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Going Under


© American Kennel Club, Inc., 2007.

No portion of this article may be reproduced without permission of the copyright holder. Reprinted with permission from American Kennel Club, Inc., ..

Although safer than ever, anesthesia still has its dangers. But a few questions and precautions can reduce the risks.

It was all supposed to be routine. On the morning of September 28, 2003, Jon Baron and Tracey Ng had left Puff, their 6-year-old Alaskan Malamute, at the vet to have her teeth cleaned.

She was a strong, healthy dog, and that's why the call that came in the afternoon so stunned the Union City, California, couple.

"They said she had gone into cardiac arrest toward the end of the dental procedure," recalls Baron. Her heart had stopped for about seven minutes.

The vet got Puff's heart beating again, but when Baron and Ng got the call she was not breathing on her own and responding to no one. Hopes for her survival were dim.

One thing seemed certain: Even if she pulled through, Puff might never be the same.

Fear of Letting Go

It's a dog owner's worst nightmare. A healthy dog goes in for a minor procedure and dies under anesthesia. The prospect is so terrifying that some people avoid important surgeries, such as spaying or removing a lump that may be cancerous.

"The fear of anesthesia is the fear of letting go and wondering if you're going to ever wake up," says John W. Ludders, DVM, professor of anesthesiology at Cornell University. "For people to have that fear for their pets is understandable."

Anesthesia is the process of using drugs to produce a state of unconsciousness and lack of pain perception for procedures that could not be performed otherwise.

Removing a small wart and other minor procedures may require local anesthesia, blocking pain in one small area of the body. Major surgery or extensive diagnostics require general anesthesia, in which the animal is rendered unconscious.

Veterinarians must rely on general anesthesia more often than doctors who treat humans, and for routine procedures, such as cleaning teeth or performing a hip X-ray.

"It's frustrating in veterinary medicine," says Helen Hamilton, DVM, MS, DACVIM, an internal medicine specialist in Fremont, California, and a Greyhound fancier. "There's so much we can do with humans. We can tell them to 'Hold still' or 'Open your mouth.' But we can't make an animal hold still for any length of time if pain is involved. They immediately want to leave."Death

Rate Dropping

While there is always a risk, Ludders says that over the years anesthesia has become much safer-for both humans and animals.

"I won't say it's perfect, but it has improved." says Ludders, noting that research has documented a decline in the anesthesia-related death rate in small animals.

One of the largest studies, conducted by a team led by James S. Gaynor, DVM, Colorado State University, looked at 2,556 dogs treated at the institution. The research was published in the Journal of the American Animal Hospital Association in 1999.

Gaynor pointed out that the death rate in the 1950s was 1.2 percent. Since then, it has dropped 64 percent, to 0.43. Ludders estimates that it is likely to be even lower in general practice because university hospitals usually treat sicker animals.

Scientists attribute the improved safety record to better anesthetic agents and monitoring techniques.

What Goes Wrong

Many veterinarians consider monitoring the most important factor in avoiding problems, along with a knowledge of the most frequent complications.

In Gaynor's study, 12 percent of the dogs experienced some kind of anesthesia-related complication. Heart problems topped the list, particularly low blood pressure (7 percent), and irregular heartbeats (2.5 percent). Respiratory problems occurred in 1.3 percent.

"We know these complications happen under anesthesia and a lot of people say, 'Oh, that shouldn't happen,' " says Ludders. "But that's really not the point. The point is that the monitoring techniques we have available to us now allow us to detect these complications."

In Hamilton's practice, every patient is assigned a nurse who does nothing but monitor vital signs and reactions to anesthesia, which are gauged by several pieces of equipment, including, for most dogs, EKGs, pulse oximeter, blood pressures, and IV pumps. High-risk dogs will have additional monitors.

"About 95 percent of the time her job is ho-hum. Nothing happens. The dog goes down, the dog comes up, the dog is fine," says Hamilton. "But for that [small percentage] of dogs whose blood pressure drops, who start having cardiac arrhythmias under anesthesia, who are not ventilating well and their oxygenation drops, then you stop what you're doing, stop that procedure, and get that dog awake."

Ideally, the experts say, an animal under anesthesia should have several physical functions monitored. These include heart rate, blood pressure, blood oxygenation, and capnometry, measures of how well the dog is breathing.

Such tests can save a life, especially in cases where no one is expecting a problem.

"We had a dog come here from a Chicago specialty practice, a 6-month-old terrier," says Lesley Smith, DVM, clinical associate professor of anesthesiology, University of Wisconsin. The dog was to be spayed, but before the surgery began she briefly went into cardiac arrest.

The dog's vital signs were being carefully monitored, so the veterinarian stopped the procedure and revived her at the first sign of trouble, says Smith. Instead of forgoing spaying, the terrier's vet referred the owners to the anesthesiologists at the University of Wisconsin.

"She did fine here," says Smith, a diplomate of the American College of Veterinary Anesthesiologists, "but we had the benefit of 20-20 hindsight, knowing how she'd reacted to her previous anesthetic." Smith used vigilant monitoring and a different combination of drugs, with careful attention to those drugs' effects on heart function.

Nothing the terrier's regular vet had done had been wrong; the protocol would have been safe for practically any other young dog, Smith says. But something in this dog's unique physical makeup reacted badly with the typical anesthetic. There was no way to anticipate it.

Know the Score

Problems with young healthy dogs are rare, Smith says, estimating that, in a general practice, the complication rate among this group is roughly 1 in 2,000. When a boardcertified anesthesiologist is part of the team, that risk is even lower. Unfortunately, she says, there are only about 175 of these specialists in the country.

But veterinarians generally have a tough task figuring out in advance which dog is most at risk.

