Contribution of Point of Care Ultrasound by the Emergency Physician to Rule Out the Small Bowel Obstruction: a Diagnostic, Multicenter Study

Small Bowel Obstruction (SBO) is a frequent pathology in the emergency department (ED). Diagnosis is currently based on abdominal CT scan (CT). Moreover, CT is warranted to determine the therapeutic strategy in patients with SBO which could include medical treatment; surgical intervention or both. However, CT is associated with drawbacks such as radiation exposure, increased cost and ED length-of-stay.

In a prospective observational study, a SBO was excluded by CT in 45% \[95%CI: 37-53\] of patients. There is, thus, a need for improving the appropriateness of CT-scan for suspected SBO.

A recent meta-analysis showed that Point of care ultrasound (POCUS) had a good diagnostic accuracy (sensitivity 83% \[95%CI 71.7%-90.4%\]), specificity 93% \[95%CI 55.3%-99.3%\]). Another meta-analysis found rather similar results (sensitivity 83% \[(95% CI 89.0% to 94.7%\], specificity 96,6% \[95% CI 88.4% to 99.1%\]).

In order to improve the negative predictive value of POCUS for its implementation as a rule-out strategy, CHU of Nantes emergency unit studied the combination of POCUS with Gestalt pre-test probability of SBO determined by the emergency physician. This SBO probability classified the patients as low, moderate or high risk of SBO. In patients with low or moderate Gestalt probability, CHU of Nantes emergency unit found that this combined strategy had a sensitivity of 100% \[95% CI: 88-100\] and NPV 100% \[92-100%\].

By (i) focusing on patients with a low or moderate Gestalt clinical probability and (ii) increasing the number of patients included, CHU of Nantes emergency unit intends to demonstrate that POCUS is able to exclude SBO in this population. This would avoid unnecessary CT and thus lower costs, ED length-of-stay and hospital radiologists workload.

A POCUS will be performed followed by a CT (gold standard). The main objective will be the ability of POCUS to rule-out SBO in patients with low or moderate Gestalt clinical probability.

Small Bowel Obstruction (SBO) is a frequent pathology, leading to admissions to emergency departments (ED). Diagnosis is currently based on an abdominal CT scan (CT). However, CT is associated with drawbacks such as radiation exposure, increased cost and ED length-of-stay.

A recent meta-analysis including 1178 patients showed that Point of care ultrasound (POCUS) had a good diagnostic accuracy (sensitivity 83% \[95%CI 71.7%-90.4%\]), specificity 93% \[95%CI 55.3% -99.3%\]). Another meta-analysis with 433 patients, found rather similar results: sensitivity 83% \[95% CI 89.0% to 94.7%\], specificity 96,6% \[95% CI 88.4% to 99.1%\]).

Since CT is almost warranted to guide the treatment strategy, which could include surgery, medical treatment or both, CHU of Nantes emergency unit explored a different approach focusing on POCUS rule-out ability. This study also introduced the notion of SBO Gestalt probability which is a global clinical evaluation by the physician. Gestalt probability has mainly been explored in patients with suspected pulmonary embolism and was found as effective as clinical prediction rules. It is used in the routine clinical evaluation of patient with suspicion of pulmonary embolism. When applied to patients with SBO suspicion, the physician chooses between low, moderate or high risk of SBO. Based on CT results, prevalence of SBO based on Gestalt probability were 21%, 45% and 87% in the low, moderate and high risks, respectively.

Our team studied POCUS with the following items that were searched in the whole abdomen divided into nine zones: dilated incompressible fluid-filled intestinal loop (\&gt;25 mm) with back-and-forth fluid movement. When at least one of these signs was present in one zone, the SBO was highly suspected. As it was an observational study, a CT was performed in all patients and was the gold standard. This approach was associated with a POCUS sensitivity in the whole population of 99% \[95% CI: 93-99.8\] \[2\]. POCUS would thus have a role in patients with low and moderate SBO risks because the prevalence of SBO was major in the high risk Gestalt probability category of patients, and thus CT is the only imaging needed in these latter. Furthermore, in patients with low or moderate probability, the sensitivity was 100% \[95% CI: 88-100\] In previous studies, the sensitivity was not able to exclude SBO with sufficient security since the lower 95% confidence interval margin was near 90%. By (i) focusing on patients with a low or moderate clinical Gestalt probability and (ii) increasing the number of patients, CHU of Nantes emergency unit intends to demonstrate that POCUS should be able to safely exclude SBO in this population.

In case of positive results, the diagnostic strategy in case of SBO suspicion could be modified in: firstly, assess the clinical Gestalt probability; secondly perform a POCUS in patients with low or moderate Gestalt probability and thirdly, prescribe a CT only for patients with high clinical probability or presence of POCUS signs of SBO. This would avoid unnecessary CT and thus lower patient's.

exposure, costs, ED length-of-stay and radiologist workload. A study performed in the USA simulated a POCUS first approach in patients with suspected SBO and found that it could save ED length of stay, radiation and money. In France in 2017, about ¾ of ED were equipped with ultrasound machines and half of the emergency physicians were trained in POCUS. Furthermore, SBO detection is easily performed: in our study, the operator self-assessed ultrasound experience was beginner or intermediate for 59% of patients. In case of positive results, this technique would be largely deployed.

Inclusion criteria will be patients with low or moderate Gestalt clinical probability of SBO. A POCUS will be performed followed by a CT (gold standard). This CT will be realized and interpreted blindly from the POCUS results. The main objective will be the ability of POCUS to rule-out SBO in patients with low or moderate Gestalt clinical probability

Eligibility Criteria:
Inclusion Criteria:

1. Major patient (age \&gt; 18 years old), no upper limit
2. Patient admitted to the ED with suspected SBO (abdominal pain, vomiting, cessation of gas and feces...)
3. Low or moderate pretest Gestalt clinical probability
4. Patient able to understand protocol and express agreement
5. Oral non-opposition given

Exclusion Criteria:

1. Patient under legal guardianship
2. Pregnant women
3. Nursing mothers
4. Patient who does not speak or understand French
5. Patient without a health insurance plan
6. Patient who already had imaging confirming the diagnosis
7. Patient who participates simultaneously in any interventional study focused on abdominal pain