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Debridement
The best way to deal with bacteria is to get rid of them, said Hendrickson, a professor in the Clinical Sciences Department at Colorado State University’s Veterinary Teaching Hospital, in Fort Collins.
“We have a tendency in veterinary medicine to want to kill the bacteria in situ, but I’m going to encourage you to remove them and throw them away and don’t let the patient have to deal with them at all,” he advised the audience.
Veterinarians can remove bacteria through debridement (removing the affected tissue), of which there are several types:
Autolytic debridement. This process uses the body’s own enzymes and moisture to liquefy and remove necrotic (dead) tissue. Hendrickson said it’s the most selective way to remove bacteria and dead cells while leaving healthy cells.
“All you’re doing is leaving the healthy wound exudate (liquid the body produces in response to tissue damage) in contact with the wound bed to accomplish this,” he said. “The normal white blood cells and proteolytic enzymes that occur in wound exudate are your best friends with regard to removing small doses of bacteria and small amounts of necrotic tissue.”
To achieve autolytic debridement, you must keep the wound environment moist (but not soupy), which you can do using dressings. If the wound has a lot of necrotic tissue, however, then you’ll need to use a more aggressive form of debridement, said Hendrickson.
Biological debridement. This method involves using an organism, such as maggots, to remove dead tissue.
“It still amazes me how effective maggot debridement is and how rarely we actually use it,” said Hendrickson. When a horse comes into the clinic with maggots in its wound, he said people tend to get squeamish and try to remove them, but “these guys are doing their job—they’re getting rid of the necrotic tissue (and pathogenic bacteria). There’s a lot of value to that, and it’s very rapid and selective.”
Enzymatic (chemical) debridement. With this method, veterinarians apply manufactured proteolytic enzymes to the wound to break down devitalized tissue.
“This is another great way (to debride wounds), but we don’t tend to use it very frequently in veterinary medicine because of the cost of the enzymes,” said Hendrickson. “Studies have found it to be very effective at reducing bacteria but not as good as autolytic debridement. So the body in and of itself is the best way to go if you have low levels of bacteria.”
Mechanical debridement. This technique involves using force to remove tissue. Examples include wet-to-dry dressings and wound irrigation. “It’s something we do really well in veterinary medicine, almost to a fault,” he explained. “We scrub, we lavage, and we cause a significant amount of trauma to the wound bed.”
On the plus side, mechanical debridement is inexpensive and effective. The downside? It can “cause shear stresses to the underlying granulation (scar) tissue, which can lead to further problems down the road,” Hendrickson said.
He recommended using the minimal amount of force and pressure necessary.
Sharp debridement. This method involves using tools such as scalpels or curettes to physically remove tissue. It’s the most aggressive form of debridement and the most effective way to remove large amounts of bacteria and necrotic tissue, said Hendrickson.
“There’s a lot of value to wound debridement—that should be your first step toward reducing bacteria numbers and necrotic tissue,” he said. “We should not be bathing them with local or systemic antimicrobials. Remove the infected tissue that’s there.”
Debridement Dressings
Veterinarians can use a variety of debridement dressings to help remove bacteria and dead tissue. Ones Hendrickson said are useful include:
Hypertonic saline. This solution comprises 20% saline, which you can buy commercially or make yourself using salt and water.
“The idea is the hypertonic environment created by this saline will kill the bacteria because they’re unable to deal with that environment, and it will also remove the necrotic tissue,” Hendrickson said.
While these are highly effective, he said they’re less selective than autolytic, biologic, or enzymatic dressings. He also cautioned against overusing them, because they have the potential to be toxic.
Honey. This substance is both hypertonic and antimicrobial. It can help heal burns, for instance, faster and with fewer adverse effects than other dressings, said Hendrickson.
Researchers have performed a variety of studies confirming the efficacy of honeys such as manuka honey. Further, said Hendrickson, “there’s some recent evidence out there that shows that local raw honey is more effective at killing local bacteria than medical grade honey.”
Polyhexanides (e.g., polyhexamethylene biguanide, or PHMB). Certain sterile antimicrobial dressings are very effective at killing bacteria, even multidrug-resistant varieties. They’re not antiseptics and should not be confused with them, said Hendrickson.
Antibiotics
He then provided the audience with smart antibiotic use tips for when they do need these drugs to combat infection, starting with a sensitivity culture to identify the specific bacteria.
“Whether it’s systemic or local antibiotic therapy, do a culture to know what’s happening, then always use the simplest, lowest level of antibiotic possible,” he said. “While your first dressing might require using an antibiotic you can’t pick because you don’t know what’s there, at least try to get a culture so you can make the decision later on.”
Only use antibiotics for short periods—two weeks or less, he said.
As for topical antibiotics, he recommended using silver dressings or, preferably, triple antibiotic, which hasn’t seen much resistance over the decades it’s been in use.
Hendrickson also reviewed promising studies looking at mesenchymal (embryonic connective tissue) stem cell use in wound treatment: “The one place there is evidence for stem cells is in the reduction of bacteria numbers in wounds.”
Take-Home Message
“There are lots of ways to reduce bioburden (number of bacteria) in wounds,” said Hendrickson. “I think wound debridement is the best way to accomplish that. Get rid of the necrotic tissue, and don’t use antiseptics in your wounds, because they just create more necrosis, thereby encouraging the number of bacteria forming.”
And if you do have to resort to antibiotic administration, choose your antimicrobials well, and use them sparingly, he said.
