Necrotizing soft tissue infections: Clinical sciences

Chapters:

Watch video only

Introduction0:00–1:08

Necrotizing soft tissue infections, or NSTIs, are rapidly progressing infections causing extensive destruction of soft tissues, including the epidermis, dermis, subcutaneous tissues, fascia, and muscle.
Because the depth of the infection can vary, NSTIs can present as necrotizing forms of cellulitis, fasciitis, and myositis.
These infections can occur anywhere in the body and rapidly lead to limb loss, severe systemic toxicity, and even death if left untreated.
Of the various types, necrotizing fasciitis is associated with the highest mortality rate because of how quickly it can spread within the body.
While the vast majority of NSTIs can be diagnosed clinically, additional tools like a CT scan and LRINEC score can be used to differentiate between NSTI, possible NSTI, and non-necrotizing infections.
When a patient presents with chief concern suggesting NSTI, your first step is to perform an ABCDE assessment to determine whether the patient is stable or unstable.

ABCDE assessment1:08–1:35

If the patient is unstable, you must stabilize the airway, breathing, and circulation first. This includes obtaining IV access, initiating IV fluid resuscitation, and continuously monitoring vital signs.Once you have initiated your acute management, your next step is to perform a focused history and physical exam.

Unstable patient1:35–3:41

History may include severe pain, fever, chills, and foul-smelling discharge. In addition, don’t forget to ask about risk factors for NSTI, such as recent trauma, recent surgery, injection drug use, immunosuppression, or diabetes mellitus.
For patients with diabetes, also ask which medications they take, because some types are associated with Fournier’s gangrene, which is necrotizing fasciitis of the perineum.
On exam, you might see signs of systemic instability such as altered mental status, tachycardia, or hypotension, which can all be attributed to sepsis or septic shock.
The exam will also reveal signs of local infection like erythema, edema, and indurated skin or soft tissue that is firm to touch.
In addition, you might find necrotic tissue with foul-smelling discharge. Finally, crepitus is another important finding to look out for because it indicates the destruction of subcutaneous tissues by gas-forming organisms.
Crepitus feels like tiny pops of air or crunch under the skin. If you find it on a physical exam, you should have a high suspicion for necrotizing fasciitis, which is the most aggressive form of NSTI and a surgical emergency.
However, even in the absence of crepitus, any combination of these clinical findings supports your diagnosis of necrotizing soft tissue infection with sepsis or septic shock.
Here’s a clinical pearl! Keep in mind that this is a clinical diagnosis, but sometimes the infection is too deep and the exam findings might be hidden, so additional diagnostic workup like imaging can be obtained but must not delay treatment.Because NSTI with sepsis or septic shock is a life-threatening infection, you need to start treatment as soon as possible.

Management3:41–4:54

First, if possible, obtain blood cultures before starting broad-spectrum IV antibiotics, but don’t delay giving the antibiotics if cultures can’t be immediately obtained.
Then, consult the surgical team to evaluate for an emergent operative exploration, debridement, and wound cultures. This is the most important part of the treatment because the infection spreads rapidly along the fascial plane, so removing the infected and necrotic tissue is the only effective method of source control.
Finally, continuously provide supportive management for sepsis or septic shock with IV fluid resuscitation and vasopressor support if needed.
Here’s a clinical pearl! Most of the time, necrotizing fasciitis is definitively diagnosed intraoperatively with direct visualization of the obliterated fascia.
The patient might need aggressive debridement with multiple surgeries over the course of days to weeks to achieve adequate source control.Now that we have discussed unstable patients, let's switch gears and talk about stable patients.

Stable patient - History and Physical4:54–6:15

Because the majority of NSTIs in stable patients are diagnosed clinically, your first step is to obtain a focused history and physical.
You can also order labs like CBC, CMP, CRP, CK, and lactate.On history, patients often report severe pain, redness, swelling, and warmth of the affected area.
Additionally, they might report systemic symptoms like fever, chills, malaise, and myalgias. In some cases, the patient may notice a foul-smelling discharge from the wound.
Again, don’t forget to ask about risk factors for NSTI, such as recent trauma or surgery, injection drug use, immunosuppression, diabetes mellitus, and which medications they take.
When it comes to the physical exam, you can expect to find erythema, edema, and firm indurated tissue with decreased sensation and foul-smelling wound discharge.
Lastly, labs typically show leukocytosis along with elevated serum creatinine, CRP, lactate, and CK levels.Now, in addition to the physical findings we just talked about, there are two very important features you should look for on a physical exam.

