International multidisciplinary consensus on the definition and nomenclature of acute mesenteric ischaemia: a modified Delphi study

Acute mesenteric ischaemia (AMI) is a life-threatening emergency with in-hospital mortality of 49–64% across recent cohort studies. Terminology and nomenclature for acute ischaemia of the gastrointestinal tract remain inconsistent across disciplines and geographies, hindering clinical communication, registry design, and research comparability. This project aimed to develop consensus definitions and clinical algorithms for AMI; the present paper addresses definitions and nomenclature, and the companion paper the algorithms. A seven-member steering committee representing intensive care, vascular surgery, general surgery, interventional radiology, and gastroenterology conducted a literature review (2020–2025) and drafted candidate definition statements. An international panel of 50 experts from 15 countries underwent a modified Delphi process comprising two electronic voting rounds (9-point GRADE scale; predefined consensus threshold: ≥75% rated 7–9 and ≤ 15% rated 1–3) via REDCap, followed by two virtual consensus meetings with live polling. Where clinical equipoise existed, competing statements were presented for independent rating. Fifty panellists completed Round 1 (22 statements) and 44 completed Round 2 (27 statements; retention 88%). Ten statements reached the predefined electronic consensus threshold, including a core AMI definition (100%), mechanism classification (100%), and subtype definitions for arterial occlusive AMI (91%), venous AMI (84%), and non-occlusive mesenteric ischaemia (NOMI; 86%). The consensus meetings adopted a novel two-tier nomenclature: Acute GastroIntestinal Ischaemia (AGII) as the umbrella term for acute ischaemia of the gastrointestinal tract, and AMI as the subset to which the clinical algorithms apply. ‘Ischaemic colitis’ was declared a misnomer (92%). The arterial territory question (superior mesenteric artery (SMA) only versus a broader mesenteric territory) was not resolved and is presented as a dual-interpretation framework. Subgroup analysis revealed a specialty-driven divergence: general (73%, n = 11) and vascular surgeons (67%, n = 9) favoured restricting AMI to the SMA distribution, whereas intensivists favoured the whole gastrointestinal tract (80%, n = 10). This international, multidisciplinary Delphi study provides consensus definitions of AMI and its subtypes and proposes AGII/AMI as a two-tier nomenclature to resolve longstanding territorial and terminological ambiguities. These definitions lay the foundation for the companion clinical algorithms and aim to provide a standardised framework for future research, clinical communication, and registry design.