Understanding 'adverse anesthetic events' in pets (Part 1: The numbers)

Patty Khuly, DVM
Published: November 16, 2008
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Sadly, everyone knows someone whose pet has died mysteriously under anesthesia. This disturbing knowledge, second-hand though it may be, makes even the most rational among us cringe when it comes to having our own pets anesthetized.

It’s one thing to know that emergencies must be dealt with anesthetically. We accept that broken bones, swallowed toys and lacerations are inevitably treated to a dose or two of a variety of drugs to render our pets unconscious as their lesions are treated. It’s quite another, however, to accept that their routine care get the same potentially dangerous treatment.

Consider my own Frenchie's brain tumor as example. All told, Sophie went under anesthesia 22 times in the course of the diagnosis and treatment regimen required for her survival. Scary as it was, I hardly allowed myself to think about it given the lack of alternatives.

Yet for the simple dental cleaning she currently requires…I find myself putting it off, week after week.

I know it’s mostly irrational, this fear of anesthesia. Sort of akin to a phobia of spiders…or to the big flying cockroaches we South Floridians famously fear. But we all suffer it, no matter how often we anesthetize others’ pets or have had our pets successfully anesthetized in the past. We intuit that each event is a new opportunity for the statistical possibility of the unthinkable.

“Adverse anesthetic events” is what we call them. And this week I’ve been playing around the Web looking for studies as back up for what my experience tells me daily: the risk of anesthetic death is a slight one.

Problem is, few good studies have been conducted in this area. The most commonly cited one is a twenty year-old study out of Ontario published in the Journal of the American Animal Hospital Association (JAAHA). It found that the risk of anesthetic death was 0.11% and 0.1%, out of 8,087 dogs and 8,702 cats, respectively. The total risk of anesthetic complications affected 2.1% and 1.3% of canine and feline patient groups in this study.

Overall, then, this means that twenty years ago, one out of every thousand patients in what we could infer to be an average small animal practice, experienced the worst possible outcome of anesthesia.

No matter how much faith you might have in this study’s methodology, the conclusion is clearly a crude estimate, at best. (Those percentages have likely come down significantly with the introduction of newer anesthetics and specialized vet medicine.)

It does, however, ring true. It’s roughly what my experience (over the past twenty or thirty years working in small animal hospitals) dictates is the norm for patients in average small animal hospital settings.

And that’s pretty scary if you think about it. Though my stats are better (I’ve never had a flat-out death, just some very scary close calls where the patients were left blind or otherwise impaired, even if only temporarily), I rarely engage in lengthy anesthetic procedures. I’m a wimp. I very seldom keep animals under anesthesia for more than an hour. I leave the longer procedures to better-equipped facilities.

Nonetheless, it’s inevitable that in the course of my career I’ll be responsible for administering anesthesia to one of these casualties. I’m not stupid enough to think that I’ll be lucky forever—or that keeping my procedures short will always be enough to keep me out of trouble. (I certainly don't consider myself to be better than others for my good fortune.)

At issue when we discuss “adverse anesthetic events” as a problem is the understanding that some of these events are avoidable…and some are not. The statistics don’t convincingly attempt to separate medical error or events that might have been averted with more diligent care. Doing so would be an onerous task more applicable to the human medical arena where generous funding and assiduous post-mortem examination is the norm. In vet medicine these commonly cited stats generally apply, then, for all types of anesthetic complications and deaths.

And that’s why everyone should be aware of what can be done to minimize the risks inherent to all patients undergoing anesthetic procedures.

Check out tomorrow’s post for a detailed breakdown of the policies, procedures and techniques we employ in doing our best to ensure the unthinkable doesn’t happen to your pets.