March 28, 2013
Even specialists can learn a lot from each other. I recently talked to an infectious disease specialist and an anesthesiologist to find answers to some common but tough questions.
Say your patient has had a TPLO, or a fracture repaired with a plate and screws. A few days, months or years after the surgery, your patient has a urinary tract infection. How worried should you be about surgical site infection (a.k.a. SSI)?
Scott Weese, a board-certified internist turned infectious disease specialist at the University of Guelph vet school (Canada), says that the risk is probably not too high. We don't have clear evidence that dogs with UTIs are likely to become bacteremic, which would be the main route of UTI-associated SSI.
Having an opportunistic pathogen in the bladder probably doesn't constitute that much added risk because the bacteria would be dwarfed by the large populations of commensal flora containing potential pathogens in the gut, skin and other locations.
Would Dr. Weese's answer change if the culprit were a methicillin-resistant bacteria?
In the case of an active or recent methicillin-resistant staphylococcus aureus or staphylococcus pseudintermedius, or for that matter, any other concerning multidrug resistant bacteria, Weese would be more worried. Not so much because bacteria would go from the bladder to the surgical site.
Rather, it's because of the odds that the dog is concurrently colonized with the evil bacteria in the gastrontestinal tract or on the skin, which would probably raise the SSI risk.
Do surgical patients with bad teeth have a higher risk of infection when we do a dental cleaning on the same day?
It is clear that “dentals” will result in bacteremia. The question is whether that poses a true surgical risk.
“We don't know,” said Weese, because “no one has really been able to look at it, in part because of the limited study of surgical site infections and probably as importantly, the inability of most SSI studies to prove something like this.”
Weese is finishing a one-year prospective study involving 30-day post-op follow-ups of around 1,000 surgical cases, using standard SSI definitions.
However, they'll never find an association between SSI and “dentals” because they ethically would never do the two procedures on the same day.
Most people probably get away with it, because the incidence of SSIs for most procedures is low, the implications are often limited, and people don't actively look for SSIs or pay much attention to associations. A superficial SSI following a spay or lumpectomy, however, is much different than a deep SSI following a more involved procedure or one involving an implant.
Many canine and equine surgeons had been happily using bupivacaine to block joints for years, until Geoff Hennig, a board-certified surgeon in Round Rock, Texas, threw a (sterile) wrench in the analgesia world by publishing an article1 explaining the chondrotoxicity of the drug.
In the human world people sue their physicians after a joint is injected with bupivacaine. So why take a chance? Should we really ignore Hennig's clear warning in the clear conclusion of his well-researched study: “Intra-articular administration of bupivacaine is not recommended for clinical use until additional studies are conducted”?
Mepivacine can be used to “block” joints; for example, before OCD surgery in this 7-month-old Labrador mix. Photos Courtesy of Dr. Phil Zeltzman
One prudent alternative is to use mepivicaine, said Kurt Grimm, a board-certified anesthesiologist at Veterinary Specialist Services in Conifer, Colo. He recommends using a dose of 5 to 8 mg/kg in cats and dogs. Because of the large volume involved, you could administer half the dose preop and the other half postop.
This local anesthetic has a quick onset (five to 10 minutes) and intermediate duration of action (two to three hours).
Bradycardia is one of the most common complications under sedation or anesthesia. Should you give atropine or glycopyrrolate to fight the slow heart rate?
Dr. Grimm confirms: When bradycardia is combined with hypotension, giving an anticholinergic (atropine, glycopyrrolate) will increase the heart rate.
Conversely, when bradycardia is combined with hypertension, giving an anticholinergic may actually be harmful, says Grimm. If all you monitor is the heart rate, you need to make an educated guess as to whether blood pressure is high or low. This is yet another reason to measure blood pressure and monitor the ECG during anesthesia.
In addition, anticholinergics usually cannot predictably raise the heart rate when the problem is low sympathetic drive instead of high vagal tone, both of which can cause bradycardia.
To read more about making anesthesia safer, click here.
Some colleagues give atropine or glycopyrrolate to every preop patient as part of their standard premedication. Grimm acknowledges that routine use of anticholinergics is a longstanding point of disagreement among veterinarians. There are valid pros and cons for each side.
Clinical experience suggests that healthy dogs and cats are able to tolerate higher heart rates and blood pressures which may accompany “iatrogenic” tachycardia, i.e. tachycardia induced by atropine or glycopyrrolate. If you anesthetize mostly healthy animals, you are unlikely to notice many complications from routine use of anticholinergics.
However, if your patient has a heart condition, which reduces the myocardial oxygen reserve (e.g., hypertrophic cardiomyopathy), or is susceptible to hypertension-associated problems (e.g., retinal hemorrhage), then tachycardia and/or hypertension can cause significant morbidity or even mortality.
Instead of using routine protocols or cocktails, you may want to consider the potential consequences caused by tachycardia and/or hypertension on a case-by-case basis.
Dr. Phil Zeltzman is a mobile, board-certified surgeon in Allentown, Pa. He is the co-author of “Walk a Hound, Lose a Pound.”
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