Surgical site infection: Clinical sciences

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Introduction0:00–0:47

Surgical site infection, or SSI for short, is a common postoperative complication. This is most commonly caused by gram-positive bacteria living on the skin, but can also be caused by other pathogens such as anaerobic gut bacteria encountered during bowel surgery.
Depending on the depth of infection, SSI is subdivided into three types. Superficial incisional SSI is the least invasive type that’s limited to the skin and subcutaneous tissue; deep incisional SSI affects deeper tissues like muscle and fascia layers; and organ space SSI, which is deep within the organ or body cavity where the surgery occurred.
The first step in approaching someone suspected to have SSI is to obtain a focused history and physical examination. The person’s history is especially important.

History & Physical0:47–3:28

Most cases of SSI develop between 4 and 30 days after surgery, but this does not include necrotizing infections like Group A strep or Clostridia, which would present within 48 hours and progress rapidly.
Individuals with SSI may report pain or tenderness at the surgical site. Importantly, the person’s surgical history will provide details to help determine their risk of infection.
Next, you can use surgical wound classification to identify those at risk for SSI. Surgical wound classification is based on the degree of contamination and includes four main categories: Clean, Clean-contaminated, Contaminated, and Dirty.
The likelihood of SSI increases drastically across these groups. Classification depends on infectious risk factors, such as location, trauma history, or breaks in sterile technique.
For example, wounds in colonized areas like the mouth or urinary tract are at a much higher risk for developing SSI, as are open traumatic wounds.Some high yield facts to keep in mind!
One major consideration when evaluating SSI is any history of surgical implant, such as joint replacement surgery or mesh hernia repair.
Implants are a big risk factor for SSI, since bacteria can cling to the foreign material and cause infection.Moving on to the physical exam, there might be peri-incisional signs of infection such as swelling, warmth, and erythema, or purulent drainage from the surgical site.
Sometimes, the incision can split open at the skin, which is called dehiscence. There could also be induration where the skin becomes harder and thicker due to inflammation, and fluctuance which is a collection of pus under the skin, giving it a “boggy” feel on palpation.
Additionally, there might be systemic signs of infection, such as fever, tachycardia, and hypotension, suggesting the infection has spread throughout the body.
Point of care ultrasound, or POCUS is often done during the physical exam to find abscesses that can’t be detected clinically.
If the wound is open and has peri-incisional signs of infection, a wound swab should be sent for culture and gram stain.
If there are systemic signs of infection, a complete blood count and blood cultures should also be sent.After the history, physical and labs have been obtained, it’s time to determine the type of infection.

Superficial incisional SSI3:28–5:19

The first type you might diagnose is superficial incisional SSI. This occurs up to 30 days after surgical intervention and is limited to the superficial incisional skin and subcutaneous tissues.
You will see peri-incisional signs of infection with purulent drainage or a positive wound culture. Peri-incisional pain or tenderness is also common.
Because these infections are so superficial, it is rare to see systemic signs of infection. When it comes to treatment, the surgical team will perform bedside wound opening.
In this procedure, sutures or staples are removed from the skin to open the affected part of the incision and allow the infection to drain.
The wound is probed to explore the depth and extent of tissue involvement. Next, any necrotic tissue is debrided, and infected fluid is collected for culture and gram stain.Tailored antibiotics should be started only if the peri-incisional signs of infection extend more than five centimeters from the wound edge, if they fail to improve after bedside wound opening, if the person has an implanted material, or is immunocompromised, or if there are systemic signs of infection.
Once we’re done with bedside wound opening, ongoing wound care should be performed to facilitate the healing process. Wound care typically includes serial irrigations to wash out the wound, as well as serial dressing changes.
Deeper wounds might require wound packing, which involves tucking sterile gauze into the open wound cavity. With basic wound care, most wounds can close by secondary intention.
This means that the wound is not re-sutured, and will fill in and close up naturally over time. Alright, let’s move in a bit deeper to the next type, which is deep incisional SSI.

