The shortage of intensive care unit (ICU) beds has increasingly necessitated the delivery of critical care within emergency departments (EDs) by emergency nurses [1]. This situation has significantly expanded the clinical responsibilities and workload of emergency nurses, particularly in light of an aging population and the rising prevalence of chronic illnesses [2]. Emergency departments are typically not structured to support prolonged patient care or continuous monitoring. Furthermore, the care priorities of intensive care nurses and emergency nurses differ considerably, leading to inconsistencies in care practices. Clinical expertise gaps and structural differences between units often result in conflicting expectations regarding patient management [1].

Access to advanced critical care resources—such as mechanical ventilation or renal replacement therapy—may be limited in the ED setting. Additionally, emergency nurses may lack sufficient training or familiarity with critical care guidelines, which can compromise the quality of care and contribute to the development of unsafe clinical environments [2,3]. The time and attention required for critically ill patients may also divert resources from the care of other ED patients, thereby affecting overall patient safety [4]. The absence of a consistently available, specialized critical care team further hinders the provision of comprehensive care in emergency settings [2].

In such complex and high-acuity clinical environments, observation and case-based decision-making alone may not be sufficient. To better understand how emergency nurses experience and manage this role expansion, and to identify systematic approaches to improve care delivery, theoretical frameworks are needed. However, existing literature reveals a lack of studies that examine the role transition of emergency nurses using theoretical models [5,6]. This indicates a clear need for theory-based approaches in the field.

Meleis’ Transition Theory provides a conceptual framework to understand developmental, situational, health–illness, and organizational transitions [7,8]. Within this study, the shift in responsibility experienced by emergency nurses as they assume care for critically ill patients is considered a situational transition. Successful transitions depend on the nurse’s readiness, clinical knowledge, and competence [8]. In high-pressure, unpredictable environments such as EDs, emergency nurses are often expected to manage these transitions despite insufficient preparation, conflicting roles, and limited resources [9,10]. In this context, the transition is viewed as a period during which nurses redefine their clinical perspectives, care priorities, and professional responsibilities.

Tanner’s Clinical Judgment Model offers a framework to analyze how emergency nurses think, make decisions, and act in the face of complex clinical situations. The model comprises four phases: noticing, interpreting, responding, and reflecting [11]. Clinical judgment enables emergency nurses to rapidly analyze clinical data, recognize early signs of deterioration, and respond appropriately. Nurses must be able to make accurate decisions based on available evidence and act swiftly to meet patients' medical needs [12]. In this study, Tanner’s model was used to explore how emergency nurses identify clinical cues, interpret them, make decisions, and reflect on their actions while managing critically ill patients in the ED. Caring for patients who require intensive care often necessitates stepping outside routine care practices, which may significantly influence nurses’ clinical judgment.

This study adopts a unique theoretical approach by combining two conceptual models that are rarely applied together in nursing research. Meleis’ Transition Theory was used to conceptualize the shift in responsibility undertaken by emergency nurses, while Tanner’s Clinical Judgment Model was employed to analyze how this transition influences clinical decision-making, patient assessment, and care planning processes.