Objective—To determine the relationship between
bispectral index (BIS) and minimum alveolar concentration
(MAC) multiples of sevoflurane in cats.
Animals—8 domestic cats.
Procedure—Each cat was anesthetized twice with
sevoflurane. First, the MAC of sevoflurane for each
cat was determined by use of the tail clamp method.
Second, cats were anesthetized with sevoflurane at
each of 5 MAC multiples administered in random
order. Ventilation was controlled, and after a 15-
minute equilibration period at each MAC multiple of
sevoflurane, BIS data were collected for 5 minutes
and the median value of BIS calculated.
Results—The mean (± SD) MAC of sevoflurane was
3.3 ± 0.2%. The BIS values at 0.5 MAC could not be
recorded as a result of spontaneous movement in all
8 cats. The BIS values at 2.0 MAC were confounded
by burst suppression in all 8 cats. Over the range of
0.8 to 1.5 MAC, BIS values decreased significantly
with increasing end-tidal sevoflurane concentrations.
Mean (± SD) BIS measurements were 30 ± 3, 21 ± 3,
and 5 ± 2 at 0.8, 1.0, and 1.5 MAC, respectively.
Conclusions and Clinical Relevance—Values of BIS
are inversely and linearly related to end-tidal sevoflurane
concentrations in anesthetized cats, and BIS may be a
useful predictor of CNS depression in this species. The
consistently low BIS values recorded in this study suggest
that clinical BIS end points used to titrate anesthetic
agents in humans may not be applicable to cats.
( Am J Vet Res 2004;65:93–98)
Objective—To evaluate the cardiovascular effects of
the α2-adrenergic receptor agonist medetomidine
hydrochloride in clinically normal cats.
Animals—7 clinically normal cats.
Procedure—Cats were anesthetized with isoflurane,
and thermodilution catheters were placed for measurement
of central venous, pulmonary, and pulmonary
capillary wedge pressures and for determination
of cardiac output. The dorsal pedal artery was
catheterized for measurement of arterial blood pressures
and blood gas tensions. Baseline variables were
recorded, and medetomidine (20 µg/kg of body
weight, IM) was administered. Hemodynamic measurements
were repeated 15 and 30 minutes after
Results—Heart rate, cardiac index, stroke index, ratepressure
product, and right and left ventricular stroke
work index significantly decreased from baseline after
medetomidine administration, whereas systemic vascular
resistance and central venous pressure
increased. However, systolic, mean, and diastolic
arterial pressures as well as arterial pH, and oxygen
and carbon dioxide tensions were not significantly different
from baseline values.
Conclusions and Clinical Relevance—When administered
alone to clinically normal cats, medetomidine (20
µg/kg, IM) induced a significant decrease in cardiac
output, stroke volume, and heart rate. Arterial blood
pressures did not increase, which may reflect a predominant
central α2-adrenergic effect over peripheral
vascular effects. (Am J Vet Res 2001;62:1745–1762)
Objective—To evaluate the effects of medetomidine
on dynamic left ventricular outflow tract (LVOT)
obstruction in cats with left ventricular hypertrophy.
Animals—6 domestic shorthair cats with echocardiographic
evidence of dynamic LVOT obstruction.
Procedure—Cats were restrained in lateral recumbency,
and baseline M-mode and Doppler echocardiographic
examinations were performed. An ECG
was recorded continuously, and blood pressure was
measured indirectly with Doppler instrumentation.
Medetomidine (20 µg/kg [9.1 µg/lb]) was then administered
IM, and examinations were repeated 15 minutes
Results—Significant decreases in heart rate, LVOT
velocity, and the LVOT pressure gradient were documented
following medetomidine administration.
