An international team of experts is working on a project called updated WSACS consensus definitions. The goals of this study are to:

1. To generate expert consensus on the definitions and classification of IAH and ACS.
2. To generate expert consensus on definitions regarding the pathophysiology of IAH and ACS.
3. To generate consensus on definitions regarding the methods of measurement of intra-abdominal pressure (IAP).

Intra-abdominal hypertension (IAH) and abdominal compartment syndrome (ACS) are frequently encountered in critically ill or injured patients and remain associated with significant morbidity and mortality. IAH is defined as a sustained increase in intra-abdominal pressure (IAP) equal to or above 12 mmHg. It is diagnosed in approximately one-third of mixed medical and surgical intensive care unit (ICU) patients at admission and develops in about half during the first week of ICU stay. IAH has consistently been shown to be an independent predictor of adverse outcomes, including multi-organ dysfunction and death.

Following the original consensus definitions and subsequent guideline updates by the Abdominal Compartment Society (WSACS), the understanding and management of IAH and ACS have evolved substantially. While surgical etiologies such as trauma and ruptured abdominal aortic aneurysm were historically predominant, more recent data highlight that IAH and ACS frequently occur in medical ICU populations as well. Contributing factors include excessive fluid resuscitation, massive transfusion, venous congestion, and capillary leak, which can lead to secondary IAH and subsequent organ failure even in the absence of direct abdominal pathology.

Despite the availability of consensus guidelines and an improved understanding of the pathophysiology, it remains unclear whether prevention or active treatment of IAH directly improves patient outcomes. Furthermore, there is growing recognition of the need to refine the definitions, measurement techniques, and classification systems for IAH and ACS to reflect current clinical knowledge and practice across diverse healthcare settings.

The WSACS - The Abdominal Compartment Society - previously published comprehensive consensus definitions and recommendations in 2013. Since then, new research has provided additional insights into epidemiology, measurement technologies, classification systems, and the broader clinical implications of IAH and ACS. A recent global survey among healthcare professionals identified emerging areas of uncertainty and priority topics for definition updates.

In response, this study will conduct an international modified Delphi process to achieve expert consensus on updated definitions and clinical practice statements for IAH and ACS. The Delphi method will systematically collect and refine expert opinions over several iterative rounds, with the goal of reaching agreement on revised definitions, measurement approaches, pathophysiological frameworks, and classification criteria.

The outcome of this Delphi process will be a set of updated, evidence-informed, and globally endorsed definitions and recommendations for IAH, ACS, and the open abdomen. These consensus statements aim to harmonize terminology, support clinical decision-making, guide future research, and ultimately improve patient care. The target audience includes physicians, surgeons, intensivists, anesthesiologists, nurses, and policymakers involved in the management of critically ill or injured patients across both high- and low-to-middle-income countries.

Inclusion Criteria: Panellists will be identified based on either of the following criteria At least 5 years of clinical experience as a staff member in Anesthesiology, Surgery or Intensive Care Medicine with involvement in care of patients with postoperative complications Author of at least one publication (observational studies or randomised controlled trials) on intra-abdominal hypertension or abdominal compartment syndrome. For patients and public involvement Individuals who have either personally experienced IAH or ACS following surgery or ICU within the last 5 years or, primary caregivers of such patients will be recruited as patient care representatives. Proficiency in English is required. To mitigate potential bias, patient care representatives mustn't maintain a professional or advisory relationship with the steering committee or panellists. Co-authors from previous WSACS survey published in 2024, former or current WSACS ambassadors, representative from WSES, ESAIC, ESICM.

Exclusion Criteria:

• None

Inclusion Criteria: Panellists will be identified based on either of the following criteria At least 5 years of clinical experience as a staff member in Anesthesiology, Surgery or Intensive Care Medicine with involvement in care of patients with postoperative complications Author of at least one publication (observational studies or randomised controlled trials) on intra-abdominal hypertension or abdominal compartment syndrome. For patients and public involvement Individuals who have either personally experienced IAH or ACS following surgery or ICU within the last 5 years or, primary caregivers of such patients will be recruited as patient care representatives. Proficiency in English is required. To mitigate potential bias, patient care representatives mustn't maintain a professional or advisory relationship with the steering committee or panellists. Co-authors from previous WSACS survey published in 2024, former or current WSACS ambassadors, representative from WSES, ESAIC, ES

The IPD is available to investigators and can be shared with appropriate requests.