Medical News Today: Why do dogs develop infections after surgery?

After canine surgery, it is relatively common for the wound to become infected. However, it is not clear how often this occurs, what increases the risk, and how much it affects treatment costs. A new study looks for answers.

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Although scientists have invested a great deal of time in understanding surgical site infections (SSI) in humans, they know much less about these infections in animals.

Researchers have a good idea about which factors are likely to increase the risk of postsurgical infection in humans, but, again, the picture is not so clear in animals.

Recently, a group of veterinary scientists set out to understand how often surgical wounds in dogs become infected. They also asked what factors make it more likely and investigated the costs associated with these infections.

The authors of the study, which features in BMJ Vet Record, explain why this work is important:

“These infections are responsible for an increase in morbidity, mortality, prolonged hospital stay, increased costs, and a negative impact on the emotional state of the owner.”

A fresh look at an old problem

Although only a few studies have investigated the prevalence of SSI in dogs, the authors of the research study note that current estimates range from 3% to 6.6%.

They explain that some of the previous results might have been open to errors. For instance, some studies could not differentiate between inflammation and infection, while others relied on diagnoses by people lacking training.

To investigate, the researchers used data from a veterinary teaching hospital. During the study, 184 male and female dogs of all ages underwent soft tissue surgery.

Alongside details on the dogs’ health following surgery, the researchers also collated information about each animal’s age, sex, reproductive status, underlying conditions, and breed.

They also looked at surgical factors, including the type of surgical scrub that the surgeons used, how many people participated in the procedure, whether undergraduates took part, the type of surgery, how long it took, and how the team sealed the wound.

Assessments of the animals took place in the hospital 5 days and 10 days after the procedure. The researchers also followed up at the 30 day mark with a telephone call.

New risk factors

Of the 184 procedures, SSI occurred in 16 cases, which equates to 8.7%. The age, sex, and breed of the dog did not influence the risk of SSI. However, as hoped, the authors did identify certain factors that were associated with an increased risk.

For instance, they found that steroidal anti-inflammatory drugs increased the risk of infection. According to the authors, this association — which is new to veterinary science — might be because steroidal anti-inflammatory drugs cause immunosuppression, making infection more likely.

The authors also found that SSI risk was greater for dogs with higher-than-normal blood glucose levels (hyperglycemia) before the operation. Although researchers have not shown this link in animals before, hyperglycemia is a known risk factor for SSI in humans.

According to the researchers, studies have shown that hyperglycemia reduces the ability of white blood cells to pass through the walls of capillaries, preventing them from reaching the site of infection.

Risk also increased for the dogs that underwent operations that lasted longer than 1 hour. The medical community also considers a long surgery time to be a risk factor for human SSI.

Similarly, animals that needed a urinary catheter had a higher risk of infection. Again, this is a new finding for veterinary science, which, the authors believe, the known link between catheters and urinary tract infections (UTIs) might explain. The authors note:

“[T]he microorganisms responsible for the development of UTIs could easily be involved in the colonization of surgical wounds.”

The scientists also showed that if animals did not receive an Elizabethan collar (also called a dog cone) after surgery, the risk of infection increased. The authors write that this “could be explained by the existence of [a] certain degree of self-mutilation in veterinary patients when the healing surgical wound is not protected.”

Bacteria from the dog’s mouth can pass freely to the surgical site and cause an infection.

Increased costs and the future

As for the cost of SSI, the researchers found that although presurgical and surgical costs did not increase in infected dogs, postsurgical costs rose by 142.2%. The authors outline the reason for the increased expense:

“This increase is mainly due to the need for a greater number of follow-up appointments, the cost of additional treatment, as well as the performance of culture and antibiotic sensitivity tests.”

In this study, the researchers used what they refer to as an “active surveillance system.” In other words, trained personnel checked the surgical wound at regular intervals.

The authors believe that this system helps explain why they reported a higher rate of infections than earlier studies that did not use such a system.

The authors conclude that “avoiding surgical infections is vital to preserve the patient’s overall health status and to avoid unnecessary expenses. In fact, the implementation of surveillance and control systems for SSIs could reduce the economic costs and improve the service offered to patient and owner.”