The Evolving Role of the Emergency Department in Mass Casualty Incident (MCI) Response: A Review of Triage, Surge Capacity, and Decontamination Strategies

Mass Casualty Incidents (MCIs) represent a critical stress test for any healthcare system, positioning the hospital Emergency Department (ED) as the fulcrum of the medical response. This review article provides an exhaustive analysis of the evolving role of the ED in MCI management, synthesizing the current body of literature across three core operational domains: triage, surge capacity, and decontamination. The article traces the evolution of ED preparedness, shaped by seminal events such as the 9/11 terrorist attacks, Hurricane Katrina, and the COVID-19 pandemic, which have collectively driven a paradigm shift from isolated, reactive planning to proactive, integrated, and community-wide response frameworks. In triage, the review examines the fundamental ethical transition from individual-focused care to a utilitarian model aimed at achieving the greatest good for the greatest number. It critically compares foundational field triage systems, including Simple Triage and Rapid Treatment (START) and the nationally proposed Sort, Assess, Lifesaving Interventions, Treat/Transport (SALT) system, while also addressing the complexities of secondary triage in the ED and the unique challenges posed by special patient populations. The concept of surge capacity is deconstructed through the '4 S' framework—Staff, Stuff, Structure, and Systems—providing a comprehensive overview of innovative strategies for managing personnel, critical resources, physical space, and command and control. Finally, the article details the principles and operationalization of hospital-based decontamination, reviewing evidence for different methods and protocols for chemical, biological, and radiological threats. Principal findings indicate that these three domains are deeply interdependent, where failure in one can cascade and cripple the others. Key research gaps are identified, particularly in the validation of triage tools, sustainable models for responder mental health, and evidence-based protocols for non-ambulatory patient decontamination. The review concludes that a modern, resilient ED must be adaptable, technologically integrated, and deeply embedded within a regional healthcare coalition, committed to continuous training, simulation, and innovation to meet the challenges of an uncertain future.