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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.
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.
Another potential danger associated with anesthesia arises if the dog 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 dog 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 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.
Pre-surgical physical examination, preoperative blood and urine tests and radiographic examination may detect clinical and sub-clinical problems. Certain medical conditions will increase the risk of having anesthetic complications. 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.
Intravenous 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 surgery 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 dog, your veterinarian needs to know about any medications or supplements that your dog 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 dog 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).
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.
All anesthesia patients are weighed on admission and are given a thorough pre-anesthetic examination. This 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. The medical history will be reviewed, and 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.
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 based on its body weight and best 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, and maintenance of the anesthetized state with an anesthetic gas mixed with oxygen. 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 while s/he is unconscious and unable to swallow.
