Validity of the American Association for the Surgery of Trauma Intestinal Obstruction Grading System

The American Association for the Surgery of Trauma (AAST) grading system for intestinal obstruction may be a useful measure of anatomic severity, but its construct validity has not yet been evaluated in patients with either large or small bowel obstruction, using the grade applicable at initial presentation (rather than after definitive management).

We conducted a retrospective case series of adult inpatients presenting with intestinal obstruction at our center during 2008-2014. We excluded patients without confirmed intestinal obstruction, those with obstruction secondary to a hernia, those who were treated for >24 hours at another hospital, and those with a previous encounter already included in the study. We measured inter-rater reliability using a weighted kappa coefficient. We used multivariable logistic regression, accounting for sampling weights, to assess the relationship of grades with complications, 30-day mortality, and 30-day readmission.

Of 287 patients, 165 (58%) had grade I anatomic severity, 75 (26%) grade II, 23 (8%) grade III, 15 (5%) grade IV, and 9 (3%) grade V. Forty-six (16%) patients had a large bowel obstruction. There was substantial inter-rater agreement in grades [weighted kappa 0.69 (95% CI 0.47-0.91)]. Compared to grade I, grades III-V [OR 12.2 (95% CI 2.26-66.2)] but not grade II [OR 2.04 (95% CI 0.79-5.28)] were associated with increased risk of a complication. grade II [OR 7.92 (95% CI 3.27-19.2)], but not grades III-V [OR 3.56 (95% CI 0.30-42.5)] was associated with increased 30-day mortality. Grades were not associated with increased 30-day readmission.

AAST intestinal obstruction grades have predictive validity for some but not all outcomes, and may serve a useful role in the measurement of anatomic disease severity.