Your Pet is Going to be Anesthetized...
This information is not meant to be a substitute for veterinary care.
Always follow the instructions provided by your veterinarian.
Before the anesthetic procedure
A thorough history of current and past medical problems can provide valuable
information about your pet’s physical condition. A history of poor ability to
exercise may indicate abnormal heart or lung function, an important
consideration when planning an anesthetic procedure. Physical examination may
reveal abnormalities of the heart or lungs that may require further evaluation
such as an electrocardiogram (ECG), chest x-rays, or heart ultrasound prior to
performing general anesthesia. Many anesthetic drugs affect blood flow to major
organs and are inactivated by the liver. Your veterinarian may evaluate a blood
sample for anemia and for kidney and liver function prior to deciding which
anesthetic technique to use.
There are many types of anesthetic regimes including the use of drugs that
are injected into a vein or muscle or inhalant drugs that are breathed in and
out of the body. Your veterinarian will select the anesthetic regime based on
the health of your pet and on the type of surgical procedure to be performed.
Many anesthetic techniques involve the administration of a sedative or
tranquilizer before the anesthetic agent is given. Tranquilizers and sedatives
can allow for less of the general anesthetic to be used. pre-anesthetic sedation
may calm a pet excited by unfamiliar surroundings. Excited animals may require
higher doses of general anesthetics and excitement may predispose to development
of an irregular heart rhythm (cardiac arrhythmia). pre-anesthetic sedation may
also make recovery from anesthesia smoother.After pre-anesthetic sedation, an
intravenous (IV) catheter is placed into a vein in either a front or hind limb,
or occasionally in the neck. An IV catheter is the patient's lifeline while
(s)he is under the effects of general anesthesia. Through the IV catheter your
veterinarian will have ready access to your pet’s blood stream to administer
fluids and other drugs during surgery. To prevent life threatening bacterial
infections, it is important that the skin overlying the catheter site be clipped
of fur and scrubbed with a surgical disinfectant.
General anesthesia is often begun by giving a short-acting anesthetic agent
IV. As soon as the pet loses consciousness, a soft plastic tube (endotracheal
tube or ET tube) is inserted into the windpipe and is connected to an anesthesia
machine. The anesthesia machine is used to deliver an inhalant anesthetic in
oxygen and other gases. Many anesthetic drugs can depress breathing; having an
ET tube in place allows the veterinarian to assist or control breathing if it
becomes necessary. The loss of consciousness that occurs during anesthesia is
often accompanied by loss of the ability to cough and gag. In awake animals,
coughing and gagging are protective reflexes which prevent inhaling stomach
contents or other foreign materials into the lungs. Insertion of a proper size
ET tube prevents inhalation of stomach contents into the airways and lungs
At the completion of the surgical procedure, the concentration of the
anesthetic that the animal is breathing is reduced and the animal slowly regains
consciousness. When the pet regains its swallowing reflexes, the ET tube is
removed and the patient is monitored until it is fully conscious.
Monitoring General Anesthesia
There are several methods by which the pet’s response to anesthesia and
surgery can be monitored during the procedure. Close monitoring during
anesthesia allows for early recognition and correction of problems.
Vital signs such as heart rate, respiratory rate, and blood pressure can be
monitored using specialized devices.
Rapid-acting, anesthetic drugs are easier to control if they are
continuously administered. The anesthetic is “titrated” to achieve the
desired level of anesthesia and analgesia. In other words, most general
anesthetics are "dosed to effect".
The animal's depth of anesthesia is determined by evaluating reflexes,
muscle tone, and response of vital signs to surgical stimulation. If an
animal is judged to be too light for the surgical procedure being performed,
an increased amount of anesthetic is administered. Conversely, if the
patient is judged to be in an excessively deep plane of anesthesia, the
amount of anesthetic administered is decreased.
Modern day inhalant anesthetics are a tremendous improvement over older
anesthetics. Inhalant agents are those that are breathed in and out rather than
being injected into a blood vessel or muscle. While the newer anesthetics are
"kinder" to an animal's organ systems, even the “safest” anesthetics are
extremely potent and potentially lethal.
Newer anesthetics such as Isoflurane are less likely to aggravate a
pre-existing abnormal heart rhythm. Additionally, inhalation agents such as
Isoflurane enter and exit the brain rapidly, allowing for a rapid onset of and
recovery from anesthesia.
Some think of general anesthesia as a relaxing sleep. It is probably much more
accurate to compare general anesthesia to a period of very strenuous exercise.
Just as young, healthy animals are more able to exercise vigorously, they are
more able to tolerate the depression in heart function caused by general
anesthesia because they have such great cardiovascular reserve. Older or
debilitated animals have less cardiovascular reserve and may have less tolerance
for general anesthesia. Older or debilitated animals often recover from general
anesthesia and surgery more slowly than a young patient, in part because of
their decreased reserve.
Breed Sensitivities to General Anesthesia
After general anesthesia, animals are likely to be affected by the
anesthetic drugs for several days.
