We wrap up our month of discussing point of care ultrasound (POCUS) papers by having our guest Michelle Perkins. Over the last couple of years a flurry of evidence has come out regarding abscess management. Now, POCUS is taking center stage in a recent paper. Here to help us discuss it is one of our favorite guests, Michelle Perkins.
Before we dive too deep into the paper, this is our reminder that Practical POCUS will be having upcoming courses in Missouri at the end of the year. With a special discount code "TOTALEM" you can get 10% off! Remember to register soon since there is limited seating and they are filling.
It is very easy to identify and distinguish cellulitis versus an abscess. These images from The POCUS Atlas demonstrate the differences nicely. In the the first image, the GIF demonstrates a scan through inflamed tissue. The top of the image demonstrates a classic "cobblestone" appearance. In the image, there is no pocket of hypoechoic fluid to suggest an abscess. However, on the next image such a pocket can be seen. Sometimes this is one black pocket, which can be seen better in the peritonsilar abscess example. If there is air in the soft tissue this should be very concerning for necrotizing fasciitis. The last image is an example of of Fournier gangrene specifically.
Now that we know what to look for, we can review this Annals of Emergency Medicine paper By Gaspari et al. titled Abscess Incision and Drainage With or Without Ultrasonography: A Randomized Controlled Trial. Although previous studies have demonstrated the benefits of ultrasound in the detection of an abscess, previous studies have not looked into the role it may play in improving patient outcomes.
They include the type of patients we often consider having a potential abscess: atraumatic swelling, pain, or erythema consistent with an abscess cavity. However, they excluded clinically ill patients (documented fever, hypotension, or "appearing clinically ill"), abscess after foreign body trauma or animal bites, paronychia, dental abscesses, genital abscess, or peritonsilar abscesses were excluded which for the most part clinically makes sense.
An abscess identified on ultrasound, like the ones seen above, was defined as either hypoechoic focus with surrounding induration or isoechoic focus with posterior acoustic enhancement and surrounding induration. For those in the POCUS arm, images were obtained by clinicians prior to the incision and drainage (I&D). Additional images were performed during or after the I&D at the discretion of the clinician performing the procedure.
In the usual care arm, POCUS may be performed if the diagnosis of abscess was in doubt by a separate clinician who would only confirm the presence of an abscess and give the treating clinician no other details. Arguably, this is a major reason why POCUS is so beneficial. If there was a doubt (and sometimes the clinician may not have doubt but later find no abscess as we discuss in the actual podcast), this is a perfect time for POCUS and why it should be included in the first place.
Although the study groups were fairly similar there was more packing and antibiotics in the usual care arm versus the POCUS arm. We have talked in the past about how to manage abscesses and explained how packing is usually not beneficial and that antibiotics have an increasingly important role based on new evidence. However, even with that difference, there was a significant difference in the primary outcome of treatment failure. This outcome, defined as a repeat I&D that produced purulent drainage, found a treatment failure rate of 17.0% in the usual care group and 3.7% in the POCUS group. This is an absolute difference of 13.3% or a number needed to treat (NNT) of 7!
Think about it like POCUS not only identifying that there is an abscess in the first place before you cut on your patient, but that it can help you confirm that you have treated the abscess sufficiently before you walk away. This may not be necessary on every abscess (especially those with clearly a single pocket where the volume removed matches the volume from the initial scan, but it can be very beneficial in helping reduce the failure rate. Add that with other recently published evidence that has low NNTs (such as antibiotics) and you can further help treat your patients.
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