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’.

Appendices

Appendix 1: Classification of the Open Abdomen: Instructions for Use

Definition of open abdomen (OA)

An abdominal wound requiring temporary abdominal closure due to the skin and fascia not being closed after laparotomy (WSACS, 2013). Note that “skin-only closure” is not OA according to this definition.

OA Classification (WSACS 2013)

Grade 1: No fixation

•  1A: clean

•  1B: contaminated

•  1C: enteric leak

Grade 2: Develo** fixation

•  2A: clean

•  2B: contaminated

•  2C: enteric leak

Grade 3: Frozen abdomen

•  3A: clean

•  3B: contaminated

Grade 4: Established enteroatmospheric fistula (EAF)

How to grade

At the end of every operation (both initial laparotomy and each dressing change), assess:

• Fixation according to 1 to 3 (no fixation – develo** fixation – frozen abdomen)

• Contamination according to A to C (clean – contaminated – enteric leak)

• Presence of enteroatmospheric fistula, grade 4

Definitions

I. Fixation

Adhesions between viscera and the abdominal wall and/or lateral retraction of the abdominal wall muscles, preventing fascial closure in the midline.

Grade 1: No fixation

• Abdominal cavity is free of adhesions all the way to the paracolic gutters laterally, over the liver cranially, and to the pelvis caudally.

• It is expected to be possible to subsequently bring the abdominal walls together in the midline.

• Limited adhesions around stomas (including gastrostomies, feeding jejunostomies, etc.) are not fixation.

• Adhesion between bowel loops do not affect fascial closure and are not fixation.

• If all adhesions between viscera and abdominal wall are released at the end of the present operation, it should be registered as no fixation.

Grade 2: Develo** fixation

• An intermediate state of adhesions or fixation.

• Adhesions between viscera an abdominal wall or abdominal wall stiffness that causes difficulties in approximating fascial edges.

• Adhesions that are released in the present operation are not develo** fixation.

Grade 3: Frozen abdomen

• Extensive adhesions or a fixated abdominal wall that precludes fascial closure.

• Other methods of abdominal closure, such as mesh reconstruction or planned ventral hernia (e.g. with skin grafting), are necessary.

II. Contamination

Grade A: Clean

• Absence of conditions defined as contamination or enteric leak. If contamination is removed, abdomen may be considered clean at the next dressing change operation, or when appropriate.

Grade B: Contaminated

• The following states are to be considered as contaminated:

  • Infections engaging the OA, such as purulent peritoneal inflammation, intra-abdominal abscess or laparotomy wound infection.

  • Infections not engaging the abdominal cavity (e.g. pyelonephritis) are not contamination

  • Necrotic tissue, such as bowel (regardless of perforation) or wound necrosis.

  • Ischemia without necrosis is not contamination.

  • Other contamination, such as traumatic wounds penetrating abdomen, perforation of genito-urinary tract (including Bricker conduit), leakage from bile ducts or bile ducts anastomoses, bowel contents from excluded rectal stump or from stoma bag.

Grade C: Enteric leak

• Perforation of any part of the gastrointestinal tract with contact to the abdominal cavity.

• Includes leakage from gastrostomy or jejunostomy entrances.

• If a perforation is successfully surgically treated (e.g. by primary suture, resection of the perforated bowel segment, exteriorization into a stoma or a controlled enterocutaneous fistula [ECF]) or ceases with conservative treatment (clean-up and drainage), then the grade is changed at next dressing change operation to clean or contaminated, as appropriate.

III. Enteroatmospheric fistula

Grade 4: Enteroatmospheric fistula (EAF)

• An enteric leak that becomes chronic with continuous leakage in the OA and at a later stage will be surrounded with granulation.

• Frozen abdomen will usually develop, unless fistula is treated actively (e.g. with VAWC).

• ECF, per definition, do not have a connection to the open abdomen and are therefore not registered as grade 4.

Appendix 2

See Fig. 1.

Fig. 1

Clinical course in 111 patients treated with VAWCM. OA grades at dressing change operations (number of dressing changes per patient was 1–22), fascial closure or death, as well as in-hospital death, presented chronologically

Appendix 3

See Table 6.

Table 6 Overview of enteric leaks and enteroatmospheric fistulas that developed during open abdomen therapy

Appendix 4

See Table 7.

Table 7 Different outcomes of the 2009 and 2013 versions of the open abdomen (OA) classification system