Pet owners are often very anxious about
veterinary procedures that involve anesthesia. This handout attempts to
alleviate some of these concerns.
The word anesthesia comes
from the Greek meaning "lack of sensation". Anesthesia is accomplished by
administering drugs that depress nerve function. With general anesthesia, the
patient is made unconscious for a short period. During this unconscious state,
there is muscular relaxation and a complete loss of pain sensation. Other types
of anesthesia include local anesthesia such as numbing a localized area of skin
or a tooth, and spinal anesthesia, such as an epidural block, that results in
anesthesia of a particular part of the body.
What are the risks of anesthesia?
There is always risk of an adverse
reaction when we use any anesthetic agent, no matter whether it is for a minor,
short-term sedation or for a complete general anesthesia lasting several hours.
It is estimated that approximately 1 in 100,000 animals will have some sort of
reaction to an anesthetic agent. These reactions may range from mild swelling at
the site of injection or a mild decrease in cardiac output, to a full-blown
episode of anaphylactic shock or death. However, many experts put the risk of
anesthetic death as less than the risk of driving to and from the hospital to
have the anesthetic procedure.
"It is estimated that approximately
1 in 100,000 animals will have some sort of reaction to an anesthetic
Another potential danger associated with
anesthesia arises if the cat is not properly fasted prior to anesthesia.
Anesthetized patients lose the normal reflex ability to swallow; during
swallowing, the epiglottis, a cartilage flap that closes over the entrance to
the windpipe, prevents food or water from entering the lungs. If there is food
in the stomach, the cat could vomit while under anesthesia or in the early
post-anesthetic period. If vomiting occurs before the swallowing reflex occurs,
the vomited material can be aspirated or enter into the lungs, causing
aspiration pneumonia, a potentially life-threatening condition.
Other rare complications of anesthesia
include organ system failure such as kidney liver or heart failure, visual
impairment, clotting disorders and seizures. We will take every precaution to
minimize these risks during your pet's anesthesia. Only when the benefits
outweigh the risks will we perform anesthesia on your pet.
What can be done to minimize the risks?
"Blood tests will increase the
chance of detecting a hidden problem that could prove to be life
physical examination, preoperative blood and urine tests and radiographic
examination may reveal clinical or sub-clinical problems. Certain medical
conditions will increase the risk of having an anesthetic complication. These
conditions include heart, liver or kidney disease, diabetes mellitus, anemia,
dehydration, and certain infectious diseases such as heartworm disease. Blood
tests will increase the chance of detecting a hidden problem that could prove to
be life threatening. In older animals, chest radiographs are recommended to
ensure there is no pre-existing pathology in the heart or lungs that might
increase the risk of an adverse reaction.
Immediate intravenous access for
emergency drug administration is one of the most important factors in the
successful treatment of cardiovascular or respiratory failure in either the
awake or the anesthetized patient. By placing an intravenous (IV) catheter and
line before anesthesia, your veterinarian can ensure that this lifeline is
already in place, should the need arise. Anesthetics, fluids and emergency drugs
can be administered through the IV line.
"All general anesthesia patients
should receive intravenous catheterization and fluid therapy."
fluids help maintain blood pressure in the anesthetized patient and will replace
lost fluids (during surgery, fluids are lost through evaporation from body
cavity surfaces, through bleeding, and in any tissues that are being removed).
Upon completion of the procedure, intravenous fluid therapy speeds the recovery
process by diluting the anesthetic agents circulating in the blood stream and by
enhancing their metabolism and elimination through the liver and kidneys.
Patients that receive IV fluid therapy generally wake up faster than those that
do not. Additionally, studies have shown that 0.9 - 2% of all patients that
receive general anesthesia will develop kidney dysfunction or failure 7-14 days
after anesthesia. This risk is significantly reduced in patients that receive
peri-operative intravenous fluid therapy. Although 98% of all pets will have no
problem, your veterinarian's goal is to eliminate that unknown 2%. For these
reasons, all general anesthesia patients should receive intravenous
catheterization and fluid therapy.
You should ensure that your pet's
complete medical history is available to your veterinarian, especially if your
pet has been seen at another veterinary clinic. Before
anesthetizing your cat, your
veterinarian needs to know about any medications or supplements that your cat
has received in the past few weeks, any pre-existing medical conditions, any
known drug reactions, the results of previous diagnostic tests, and whether the
cat has undergone any anesthetic or surgical procedures in the past. Other
useful information includes the pet's vaccine status and reproductive status
(i.e. when was its last estrus or heat cycle).
