How many of you have had an experience where either general or local anesthesia was used in order to allow a painful procedure to be performed? Would you have preferred to go without the anesthesia? I seriously doubt it! Anesthesia is one of the greatest innovations in recent medical history allowing the discipline of surgery to be born as well as being useful in a variety of other situations. However, many people are uncomfortable with the “loss of control” that general anesthesia represents. The brain is “asleep” and there is the fear that it will not “wake up” again leaving the patient damaged or deceased. In addition, many people are afraid of surgical procedures because they fear that mistakes will be made during the surgery leading to further problems, or again, death. Fortunately, in this day and age, with improved and safe anesthetic agents, specialized anesthetic and surgical equipment and the ever-expanding knowledge of the medical/veterinary profession, the chances of serious problems with anesthesia or surgery have been greatly reduced.
As with any part of your pet's (or your own) care, the better educated you are about a subject, the more effectively you will be able to make an informed decision. Anesthesia is the subject that is probably the most frightening to rabbit owners because of misinformation, myths and possibly some previous unpleasant experiences. If anesthesia is not allowed, then obviously all surgical and some diagnostic procedures become impossible. In the presentation today, we hope to arm you with not only good information to increase your understanding of what is happening when your pet undergoes anesthesia/surgery, but also give you guidelines to use when communicating with your veterinarian on these important subjects. Remember that ONLY YOU can take charge of your pet's health, no one else is going to do it for you. You must be willing to ask the questions, feel comfortable with your decisions and not wait for others to anticipate any difficulties you are having.
Myths About Rabbits
Rabbits are Fragile
While it is true that rabbits have unique requirements that may be different than those of a dog or cat, they are not “fragile”. We have found over the last 25 years of practice that rabbits can undergo most medical procedures as successfully as any other mammal patients. This myth is primarily based on the fact that in the past owners often didn't recognize that their pet was ill until it was critical. By the time the veterinarian was involved, it was often too late to reverse the process. In addition, the methods and medications used in rabbits in the past were not always appropriate due to our lack of knowledge of pet rabbit requirements. The successful treatment and survival rate of our rabbit patients has more than tripled over the last 15 years due to better informed owners who recognize disease more quickly and improved and more appropriate treatment options.
Rabbits are “High Risk” Anesthetic/Surgical Patients
We do not feel that rabbits are at higher risk with anesthesia or surgery than other patients that we see are. The one exception is that rabbits are more sensitive to surgery involving the gastrointestinal tract that will be discussed in the surgery section of this paper. The “high risk” myth originated in the past from situations where veterinarians did not properly evaluate, prepare or monitor their rabbit patients during anesthetic and surgical procedures. In addition, the anesthetic agents available for rabbits in the past were not as safe as what we have now. Properly evaluated and monitored rabbit patients make excellent anesthetic and surgical candidates.
Effects of Extreme or Prolonged Stress on Rabbits
The main purpose of anesthesia is to reduce or relieve pain. Pain can represent a powerful stress factor in a rabbit's life. It is therefore helpful to understand what happens to a rabbit when it undergoes extreme or prolonged stress in order to appreciate the positive qualities that anesthesia can have. Studies in rabbits indicate that several things can happen under extreme or prolonged stress including; a drop in body temperature, a drop in blood pressure, damage to the kidneys, loss of appetite, stomach ulcers, cardiomyopathy (heart muscle disease) and ultimately death. Anesthesia can alleviate these problems by relieving pain, which is a stressor.
DEFINITION: Anesthesia is achieved when there is a loss of sensation to either a part or all of the body. General anesthesia renders the patient completely unconscious. Sedation is similar to general anesthesia but the patient remains semi-conscious.
Anesthesia and sedation are used in a variety of situations in veterinary practice including diagnostic sample collection (X-rays, blood work, urine, biopsies), examination (calming difficult to handle or painful animals, thorough examination of the oral cavity), and surgical procedures.
