Development of a nomogram to predict small bowel obstruction using point-of-care ultrasound in the emergency department

Abstract

Objective: Early diagnostic prediction in patients with small bowel obstruction (SBO) can improve time to definitive management and disposition in the emergency department. We sought to develop a nomogram to leverage point-of-care ultrasound (POCUS) and maximize accuracy of prediction of SBO diagnosis.

Methods: Using data from a prospective cohort of 125 patients with suspected SBO who were evaluated with POCUS in the ED, we developed a nomogram integrating age, gender, comorbidities, prior abdominal surgery, physician's pre-test probability, and POCUS findings to determine post-test risk of SBO. The primary outcome was to develop a nomogram to allow calculating output probabilities for predictive models using POCUS findings. The discriminative ability of the nomogram was tested using a C-statistics, calibration plots, and receiver operating characteristic curves.

Results: The derivation cohort included 125 patients with a median age of 54 years who underwent POCUS for a suspected SBO. One-fourth of the patients (25.6% [32/125]) had SBO. Using a retrospective stepwise selection of clinically important variables with the POCUS results, the final nomogram incorporated four relevant factors for the prediction of SBO: small bowel diameter (odds ratio [OR] per 1 mm increase, 1.10; 95% CI, 1.03-1.17; P = 0.001), positive free intraperitoneal fluid between bowel loops (OR, 8.19; 95% CI, 2.62-25.62; P < 0.001), clinician's moderate (OR, 5.94; 95% CI, 0.83-42.57; P = 0.08) or high pretest probability (OR, 11.26; 95% CI, 1.44-88.25; P = 0.02), and patient age (OR per 1 year increase, 1.03; 95% CI, 1.00 to1.07; P = 0.08).The discriminative ability and calibration of the nomogram revealed good predictive ability as indicated by the C-statistic of 0.89 for the SBO diagnosis.

Conclusion: A unique nomogram incorporating patient age, physician pretest probability of SBO, and POCUS measurements of small bowel diameter and the presence of free intraperitoneal fluid between bowel loops was developed to accurately predict the diagnosis of SBO in the emergency department. The nomogram should be externally validated in a novel cohort of patients at risk for SBO to better assess predictability and generalizability.