SGEM#274: Hocus POCUS for Appendicitis?

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Date: November 2nd, 2019

Reference: Lee and Yun. Diagnostic Performance of Emergency Physician-Performed Point-of-Care Ultrasonography for Acute Appendicitis: A Meta-Analysis. AJEM 2019.

Guest Skeptic: Chip Lange is an Emergency Medicine Physician Assistant (PA) working primarily in rural Missouri in community hospitals. He also hosts a great #FOAMed blog and podcast called TOTAL EM. Chip is the CEO of an ultrasound education company called Practical POCUS which is based in the United States but is expanding into an international market.

Case: A 6-year-old boy comes into your emergency department at around midnight with his parents complaining of abdominal pain. His mother reports that the symptoms began a couple of days ago and he did not eat today. Now, the patient has been vomiting for the last couple of hours. Initially, he would point to the periumbilical area, but his father says that now he points to the right lower portion of the abdomen as his area of pain. You do not have an ultrasound tech available at night and you are thinking of using your point of care ultrasound (POCUS) skills to look for a possible appendicitis, but you are unsure how accurate this test would be especially compared to other modalities such as radiology performed ultrasound.

Background: We have reviewed papers on POCUS many times over the years on the SGEM. This has included performing lumbar punctures, diagnosing acute abdominal aneurysms, acute heart failure, pediatric fractures, retinal detachments and endotracheal tube placement.

SGEM#41: Ultra Spinal Tap (Ultrasound Guided Lumbar Puncture)
SGEM#94: You Better Think Ultrasound for Acute Abdominal Aneurysm
SGEM#97: Hippy Hippy Shake – Ultrasound Vs. CT Scan for Diagnosing Renal Colic
SGEM#119: B-Lines (Diagnosing Acute Heart Failure with Ultrasound)
SGEM#124: Ultrasound for Skull Fractures – Little Bones
SGEM#153: Simulation for Ultrasound Education
SGEM#177: POCUS –A New Sensation for Diagnosing Pediatric Fractures
SGEM#245: Flash-errrs (POCUS for Retinal Detachments)
SGEM#249: Ace in the Hole –Confirming Endotracheal Tube Placement with POCUS

Ultrasound, especially in the pediatric population, has been a common form of imaging for the diagnosis of appendicitis. It avoids the concerns for radiation and contrast that is seen with CT. MRI is not practical in many situations, especially in rural or remote environments.

However, ultrasound does have its limitations especially in obese patients or those unable to comply with the exam for reasons such as pain.

Clinical Question: What are the diagnostic performance of point of care ultrasonography (EP-POCUS) for diagnosing acute appendicitis?

Reference: Lee and Yun. Diagnostic Performance of Emergency Physician-Performed Point-of-Care Ultrasonography for Acute Appendicitis: A Meta-Analysis. AJEM 2019.

Population: Patients in original research articles with right-lower quadrant (RLQ) abdominal pain with EP-POCUS being performed as the index test and the use of surgical or pathological findings as the reference standard for acute appendicitis. There had to be sufficient information to reconstruct a 2×2 contingency table regarding sensitivity and specificity.
- Excluded: Case reports, case series, review articles, guidelines, consensus statements letters, editorials, clinical trial, and conference abstracts. Additionally, studies that did not pertain to the field of interest, insufficient data to create the 2×2 tables, POCUS was not performed by emergency physicians (EPs), and studies that only used the radiologists’ final report.
Intervention: EP-POCUS for diagnosing acute appendicitis.
Comparison:Radiologist-performed ultrasonography (RADUS)
Outcome:
- Primary Outcome: Diagnostic parameters of EP-POCUS for acute appendicitis (sensitivity, specificity and likelihood ratios).
- Secondary Outcomes: Subgroup analysis of pediatric patients comparing EP-POCUS to radiologist-performed ultrasonography (RADUS).

