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)