Deep incisional SSI5:19–7:06

This type of infection occurs within 30 days of surgeries that have lower risk of infection, or 90 days of surgeries that have higher risk of infection such as abdominal surgeries.
The infection extends deeper to peri-incisional muscle and fascia layers, so you will see signs like dehiscence, purulent drainage, or a positive wound culture from these deep tissues.
When you palpate the incision, there can be pain and tenderness, and sometimes you can feel a fluctuant, or soft and fluid-like mass, suggesting an abscess pocket.
Because of the deeper involvement, systemic signs of infection like fever are more common.Just like in superficial incisional SSI, initial treatment of deep incisional SSI requires bedside wound opening.
However, unlike a superficial infection, all cases of deep incisional SSI require antibiotic treatment, which should be started empirically.
Once we have wound culture results, we can switch to tailored antibiotics. In some situations, deep incisional SSI may require a trip back to the operating room for surgical re-exploration.
This is typically reserved for extensive or severe infections, especially those that did not improve after bedside wound opening and antibiotics.
Re-exploration requires a full opening of the surgical incision, allowing exploration and irrigation of the infected area.
If a surgical implant is present, removal should be considered. Once re-exploration is complete, the surgical incision might be re-closed or left open for ongoing drainage.
If the incision is left open, long-term wound care will be needed until the wound fully heals or is closed at a later time.Alright, the final and deepest type of surgical site infection is called organ space SSI.

Organ space SSI7:06–9:34

This type also occurs within 30 or 90 days of surgery, depending on the surgery’s classification for infection risk. Be on the lookout for this type of SSI after procedures involving implants or bowel anastomosis.
Anastomosis means the surgical creation of a new connection, so bowel anastomosis means opening the intestinal tract and then re-forming a new connection.
If this new connection is leaky, gut bacteria can spill into the abdominal cavity, which is a common cause of organ space SSI.
Unlike in the previous two types, individuals with organ space SSI usually lack peri-incisional signs of infection, but they do present with systemic signs of infection, such as fever or hypotension.
Sometimes a drain is present from the initial surgery, allowing excess fluid from the affected organ or space to drain out postoperatively.
If you suspect organ space SSI and the person has a drain in the surgical space, examine the drainage and send the fluid for culture and gram stain.
If the drainage is purulent or if the culture comes back positive, this is enough to diagnose organ space SSI. If the person doesn’t have a drain, or the diagnosis is still unclear, you should order a CT or MRI.
Imaging will show signs of infection in the affected organ or space, typically an abscess or fluid collection that is deep to skin, fascia, and muscle layers.
Once you diagnose organ space SSI, call Interventional Radiology for image-guided percutaneous drain placement. This procedure uses real-time image guidance to thread a suction drain through the skin into the deep fluid collection.
This is especially important if there’s no drain in place, but even if there is a drain, they might be able to place a bigger one.
This drain will stay in place temporarily for ongoing infection control, and any drained fluid should be sent for culture and gram stain.
Also, you should administer empiric antibiotic therapy and then tailor it based on the culture results. If the infection cannot be fully treated with drain placement and antibiotics, surgical re-exploration is required.
This is particularly important for source control, such as repairing an anastomotic leak or removing an implant. As a recap…surgical site infection, or SSI is divided into three types based on the depth of infection and this is mainly based on the physical exam and a recent history of surgery.

Review9:34–10:24

Superficial incisional SSI is the least invasive type that’s limited to skin and subcutaneous tissue near the surface of the surgical incision.
Deep incisional SSI affects deeper tissues within the incision like muscle and fascia layers. Lastly, organ space SSI describes an infection deep within the organ or body cavity where the surgery occurred.
Treatment varies by type of SSI, but usually involves opening the infected area for drainage and debridement of necrotic tissue, and antibiotics when appropriate.
For deep incisional SSI and organ space SSI,