Veterinary Anesthesia and Monitoring Equipment
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SurgiVet, Inc.
N7 W22025 Johnson Road, Suite A
Waukesha, WI 53186 USA
Phone: 262-513-8500 Fax: 262-513-9069
www.surgivet.com
3. What is the most important thing to monitor during anesthesia?
You simply cannot choose one thing to monitor, because every variable only tells you
one piece of information about an animal. It is as if the animals are a puzzle and each variable
we monitor is one piece. Perhaps one day we will have a monitor, which will give a certain
score for cardiac output, oxygenation and brain function and add them together to display one
"score" which tells us how our patient is doing. But at the present time, we have to try to
evaluate cardiovascular function, oxygenation, ventilation and depth of anesthesia (ie, CNS
function) separately.
4. What drugs cause problems for monitors?
Many drugs will affect the ability of noninvasive monitors to function, since they affect
peripheral vessels. For instance, the alpha-2 agonists (xylazine, medetomidine) cause peripheral
vasoconstriction, which may prevent the pulse oximeter from finding a peripheral capillary bed.
Ketamine may cause more difficulty for non-invasive blood pressure monitors because it
may elevate diastolic pressure; this makes the pulse pressure (difference between systolic and
diastolic) smaller. It is unfortunate but true, that these commonly used injectable anesthetics
make monitoring more difficult.
5. What are the causes for changes in blood pressure during anesthesia?
Most anesthetic drugs produce cardiovascular depression, which tends to decrease blood
pressure. In most cases, this depression is in a dose-dependent manner, which is why turning
down the vaporizer (hence decreasing the dose of an inhalant) increases blood pressure. If the
animal has "read the book" and is responding in a normal physiological manner as blood
pressure decreases, heart rate will tend to increase to compensate. Under anesthesia, these
compensatory mechanisms may be blocked. It is possible to see a decrease in heart rate with a
decrease in blood pressure. In this case, cardiovascular depression may be more severe and this
decrease should be addressed. There are many other causes for a decrease in blood pressure,
which may include increasing depth of anesthesia, blood or volume loss, hypothermia or
decreased surgical stimulation.
