Utilization of ultrasound for the evaluation of small bowel obstruction: A systematic review and meta-analysis

James Fitzgibbon MS4

Article: Gottlieb M et al. Utilization of ultrasound for the evaluation of small bowel obstruction: A systematic review and meta-analysis. American Journal of Emergency Medicine. 2018;36(2):234-242.

Background: In the Emergency Department (ED), small bowel obstruction (SBO) is a common diagnosis, which can lead to significant morbidity and mortality. Often CT scan is used as the definitive imaging tool, but this test is expensive, exposes the patient to radiation, often associated with time delays, and may not be universally available. Therefore, ultrasound has been increasingly utilized in the diagnosis of SBO. The aim of this study was to perform a systematic review and meta-analysis of available studies to determine the diagnostic accuracy of ultrasound in detecting SBO.

Study:

Type:  meta-analysis

Population: patients presenting with concerns for SBO.

Clinical Setting: Both Emergency Department and Non-Emergency Department setting.

Inclusion Criteria: all prospective, observational, and randomized controlled trials assessing the utility of ultrasound for detecting small bowel obstruction vs. a gold standard (CT, surgery, discharge diagnosis, enteroclysis, or follow up) from inception till March 17, 2017.

·      Written in English or Spanish

Exclusion Criteria:

·      Prenatal assessments

·      Two physician-investigator screening panel for eligibility

Data Abstracted: last name of author, study title, publication year, population size, country, location, mean age, gender, ultrasound machine, ultrasound probe, ultrasound training protocol, ultrasound criteria for SBO, gold standard SBO diagnosis, generation of CT scanner, study design, true positives, true negatives, false positives, false negatives, indeterminate scans. 

Statistical Analysis: Sensitivity, Specificity, +LR, -LR, forest plots (Sn, Sp) and summary ROC curve for the pooled estimates. Publication bias was assessed with funnel plot. Subgroup analysis of outcomes in ED vs. non-ED setting.

Results: 11 studies comprising 1178 patients in total.

Primary: Overall found to be 92.4% sensitive (95% CI 89%-94.7%) and 96% specific (95% CI 88.4%-99.1%). +LR of 27.5 (95% CI 7.7 – 98.4) and –LR of 0.08 (95% CI 0.06 – 0.11 ). No evidence of publication bias.

Secondary: similar results found in ED (sensitivity 93%, specificity 96%) and non-ED (sensitivity 92%, specificity 99%)

Limitations: No randomized controlled trials were present in the 11 studies. There was also heterogeneity between the 11 studies in terms of ultrasound diagnostic criteria, ultrasound experience, and gold standard test. Only 3 of 11 studies were performed by ED providers, which prohibited a meta-analysis of this subset. Two studies did not differentiate SBO from large bowel obstruction. There was also limited data in respect to the pediatric population.

Takeaway: Although the data is limited by the lack of randomized control trials and heterogeneous studies, ultrasound should be considered a useful tool for the diagnosis of SBO in the ED, especially when CT scan is unavailable or delay is expected.