title: Evaluation of the open abdomen classification system: a validity and reliability analysis.
abstract: BACKGROUND
  Classification of the open abdomen (OA) status is essential for clinical studies on the subject and may help to improve OA therapy. This is a validity and reliability analysis of the OA classification proposed by the World Society of the Abdominal Compartment Syndrome in 2013.
  
  
  METHODS
  Prospective data on 111 consecutive OA patients treated with vacuum-assisted wound closure and mesh-mediated fascial traction (VAWCM) was used. For validity analysis, OA grades were compared with fascial closure and mortality. For reliability analysis, operative reports were graded by three external raters on two different occasions and the results compared. Instructions for use of the classification were constructed and studied by the external raters beforehand.
  
  
  RESULTS
  The in-hospital mortality rate was 30 % (33/111). The delayed primary fascial closure rate was 89 % (85/95). Most complex grade (p = 0.033), deteriorating grade (p = 0.045), enteric leak (p = 0.001), and enteroatmospheric fistula (p = 0001) were associated with worse clinical outcomes, while initial grade, grade 1A only, contamination, fixation, and frozen abdomen were not. A floor effect was observed, with 20 % of patients receiving the lowest grade throughout OA period. Inter-rater reliability, expressed as intra-class correlation coefficient (ICC), was 0.77, 0.76, and 0.88 (95 % confidence interval 0.66-0.84, 0.65-0.84, and 0.81-0.92, respectively) and test-retest reliability 1.0, 0.99, and 0.95, respectively.
  
  
  CONCLUSIONS
  More complex OA grades were associated with worse clinical outcomes. However, favorable clinical results with the VAWCM technique caused many patients to receive the lowest grade, thus causing a floor effect and lower validity. Inter-rater and test-retest reliability was 'good' to 'very good'.
authors.affiliation: Department of Surgery, Skåne University Hospital, Malmö, Sweden, thordur.bjarnason@med.lu.se.
authors.forename: Thordur
authors.initials: T
authors.lastname: Bjarnason
authors.forename: Agneta
authors.initials: A
authors.lastname: Montgomery
authors.forename: Stefan
authors.initials: S
authors.lastname: Acosta
authors.forename: Ulf
authors.initials: U
authors.lastname: Petersson
mesh_terms: D000005:Abdomen / Q000601:surgery*; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002965:Classification; D000071938:Fasciotomy; D017052:Hospital Mortality; D006801:Humans; D007412:Intestinal Fistula / Q000209:etiology*; D008875:Middle Aged; D054843:Negative-Pressure Wound Therapy; D011446:Prospective Studies; D015203:Reproducibility of Results; D013526:Surgical Mesh; D014143:Traction; D055815:Young Adult