Anesthesia-General Information
Anesthesia comes from the Greek word 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 of time. 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 an area of skin or a tooth, and spinal anesthesia, such as an epidural block, that results in anesthesia of the spinal nerves to a particular part of the body.
Preoperative blood tests can be used to screen for subclinical problems. Certain medical conditions will increase the risk of having an anesthetic complication. These conditions include liver or kidney disease, diabetes, anemia, dehydration, and certain infectious diseases such as Feline Leukemia and Feline Immunodeficiency Virus. Blood tests will increase the chance of detecting a hidden problem that could prove to be life threatening. In older animals, chest radiographs may be recommended to ensure that there is no pre-existing pathology in the heart or lungs that might increase the risk of an adverse reaction.
There are many reasons to perform pre-anesthetic testing. First, you deserve peace of mind. Testing can significantly reduce medical risk and ensure your pet’s health and safety. Secondly, pets can’t tell us when they don’t feel well. A healthy-appearing pet may be hiding symptoms of a disease or ailment. For example, a pet can lose up to 75% of kidney function before showing any visible signs of illness. Testing helps us evaluate your pet’s health up front, so we can avoid problems related to anesthesia. Also, testing can reduce risk and consequences. If preanesthetic results are within normal ranges, we can proceed with confidence, knowing that anesthetic risk is minimized. On the other hand, if results are not within the normal ranges, we can alter the anesthetic procedure, or take other precautions to safeguard your pet’s health and reduce the risk of potential complications. Lastly, testing can help protect your pet’s future health. These tests provide baseline levels for your pet and become part of his or her medical record for future reference.
You should ensure that the pet’s complete medical history is available to your veterinarian, especially if your pet has been seen at another veterinary clinic. Important information for your veterinarian to know prior to anesthetizing your pet includes the immunization status of the pet, the results of any tests for diseases such as Feline Leukemia and Feline Immunodeficiency Virus, any pre-existing medical conditions, any known drug reactions, any medications or supplements that have been given in the past few weeks, the pet’s reproductive status (ie whether it has recently experienced an estrus or heat cycle), and whether any surgical procedures have been performed in the past.
It is important that you fully understand what will happen to your pet, and that you acknowledge that the risks have been explained to you. 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 then undergo a thorough pre-anesthetic examination, which 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, electrocardiogram (EKG) 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, a combination of sedatives and anesthetic agents that is best suited to the individual patient’s needs is administered. 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. In order 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 fluids cannot be accidentally aspirated while the patient is unconscious and unable to swallow.
Anesthetic monitoring is in our veterinary hospital is similar to that found in any human hospital. In our hospital the Surgery Assistant is the most important monitor during an anesthetic procedure. The assistant is professionally trained to observe and monitor the patient throughout the entire procedure, from induction until recovery. The assistant adjusts the anesthetic levels according to the patient’s vital signs and ensures that the patient remains stable throughout the procedure. We also use Pulse Oximetry is to monitor the amount of oxygen in the patient’s blood and the pulse rate. This instrument should always be used in conjunction with other pieces of monitoring equipment, such as the electrocardiogram. The Electrocardiogram (ECG) is sometimes referred to as an EKG from the German term. It is used to observe the pattern of the heartbeat. It is very important to detect abnormal heartbeats called arrhythmias. If abnormal heartbeats are observed, appropriate changes in anesthesia and/or emergency medications can be administered. In addition, Blood Pressure Monitors generally measure the systolic (when the heart contracts or pumps) and occasionally the diastolic (when the heart relaxes or refills) blood pressure. Coupled with other monitoring equipment, this gives detailed information on the cardiovascular status of the patient. The use of our Respirometer measures the number breaths per minute and the Core Body Temperature is also monitored, especially during a prolonged surgery, by inserting a probe into the esophagus (‘food tube’) or rectum. Low or high body temperature can cause dangerous complications. Maintenance of normal body temperature is especially important in small, young patients. The Heart Rate Monitor measures the number of heartbeats per minute. This is important to monitor so that increases or decreases can be detected early and anesthetic adjustments made quickly, resulting in smoother anesthesia for our patients.
With today’s anesthetics, many of which are reversible, your pet should be almost completely normal by the time of discharge. Many pets are sleepy or tired for twelve to twenty-four hours after anesthesia. If your pet appears to be unusually sluggish or you can’t arouse them easily, notify the hospital for further instructions
What are the risks of anesthesia?
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.
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.
This client information sheet is based on material written by Ernest Ward, DVM
© Copyright 2005 Lifeleam Inc. Used with permission under license. June 25, 2007