After adjusting for the effects of heart rate by
ANCOVA, there were no significant differences in
any other systolic or diastolic indices of left ventricular
Conclusions and Clinical Relevance—Results suggest
that administration of medetomidine to cats with
dynamic LVOT obstruction may result in elimination of
outflow tract obstruction; medetomidine may be a
suitable sedative and analgesic agent in this subpopulation
of cats. (J Am Vet Med Assoc 2002;221:1276–1281)
Objective—To compare the effects of xylazine bolus versus medetomidine constant rate infusion (MCRI) on cardiopulmonary function and depth of anesthesia in dorsally recumbent, spontaneously breathing, isoflurane-anesthetized horses.
Design—Prospective, randomized crossover study.
Animals—10 healthy adult Standardbreds.
Procedures—Horses were premedicated with xylazine or medetomidine IV. Anesthesia was induced with diazepam and ketamine and maintained with isoflurane for 150 minutes. For the xylazine treatment, end-tidal isoflurane concentration was maintained at 1.7%, and xylazine (0.2 mg/kg [0.09 mg/lb], IV) was administered as a bolus at the end of anesthesia. For the MCRI treatment, end-tidal isoflurane concentration was maintained at 1.4%, and medetomidine (0.005 mg/kg/h [0.0023 mg/lb/h], IV) was infused throughout anesthesia. Physiologic data (ie, heart rate, respiratory rate, rectal temperature, bispectral index, and electromyographic values) were compared between treatments with xylazine bolus versus MCRI.
Results—Heart rate was lower, but mean arterial blood pressure was higher from 20 to 40 minutes with MCRI treatment, compared with conventional treatment with xylazine. Respiratory rate and rectal temperature were greater with MCRI treatment. Bispectral index was lower with MCRI treatment from 80 to 150 minutes, and electromyographic values were lower with MCRI treatment from 30 to 150 minutes.
Conclusions and Clinical Relevance—In isoflurane-anesthetized horses, premedication with medetomidine followed by administration of medetomidine as a constant rate infusion resulted in decreased heart rate, higher arterial blood pressure from 20 through 40 minutes after induction of anesthesia, and better preserved body temperature, compared with conventional treatment with xylazine. Greater depth of anesthesia and muscle relaxation were seen with MCRI treatment, despite the lower isoflurane concentration.
Objective—To compare the effect of xylazine bolus versus medetomidine constant rate infusion (MCRI) on serum cortisol and glucose concentrations, urine production, and anesthetic recovery characteristics in dorsally recumbent, spontaneously breathing, isoflurane-anesthetized horses.
Design—Prospective, randomized crossover study.
Animals—10 healthy Standardbreds.
Procedures—Horses were premedicated with xylazine or medetomidine IV. Anesthesia was induced with diazepam and ketamine and maintained with isoflurane for 150 minutes. For the xylazine treatment, end-tidal isoflurane concentration was maintained at 1.7% and xylazine (0.2 mg/kg [0.09 mg/lb]), IV) was administered as a bolus at the end of anesthesia. For the MCRI treatment, end-tidal isoflurane concentration was maintained at 1.4% and medetomidine (0.005 mg/kg/h [0.0023 mg/lb/h], IV) was infused throughout anesthesia. Serum cortisol and glucose concentrations were measured before, during, and after anesthesia. Urine specific gravity and volume were measured during anesthesia. Unassisted anesthetic recoveries were recorded by a digital video camera for later evaluation by 2 observers who were blinded to treatment.
Results—Serum cortisol concentration was lower and serum glucose concentration was higher with MCRI treatment, compared with xylazine treatment. Time to sternal recumbency was longer with MCRI treatment, but no difference was seen between treatments for times to extubation, first movement, or standing. Objective (mean attempt interval) and subjective (visual analog score) recovery scores were significantly better with MCRI treatment, compared with xylazine treatment.
Conclusions and Clinical Relevance—In isoflurane-anesthetized horses, premedication and administration of medetomidine as a constant rate infusion resulted in decreased serum cortisol concentration, increased serum glucose concentration, and superior anesthetic recovery characteristics, compared with conventional treatment with xylazine.