Podcast #161 - POCUS for Appendicitis

As point of care ultrasound (POCUS) continues to expand in roles, the diagnosis of appendicitis using POCUS is one application with growing evidence.  This is especially true for the pediatric population.  In this blog and podcast learn how to diagnose appendicitis by POCUS and some of the most recent evidence.

There are three main imaging modalities to diagnose acute appendicitis: ultrasound, CT, and MRI.  MRI is not practical in many situations due to cost and time.  It is especially not helpful in the rural and remote environments where such machines may not even exist.  CT has been the standard in many ways but the radiation is of concern, especially in the pediatric and pregnant populations.  Ultrasound is fast, reliable, and avoids the concern of radiation.

The appendix can be difficult to visualize, especially if it is normal.  A blind-ended tubular structure that can contain fluid is what is normally observed for the appendix.  During appendicitis, the walls become thickened (>2mm for single wall), the overall size increases (usually considered >6mm), it is non-compressible ("target sign"), and can have a "ring of fire" appearance from increased vascular blood flow.  See the diagram below for some of the main details.

We know what we are looking for, but what is the evidence that those working in emergency medicine are good enough to perform the exam?  A recent study by Lee and Yun in the American Journal of Emergency Medicine, 2019 titled "​Diagnostic Performance of Emergency Physician-Performed Point-of-Care Ultrasonography for Acute Appendicitis: A Meta-Analysis" investigated this very concern.  It found that the diagnostic performance by both emergency medicine and radiology was excellent with emergency medicine being even better for pediatric acute appendicitis.  In that study, they recommended an outer diameter cutoff of 7mm.

Here are the numbers:

• In 17 studies involving 2385 patients, EP-POCUS for diagnosing AA exhibited a pooled sensitivity of 84% (95% confidence interval [CI]: 72%-92%) and a pooled specificity of 91% (95% CI: 85%-95%), with a positive likelihood ratio (PLR) of 7.0 (95% CI: 3.2-15.3) and a negative likelihood ratio (NLR) of 0.22 (95% CI: 0.12-0.42).
• There was even better diagnostic performance for pediatric AA with a sensitivity of 95% (95% CI: 75%-99%) and specificity of 95% (95% CI: 85%-98%).  
• A direct comparison revealed no significant differences (p = 0.18-0.85) between the diagnostic performances of EP-POCUS (sensitivity: 81%, 95% CI: 61%-90%; specificity: 89%, 95% CI: 77%-95%) and RADUS (sensitivity: 74%, 95% CI: 65%-81%; specificity: 97%, 95% CI: 93%-98%).

There are some limitations to remember when reading results such as these:

1. In the studies evaluated there were a wide range of cut-offs for appendicitis including the diameter and the concurrent findings.  This has helped attribute to the heterogeneity of the studies.  We care about this primarily because it makes it more difficult to see if certain parameters are most beneficial for diagnostic cut-offs.  However, from this particular data set, the 7mm cut-off for appendiceal diameter seems to be better than the 6mm cut-off used in other studies.
2. There was significant heterogeneity.  This will affect pooled estimates and we see this all with the wide confidence intervals that were present.  We should be wary of these results, especially given the data used.
3. All of the data was from studies that had positive results.  While this is not necessarily negative, it is more likely for there to be publication bias.  For the studies that were used, there was a low probably of publication bias (p = 0.62).
4. Like most studies regarding POCUS, this used resident and attending physicians in academic centers and does not speak to the abilities of other types of clinicians (such as PAs and NPs or those in rural or remote environments).  It would be fantastic to see future studies that addressed these issues specifically to see how much of an impact there is with these groups of clinicians.
5. Evidence is strongest for pediatric exams which may be related to the difference in barriers to ultrasound.  Primarily, the concern is in regards to body habitus.  The larger the patient, the harder it is to visualize abdominal organs, especially the appendix.  Also, in small pediatric patients the high-frequency linear probe is frequently used which provides even more detailed visualization of the appendix compared to the more classically use lower-frequency curvilinear or phased array probes.
   
   

These are not necessarily bad things in all regards, but we must remember how they can effect our potential application of the results.  Overall, POCUS seems to be a beneficial way to help diagnose appendicitis.  Considering the number of patients who present in rural areas that may not otherwise have access to imaging or surgery, this can help speed up their disposition to appropriate care.

Let us know what you think by giving us feedback here in the comments section or contacting us on Twitter or Facebook.  Remember to look us up on Libsyn and on iTunes.  If you have any questions you can also comment below, email at [email protected], or send a message from the page.  We hope to talk to everyone again soon.  Until then, continue to provide total care everywhere.

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