Medicine: All about anesthesia

Anesthesia is a routine part of veterinary medicine, yet it is the source of a lot of concern from pet owners. In this article, we will address what anesthesia is, what it does, and what we try to do to minimize any risks associated with it. We will also discuss what your rights as pet owners when it comes to creating an anesthetic plan for your pets: your Anesthesia Bill of Rights.
Anesthesia is the total loss of sensation in a body part or in the whole body, generally induced by a drug that depresses the activity of nervous tissue either locally or generally. The goals of anesthesia are to produce:

· Analgesia: decreased to no pain during and after the procedure. Studies on humans have found that stopping pain before surgery reduces pain after the surgery and decreases the need for post-operative pain medication.
· Restraint: Keeps the pet from moving and allows for safe procedures and reduces movement. This is called akinesia.
· Amnesia: General anesthetics produce amnesia, so the whole procedure is not remembered. This reduces stress. Any of you who have had sedation or general anesthesia will remember the episode only hazily.

To perform various procedures, we perform different types of anesthesia

Local anesthesia: is when a body part is numbed by injection at the site of interest. This can only be done for small procedures on cooperative pets. It produces analgesia only. With some procedures we perform a general anesthesia and a local anesthesia to minimize pain afterwards. We do this with our declaws for example.

Sedation: is when sensation is decreased but not eliminated and the pet is in tranquil state. We perform this with a combination of a tranquilizer (for restraint and partial amnesia) and a narcotic (analgesia and restraint). Using both drugs together causes a strong sedation without many side effects. The pet is sleepy and calm, but still conscious. Tranquilizers are contraindicated with any pet with a history of seizuring. Sedation is sometimes given before general anesthesia to reduce the amount of anesthetic required.

Epidural causes analgesia by injecting the tissues around the spinal cord with a local anesthetic or narcotic. In veterinary medicine, this is only performed with pets under general anesthesia to reduce the amount of anesthetic required and to reduce post-operative pain. This is done primarily with invasive orthopedic (bone) procedures. We do not perform this at our hospital due to its risk of complication.

General anesthesia: causes complete unconsciousness, analgesia, and amnesia. This is the most common type of anesthesia that we perform. Normally, we give an injectable anesthetic followed by an inhalant anesthetic for maintenance. For our younger patients, we use a combination of Valium (diazepam) and ketamine as the injection. We use a very safe anesthetic gas called isoflurane to maintain the anesthesia. For our older or debilitated patients we use a very rapid-acting anesthetic called Propofol. We don't use it on all of our patients due to the fact that it is more expensive.
The most concern from pet owners is about general anesthesia, so we will confine the rest of our discussion to general anesthesia.

Is general anesthesia a risk? Can my pet die from anesthesia?

The answer is yes. General anesthesia always carries some risk. Anesthetic agents are drugs and all drugs can cause adverse reactions. The risk is low though. Newer anesthetic agents are much safer than those used even a few years ago. Here at the Orange Villa Veterinary Hospital, we also do extensive anesthetic monitoring to minimize this risk further. The most common side effect of anesthesia is a drop in blood pressure. This reduces the amount of blood and oxygen, which reaches the internal organs and the brain. A lack of oxygen does damage, and if the organ already has borderline function, this can predispose organ failure. We take a lot of measures to reduce the risk of organ failure that causes anesthetic death?

What are these measures? What do you do to monitor them?

We have been accused in the past of being too aggressive in our anesthetic monitoring by some pet owners. I don't think that it is possible to be too aggressive. We try to envision how we would like our own pets treated in the same situation, and I can guarantee that with my precious ones, I would want everything possible to prevent problems from occurring.

The first thing that we do is a thorough examination before any anesthetic is performed. State law requires that an examination be performed within 12 hours of any general anesthetic procedure.

