ANESTHESIA IN POTBELLIED PIGS
by Etta M. Weertz, DVM, MS and
Anne E. Wagner, DVM, MS
Introduction
In an attempt to better understand successful anesthesia protocols for
potbellied pigs, the following will serve as a review of an article from the
Compendium On Continuing Education Of The Practicing Veterinarian, Vol.
17(3), March 1995 entitled Anesthesia in Potbellied Pigs. The authors, Drs.
Wertz and Wagner, are Diplomates of the American College of Veterinary
Anesthesiology and are affiliated with the Department of Clinical Sciences,
College of Veterinary Medicine and Biomedical Sciences, Colorado State
University, Fort Collins Colorado. This is a very technical article written
for veterinarians that I have summarized as best I can for the lay audience.
Presurgical Considerations
Any pig requiring sedation must have a physical exam to determine the
patient's physiological status and anesthetic risk. A decision based on the
results of this exam will determine what anesthetic protocol is appropriate.
Food and water are withheld from the patient dependent upon the age of the
pig, but twelve hours is a good rule of thumb for food, and four to six hours
for water. It is important to handle the pig gently. Avoid excitement and
keep stress to a minimum. Use correct restraint techniques to reduce the
chance of injury.
Preanesthetic Medications
Preanesthetic tranquilization or sedation is difficult to achieve in
pigs. The drugs most commonly used before administration of an anesthesia
were discussed for their merits and shortcomings, with proper dosages
indicated. These drugs include Acepromazine, Xylazine, Diazepam, Fentanyl
citrate and droperidol, and Azaperone.
GENERAL ANESTHESIA
Induction
There are three techniques available to induce general anesthesia in
pigs.
1. intravenous injection
2. deep intramuscular injection
3. inhalant anesthetics (mask administration)
Intravenous injection is not recommended because the vein is often too
small and too fragile for administration of intravenous agents.
Intramuscular injection of anesthetic drugs does not seem to cause undue
stress in the patient; however, absorption of the drug is slow, therefore
causing the onset of drug action to be prolonged with its effect often less
pronounced.
Induction of anesthesia by face mask administration of inhalant
anesthetics may be the best option. Isoflurane is recommended for two
reasons: low blood-gas coefficient and rapid induction. Halothane, another
inhalant anesthetic, has a high blood-gas coefficient and induction time may
be slightly longer. Methoxyflurane is not recommended because of its high
blood-gas coefficient, causing prolonged and stormy induction. There is a
slight chance that malignant hyperthermia may occur during anesthesia.
Malignant hyperthermia is related to porcine stress syndrome which is an
acute death syndrome in pigs occurring usually after transportation,
fighting, exercise, or even high environmental temperature. Signs include
increasing dyspnoea (labored or difficult breathing), tremor, and stiffness,
severe hyperthermia, and a rapid onset of rigor mortis after death. The
incidence of malignant hyperthermia, however, is very low and it is believed
that due to the potbellied pig's genetic makeup, this syndrome is minimized.
Tracheal Intubation
Tracheal intubation refers to the passage of an endotracheal tube for
the purposes of anesthesia, resuscitation, or external control of respiration
for any other reason. With all inhalant anesthetics, tracheal intubation is
recommended. This protects the airway and allows a means of ventilation.
Maintenance
Maintenance refers to keeping the patient correctly anesthetized for the
duration of a procedure. That is not supplying more anesthesia than required
or too little, but maintaining the patient at the appropriate level of
sedation.
If parenteral (injectable) drugs are used, less inhalation anesthesia is
required. Conversely, if no parenteral agents are administered, higher
levels of inhalation anesthesia are necessary. Because the depth of
anesthesia may be changing during a procedure, it is recommended that
anesthetic depth be monitored.
Support and Monitoring
Throughout anesthesia many functions need to be monitored. These
include: eye signs (difficult to interpret in pigs), cardiac and respiratory
function, breathing, body temperature, blood pressure, ventilation and pulse.
Recovery
To accommodate a smooth recovery from anesthesia, the pig patient should
be placed on his or her side in a warm, dimly lit cage with good footing.
Body temperature needs to be monitored and if hypothermia occurs, it should
be treated. The endotracheal tube should not be removed until the patient
has a strong swallowing reflex. Various pain-killing drugs and dosages to
relieve postsurgical distress were discussed .
"Recovery from anesthesia is usually of short duration when only
inhalation agents have been used. When parenteral agents have been used for
induction, the recovery time is generally prolonged because the drugs must be
metabolized and eliminated."
Closing Comments
Hopefully by spreading the word on appropriate drug protocols for
potbellied pigs we will see a decrease in the number of pigs experiencing
stormy recoveries from anesthesia as well as upset, scared-to-death pig
owners. What I have found to be the common consensus among pet owners is
that if isoflurane is used alone, the pig recovers very quickly and without
incident. From talking with my pig anesthesiologist, however, he cautions
that the veterinarian doing the procedure must feel comfortable with the drug
protocol he knows and chooses to use. If your vet does not use isoflurane
and this is what you prefer, it would be wise to find a veterinarian who
routinely uses isoflurane as a means of sedation.