy cats undergoing laparoscopic procedures; however, whether the situation is similar in diseased or elderly cats remains to be determined.
Objective—To evaluate the exposure obtained for minimally invasive abdominal organ biopsy (MIOB) from 3 access incisions in cats.
Design—Prospective experimental study and clinical case series.
Animals—6 purpose-bred research cats and 6 feline clinical patients with indications for abdominal organ biopsy.
Procedures—Three 3-cm incisions into the peritoneal cavity were created at different locations along the linea alba in research cats in randomized order. A wound retraction device was inserted in each incision. Ability to exteriorize various abdominal organs to the extent required to reasonably perform a surgical biopsy was recorded, and results were compared among incision sites. On the basis of results obtained, the access incision that provided exposure of the most frequently biopsied abdominal organs was used to perform MIOB in 6 feline clinical patients with various underlying pathological conditions.
Results—On the basis of experiments with research cats, a 3-cm access incision centered midway between the caudal margin of the xiphoid cartilage and the umbilicus was found to provide access for MIOB for most organs. In 5 of 6 clinical patients, all of the organs of interest were biopsied successfully via this incision location, although access to all hepatic lobes and all parts of the pancreas was inconsistent. In 1 cat, conversion to an open approach was performed because a palpable mass was detected in the area of the duodenocolic ligament.
Conclusions and Clinical Relevance—Optimization of access incision location for MIOB allowed biopsy specimen collection from organs of interest to be performed in a minimally invasive manner in cats.
Objective—To determine the effects of body position on lung and air-sac volumes in anesthetized and spontaneously breathing red-tailed hawks (Buteo jamaicensis).
Animals—6 adult red-tailed hawks (sex unknown).
Procedures—A crossover study design was used for quantitative estimation of lung and air-sac volumes in anesthetized hawks in 3 body positions: dorsal, right lateral, and sternal recumbency. Lung volume, lung density, and air-sac volume were calculated from helical computed tomographic (CT) images by use of software designed for volumetric analysis of CT data. Effects of body position were compared by use of repeated-measures ANOVA and a paired Student t test.
Results—Results for all pairs of body positions were significantly different from each other. Mean ± SD lung density was lowest when hawks were in sternal recumbency (–677 ± 28 CT units), followed by right lateral (–647 ± 23 CT units) and dorsal (–630 ± 19 CT units) recumbency. Mean lung volume was largest in sternal recumbency (28.6 ± 1.5 mL), followed by right lateral (27.6 ± 1.7 mL) and dorsal (27.0 ± 1.5 mL) recumbency. Mean partial air-sac volume was largest in sternal recumbency (27.0 ± 19.3 mL), followed by right lateral (21.9 ± 16.1 mL) and dorsal (19.3 ± 16.9 mL) recumbency.
Conclusions and Clinical Relevance—In anesthetized red-tailed hawks, positioning in sternal recumbency resulted in the greatest lung and air-sac volumes and lowest lung density, compared with positioning in right lateral and dorsal recumbency. Additional studies are necessary to determine the physiologic effects of body position on the avian respiratory system.
Objective—To determine induction doses, anesthetic
constant rate infusions (CRI), and cardiopulmonary
effects of propofol in red-tailed hawks and great
horned owls and propofol pharmacokinetics in the
owls during CRI.
Animals—6 red-tailed hawks and 6 great horned
Procedure—The CRI dose necessary for a loss of
withdrawal reflex was determined via specific stimuli.
Anesthesia was induced by IV administration of
propofol (1 mg/kg/min) and maintained by CRI at the
predetermined dose for 30 minutes. Heart and respiratory
rates, arterial blood pressures, and blood gas
tensions were obtained in awake birds and at various
times after induction. End-tidal CO2 (ETCO2) concentration
and esophageal temperature were obtained
after induction. Propofol plasma concentrations were
obtained after induction and after completion of the
CRI in the owls. Recovery times were recorded.
Results—Mean ± SD doses for induction and CRI
were 4.48 ± 1.09 mg/kg and 0.48 ± 0.06 mg/kg/min,
respectively, for hawks and 3.36 ± 0.71 mg/kg and
0.56 ± 0.15 mg/kg/min, respectively, for owls.
Significant increases in PaCO2, HCO3, and ETCO2 in
hawks and owls and significant decreases in arterial
pH in hawks were detected. A 2-compartment model
best described the owl pharmacodynamic data.
Recovery times after infusion were prolonged and
varied widely. Central nervous system excitatory
signs were observed during recovery.
Conclusions and Clinical Relevance—Effects on
blood pressure were minimal, but effective ventilation
was reduced, suggesting the need for careful monitoring
during anesthesia. Prolonged recovery periods
with moderate-to-severe excitatory CNS signs may
occur in these species at these doses. (Am J Vet Res 2003;64:677–683)