Authors’ Conclusions: “The diagnostic performances of EP-POCUS and radiologist-performed ultrasonography (RADUS) were excellent for AA, with EP-POCUS having even better performance for pediatric AA. Accurate diagnoses may be achieved when the attending EP is the initial POCUS operator and uses a 7mm cut-off value.”

Quality Checklist for Systematic Review Diagnostic Studies:

The diagnostic question is clinically relevant with an established criterion standard. Yes
The search for studies was detailed and exhaustive. No
The methodological quality of primary studies were assessed for common forms of diagnostic research bias. Yes
The assessment of studies were reproducible. Yes
There was low heterogeneity for estimates of sensitivity or specificity. No
The summary diagnostic accuracy is sufficiently precise to improve upon existing clinical decision-making models. Unsure

Key Results: Their search identified 17 studies involving 2,385 patients. The mean age ranged from 6 to 37 years of age and the mean proportion of male patients were 26% to 61%.

EP-POCUS exhibited a pooled sensitivity of 84% and a pooled specificity of 91%, with a positive likelihood ratio of 7.0 and a negative likelihood ratio of 0.22 for diagnosing acute appendicitis.

There was better diagnostic performance for pediatric acute appendicitis with a sensitivity of 95% (95% CI: 75%-99%) and specificity of 95% (95% CI: 85%-98%).

A direct comparison revealed no statistical 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%).

The meta-regression analyses revealed that study location, acute appendicitis proportion, and mean age were sources of heterogeneity. Higher sensitivity and specificity tended to be associated with an appendix diameter cut-off value of 7 mm and the EP as the initial operator.

1. Wide Range of Cut-Offs:There was 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. Heterogeneity: There was large heterogeneity as reported by the I2 metric. It was 94% for sensitivity and 89% for specificity. This will affect pooled estimates and we see this all with the wide confidence intervals that were present. It is reasonable to question whether or not these studies should have been meta-analysed given the large heterogeneity. We should be skeptical of these results, especially given the data used.

3. Likelihood Ratios: We like to see LR+ greater than 10 to rule in a diagnosis and LR- less than 0.1 to rule out a diagnosis. Only the RADUS had a LR+ of >10. Neither RADUS nor EP-POCUS had a LR- of less than 0.1.

4. Clinicians: 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. Pediatric Patients: The evidence for EP-POCUS is strongest for pediatric examinations. This may primarily be related 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.

Comment on Authors’Conclusion Compared to SGEM Conclusion:We think that the diagnostic accuracy of EP-POCUS is good but not excellent for diagnosing acute appendicitis. It is better in pediatric populations and that the use of a 7mm cut-off appears to be more accurate.

SGEM Bottom Line: EP-POCUS has the potential to diagnose acute appendicitis especially in pediatric populations and appears to be better at ruling in rather than ruling out.

Case Resolution: With consent from the parents and patient, you are able to use your bedside ultrasound and find an 8mm non-compressible and aperistaltic appendix. You call the pediatric general surgeon who takes the patient to the OR for further management including appendectomy.

Chip Lange PA

Clinical Application: POCUS continues to play an important role in emergency medicine and is being embraced more over time. We should consider using ultrasound for a variety of conditions including for the diagnosis of appendicitis. Given the issues of operator experience, study heterogeneity and wide confidence intervals we do not think EP-POCUS should be the sole criteria in diagnosing acute appendicitis.

What Do I Tell the Patient? I would tell the parents and patient that we are going to use a special machine that uses sound waves to look into his abdomen to see if his appendix, a small tube in his stomach that can become sick and be causing his symptoms. It is a good test, but it is far from a perfect test. If I see a swollen appendix with the ultrasound machine your son probably has appendicitis. If I do not see his appendix, we probably will need to do more testing.

Keener Kontest: Last weeks winner was Dr. Steven Stelts from Auckland, New Zealand. He knew the term that originally used to describe a break in the 4th or 5th metacarpal was “bar room fracture”.

Listen to the podcast to hear this weeks’ trivia question. If you know the answer, send an email to TheSGEM@gmail.com with “keener” in the subject line. The first correct answer will receive a cool skeptical prize.