HRS Article:   What's Up, Doc?
 
by Susan Brown, D.V.M.
 
PART ONE: TAKING THE FEAR OUT OF RABBIT ANESTHESIA
 
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 have gone 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 exists the fear that it will not "wake up" again leaving the patient brain damaged or deceased. Fortunately, in this day and age, with improved and safe anesthetic agents, specialized anesthetic equipment and the ever-expanding knowledge of the medical/veterinary profession, the chances of serious problems with anesthesia 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 this discussion, I hope to arm you with not only good information to increase your understanding of what is happening when your pet undergoes anesthesia, but also give you guidelines to use when communicating with your veterinarian on these important subjects. Remember 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 22 years of practice that rabbits can undergo most medical and surgical 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 10 years due to better informed owners who recognize disease more quickly and improved and more appropriate treatment options.
 
Rabbits are "high risk" anesthetic patients - We do not feel that rabbits are at any higher risk with anesthesia than any other patient that we see. 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, we had less acceptable anesthetic agents available for rabbits in the past. Today we have excellent, safe anesthetic choices. Properly evaluated and monitored rabbit patients makes excellent anesthetic 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 they undergo 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 (some may be penetrating), cardiomyopathy (heart muscle disease) and ultimately death. Anesthesia can alleviate these problems by relieving pain (a stressor). In fact, it is often safer to use appropriate anesthesia or sedation in a rabbit then to submit it to an uncomfortable procedure that may result in state of shock from which it cannot recover.
 

ANESTHESIA AND SEDATION: DEFINITION, USES AND TYPES

Anesthesia is achieved when there is a loss of sensation to either a part or all of the body. General anesthesia also renders the patient unconscious. Sedation is similar to general anesthesia but the patient remains semi-conscious.
 
Anesthesia and sedation are used for 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.
 
There are three types of anesthesia:
1. 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 IV or IO catheters, or for ophthalmic procedures (the surface of the eye is anesthetized with drops). The most common and use in our practice is to allow flushing of the tear ducts in the awake patient. The main drawback of local anesthesia when used for minor skin surgeries in the rabbits is that the patient must remain very still during the procedure.
 
2. Regional anesthesia is where a larger and deeper area of the body is anesthetized. The anesthetic agent is injected into the spinal fluid (to anesthetize all sensation from that point of the spine to the back of the animal) or into a specific nerve (which anesthetizes all the tissues that the nerve branches reach). The rabbit remains fully conscious. Although this anesthesia has been described for rabbit, it is still rarely used in clinical practice. This is primarily because for most major surgical procedures a general anesthesia is preferred with the patient being unconscious.
 
3. General anesthesia circulates through the bloodstream to all areas of the body, including the brain, and causes a loss of consciousness. There are basically two ways to administer general anesthetic agents, by injection or inhalation. The injectable anesthetics can be given intravenous (IV), intramuscular (IM), intraperitoneal (IP) or subcutaneously (SC). The advantages of injectable anesthetic agents include use for short surgical procedures, (particularly those in the mouth), or use as a preanesthetic to an inhalant agent. Preanesthetic drug(s) are used to calm the rabbit to allow handling for the administration of the inhalation agent or to allow passage of an endotracheal (ET) tube (which is often not possible when only inhalation anesthesia is used). 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 among different rabbits. Fortunately the most common error is under dosing, which then requires additional doses to achieve the proper state of relaxation. Injectable anesthetics are not suitable for prolonged surgical procedures. The recovery period varies with the agent used. In addition, some of the injectable anesthetics are not appropriate with certain types of illness, such as cardiac or kidney disease. Your veterinarian should be familiar with the limitations of these drugs. 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 and xylazine. A fairly new anesthetic, medetomidine, has become available in the last couple of years. MedetomidineÆs anesthetic effects can be quickly reversed with another drug (atipamazole) which greatly reduces the recovery period and any chances for an overdose.
 

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 anesthetic gas. The anesthetic gas is administered either through a mask placed over the rabbit's face, or through an endotracheal (ET) tube. With inhalant anesthesia the patient is connected directly to an anesthetic that delivers the anesthetic agent in a flow of oxygen. The advantages of the 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 preferred gas anesthetic) can be used safely in rabbits with a wide variety of illnesses. The drawbacks to inhalant anesthesia in the rabbit are minor, the main one being the difficulty in placing an ET tube to deliver the anesthetic agent. The tracheal opening can be difficult to visualize without specialized equipment and the angle and small size of the trachea causes further difficulty. Even experienced veterinary staff can sometimes meet with failure. It is not always necessary to place an ET tube for every procedure and the anesthetic can be delivered effectively with a face mask or an ET tube placed near the entrance of the trachea, but not inside the trachea. Occasionally a rabbit will hold its breath during induction with gas anesthesia, but this problem can be easily overcome with proper monitoring of the patient during induction. Anesthetic equipment must be maintained in good condition for safe delivery of the agent, and fortunately this is easy to accomplish.
 
The most common and overwhelmingly preferred gas anesthesia in rabbits is isoflurane. Is safe not only for the rabbit, but for the humans who also have to be exposed to it. Methoxyflurane and halothane have been used successfully 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.
 

RISKS OF GENERAL ANESTHESIA

With care, the risks of general anesthesia in the rabbit are minimal. However, I would not be truthful if I told you there were none. 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. 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 factors including pre-existing thoracic disease (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). Hypothermia occurs naturally during general anesthesia. If you have ever had general anesthesia you may remember waking up shaking and feeling very cold. We are dealing with animals with a small body mass compared to their surface area which allows heat to be released much 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 (such as the vena cava) or if the rabbit had a serious bacterial or fungal infection prior to the procedure.
 

FACTORS AFFECTING ANESTHETIC RISK

Fortunately there are many things that can be done to greatly reduce the anesthetic risk in rabbits. Things 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. So, what things can be done to decrease the risk of anesthetic complications.
 
Here is a summary of the most important items:
 
1. Perform a thorough preanesthetic/surgical examination including diagnostics if appropriate.
 
2. Stabilize/treat pre-existing conditions 4. Constantly monitor the patient during the anesthetic/surgical procedure.
 
5. Closely monitor the patient during the recovery period until ambulatory.
 
In the next issue I will take you through the process of taking your rabbit in for an examination through the induction of general anesthesia, monitoring and the recovery period so you can understand what you should expect from your veterinarian when anesthesia is proposed for your pet.