What happens during anesthesia?
Dr. Stephen M. Sheldon, practices at and owns Hammocks Veterinary Hospital in Miami, Florida.

Well, I can tell you one thing, there is a good chance neither you nor your pet will remember what happened during anesthesia. I decided to write this article when, during a cross-training session with our receptionists, they all uttered in unison, "Wow, I had no idea all this went into anesthesia."

 General anesthesia is a routine and safe procedure when performed by competent doctors and staff. If you have confidence in your veterinarian and, equally important, their nurses and technicians, then you should not worry. Statistically about one in 10,000 healthy animals will have an adverse reaction. That is actually a very low number. Unfortunately, since anesthesia is performed at most hospitals three to four times daily, I have seen doctors and staff take it lightly. Read on and you'll know what questions to ask your veterinarian before anesthesia.

General anesthesia, for the purpose of this article, will be defined as gas anesthesia. Gas anesthesia has many advantages over intravenous (IV) or intramuscular (IM) anesthetics. Namely, it is very easy to control, as the lungs are full of blood vessels, which exchange the gas into and out of the blood. It is the out-of-the-blood portion that is important because it allows us to very easily control how deep the level of anesthesia is. Once a drug is given IV or IM, it needs to go through critical organs, such as the kidneys and liver, to be eliminated. This takes time. Gas is king.

Preparation for anesthesia starts at home. A 12 hour fast is required so usually, at 10 p.m. or so the night before, you must stop feeding and give only small amounts of water. Pick up the water before you go to bed. The reason for the fast is that some animals get nauseous from the anesthesia and pre-medications. If they vomit while under anesthesia, they cannot swallow; the tube that carries food to the stomach (esophagus) is near the tube that caries air to the lungs (trachea). The larynx is the valve that makes sure food goes down the esophagus and air goes down the trachea, and it becomes paralyzed during anesthesia. If your pet vomits, there is a chance it could end up in the lungs. This would be bad. We do have some back-up tools in case your pet does vomit; this would be the tube that is placed in the trachea to deliver the gas ... it has a cuff to keep any liquid from going into the lungs. Relax, I told you we would be well-prepared.

Once you drop your pet off the morning of surgery, he will be given a pre-medication before the anesthesia. The purpose of the pre-med is two-fold: One is to dry up secretions, such as saliva, so that fluid doesn't try to make its way into the lungs, and the other is to administer a mild sedative, such as valium or acepromazine. The sedative is very important as it makes the anesthesia smooth on the way down and, more important, smooth waking up.

At the time we give the pre-med we draw blood for pre-op blood tests; these may have been done in advance. Depending on the age of your pet, other tests may be required, such as electrocardiogram (EKG), chest radiographs, urinalysis or thyroid tests. Even the youngest of patients need to have a complete blood count and basic kidney/liver/blood sugar tests. To make you feel more at ease, I can tell you that one study showed that the best predictor of problems in animals undergoing anesthesia was, in fact, a good physical exam by the doctor. A trained doctor knows, often just by looking, when a patient isn't right. I know that sounds simple and I am not advocating bypassing important pre-op tests (I have cancelled countless surgeries because of problems detected only by these tests), but there is no substitute for good eyes and ears and a functional brain.

After we draw blood and do the pre-op testing, we place an intravenous catheter in the front leg of your pet; in people, they call these hep-locks. This is one very important little piece of Teflon. Heaven forbid, if there is an emergency during anesthesia, the doctor will need to administer lifesaving drugs into a vein. 

Without a catheter, this could take 30 to 90 seconds. This critical time could be the difference between life and death. Our receptionists were shocked when we showed them the time difference and also how difficult a "direct stick" can be on some animals. It adds to the cost, but insist on IV catheter.

We are three quarters through this article and we haven't even given any anesthesia yet. See, this is not such a simple project. To administer the gas we must give an ultra-short acting agent, such as ketamine, thiopental, or propofol. These allow us to place the endotracheal tube into the trachea to give the gas. We do not place a mask over the face and ask the pet to count back from 99; it takes too much time and the animals struggle too much. When they struggle they release epinephrine, which can have a bad effect on the anesthesia. The ultra-short acting agents take them right through this "struggle phase" and last only five to 10 minutes. Nonetheless, there are a few select instances where we will "mask" animals down. 

Now we start the oxygen/anesthesia mix; most practices use isoflourane, which is very safe for both the patient and the OR personnel to breathe (we do have scavenger systems, so OR personnel don't breathe the gasses). Until a few years ago, it was the mainstay of human anesthesia as well. We will then hook your pet up to a pulse-ox monitor, which gives us critical pulse rate and oxygen-saturation information. If your veterinarian doesn't have one, he is practicing in the Dark Ages. I pull no punches when it comes to your pets' health; you know that by now. We constantly monitor your pets' depth of anesthesia by checking reflexes (eyelid, cornea, anus), response to stimulus, and jaw tone. These are important, too; we want your pet to be only as deep as is needed to get the job done. My favorite national board question is "What is the correct dose of pentothal?" (the drug that enables us to get the endo tube in the trachea). Answer: "to effect" (meaning, give just enough to get the tube in; no more, no less).

After anesthesia your pet will be watched closely and kept warm. With isoflourane, most pets wake up smoothly. Surgical patients will need post-op medications to keep pain at bay and others who wake up roughly may need more sedatives. More often than not, the rough ones just need a soothing human hand and voice! We leave the IV catheter in place for a few hours. Since pets can't talk and the catheter is bandaged there is a very small chance your pet may get home with it still in place. Oops. Don't worry, since it is wrapped just come back the next day.

I hope this journey through anesthesia has enlightened you and made you feel more comfortable. In competent hands your pet will be very safe. Like flying in airplanes or going to war, many vets are superstitious and don't want to tell you how safe anesthesia is for healthy pets. However, statistics don't lie.

Dr. Stephen M. Sheldon, practices at and owns Hammocks Veterinary Hospital in Miami, Florida. A University of Florida graduate, he is President of the South Florida Veterinary Medical Association and a member of the Veterinary Cancer Society. He can be reached at (305) 388-0880. Dr. Sheldon no longer maintains his website for public use. http://www.hammocksvet.com/

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