An animal may exhibit behavioral changes for several days after general
anesthesia. They may act as if they do not recognize familiar surroundings,
people or other animals. Behavioral changes after general anesthesia are
extremely common; fortunately they usually resolve within a few days. Do not
leave young children unattended with an animal that has just recovered from
general anesthesia no matter how trustworthy that animal normally is. Remember,
your pet has been through a lot and probably won't fully recover and be
himself/herself for several days. There are reports of normally well-behaved
dogs returning home after surgery and anesthesia and biting young children for
no apparent reason.
The pet’s ability to control its body temperature may be affected during the
recovery period. Many anesthetics alter the temperature set point in the brain
and cause blood vessels in the skin to dilate promoting heat loss. Conversely,
an animal's natural cooling mechanisms may be unable to adequately respond to
increases in environmental temperature. For the first few days after general
anesthesia, it is recommended to keep your pet in a warm, though not overly hot
room. Cold weather breeds such as Malamutes and Huskies tend to retain heat
easily and a cooler environment may be more appropriate for these breeds.
Obese animals often have delayed recoveries. Most general anesthetics are
very fat soluble so the greater the amount of body fat and the longer the animal
is anesthetized, the greater amount of anesthetic agent that will be absorbed
into body fat. Anesthetic taken up by body fat will leach back into an animal’s
blood for days or even weeks after anesthesia. This low residual amount of
anesthetic may continue to affect an animal's behavior for several days.
Purebred dogs have been selectively bred to perform specific tasks such as
retrieving or racing or have been bred to develop specific physical
characteristics. Often, less desirable traits emerge as a result of selective
A common question posed to veterinarians is about the "sensitivity" of a
particular breed of dog or cat to anesthetic drugs. This is a difficult question
to answer, as there are few scientific studies that have evaluated the
sensitivities of different breeds of animals to anesthetics. Many of the
reported breed sensitivities are based on the clinical experience of
veterinarians. Many giant breed dogs seem to require less of a pre-anesthetic
sedative (a smaller dose per unit of body weight) than miniature or toy breeds.
The reason for this apparent difference is unclear.
It has been documented that sight hound breeds of dogs are more sensitive
to some of the ultra short-acting thiobarbiturate induction drugs. The
administration of thiobarbiturates for induction of anesthesia in sight
hound breeds has been associated with a slower recovery from anesthesia. The
reason for this breed sensitivity is unclear at this time but may be related
to a difference in liver metabolism of the drug and/or differences in body
fat. When sight hound breeds are to be anesthetized, it has been recommended
that non-thiobarbiturate induction drugs be used to prevent a prolonged
recovery from anesthesia.
Within the same breed, individual animals respond to the same anesthetic in
differing degrees. Vigilant monitoring of vital signs during general
anesthesia will enable the veterinarian to recognize and respond to
life-threatening changes in heart and lung function.
A patient who displays an abnormal response to any drug (anesthetic or not)
should be monitored carefully if the situation dictates that the same drug
be re-administered at a later date.
The Perfect Anesthetic Drug
Preparing your Pet for General Anesthesia
The perfect anesthetic is a drug that produces no heart or lung depression,
provides adequate analgesia, provides excellent muscle relaxation, is not
metabolized by the patient, is not toxic, and is readily reversible. Although
the general anesthetics in use in veterinary anesthesia today are great
improvements compared to the anesthetics of yesteryear, they still fall far
short of the perfect agent.
Probably, the most desirable general anesthetic for a young, healthy dog is
the one your veterinarian is most familiar with. There are a great many
anesthetic drugs available to today's practicing veterinarian, however most
practitioners use a few carefully chosen anesthetics with which they have the
most experience and the most confidence. Your veterinarian's experience in the
use of a certain anesthetic drug often will more than offset one or two
undesirable properties of a general anesthetic agent.
There are several steps that a pet owner may take to help your veterinarian
plan for a successful general anesthesia and surgery.
- Communicate concerns about your pet’s health to your veterinarian prior
to scheduling surgery. Any signs of exercise intolerance, weight loss, a
recent change in urination or defecation, and mental alertness are
particularly informative and may require further diagnostic workup.
- Withhold all food from pets scheduled for elective surgery for at least
12 hours prior to arriving at your veterinarian's clinic. The presence of
food in a pet's stomach will greatly increase the likelihood of aspiration
of food into the lungs, should your pet vomit during induction of general
anesthesia. Usually water is NOT with held but check with your
- Balance your desire to keep your pet in show condition with the
knowledge that the risk of infections increases greatly if the skin
overlying the IV catheter site is not properly disinfected prior to IV
catheter placement. Proper disinfect ion requires clipping of the fur
overlying a suitable vein.
- Follow your veterinarian's discharge instructions. If you have small
children at home, be careful not to leave your dog alone with the small
child even for just a few minutes. Remember, all animals recovering from all
general anesthetics may react unpredictably for several days.
This Pet Health Topic was written by:
Robert D. Keegan, DVM, Diplomate, ACVA
Department of Veterinary Clinical Sciences
Washington State University
A longer version of this topic has been published in: The AKC Gazette
Washington State University assumes no liability for injury to you
or your pet incurred by following these descriptions or procedures.
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