Why do I have to sign an anesthetic
It is important that you fully
understand what will happen to your pet, and that you acknowledge that you
understand the risks. Usually, the form will also include consent to perform
surgery or other specified diagnostic testing, and will provide an estimate of
the expected costs of the procedures. In many areas, the veterinarian is
required by their regulatory organization to obtain written consent from the
client prior to performing anesthetic procedures.
Can you describe a typical anesthesia?
All anesthesia patients are weighed on
admission and are given a thorough pre-anesthetic examination, which includes an
examination of the chest, palpation of the
abdomen, and assessment of the gums
(checking for hydration status and evidence of good circulatory status. After
reviewing the medical history, additional diagnostics such as blood or urine
testing, blood pressure, electrocardiogram (ECG) or x-rays of the chest or
abdomen may be performed prior to administration of any anesthetic drugs.
"With balanced anesthesia, the
patient receives a combination of sedatives and anesthetic agents that is
suited to its individual needs."
In the great majority of cases, a
technique called 'balanced anesthesia' is used. With balanced anesthesia, the
patient receives a combination of sedatives and anesthetic agents that is suited
to its individual needs. The most common combination is a pre-anesthetic
sedative and analgesic combination that is administered by injection, followed
by an induction agent that is also administered by injection; the anesthetized
state is maintained with an anesthetic gas mixed with oxygen. In order to ensure
accurate delivery of the gas anesthetic, a breathing tube, called an
endotracheal tube, is inserted into the windpipe or trachea. In addition to
delivering the gas to the lungs, the endotracheal tube seals off the airway so
that the patient does not accidentally aspirate fluids or other foreign material
into the lungs while unconscious and unable to swallow.
How do you monitor an anesthetized cat?
Anesthetic monitoring in a veterinary
hospital is similar to that found in any human hospital. Below is a list of
common veterinary anesthesia monitoring equipment and personnel:
"The Surgery Assistant is the most
important monitor during an anesthetic procedure."
Surgery Assistant is
the most important monitor during an anesthetic procedure. This professional
staff member is trained to monitor the patient throughout the entire procedure,
from induction until recovery. The assistant adjusts the anesthetic levels
according to the patient's vital signs and ensures that the patient remains
stable throughout the procedure.
abbreviated as ECG (or EKG, referring
to the original German term), shows the rate and pattern of the heartbeat. It
will detect and show abnormal heartbeats called arrhythmias. If
abnormal heartbeats are observed, the anesthetist will make appropriate changes
in anesthesia and/or emergency medications.
The Heart Rate Monitor measures
the number of heartbeats per minute. Heart rate must be maintained within a
certain range. The depth of anesthesia and surgical stimulation can both affect
heart rate. By monitoring heart rate, increases or decreases can be detected
early and anesthetic adjustments made quickly, resulting in smoother anesthesia
for our patients.
The Blood Pressure Monitor measures
the systolic (when the heart contracts or pumps) and occasionally the diastolic
(when the heart relaxes or refills) blood pressure. Coupled with other
monitoring equipment, this gives detailed information on the cardiovascular
status of the patient.
The Respirometer measures
the number of breaths per minute.
The Core Body Temperature is
monitored, especially during a prolonged surgery, by inserting a temperature
probe into the esophagus or the rectum. Either too low or too high a body
temperature can cause dangerous complications. Maintenance of normal body
temperature is especially important in small or pediatric patients.
Pulse Oximetry may
be used to monitor the amount of oxygen in the patient's blood (Sp02) and the
pulse rate. This instrument should always be used in conjunction with other
pieces of monitoring equipment.
The End-tidal C02 Monitor is
often used in conjunction with a pulse oximeter. This device measures the amount
of expired C02 and helps determine if the patient is receiving adequate oxygen
How long will it take my cat to recover
With today's anesthetics, many of which
are reversible, your pet should be almost completely normal by the time of
discharge, although many pets will sleep more for twelve to twenty-four hours
after anesthesia. If your pet appears to be unusually sluggish or you cannot
arouse him/her easily, contact the hospital immediately to receive specific