A four-year-old Labrador retriever presents to you after a few days of vomiting. You work the dog up and find small intestinal distension consistent with an obstruction on radiographs. Off to the operating room you go!
After exploring the abdomen, you find a sock causing a complete obstruction of the mid-jejunum. The intestine orad to the obstruction is distended with mild bruising. A single enterotomy and the offending object is removed. You finish the surgery and, aside from some hypotension, your patient does well with anesthesia.
You’re feeling great! You go ahead and pat yourself on the back as the dog is discharged the day after surgery, eating and wagging its tail. About a week after surgery the dog, presents with drainage from the incision site. Ugh. The dreaded surgical site infection. Why did this happen? Were there missed risk factors? What is the best treatment, and how can this be prevented for future cases?
Surgical site infections (SSI) are a risk for any surgical endeavor. They are defined as an infection occurring anywhere in the operative field after a surgical procedure. SSIs are further defined by their location (superficial, deep, body cavity) and time frame of development relative to the surgery (within 30 days vs. longer than 30 days). The type of surgery also influences the risk of development—clean, clean-contaminated, contaminated, and dirty.
Clean surgeries are ones where the abdominal viscera are not entered (i.e. ovariohysterectomy, castration). These surgeries have the lowest complication rates and are reported to be only around two percent. Dirty surgeries are those such as septic abdomens, draining tracts, and necrotic wounds and have the highest reported SSI rate—close to 20 percent. Surprisingly, some clean orthopedic procedures, such as a TPLO, have infection rates reported to be as high as 18 percent (Watson Vet Surg 2019)!
Patient risk factors
Patients with endocrine disorders, especially hyperadrenocorticism and hypothyroidism, have an increased risk of developing infection after surgery. What about our allergic patients? Dogs with uncontrolled allergic disease tend to carry more bacteria on their skin and have an environment more likely to promote infection.
A thorough pre-operative exam is prudent to catch evidence of pyoderma. If possible, elective procedures can be delayed until pyoderma resolves, or at least until initial treatment is started.
Anesthesia risk factors
The American Society of Anesthesiologists Classification System can help determine the stability of a patient pre-operatively. A score greater than three has an increased risk of surgical site infection. Longer anesthesia times can lead to a higher infection rate, and this can be independent of length of the surgical procedure itself.
Procedures/tasks that may prolong anesthesia time include pre/post-operative imaging, ear cleanings, etc. Each hour of anesthesia can increase the risk of infection by about 30 percent. Peri-anesthetic hypotension has inconsistently been associated with infection. Monitoring and appropriate intervention for anesthetic abnormalities can help with improved outcomes and potentially decreased risk of development of a SSI.
Hospital risk factors
Clipper blades can be fomites for infection, as well as cause micro-trauma to the skin if not appropriately sharp. One study found more than 50 percent of clipper blades cultures in veterinary hospitals cultured positive (Mount, J Am Anim Hosp Assoc 2016). The surgical site should not be clipped until immediately prior to surgery.
Other potential fomites include scrub bowls, cages, multi-dose medication vials, and endotracheal tubes.
If there seems to be an uptick in surgical site infections in your hospital, it’s worth taking a look at what may have changed. Is there a new technician responsible for pre-operative scrubbing? Has there been a change in surgical scrub that needs a longer contact time? Have clipper blades become dull and need to be replaced?
A review of proper hand hygiene practices with all staff members is never a bad idea.
Surgeon risk factors
The longer the surgical procedure, the higher the risk of infection. The risk of surgical site infection can double with every hour of procedure time.
We also see less infection with a more experienced surgeon. This is likely due to shorter surgical time, more accurate surgical approach and dissection, as well as less traumatic tissue handling. The more people in the operating room, the greater the risk of infection after surgery. This can be especially problematic in teaching institutions, or when training new staff members.
Licking at the surgical site and too much motion can contribute to inflammation and infection. The use of an E-collar or similar deterrent is advised, even after the simplest procedures. Client education about activity restriction prior to the procedure is important to ensure the expectations are clear.
Clients should be advised if the patient is allowed to lick at the incision, additional costs are likely to be incurred including additional office visits, antibiotics, and wound management.
Practices that do not help
Therapeutic antibiotics have not been shown to be beneficial at preventing infection, unless there was an unexpected change in classification of surgery (clean-contaminated surgery becomes a contaminated surgery) or there is a major break in sterile technique.
This is different from prophylactic antibiotics—an antibiotic given within one hour of the start of surgery for anticipated bacterial invasion. The general recommendation for clean surgeries is to discontinue antibiotics within about 24 hours of surgery.
Even with meticulous aseptic technique, excellent tissue handling skills and appropriate prophylactic antimicrobial administration surgical site infections will still happen. Early recognition of the infection is key for successful and efficient resolution.
One challenge is most infections develop after the patient has been discharged from the hospital. Educate clients on what changes to look for so they can notify you if any concerns arise. Early postoperative inflammation can be difficult to distinguish from infection.
If possible, based on the location of the infection, drainage is appropriate. For a ventral midline incision after an abdominal explore, this may be as simple as removing some of the skin sutures/staples.
Additionally, lavage of the fluid pocket can decrease the bacteria load at the site. If unhealthy tissue is present, sharp debridement will help clear inflammation and infection sooner.
Surgical/wound drains can be a double-edged sword. They can be helpful if large fluid pockets are present to facilitate drainage and decrease dead space; however, they come with their own problems and limitations—potentially introducing bacterial contamination to the site. Bandaging can limit further contamination of the site with environmental pathogens, as well as protect the inflamed and infected site. Any surgical implants may need to be removed to help clear the infection.
Ideally, a culture of the site should be obtained. Starting broad-spectrum empirical antibiotics until culture results are available is recommended. If an implant has been removed, it can be included in the culture (a screw from a bone plate, extra-capsular suture, etc.).
Let’s take a look back at our patient. Were there risk factors for SSI development we missed? Looking back in the medical record we see that this patient had a history of allergic disease and had been treated for Staphlococcus pyoderma infections a few times in the past.
Pre-operative blood work identified mild hypoalbuminemia. After some discussion with the client, this patient was allowed free access to the backyard a few days after surgery because the dog was feeling so well.
Possible factors increasing this patient’s chances of developing an incision infection were allergic skin disease, clean-contaminated surgery, hypotension, and owner compliance. Some of these factors we can try to control—strict adherence to Halsted’s principles for surgical technique (gentle tissue handling, hemostasis, preservation of blood supply, strict aseptic technique, minimizing tension, accurate apposition, and removal of dead space), anesthetic monitoring, and intervention for hypotension and other abnormalities, and client communication to encourage appropriate aftercare.
Even under perfect conditions, surgical site infections can happen. Knowing how to deal with the infection so that the patient can heal efficiently without contributing to bacterial resistance is key!
Kendra Freeman, DVM, MS, DACVS (large animal), DACVS (small animal), is a graduate of Colorado State University and maintains dual certification with the American College of Veterinary Surgeons. She is an associate surgeon in Albuquerque, New Mexico. Her case load consists of orthopedics, general soft tissue and sports medicine cases with the occasional return to her roots in large animal lameness and surgery.