Objective—To compare the disposition of lidocaine
administered IV in awake and anesthetized horses.
Procedure—After instrumentation and collection of
baseline data, lidocaine (loading infusion, 1.3 mg/kg
administered during 15 minutes (87 µg/kg/min); constant
rate infusion, 50 µg/kg/min) was administered IV
to awake or anesthetized horses for a total of 105 minutes.
Blood samples were collected at fixed times during
the loading and maintenance infusion periods and
after the infusion period for analysis of serum lidocaine
concentrations by use of liquid chromatography with
mass spectral detection. Selected cardiopulmonary
parameters including heart rate (HR), mean arterial
pressure (MAP), arterial pH, PaCO2, and PaO2 were also
recorded at fixed time points during lidocaine administration.
Serum lidocaine concentrations were evaluated
by use of standard noncompartmental analysis.
Results—Serum lidocaine concentrations were higher
in anesthetized than awake horses at all time points
during lidocaine administration. Serum lidocaine concentrations
reached peak values during the loading
infusion in both groups (1,849 ± 385 ng/mL and
3,348 ± 602 ng/mL in awake and anesthetized horses,
respectively). Most lidocaine pharmacokinetic variables
also differed between groups. Differences in cardiopulmonary
variables were predictable; for example,
HR and MAP were lower and PaO2 was higher in anesthetized
than awake horses but within reference
ranges reported for horses under similar conditions.
Conclusions and Clinical Relevance—Anesthesia
has an influence on the disposition of lidocaine in horses,
and a change in dosing during anesthesia should
be considered. (Am J Vet Res 2005;66:574–580)
Objective—To investigate the clinical, clinicopathologic, and diagnostic characteristics; treatment; and outcome associated with acute traumatic brain injury (TBI) in horses and assess risk factors for nonsurvival in TBI-affected horses.
Design—Retrospective case series.
Animals—34 horses with TBI.
Procedures—Medical records of horses that had sustained trauma to the head and developed neurologic signs were reviewed. Data that included signalment, clinicopathologic findings, diagnosis, treatment, and outcome were analyzed. Clinicopathologic variables among horses in survivor and nonsurvivor groups were compared, and risk factors for nonsurvival were determined.
Results—Median age of affected horses was 12 months. Findings of conventional survey radiography of the head alone failed to identify all horses with fractures of the calvarium. Horses with basilar bone fractures were 7.5 times as likely not to survive as horses without this type of fracture. Depending on clinical signs, horses received supportive care, osmotic or diuretic treatments, antimicrobials, anti-inflammatory drugs, analgesics, or anticonvulsants. Twenty-one (62%) horses survived to discharge from the hospital. In the nonsurvivor group, mean PCV was significantly higher, compared with the value in the survivor group (40% vs 33%). Risk factors associated with nonsurvival included recumbency of more than 4 hours' duration after initial evaluation (odds ratio, 18) and fracture of the basilar bone (odds ratio, 7.5).
Conclusions and Clinical Relevance—Results suggest that prognosis for survival in horses with acute TBI may be more favorable than previously reported. Among horses with TBI, persistent recumbency and fractures involving the basilar bones were associated with a poor prognosis.
Procedure—Lidocaine hydrochloride (loading infusion, 1.3 mg/kg during a 15-minute period [87.5 μg/kg/min]; maintenance infusion, 50 μg/kg/min for 60 to 90 minutes) was administered IV to dorsally recumbent anesthetized horses. Blood samples were collected before and at fixed time points during and after lidocaine infusion for analysis of serum drug concentrations by use of liquid chromatography-mass spectrometry. Serum lidocaine concentrations were evaluated by use of standard noncompartmental analysis. Selected cardiopulmonary variables, including heart rate (HR), mean arterial pressure (MAP), arterial pH, PaCO2, and PaO2, were recorded. Recovery quality was assessed and recorded.
Results—Serum lidocaine concentrations paralleled administration, increasing rapidly with the initiation of the loading infusion and decreasing rapidly following discontinuation of the maintenance infusion. Mean ± SD volume of distribution at steady state, total body clearance, and terminal half-life were 0.70 ± 0.39 L/kg, 25 ± 3 mL/kg/min, and 65 ± 33 minutes, respectively. Cardiopulmonary variables were within reference ranges for horses anesthetized with inhalation anesthetics. Mean HR ranged from 36 ± 1 beats/min to 43 ± 9 beats/min, and mean MAP ranged from 74 ± 18 mm Hg to 89 ± 10 mm Hg. Recovery quality ranged from poor to excellent.
Conclusions and Clinical Relevance—Availability of pharmacokinetic data for horses with gastrointestinal tract disease will facilitate appropriate clinical dosing of lidocaine.