TYPES OF ANESTHESIA
- Local or topical anesthesia is applied on top of or injected into the skin to remove the sensation from a small area. The anesthesia does not extend more than the thickness of the skin nor wider than the area that the anesthetic is applied. The rabbit remains fully conscious. Local anesthesia might be used for minor skin surgeries or biopsies, placement of intravenous (IV) or intraosseous (IO) catheters, or for ophthalmic procedures. We commonly use a topical anesthetic in the eyes to allow flushing of the tear duct in the conscious pet.
- Regional anesthesia is where a larger and deeper area of the body is anesthetized. The anesthetic agent is injected into the spinal fluid, which numbs all sensation from that point of the spine to the back of the animal. The agent can also be injected into a specific nerve, which anesthetizes all the tissues that the nerve reaches. During regional anesthesia the rabbit remains fully conscious. This type of anesthesia has been successfully used in the rabbit, however many veterinarians are still unfamiliar with the technique.
- General anesthesia circulates through the bloodstream to all areas of the body, including the brain, and causes a complete loss of consciousness. There are basically two ways to administer general anesthetic agents, by injection or inhalation.
- Injectable anesthetics can be given IV intramuscular (IM), intraperitoneal (IP) or subcutaneously (SC). Injectable anesthetic agents are often used for short surgical procedures, (particularly those in the mouth), or used as a preanesthetic to an inhalant agent. Preanesthetic drugs are used to calm the patient to allow handling for the administration of the inhalation agent or to allow passage of an endotracheal (ET) tube. The biggest drawback to injectable anesthetics is that there is no control over the dose once it has been injected (except in the case of reversible drugs). There is tremendous variation in dosages amongst different rabbits. Injectable anesthetics are not suitable as the only anesthetic agent for prolonged surgical procedures. The recovery period varies with the agent used. In addition, some of the injectable anesthetics are not appropriate in the presence of certain disorders, such as cardiac or kidney disease. Currently, the most commonly used injectable anesthetic agents in rabbits include any of the following (some are used in combination to improve their anesthetic properties); ketamine, diazepam (Valium), butorphanol, propofol, medetomidine and opiods.
- Inhalant (gas) anesthesia is the first choice for any major surgical procedure. As mentioned, it is common to use a sedative or preanesthetic agent of some type to relax the rabbit before using an inhalant anesthesia. The anesthetic gas is administered either through a mask placed over the rabbit's face, or through an ET tube. With inhalant anesthesia the patient is connected directly to a machine that delivers the anesthetic agent in a flow of oxygen. The advantages of gas anesthesia are that the concentration of the anesthetic agent and therefore the level of anesthesia can be quickly adjusted, the patient is always connected directly to an oxygen source and recovery is usually rapid and smooth. In addition, isoflurane, the most commonly used gas anesthetic, can be used safely in rabbits with a wide variety of illnesses. Isoflurane is safe not only for the rabbit, but for the humans who are exposed to it in the surgical suite. Methoxyflurane and halothane have been used in rabbits in the past, however, they hold a higher risk of causing medical problems in humans exposed. In addition, methoxyflurane is dangerous to use on overweight rabbits.
With careful preparation and monitoring, the risks of general anesthesia in the rabbit are minimal. However, we would not be truthful if we told you there were no risks at all. Medicine is not an exact science because we are dealing with complex individuals and it is impossible to know every conceivable outcome to every situation.
The complications of general anesthesia range from temporary or intermittent changes in respiration, heart rate and blood pressure to brain damage to death. In experienced hands, anesthetic deaths are rare. The most common causes of anesthetic death include respiratory or cardiac arrest, hypothermia (low body temperature), hypovolemia (low blood volume) and embolism (blood clot). Respiratory or cardiac arrest can be caused by a variety of factors including pre-existing disease of the thorax, (including the heart or lungs), other systemic disease (particularly involving the liver and/or kidneys where anesthetics must be cleared from the body), blockage of the air passageway (blocked ET tube, regurgitation of material from stomach, blood) and overdose of the anesthetic agent(s).
