Q We are facing an orthopedic procedure on our dog, Choco. We are concerned because he is 11, and has only been under anesthesia once, when he was neutered as a puppy. How do we determine if anesthesia is safe for our dog? We want him treated but are terrified that he will have an anesthetic reaction and not wake up.
A: This is a great question, and it's one we face every day at our hospital. In those cases, however, we usually know more than just the patients' age, sex and name. But this helps to illustrate the point that the more we know about the patient, the better we can formulate an appropriate anesthetic plan.
In the old days of veterinary medicine, anesthesia was simply to control the animal while the vet performed a procedure. They used to castrate horses with an agent that only paralyzed them. It provided no pain control, and they were fully conscious. I (Henri Bianucci) remember hearing an old timer, amusedly recounting how, "once you castrated a horse, he never forgot you."
He wasn't cruel, he just didn't think of that horse as something that perceived pain as you or I would.
With food animals, that mentality, or denial, still persists in many cases.
Thankfully, for our pets, the old farm animal mentality has given way to our current view, where these pets are part of the family and are entitled to the same level of care that we expect for ourselves.
I tell every client that anesthesia is very safe, but not 100 percent so. If anyone ever tells you otherwise, go somewhere else.
You have to respect the fact that, for a time, that animal will be completely dependent upon your support and monitoring.
All of our patients are anesthetized with a short-acting drug and immediately intubated. They are provided 100 percent oxygen and inhalant anesthesia. This allows control of their airway and moment-to-moment adjustments in anesthetic depth.
All patients have IV catheters, so emergency fluids and drugs can be quickly given if necessary. An anesthetist continuously monitors their blood-oxygen saturation, exhaled CO2, blood pressure, EKG, respirations and other external physical signs.
When possible, we practice a combined anesthesia approach. This means using things such as epidurals and local nerve blocks along with general anesthetics. This allows a reduction in the amount of general anesthetic required, which improves safety and optimizes pain control.
Certain conditions may be seen exclusively, or more commonly, in association with certain breeds. The breed can be an important factor in your anesthetic plan.
Although pure anesthetic reactions rarely happen, they do occur. Greyhounds and other sighthounds such as whippets, metabolize many anesthetic drugs more slowly than other breeds, causing prolonged or pronounced anesthetic effects.
Herding breeds such as collies, border collies, Australian shepherds, shelties, etc, have a high prevalence for a mutation at the ABCB1 gene (formerly known as MDR1). This defect diminishes effectiveness of the blood-brain barrier, which normally prevents drugs and toxins from accumulating in brain tissue. This defect can result in severe, even fatal, drug reactions to certain anesthetic agents, and a host of other non-anesthetic drugs.
Other breed factors do not relate specifically to drug metabolism but can influence anesthetic risk. For example, bulldogs and similar breeds such as pugs are called brachycephalics. They tend to have smaller tracheas, so we plan for smaller tubes. They have narrow nasal passages, and lots of tissue that can block their airways. We always have to take special care in monitoring these patients as they pose a special risk for developing breathing problems hours after anesthesia has ended.
Some breeds, such as boxers and Doberman pinschers, have higher than average incidence of cardiac issues. Particular care should be taken in screening these cases.
Individual patient factors are by far the most important part of the plan. These relate to the actual issues affecting an individual patient and are elucidated by compiling existing medical records, physical examination findings and diagnostic test results.
Age, for example, is a patient factor, but by itself means little. In veterinary anesthesia, we say that age is not a disease. That said, we do recognize that age carries increased odds that there is something going wrong. So we may perform a bit more of a diagnostic screen in a 12-year-old than we would in a 6-year-old.
Obesity, cardiac issues, lung disease and metabolic problems are just a few examples from an endless list of factors that influence anesthesia.
Anesthesia is the controlled loss of consciousness and absence of pain perception, but a balanced anesthetic plan provides for the support and monitoring of the patient from the administration of premedications completely through recovery. Close patient monitoring, sometimes for many hours following recovery, is essential to anesthetic safety. How often have we heard of the patient that was doing well after surgery, who was later found to have died in the cage?
Anesthetic reaction? Not likely. In fact, most cardiac arrests attributed to anesthesia occur after the surgical procedure has been completed. When a patient is hypothermic and shivering, as many, if not most, post-op cases are, their oxygen requirements can go up by 200 percent to 400 percent. Combine that with a patient who has woken up crying and was immediately given a dose of morphine. Now their respirations are depressed but their oxygen needs are quadrupled. That's a complication in the making, and without close monitoring, a possible fatality.
In summary, anesthesia can be performed safely on virtually a healthy animal of any age, but one size does not fit all. The protocol should be tailored to the individual based upon its breed and physical traits. Safety measures, such as IV catheters, must be built in. Most importantly, the patient must be monitored from the moment pre-anesthetics are given until they have completely regained their pre-anesthetized balance. This may be many hours. Under these circumstances, your anesthetic risks are truly minimal.