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Anesthesia And Use Of Anesthetic Agents At Cat Hospital of Chicago

At Cat Hospital of Chicago, we take anesthesia very seriously. Most owners are understandably concerned about the potential risks associated with general anesthesia. Modern anesthetic agents and techniques are designed to minimize risks, not only of obvious complications but also of hidden ones, and to maximize the odds of a favorable outcome. In an abstract from the Journal of the American Animal Hospital Association from early 1999, it was noted that the peri-operative mortality rate in all feline anesthetic cases, in a study performed at a veterinary teaching hospital at the time, was 0.43%. Since Cat Hospital of Chicago opened its doors in December of 1998, our intra-operative/peri-operative mortality rate has been much lower: .00046%. We have always prided ourselves on our aggressive anesthetic safety protocols, and continue to update them when appropriate.

Prior to any cat being put under anesthesia for a surgical or other procedure, a thorough physical exam is performed, no matter how recently one was previously done. Additionally, we require that pre-operative laboratory work be performed (as is done in human medicine) to make sure the cat's major organs and body systems are functioning satisfactorily. (Many owners are concerned, or have been previously told, that their cat is "too old" to undergo anesthesia. Age itself is not a contraindication for general anesthesia, especially if the cat is relatively healthy, pre-operative laboratory work is satisfactory, and the anesthesia is warranted for a procedure that will improve the cat's quality of life. Our patient caseload at Cat Hospital of Chicago is heavily weighted in the geriatric cat department, and although we weigh the pros and cons heavily before anesthetizing an elderly cat, we certainly are not hesitant to proceed if it is in the cat's best interest to do so). All of our veterinarians, as well as our surgical nurses, have expertise in geriatric feline anesthesia. In addition to the above pre-operative laboratory work, we may sometimes also need to perform more advanced testing (x-rays, ultrasound referral, etc) prior to anesthesia if we feel that the cat's medical condition requires this to be done.

After the above pre-operative exam and testing have been done and evaluated and a decision has been made that a surgical procedure with general anesthesia will be performed, Cat Hospital of Chicago will customize an anesthetic regimen according to the needs of the cat (age, health status, weight, etc.,).

A pre-anesthetic tranquilizer/analgesic (pain) injection is administered (along with any other pre-op medications that may be warranted, including additional pain medication, antibiotics, etc.) and the cat is placed in a hospital cage with a "kitty condo." After the tranquilizer takes effect, general anesthesia is induced with either an injectable or gas anesthetic. "Inducing anesthesia" means that we want to get the cat to the point where he or she is sedated enough so that we can place an endotracheal tube (breathing tube).

Once the anesthesia is induced, and the breathing tube is placed in the cat's trachea (windpipe), the general anesthesia is subsequently maintained with gas anesthesia that is hooked up to the endotracheal tube. The pre-anesthetic "cocktail" heavily sedates the patient, and because of its sedative and pain management abilities, the amount of gas or inhaled anesthetic needed is reduced.

At Cat Hospital of Chicago, we have chosen Isoflurane as our gas anesthetic agent. It is considered to be a safe inhalant anesthetic in veterinary medicine. Induction and recovery are both rapid. Veterinary anesthesiologists, both in academia and in private referral animal hospitals, recommend use of Isoflurane in feline anesthesia maintenance, and speak of it as an excellent gas anesthetic agent.

Once maintenance anesthesia has begun, anesthetic monitoring devices are attached to the cat in order to ensure his or her safety during the surgery. These include:

  1. Anesthetic monitor that gives a constant measurement of heart rate, respiratory rate, level of oxygen saturation of the blood hemoglobin, known as "pulse oximetry", EKG, and body temperature.
  2. Anesthetic monitor, called a capnograph, which estimates the efficacy of ventilation (we want to make sure the cat is effectively "blowing off" carbon dioxide waste gases); this monitor may also indicate anesthetic circuit problems and cardiovascular dysfunction.
  3. Blood pressure cuff is placed around the cat's paw so that the blood pressure can be monitored frequently throughout the surgical procedure (a veterinary technician or nurse takes manual readings every 1-3 minutes). Feline blood pressure is most accurately measured through use of a Doppler blood pressure machine, which is best able to pick up readings in smaller animals like cats with tiny arteries. Low blood pressure can happen in any animal under anesthesia "not just old or sick animals," and may often be the first indicator that an adjustment in the anesthetic level or intravenous fluid rate needs to be made, or that additional measures need to be taken in order to prevent subsequent or progressive anesthetic problems that may be either life-threatening at the worst, or damaging to internal organs, particularly the kidneys, at the very least. (The kidneys, which require a minimum blood pressure in order to maintain adequate perfusion, can be damaged by low blood pressure that is not appropriately addressed).

Monitoring of these above parameters is all done non-invasively, and is a major factor in helping the doctors to assess cardiac and respiratory function under anesthesia. Obviously, we are also very aware of the patient'sbreathing pattern, gum color, heart sounds, depth of anesthesia, etc., independent of all the equipment to which the cat is attached. All anesthetic procedures include a dedicated anesthetist. It is vitally important for your cat's safety that there be someone present during the procedure whose only task is to monitor your cat. Would you be comfortable going under anesthesia if the only person in the room with you was the person performing the procedure?

Additionally, because low body temperature can adversely affect many of the above measured parameters, and thus the overall safety of anesthesia, we also make use of a water-circulating heating pad, as well as a pediatric Baer Hugger warming blanket (just as is used in human hospitals for children) for all anesthetized patients. Additionally, we apply infant "booties"to our patient's paws in order to further aid in heat retention. We have found that the majority of our patients remain normothermic (normal body temperature) with these preventive measures being taken.

While the cat is being hooked up to the anesthetic equipment by one of our hospital technicians or nurses, a second nurse or technician places an intravenous catheter in those cats in whom this has not already been done pre-operatively. Fluid administration through the catheter is then begun. The fluid is a balanced electrolyte solution that helps to combat both dehydration, always a possibility in cats that have had food withheld prior to anesthesia, as well as an unwanted anesthesia-induced drop in blood pressure. The fluid is warmed before entering the cat's body via the Baer Hugger IV fluid warming unit.

At Cat Hospital of Chicago, we are very aggressive with pain management in cats. All surgical cases are given pain medication, no matter what surgical procedure is involved. The type of pain medication used depends on the severity of anticipated pain (i.e., we'll use stronger medication, and/or often two or three different analgesics, for those procedures in which we predict moderate to severe pain). Pain can also contribute to anesthetic complications, internal organ damage, and prolonged or difficult post-op recovery periods. Pain is something none of us want our feline friends to experience. Because recognizing pain in the post-operative period can be difficult in cats (in addition to the fact that cats are well known for not outwardly exhibiting signs of obvious pain, some of the residual anesthetic drugs and tranquilizers may mask the demonstration of post-op behavior that might suggest pain), our philosophy at Cat Hospital of Chicago is to assume that all surgical procedures inflict pain in cats. Thus, we proactively use analgesics (pain medications) in all surgical patients to minimize postoperative pain because we feel it is a fundamental principle in providing quality medicine to each of our feline patients.

After surgery is completed, our patients are recovered in cages with heated floors and monitored closely. (If necessary, cats can be recovered in an intensive care cage that is designed for this purpose. It is heated, humidified, and has an enriched oxygen atmosphere that will help to enhance recovery in those patients that need these additional measures).

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