Some degree of hypothermia occurs naturally during general anesthesia because the metabolic rate drops and the body cools. In addition if large areas of the internal surface of the body are exposed, more heat is lost. Anyone who has ever had general anesthesia will probably remember waking up shaking and feeling very cold. Rabbits have a small body mass compared to the surface area of the skin which allows heat to be released even more quickly than in humans. A rabbit's body temperature can drop very quickly to dangerous levels particularly if the abdominal cavity is opened or the procedure is lengthy. Hypovolemia occurs if the patient loses a critical amount of blood or other body fluids during a surgical procedure or a state of dehydration presurgically is not corrected. An embolism (blood clot), although fortunately rare, can occur anytime, particularly if the surgery involves manipulation of a large blood vessel, bone tissue or if the rabbit had a serious bacterial or fungal infection prior to the procedure.
Fortunately there are many things that can be done to greatly reduce the anesthetic risk in rabbits. Factors that increase anesthetic risk include; no presurgical physical exam, pre-existing disease (particularly respiratory, heart, liver or kidney disease, dehydration or obesity), inappropriate anesthetic agent or dose, absence of regular anesthetic monitoring, and absence of adequate postanesthetic monitoring and care.
Here are some things that the veterinary staff can do to minimize anesthetic/surgical risk:
- Perform thorough preanesthetic/surgical examination including diagnostics if appropriate.
- Stabilize/treat pre-existing conditions
- Use anesthetic agents/dosages appropriate for rabbits. Obtain accurate body weight.
- Continuously monitor the patient during the anesthetic/surgical procedure.
- Closely monitor the patient during the recovery period until awake and moving.
Now let us now go through the process of taking your rabbit in for a surgical procedure from beginning to end so you can understand what to expect.
Every rabbit that is going to undergo an anesthetic or surgical procedure should have a thorough physical examination performed. There is no exception to this rule! You would not expect your doctor to put you under anesthesia unless you had been thoroughly examined and you should not expect less for your pet. Depending on the type of procedure being suggested and the age and condition of the rabbit, your veterinarian may also suggest certain diagnostic tests. The most common tests include any of the following; a complete blood cell (CBC) count, serum biochemistries, X-rays, ultrasound, ECG and/or urinalysis. Your veterinarian can explain the reason for the tests in each case.
*Important: In situations where owners decline recommended preanesthetic/surgical diagnostics, the risk factor for the rabbit may increase because the veterinarian cannot acquire all the needed information to make an informed decision on the suitability of the patient to undergo anesthesia/surgery.
It is important to stabilize or treat any disorder present at the time of the physical examination, such as dehydration, infections, liver or kidney disorders, heart or lung disease or breathing difficulties prior to the administration of the anesthetic. The most common condition that we see that interferes with anesthesia and surgery is obesity. Overweight rabbits are always considered high-risk patients due to the possibility of concurrent liver disease (fatty liver) and respiratory problems due to the pressure of excess fat on or in the chest cavity. Unless there is a life-threatening situation that requires immediate surgery, overweight rabbits should complete a weight reduction program prior to anesthesia.
*Important: It should be noted that there are rare situations where a preexisting health condition that interferes with safe anesthesia/surgery is not detected in a rabbit. As mentioned previously, we are dealing with complex creatures and all our tests are not infallible. However the occurrence of such situations when a thorough preanesthetic evaluation is done are extremely uncommon.
Anesthetic induction is the administration of the anesthetic agent(s). Due to the nature of the rabbit gastrointestinal (GI) tract and the fact that they cannot vomit, it is not necessary to fast a rabbit prior to induction. Some veterinarians prefer to remove the food one to two hours presurgically to make sure the rabbit's mouth is clear of food. As previously discussed, your rabbit may be given preanesthetic drugs, including pain medications, prior to receiving general anesthesia. The general anesthetic is administered either by injection or by inhalation. Induction with gas anesthesia can be accomplished via an anesthetic chamber, a face mask or an ET tube. The rabbit is maintained under general inhalation anesthesia with either a face mask or ET tube.