Next we perform lab work to make sure that all organ function and red cell, white cell, and platelets are adequate for anesthesia. On young pets, we perform a small pre-operative blood panel. For older or sick pets, we perform more comprehensive blood and urine tests. We need lab work to have been done within the last month. Young pets, even puppies and kittens could have congenital problems that don't show symptoms, yet anesthesia could prove fatal. While rare, these problems, such as liver shunts, need to be fixed before an elective anesthetic is performed. With elective procedures (non-urgent), if we find a problem, we can work on diagnosing and treating the problem beforehand and/or adjust our anesthetic plan. With urgent cases, it may affect our anesthetic plan and aftercare.

Chest radiographs: These are indicated in older pets, or pets that have heart or lung changes on examination. Heart disease causes increased anesthetic risk. Radiographs help identify heart or lung disease, or tumors in the chest. In dogs and cats, malignant tumors frequently spread to the chest. Pets can have problems with the heart and lungs without any symptoms identifiable on examination. We recommend this on all pets over seven. If they have a heart condition, the cause of, which is not known yet, then an echocardiogram (ultrasound of the heart), may be indicated.

Anesthetic drugs: We use different drugs for different patients. The reason that we do this is to save cost to you. For younger patients, we use the diazepam/ketamine combination to induce anesthesia followed by the isoflurane. We use torbugesic (a narcotic) for pain control and mild sedation after the procedure. This is a safe anesthetic plan for young, healthy animals. For our older or debilitated patients, we use a drug called propofol. This drug is much more rapid acting, and metabolized in the lungs instead of the liver. They recover much quicker and it is much safer. It is also much more expensive. We also use it for very short procedures, so the pet may go home quicker.

Antibiotics and aseptic techniques: For all invasive procedures (such as spays, neuters, and other surgeries) we wear surgical gowns and gloves, caps, and masks. We disinfect our surgery room after every patient and we scrub well before surgeries. To prevent infection from bacteria from the patient's skin, we clip the fur in a wide margin from the site and scrub with a disinfectant. We also give intra-anesthetic antibiotics. This helps to kill any bacteria that could end up in the incision during surgery. Unless we suspect a break in the sterile field or infection was already present we do not send home antibiotics.

Monitoring devices: We use pulse oximetry, ECG, blood pressure, and respiratory monitoring to continuously assess patients under anesthesia. One of our technical staff members is always present to continually monitor the patient from when the drugs are first administered until the pet is conscious and able to swallow.

For lengthy anesthetics or older or debilitated patients, we use intravenous fluids. Anesthesia reduces blood pressure, which can cause organ damage. High volumes of fluids help to support the organs and reduce risk of organ damages. Pets with heart disease cannot tolerate this high rate of fluids, so they are treated a little differently. We start the fluids before the anesthesia and continue them until they are fully awake.

After care: After the anesthesia the patient is watched in our recovery area to watch for complications. For some procedures, the pet can go home soon after, for some we have them spend the night. While we do not have overnight technicians, we like to keep the pet in a confined environment (since the pain medication makes them unsteady on their feet) and so we can examine them again the following morning. If we feel that the pet is unstable, we will have them sent to a critical care facility for overnight observation.
This goes over what we do about anesthesia with our patients. What decisions in the process do you have?

Our recommendations for healthy pets are:

Under 7 years of age:

Pre-operative lab work
Ketamine/diazepam anesthesia

Over 7 years of age:

Pre-anesthetic comprehensive blood panel
Urine testing
Chest radiographs
Intravenous fluids
Propofol anesthetic

Sick or debilitated patients anesthetic plan is by doctor's discretion

You have the option of accepting or declining any portion of the anesthetic plan. You may also request a more aggressive anesthetic plan than we recommend. We would do the anesthetic plan for pets over 7 years for all pets if money were no issue. If you do decline an anesthetic plan, we may decline to perform the anesthesia due to health risk.

i Anesthesia information courtesy of Handbook of Veterinary Anesthesia Muir, et.al Mosby 1995.

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