"It's very hard to predict that a particular patient will have problems," Ludders says. Anesthesiologists treating both humans and animals rate a patient's potential for problems on a 5-point "physical status" scale, established by the American Society of Anesthesiologists.

"Basically, if it's a very healthy animal, say a young bitch going in for a spay, absolutely in good health, that would be a physical status 1," he says.

The higher the score, the greater the danger, with 5 being dogs at death's door, with a life expectancy of a day or so.

"Does that mean that the animal with the lower score will not have any problems? No, because there are still risks with anesthesia and it's hard to calculate what those would be," says Ludders.

Risks Rise With Age

As with humans, seniors are more likely to have a problem because their hearts, lungs, kidneys, and livers are weaker than those of a younger dog and may not be able to process the drugs as well.

Older dogs are also more likely to be suffering from one or more conditions, such as heart, kidney, and thyroid disease or diabetes. Obesity, an epidemic among old and young, impairs breathing and circulation and can have a significant impact on how a dog comes through surgery.

"Obviously a good physical exam is top of the list for any patient, but certainly for the geriatric patient," says Smith. This may alert doctors to an underlying condition that could rule out the use of certain drugs. In old or seriously ill patients, the veterinarian may decide that the risks of the procedure outweigh the benefits.

Some of the recommended pre-anesthesia tests include a complete blood profile, serum chemistry panel, and urinalysis to check for abnormalities in organ function. Chest X-rays are also needed to reveal signs of cardiac disease or changes in pulmonary function.

Metabolic Quirks

Certain breeds are known to have sensitivity to anesthetics. Chief among these are sighthounds, with their supermodel-lean physique and unusual metabolism.

"The typical body fat of a sighthound is 17 percent versus 35 percent for other dogs. This may affect the redistribution of certain drugs, thus slowing their recovery time," says Hamilton.

They are also prone to hypothermia; they get cold quickly and it takes a long time for them to warm up, which can delay recovery.

Among the sighthounds, Greyhounds, in particular, have many "oddities" requiring special attention, Hamilton says. They have low levels of a liver enzyme that delays metabolism of some medications. Drugs in the thiobarbituate class, such as thiopental and thiamylal, should not be used in these dogs.

Hamilton notes that Greyhounds also appear to be prone to a rare but life-threatening condition-malignant hyperthermia. In this genetic disorder, which has also been seen in Oil humans, certain strains of purebred swine, and dog breeds other than Greyhounds, administration of anesthetics causes a dangerous spike in body temperature. If the signs are noticed early, it may be possible to stop the anesthesia and cool the dog down. But the condition quickly gets out of control and, once that happens, it is always fatal.

Although not as well-documented as the problems in sighthounds, bad reactions to anesthesia have been reported in many other breeds. Some Boxers have impaired tolerance for a commonly used anesthetic, acepromazine. "Boxer-ace syndrome" is characterized by dangerously low blood pressure. Scientists say it appears to be prevalent in certain bloodlines, but so far they do not know what causes it.

Bulldogs and other brachycephalic or pug-nosed dogs often have breathing problems that can be exacerbated by sedation. These dogs may require lower doses of certain drugs and may benefit from additional oxygen before the procedure. Toy breeds tend to develop hypothermia, which can delay recovery.

What's an Owner to Do?

One of the most important things a dog owner can do is to talk openly with the vet before the procedure, especially regarding a breed with a known sensitivity.

"Veterinarians are not all knowledgeable about sighthounds. If I went to a vet I would probably nicely try to ask what anesthetic and what monitoring they are planning to use," says Hamilton.

It's also extremely important, Ludders says, to discuss all over-the-counter supplements or medications the dog may be taking.

"We really need to know if the owner has been treating the patient with an herbal [medication or supplement]. Some of the herbals or the homeopathic medicines are actually quite potent drugs and can have significant effects on the cardiac system, but also on blood pressure regulation," says Ludders. "Herbal or homeopathic medication may interact with the anesthetic drug and produce a more pronounced effect than predicted."

Then ask questions, about how the vet picks the drugs, the people and machines that will be monitoring anesthesia, the recovery.

Ludders says that the most important question an owner can ask is whether the vet uses one anesthetic protocol for all dogs, or whether they tailor the protocol to the needs of the particular patient.

Freak Accident

Even so, no matter what precautions are taken, there are rare instances, as in Puff's case, where a reaction comes as a terrible surprise.

"They used the same anesthetic as when she was spayed. They even used a lighter dose than normal since it was only a dental procedure. Unfortunately the tech performing the dental was also the one monitoring her and didn't notice anything until minutes into the cardiac arrest," says Baron. "I was told later that this is the normal standard of care in most similar clinics."

They are still not sure what went wrong.

As soon as they got the call from the vet, Baron and Ng rushed to the clinic, where they tried to coax any kind of response from their dog. They called her name, rattled her leash, pinched her, rubbed her, popped the tops of soda cans, a sound that she liked, and turned on a vacuum, a sound that scared her.

"Anything that she had a strong reaction to," Baron says. After several hours, Puff lifted her head and seemed to look at them. They decided to keep trying.

It was touch-and-go for weeks. Puff couldn't see, stand, and sometimes she'd howl through the night. But every day, Baron says, there was some slight improvement, some glimmer of hope, so they refused to give up.

Eventually, after months of nonstop care and rehabilitation, including syringe feedings and hydrotherapy, Puff was out of the woods, although she suffered brain damage that left her blind. Her owners wondered how much of the old Puff would return.

Then one day, when Baron opened a can of Coke, Puff came running over to him. "This was not some natural response," he says. "It was memory."

Months after they almost lost her, Baron knew their dog had come back to them.

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