Once your rabbit is unconscious, he or she is placed on a warm pad to help prevent heat loss. In some cases an overhead source of heat is also be used. The mouth is cleaned of any food or excessive saliva. At this time if an ET tube is going to be used, it is put in place. If an IV catheter was not placed prior to surgery, it will be placed now that your pet is unconscious. Except for short procedures in healthy animals, it is advisable to have an IV catheter in place in case emergency drugs need to be given quickly and to be able to administer fluids. Most rabbits undergoing lengthy surgical procedures will receive IV fluids to prevent dehydration and replace blood loss. It is preferable that the fluids be warmed to help maintain normal body temperature. At this time monitoring devices will be attached.
There are several parameters that are monitored during an anesthetic/surgical procedure and a variety of monitoring devices can be used.
- Respiration - Respiration can be monitored visually by an assistant, through a regular or esophageal stethoscope, by a respiratory monitor (attaches between the ET tube and the anesthetic machine to measure changes in airflow), or by a pulse oximeter (measures oxygen saturation of the blood).
- Heart Rate/Pulse - The heart rate or pulse can be monitored by a regular or esophageal stethoscope, an ECG machine, a Doppler or a pulse oximeter.
- Body Temperature - The body temperature is monitored with a rectal thermometer.
- Reflexes - Monitoring the rabbit's response to certain stimuli helps to assess the depth of anesthesia. There are several ways of doing this, but the most commonly used tests are pinching the toe and touching the eye. If the toe is pinched and the rabbit tries to pull its foot away or if the eye is touched and the rabbit tries to blink the anesthesia is too light. The rabbit may appear to be unconscious, but positive reactions to these tests indicate that it can still feel pain, so the anesthetic will be adjusted accordingly.
Once the procedure is completed your rabbit will enter the recovery period. Inhalant anesthesia will be discontinued and oxygen will be administered for a few minutes prior to disconnecting the anesthetic machine. The ET tube will be removed as your rabbit starts to show signs of awakening. Reflexes will be checked with increasingly strong responses indicating recovery from anesthesia. Your rabbit will be moved to a recovery area. It is preferable that this area be quiet but visible to the veterinary staff who is monitoring the recovery. The amount of warmth your rabbit will need during recovery will depend on the body temperature at the end of the procedure. Most rabbits need only a brief period of extra warmth until recovery. Respiration and heart rate will continue to be monitored, usually by direct observation and stethoscope, until your rabbit is fully awake.
Although this is primarily a discussion on anesthesia and surgery, we cannot leave out the important aspect of pain control in the rabbit after a painful procedure is performed. As mentioned, moderate to severe pain can represent a serious stress to the rabbit and can result in some potentially dangerous consequences. Many years past when we did not understand the full significance of pain management in rabbits, they would often survive a surgical procedure, only to die within the next 36 hours. The old cliché of 'the operation was a success, but the patient died” would apply to those situations. Some of these cases would most likely have survived if postsurgical pain had been managed thereby reducing the stress on the rabbit. You know that if you have had a painful procedure performed that you would prefer pain-alleviating medications to being uncomfortable. Rabbits in pain recover more slowly. Analgesics may not always be needed for minor procedures, but should consistently be used for all major surgeries.
The most common analgesics currently used in rabbits include butorphanol, buprenorphine and nonsteroidal anti-inflammatory drugs ( NSAIDs) such as aspirin, carprofen, diclofenac, flunixin, ibuprofen, indomethacin, ketoprofen, meloxicam, acetominophen and piroxicam. An alternative source of analgesia for chronic mild to moderate chronic pain relief is acupuncture or acupressure.
Your veterinarian should advise you on the specific signs to be aware of in your rabbit after an anesthetic/surgical procedure. Here are some general behaviors that might be observed:
- Quiet Behavior - Your rabbit may want to sleep and stay quietly in one area. The lack of activity can be caused by residual anesthetic in the body, pain, or medication. Some analgesics have sedative properties and may add to the lethargy. Check with your veterinarian about what you should expect with any drugs you are giving to your rabbit. If your pet is extremely lethargic, is crying out or appears unable to move normally and sits hunched in one spot, you should contact your veterinarian immediately.