Necrosis and/or crepitus6:15–7:03

First is necrosis, which looks like gray, boggy tissue with bullae; and second is crepitus. If either of these is present, you can make your diagnosis of necrotizing soft tissue infection.
If this is the case, start the treatment right away. This involves obtaining blood cultures, starting broad-spectrum IV antibiotics, and surgical consultation for emergent wound exploration and debridement.
Keep in mind that, prior to going in the operating room, the surgical team may request imaging to determine the extent of the infection, and NSTIs can spread into body cavities.Alright, let’s take a step back and talk about a patient without necrosis or crepitus on physical exam.

No necrosis or crepitus7:03–7:31

Even in the absence of necrosis and crepitus, findings of erythema, edema, and induration indicate cellulitis which needs antibiotic therapy without any delay.
So, your first step here is to obtain blood cultures and start broad-spectrum IV antibiotics.Then, obtain imaging, such as an x-ray or a CT scan, to further evaluate the affected area for any signs of inflammatory changes within the tissue including gas bubbles that may not be palpable on physical exam.

Diagnostic work-up7:31–9:25

Imaging can also help you determine the depth of infection including the levels of soft tissues involved. Although tissue necrosis is not a radiologic diagnosis, significant infectious or inflammatory changes, or the presence of gas, seen on imaging are associated with an increased risk of a concurrent necrotic process.Here’s a high-yield fact!
Group A strep is the most common cause of NSTI, but clostridia are the common gas-forming organisms. Okay, back to our patients.
Next to imaging, you need to calculate the Laboratory Risk Indicator for Necrotizing Fasciitis or LRINEC score, which can help you stratify the risk of necrotizing soft tissue infections.
The LRINEC score uses laboratory findings like CRP, WBC count, Hemoglobin, Sodium, Creatinine, and Glucose to generate a score between 0 and 14.
Scores are then divided into three groups: low for scores of 5 or less, moderate for scores between 6 and 7, and high risk for scores of 8 or greater.
Keep in mind that the LRINEC score doesn't make the diagnosis; it basically shows that people with bad labs are sicker and is consistent with an aggressive infection, and is meant to be used clinically to indicate that you should look into a more definitive diagnosis, since imaging is often delayed in necrotizing soft tissue infection.

Necrotizing soft tissue infection9:25–9:57

Now, let's see how both imaging findings and the LRINEC scores can be applied to help you make your diagnosis. Alright, if the imaging study shows gas, fluid collection, edema or inflammatory changes within the soft tissue, muscle, or fascia and or the LRINEC score is greater than 8, then you can make your diagnosis of necrotizing soft tissue infection.
If either one is present, your next step is to consult the surgical team for emergency exploration and debridement.Okay, let’s talk about another category of findings.

Possible necrotizing soft tissue infection9:57–10:26

If the imaging study reveals infectious or inflammatory changes without any signs of gas, you can use the LRINEC score to help you with your diagnosis.
A LRINEC source is 6 or 7 indicates that the patient likely has an NSTI. The treatment in this case still involves consulting the surgical team for emergency exploration and debridement.
Now that patients with NSTI are taken care of, let’s discuss our final set of findings. On imaging, if you see some infectious or inflammatory changes without any signs of gas within the tissue and the LRINEC score is less than or equal to 5, the patient likely has a non-necrotizing soft tissue infection.

Non-necrotizing soft tissue infection10:26–11:02

For non-necrotizing infections, the treatment includes continuing IV antibiotics, supportive care, and observation with frequent reevaluations to ensure that the infection is not worsening.Alright, as a quick recap… Necrotizing soft-tissue infections are rapidly progressing infections causing extensive destruction of soft tissues.
Unstable patients with an NSTI and sepsis or septic shock are diagnosed clinically. The treatment involves obtaining blood cultures, starting IV antibiotics, and consulting the surgical team for an emergent operative exploration and debridement, as well as supportive care to treat sepsis or septic shock.

Review11:02–12:11

For stable patients, first, look for signs of necrosis or crepitus on a physical exam to confirm your diagnosis of NSTI.
If neither is present, obtain imaging like x-ray or a CT scan and calculate the LRINEC score to aid your diagnosis. Patients with sure signs of NSTI or possibly require an emergent surgical exploration and debridement.
Patients with possible NSTI also need surgical exploration and debridement. Finally, if the patient has a non-necrotizing soft tissue infection, continue antibiotics, start supportive care, and observe them.
with possible NST also need surgical exploration and debridement Finally if the patient has a non-necrotizing soft tissue infection continue