Biliary disease places a significant burden on the United States healthcare system with up to 20% of the more than 20 million with disease developing potentially life-threatening complications. Knowing that medical history and physical exam cannot reliably identify biliary disease, a rapid but accurate screening test is desirable. This is beneficial for multiple reasons, including early identification of complications, as well as ED throughput. Avoiding the need for further imaging could decrease time to disposition, and improve patient outcomes through earlier identification of significant complications and thus earlier intervention. When compared to RADUS, we found that ECUS was slightly less sensitive (67% vs. 76%) and specific (88% vs. 97%) for acute cholecystitis when using discharge diagnosis as the gold standard.
In the 17 patients who received HIDA scan none had a change in their diagnosis. The average delay in diagnosis between HIDA and ECUS was over 13 h. This result is consistent with previous studies showing no benefit to HIDA scan in the ED [17].
After dichotomization of patients into those with pathology and those with no significant sonographic findings by ECUS, the sensitivity of ECUS for determining presence of disease was 93.6% (90–97.1%). None of the 103 patients with negative ECUS had a diagnosis of acute cholecystitis or returned to the study institution within 6 months with acute cholecystitis. This makes ultrasound a valuable screening tool in the hands of the emergency physician, and can allow for earlier discharge of well appearing patients if there is no concern for alternate etiology.
In a patient in which the emergency physician has a high pretest probability for acute cholecystitis, the positive likelihood ratio of 5.6 (3.9–8.2) for ECUS can be considered diagnostic and the emergency physician could possibly forego further imaging prior to surgical consult. Given its lower specificity in detecting pathology in general, it could be argued that ECUS lacks the test characteristics to be diagnostic if the clinical picture is unclear; therefore, a confirmatory radiology study may be considered at the discretion of the emergency physician.
Many EDs around the country are experiencing significant boarding and throughput issues. Previous studies have shown that pelvic ECUS was 66 min faster than RADUS, which lead to a 120-min shorter LOS [18, 19]. At our institution, ECUS lead to a 124-min decrease in time to result compared to RADUS. This finding is in agreement with previous literature that indicates that there could potentially be even more time saved in time to disposition.
Finally, it is prudent to consider the possible financial implication of ECUS in addition to the improved throughput time. Previous work has shown that ECUS programs as a whole, including procedural use, have increased ED revenue by $35,500 with a potential for a $107,700 revenue increase with improved utilization and documentation [20]. This does not take into account the reduction in expenses of formal RADUS. To our knowledge, no study has investigated the potential cost savings of a negative biliary ECUS that does not require a more expensive follow-up RADUS.
This study relied on image acquisition and interpretation by emergency physicians with variable levels of training in performing ECUS. It has been demonstrated in several previous studies that interpretation accuracy improves with increasing number of biliary studies [21], with no improvement over 50 studies [22]. In our study, the attending physician assigned to each case reviewed and attested to the ECUS interpretation prior to it becoming final, per department policy. These physicians were credentialed in ultrasound per the ACEP guidelines, having completed a minimum of 25 prior biliary studies.
Another limitation to consider is the median time to receive the RADUS interpretation may be longer depending on the indication for scan. For example, if a “right upper quadrant” RADUS was ordered this would increase the time the technician would spend obtaining the imaging when compared to a specific “biliary” RADUS. Furthermore, compared to a clinical ultrasound exam fewer views are required to adequately diagnose biliary pathology when compared to a more comprehensive right upper quadrant RADUS.
Like many busy EDs, our emergency department has a physician in triage that may order RADUS studies before the ECUS can be performed. This led to 11 studies being performed by RADUS prior to the treating physician seeing the patient. While these studies were excluded, because no ECUS was performed, accounting for these studies could have shortened the time difference noted between ECUS and RADUS.
The gold standard we used was the diagnosis given to the patient at discharge. While we believe this to be a meaningful patient-oriented outcome, recorded discharge diagnoses are subject to inherit human recording error. To mitigate any discharge diagnosis error that may have occurred, each patient was followed for 6 months by chart review to ensure there was no return to the study institution for repeat assessment. It is conceivable that a follow-up visit occurred elsewhere.
Finally, it should be noted that the retrospective nature of this study opens it to selection bias. The patients who had clear diagnosis made on ECUS could have not received a formal RADUS. Therefore, patients with unclear diagnoses or physically difficult to perform ultrasounds may have been more likely to receive both a ECUS and a RADUS of the gallbladder.