October 13, 2015
The body doesn’t always perform, live or die, as expected. The medicine that worked before in a given situation, doesn’t. Or wondrously, against the textbook prediction (prognosis) a full cure is effected when…. It shouldn’t have? Of all the internal medicine problems, the surgeries, the diseases and treatments that veterinarians must try to explain to their clients, it is possible that anesthesia is the most difficult subject to explain and often creates more anxiety than the surgical procedure accompanying it.

Anesthesia is the administration of a chemical substance by pill, injection, or as an inhaled gas that will induce a state most similar to heavy sleep, but at a level of decreased consciousness where pain is not felt. This allows surgery to take place. “A chance to cut is a chance to cure!” was a motto endorsed by my surgical professors. Most veterinarians learn very quickly that no matter how great a surgeon they become, it is as nothing if their patient does not wake up afterwards. Anesthesia is indeed a very important factor in the final outcome.

There is much that goes into the training. With todays’ computer applications, you can punch in a pet’s weight, age and species and the computer will print out a list of combinations and choices of anesthetic for that particular patient. Ahhh, but here is where the art of science comes in. Science, applied to a living creature, is not that cut and dried. Is the patient very tiny or young? She might not take deep, regular breaths under anesthesia and may require assisted ventilation. How to best smooth out the adrenaline rush of a frightened pet so he’ll transition easily into anesthetic sleep? Is the patient very thin or very fat? A heart murmur? Epileptic seizures? So many different considerations must be factored in to choose a correct anesthetic regimen.  Each patient’s case is reviewed individually. Your veterinarian will perform a pre-operative exam looking for signs of underlying disease that might complicate anesthesia. What must be tolerated in an emergency will be refused for an elective surgery : for example, a cat with a snotty nose will be refused a spay surgery.

Most pets receive a preanesthetic medication, called a “pre-med”. This is often a mild tranquilizer or sedative mixed with medication to dry up respiratory secretions. The pre-med serves multiple functions : it dries up fluids, keeping the nose and airway passages clear and it helps to calm and quell that adrenaline rush, as  pre-medicated patients actually need less anesthetic agent throughout their surgery. Pre-emptive pain medication may be given at this early stage, which has been proven to tamp down pain so much before surgery that pain never peaks as high after surgery.

Pre-meds are given about thirty minutes before surgery. The drowsy patient is more relaxed for the second phase, anesthetic induction. Induction anesthetic brings the pet rapidly into deep sleep, often via an intravenous injection. Small patients may induce themselves into sleep with the same anesthetic gas that will be used throughout surgery. If induction is not followed by maintenance with a gas anesthetic it may only last for 5 minutes! This initial state of unconsciousness allows placement of an endotracheal tube, a long flexible tube through the mouth into the windpipe, or trachea, which creates a wide-open passageway for air, oxygen, and the anesthetic gas to be delivered. From this point your pet keeps itself asleep by regularly breathing this anesthetic gas in and out. Monitoring equipment that follows your pet’s heart rate and other parameters are used while under anesthesia. A variety of anesthetic gases are used today in veterinary medicine and can be reversed by simply disconnecting from the machine. The majority of pets in a short procedure, under one hour, will awaken in a few minutes and be walking within 15 minutes!

There is much anxiety about anesthesia, the fear of going to sleep and never waking up, of an unexpected death. The reality is that there are few complications with anesthetics using the drugs and protocols available today. Surgery is recommended for the health benefit of your pet, to repair broken bones, remove cancers, etc. and these benefits far outweigh the risk from anesthetic complications for most pets. Many of our pastimes, whether driving a car or playing in sports, are more risky. I sincerely hope this gives you a foundation for understanding the art and science of anesthesia.

Christine B. McFadden, DVM
drmc@mcmenagerie.com