Anesthesia In Your Dog And Cat

Ron Hines DVM PhD

When your cat or dog is scheduled to undergo a surgical procedure many pet owners’ first thought is the risks of anesthesia. That’s perfectly natural – the risks of general anesthesia in some pets is greater than that of the surgery itself.

All veterinarians know this and most of us share your concerns. Today’s veterinarians are fortunate in that older, less predictable, anesthetics have been replaced by compounds that are very predictable and safe when properly used. The gas anesthetics we use today quickly dissipate from your pet’s body. Their effects are quickly reversed by natural or assisted ventilation (breathing) to get them out of your pet’s system rapidly. Almost every injectable anesthetic now has its own special reversal agent. These agents have dramatically reduced surgical anesthetic risk to your pet. Pet owners often wonder which anesthetic is the safest. The answer is that whichever anesthetic your veterinarian and his/her assistants are most familiar and comfortable using is the safest.

Many of the drugs that veterinarians use for anesthesia – especially those that are given by injection – are general anesthetics at one dose and sedatives at a lesser dose. So the difference between your pet being sedated and your pet being anesthetized it blurry. As a rule, veterinarians never give more than just enough of an anesthetic to do the procedure painlessly. Giving lower doses of several pain-alleviating medications rather than a large dose of a single medication is often the safer method.

Because it is common for pets to be apprehensive in animal hospitals, veterinarians use general anesthetics more frequently than your human physician probably would. Procedures such as x-rays, joint examinations and laparoscopy that your human physician would do while you were awake with no more than a local anesthetic block can very rarely be done safely animals without general anesthesia or profound sedation.

Pre-anesthesia Testing:

There are two components of safety in the use of anesthetics.

The first is proficiency in their use. Proficiency comes with experience – using the same procedures (protocol), the same medications, day after day, year after year. The same goes for the surgical staff. With time everyone who assists knows the choreography. They can anticipate their colleagues’ next move and need and assist without request.

The second component is evaluating the anesthetic risk in each individual pet. When your veterinarian is dissatisfied with the results of his/her pre-surgical physical exam, when breed, coexisting health issues or the results of  pre-surgical laboratory tests  give concern, your veterinarian may try to dissuade you from a general anesthetic procedure. Most veterinarians, comfortable in their profession, have no problem if you ask for a second opinion. Almost all areas of North America are not that far from veterinary centers and university veterinary colleges where board-certified veterinary surgeons and anesthesiologists practice. Like airline pilots, these veterinary specialists tends to be very organized, precise and thorough. (ref) By the time veterinarians are midway into their careers, most have developed a keen sense of surgical risk that is quite accurate but hard to quantify.

Pre-Anesthetic Blood Work Up:

Before major surgery, many veterinarians request that BUN and creatinine blood tests be run to gauge your pet’s kidney health and that ALT, AP  and a bilirubin test be run to detect liver problems. Glucose  analysis can detect potential diabetes. A WBC count and differential is often included and an EKG  helps to detect possible heart problems. It is not uncommon for the results of a few of these tests to be slightly above normal in a midlife dog or cat – many minor elevations turn out not to be significant. But when your veterinarian knows of potential problems in advance she/he can make modifications in the anesthesia, surgical and aftercare procedures that protect your pet’s life.

Pre-anesthetic Administration:

Veterinarians usually give pre-anesthetic sedation agents such as acepromazine, butophanol, diazepam (Valium®) or a combination of them and similar drugs to pets to calm them down and relax them before surgery (an anesthetic cocktail). Excited pets might require more sedatives and pre-anesthetics. Once the sedative or tranquilizer has taken effect, an intravenous catheter can be placed into the pet’s vein so fluids and additional medications can be given as the surgery progresses. A leading veterinary anesthesia/analgesia specialist put together a checklist of anesthesia and pre anesthesia techniques and medications for veterinarians and their technicians. You can read it here.

Selection Of The Safest Anesthetic Agent:

Anesthetics are administered in one of six ways. They can be injected locally around nerves. There they block local nerves that carry sensations of pain to the brain (a nerve block). They can be placed by injection in the tissues surrounding the spinal cord where they block sensations of pain (a “spinal“). They can be injected into the pet’s muscle or a vein to be absorbed into the pet’s general blood stream. From there they are carried to the pet’s brain. (ref) Many of these same agents can be added to bags of sterile fluid and given intravenously as a slow drip. That allows your veterinarian to lighten or deepen the degree of anesthesia as the surgery progresses. Special gases, most of them modified ethers, are administered by inhalation. (ref)

As I mentioned earlier, ideal anesthesia uses neither more nor less of the anesthetics than the amounts necessary to perform the procedure pain-free. This must be monitored throughout the procedure. So a special non-distracted person is generally assigned to watch your pet closely. One tries to give just enough of the drugs to maintain the pet pain-free and relaxed during the procedure so that it will regain consciousness quickly once the surgery is complete. The small amount of the drugs that remain in the pet’s system help ease immediate post-operative pain. Others to combat pain are given later. This amount is different for each patient. More painful procedures, such as intra-abdominal surgery, or spaying and orthopedic surgery require more anesthetics than procedures such as teeth cleaning or superficial tumor removal. Often, a combination or two or more anesthetics, given in different ways, works better than a single agent given alone.

