Revision of the AAST grading scale for acute cholecystitis with comparison to physiologic measures of severity.

Background: Grading systems for acute cholecystitis are essential to compare outcomes, improve quality, and advance research. The American Association for the Surgery of Trauma (AAST) grading system for acute cholecystitis was only moderately discriminant when predicting multiple outcomes and underperformed the Tokyo guidelines and Parkland grade. We hypothesized that through additional expert consensus, the predictive capacity of the AAST anatomic grading system could be improved.
Methods: A modified Delphi approach was used to revise the AAST grading system. Changes were made to improve distribution of patients across grades, and additional key clinical variables were introduced. The revised version was assessed using prospectively collected data from an AAST multicenter study. Patient distribution across grades was assessed, and the revised grading system was evaluated based on predictive capacity using area under receiver operating characteristic curves for conversion from laparoscopic to an open procedure, use of a surgical "bail-out" procedure, bile leak, major complications, and discharge home. A preoperative AAST grade was defined based on preoperative, clinical, and radiologic data, and the Parkland grade was also substituted for the operative component of the AAST grade.
Results: Using prospectively collected data on 861 patients with acute cholecystitis the revised version of the AAST grade has an improved distribution across all grades, both the overall grade and across each subscale. A higher AAST grade predicted each of the outcomes assessed (all p ≤ 0.01). The revised AAST grade outperformed the original AAST grade for predicting operative outcomes and discharge disposition. Despite this improvement, the AAST grade did not outperform the Parkland grade or the Emergency Surgery Score.
Conclusion: The revised AAST grade and the preoperative AAST grade demonstrated improved discrimination; however, a purely anatomic grade based on chart review is unlikely to predict outcomes without addition of physiologic variables. Follow-up validation will be necessary.
Level of Evidence: Diagnostic Test or Criteria, Level IV.
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