- Poor Appetite - Your rabbit may not eat or drink at all for the first 24 hours after returning home. Analgesics may improve this situation but not completely eliminate it. You can syringe feed your pet thin slurry blenderized fresh vegetables mixed with fruit juice or canned pumpkin (not pumpkin pie filling) one to two times during this initial 24-hour period. If your rabbit still refuses to eat after 24 hours, you should contact your veterinarian immediately.
- Abnormal or Absence of Stools - Anesthetic and analgesic agents can alter the motility of the GI tract. In addition, the rabbit may have eaten poorly just prior to surgery, therefore, there may be an absence of stools for a period up to three days after anesthesia/surgery. If stools are present, they may initially be smaller than normal, misshapen or soft. This condition should clear up within three days. Watery, diarrhea should not be present and is cause for immediate concern. Please contact your veterinarian should you have any questions about your rabbit's stools or urine.
To summarize what you have learned, here are questions that you can ask your veterinarian that cover the areas of concern regarding anesthetic/surgical procedures.
- Experience Level - Ask about the experience level of the veterinarian regarding rabbits in general and about the procedure in question. Your veterinarians may not have had a lot of experience, but based on the answers to the other questions here and the willingness to work with you, you may decide to go ahead with the procedure.
- Types of Anesthetic Agents Used - You now have a list of anesthetic agents that are commonly used. If your veterinarian is using something else, ask for some type of literature or their experience in using these drugs before making your decision.
- Explain the anesthetic/surgical procedure – You are entitled to know how your pet is going to be handled throughout the anesthetic/surgical process. You now have a detailed description of the kinds of things that should be happening to decrease risk. In particular, find out about preanesthetic evaluation, anesthetic monitoring, recovery monitoring and use of analgesic agents.
- OVARIOHYSTERECTOMY (SPAY) - This is the complete removal of the uterus and ovaries in the female rabbit. Spays are done to prevent pregnancy and uterine cancer and to help control some behaviors such as urine marking, aggression and false pregnancy. The surgery should be performed after four months of age and before two years of age. The risk of uterine cancer increases significantly after two years of age.
- CASTRATION - This is the complete removal of the testicles of the male rabbit. There are several surgical approaches possible. Castration is performed for birth control and behavior modification such as urine marking and aggression. It will also prevent testicular cancer, although reproductive cancer is more rare in male rabbits than in female rabbits.
- DENTISTRY - Dental disease is common in rabbits due to such things as inappropriate diet, genetics and trauma. Because rabbit teeth grow continuously, dental malocclusions require continual reshaping of the teeth throughout the pets' life. In some situations the teeth need to be completely removed. Difficulties in rabbit dentistry include the small size of the oral cavity, which limits visibility, and work area, and the long extensive roots of the teeth. It is best to have dental procedures such as trimming or extractions performed as early as possible in the disease to avoid further complications.
- ABSCESS REMOVAL - Abscesses can occur in or on any part of the body, but have a particular propensity for the head. Most of the facial abscesses are related to dental disease. If at all possible, abscesses should be completely removed. There are often draining tracts that go between tissue planes and if left behind they can become sources for future abscesses.
- GASTROINTESTINAL SURGERY - GI surgery is most often done to remove blockages in the GI tract. These can occur anywhere along the tract and can be caused by dried pieces of stomach contents, carpet fibers and rubber or plastic objects. GI surgery holds the highest risk of complication in rabbits because of two factors:
1. The rabbit is often already in a deep state of shock once the obstruction is discovered placing it at high risk for anesthesia or surgery and 2. Because the GI tract is very sensitive to surgical manipulation.
The GI tract (particularly the cecum) may not heal well after surgery and the surgical site can break down. Abdominal adhesions are more common after GI tract surgery. In addition, GI motility can be affected causing a GI shutdown. These patients need an extraordinary amount of medical care and monitoring. The first three days after surgery are the most critical and the rabbit should be hospitalized during this period.
- OTHER SURGERIES - Surgery can be performed in the rabbit on any system or organ, just as in other animals. A list of other commonly performed surgeries includes cystotomy (opening the bladder usually for tumor or stone removal), orthopedic, laceration repair and tumor removal. Your veterinarian can give you details on these surgeries should your pet require them.