Preparing Your Pet for General Anesthesia:

There are several things that you as a pet owner can do to help your veterinarian plan for successful general anesthesia and surgery.

First, if you have fears about your pet’s ability to tolerate anesthesia let your veterinarian know a week or so before the scheduled surgery. Most veterinarians will be happy to explain the benefits and risks of anesthesia and other treatment options that may be available. Let the veterinarian know if you have noticed any lethargy, exercise intolerance, weight loss, tendency to bleeding (read about why here) or changes in body functions that may need to be explored. Ask that complete pre-anesthetic blood work be performed on your pet prior to surgery. Be sure to let your veterinarian know if your pet has reacted badly to anesthetics or medications in the past. Even the fact that a close relative of your pet did not tolerate anesthesia well is something your veterinarian will want to know. Dogs and cats are extremely perceptive as to your fears and worry and it is not unusual for them to show “empathy” illness in response to your concern and worry regarding their coming surgery.

Withhold all food from your pet for at least twelve hours prior to surgery unless your veterinarian specifically tells you not to. This is to help prevent the pet from vomiting and inhaling stomach contents into its lungs during the procedure. Fasting also helps lessen nausea in the pet as it is regaining consciousness. It is amazing how many pets that I have operated on had food in their stomachs despite my advice not to feed them. So all members of your household need know your veterinarians instructions. Removing kitchen garbage containers from the pet’s ability to reach is also a good idea. Many vets suggest that you allow your pet to drink water up to 4 hours before the surgery, but ask the receptionist since veterinarians differ in that advice.

If the pet is not ill, groom and comb it prior to bringing it to the hospital. Allow it to relieve itself before entering the hospital. If your pet is not on a flea preventative, let them know. Don’t spray pets down with strong smelling, perfumed flea mists and colognes (eg Adams Mist), the staff will check them for parasites and use whatever flea meds they prefer. Surgery time is not vaccination booster time. Find out what the clinic’s immunization guidelines are in advance.

Many smaller veterinary hospitals do not routinely have twenty-four hour staff to observe your pet after surgery. That might mean that your pet would spend the night after surgery alone in the hospital. If you desire round the clock monitoring, let the animal hospital staff know sufficiently prior to the surgery date so that they can arrange it. If that is not possible and if you have a nurse’s temperament and abilities, I suggest you pick your pet up just prior to hospital closing and watch over it yourself that evening. Keep the veterinarian’s emergency phone number or the number of a 24-hour emergency care service at hand. Dogs and cats are homebodies who find the familiar odors, sites and sounds of home a powerful incentive to getting well.

You should leave the hospital with a set of discharge instructions. If you have small children at home be careful that they do not bother the pet during its recovery. It is not unusual for dogs and cats to be snappy for a few days subsequent to surgery, particularly when the area surrounding their incision site is touched. Call the clinic immediately if drainage continues longer than the staff told you it would. Call if the pet runs a  fever . Call if it will not eat. Call if the dressing has odor. In fact, call if you are uncertain about any aspect of your pet’s recovery. A time will already have been set for your pet’s skin sutures to be removed (unless the sutures were placed subcuticularly).

Stages Of Surgical Anesthesia:

Induction is the first stage of anesthesia as the pet gradually looses consciousness. Once a dog or cat is sufficiently relaxed and its cough and gag reflexes eliminated, it can be intubated. A plastic tube of suitable diameter and length is placed in its windpipe to facilitate breathing, to be sure its airway to the lungs remains unobstructed and to facilitate assisted respiration should that be required. This is especially important in flat-faced breeds such as Persian cats, pekingeses, pugs and bulldogs whose facial conformation makes breathing a challenge.

The anesthesiologist will regulate the depth of your pet’s anesthesia (anesthetic plane) by increasing or decreasing the amount of gas administered through the endotracheal tube or administering more injectable agent. Reversal medications allow veterinarians to decrease the depth of anesthesia from injectable anesthetics. Sick, weak and older pets require less of these anesthetic agent and very close monitoring throughout and after the procedure.

During surgery the depth of your pet’s anesthesia will be gauged by the animal’s eye blink reflexes, pulse strength, heart rate, gum color and jaw muscle tone. Blood pressure, heart monitors and a pulse oximeter clipped on your pet’s tongue to access its blood oxygen saturation are often in place as well.

Monitors are often left in place during recovery to be certain wake up is uneventful. Sometimes, during slow recovery reversal drugs are given to wake the patient up more quickly. Pets are often chilled and shivering as they come up from extended anesthesia and surgery – particularly the smaller breeds, cats and thin pets. They really appreciate being wrapped in a heated towel or blanket fresh from the dryer, or being placing on a cloth-wrapped hot water bottle.

Post Anesthetic Pain Control:

Pets, like people, are in considerable pain after major surgery. One must balance the desire for pain control with the side effects of all effective pain control medications. Most drugs that block pain also depress the heart, circulatory system and respiration.

Never reach into your medicine cabinet for human pain relief medicines with the intent of giving them to your dog or a cat. Some of those medications that are safe for you are definitely not safe for your dog or cat.

There are two links at the beginning of this article that discuss pain control medications

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