Complex abdomen: proposal of a preliminary conceptual framework, clinical implications, and contemporary perspectives

The open abdomen has become a cornerstone in the care of critically ill patients undergoing damage control surgery, with severe abdominal sepsis, or at risk of abdominal compartment syndrome. These patients frequently develop a multidimensional clinical course - persistent infection, organ failure, loss of abdominal wall integrity, nutritional depletion, and entero-atmospheric fistulas - whose severity appears to emerge from the dynamic interaction among these factors rather than from visceral exposure alone. Current classifications, notably Björck's amended classification, describe the anatomical progression of the open abdomen but do not integrate the physiological, infectious, nutritional, and organizational dimensions of care. The aim is to propose the term "complex abdomen" as a preliminary conceptual framework complementary to - and not a replacement for - existing classifications.

Conceptual scientific communication grounded in a narrative review of the literature (MEDLINE/PubMed, Embase, Cochrane Library, SciELO, and LILACS; 2000 to 2025; Portuguese, English, and Spanish), reported according to the SANRA scale. The synthesis followed best-fit framework synthesis, with the Cumulative Complexity Model as the a priori framework.

Five constitutive domains are proposed - physiological instability; uncontrolled intra-abdominal infection; loss of abdominal wall domain; entero-atmospheric or complex enteric fistula; nutritional and intestinal failure - together with their associated cut-offs, a contextual organizational modifier recorded separately, and the criterion of simultaneous involvement of two or more domains. The domains, the cut-offs, and the criterion were proposed by the authors on the basis of the literature and clinical experience, without formal consensus and without empirical validation. The construct is presented as a dynamic clinical phenotype assessed at defined time points, not as an obligatory evolutionary stage or a prognostic score.

This is a preliminary framework rather than a validated definition. Formalizing this phenotype may improve clinical reasoning, multidisciplinary communication, and the selection of more homogeneous study populations. A three-step validation agenda - modified Delphi consensus, reliability and content validity assessment, and prospective prognostic testing within a multicenter registry - is proposed, together with explicit refutation criteria.