The evolution of European healthcare systems over recent decades has been marked by a progressive reassessment of the centrality of inpatient hospitalization as the standard response to care needs. This process cannot be attributed to a single cause, but rather to the interaction of clinical, technological, demographic and economic factors. Increased life expectancy and the resulting rise in chronic diseases and multimorbidity have led to growing demand for healthcare services, often episodic but characterized by high decision-making complexity. In parallel, advances in diagnostic and therapeutic technologies have enabled increasingly rapid and targeted clinical management, reducing the need for prolonged inpatient observation. In this context, hospitalization has gradually shifted from being an implicit prerequisite for clinical safety to a resource to be used selectively, reserved for cases in which clinical risk, care complexity or the need for continuous monitoring make it truly indispensable. As a result, the concept of appropriateness has moved from where care is delivered to how and with which tools timely and informed clinical decisions are made.

Outpatient surgery represents the first area in which this paradigm shift has become structurally established. The introduction of minimally invasive surgical techniques, advances in anesthesiology toward fast-recovery approaches and the standardization of perioperative protocols have made it possible to perform procedures once considered highly resource-intensive without requiring inpatient admission. From a hospital engineering perspective, outpatient surgery introduced a key principle: patient safety is not directly proportional to infrastructural complexity, but to the appropriateness of the care setting relative to clinical risk. This principle has had significant implications for spatial design, technological equipment and workflow organization. The outpatient surgical unit is not a “reduced operating room” but an environment designed around a selected case mix, with proportional technical, logistical and technological requirements. Outpatient surgery has also highlighted the central role of patient selection, continuity of care and structured follow-up management—elements that would become essential in subsequent care models.

Extension of the outpatient model to other disciplines

The success of outpatient surgery has fostered the extension of the outpatient model to other clinical areas, particularly internal medicine and specialties with a strong diagnostic component. High-complexity outpatient clinics, multidisciplinary day services and concentrated diagnostic-therapeutic pathways have demonstrated that many acute conditions or exacerbations of chronic diseases can be managed safely without hospitalization, provided that timely diagnostic services, integrated specialist expertise and clear decision-making criteria are available. From a technical and organizational perspective, this evolution has reduced the traditional distinction between “outpatient” and “inpatient” care, introducing a continuum of care settings differentiated by intensity of care. Within this continuum, the discriminating factor is not the presence of an inpatient bed, but the system’s ability to make rapid clinical decisions supported by objective data.

Emergency care is the area in which the limitations of the traditional model have become most evident. The progressive increase in emergency department visits, combined with structural reductions in inpatient bed capacity in many European countries, has led to overcrowding, prolonged stays and hospital admissions driven primarily by organizational needs rather than optimal clinical decision-making. In this context, hospitalization has often functioned as a containment solution rather than a clinically appropriate choice.
Revising the emergency care model therefore required a shift in perspective: separating the need for urgent clinical assessment from the need for inpatient admission. This conceptual shift laid the foundations for applying outpatient principles to emergency care, paving the way for Ambulatory Emergency Care models.

Ambulatory Emergency Care (AEC), also referred to as Same Day Emergency Care (SDEC), formalizes a model in which selected patients with acute conditions are assessed, diagnosed and treated on the same day, with safe discharge and appropriate follow-up when indicated. From a technical standpoint, AEC is not defined by a specific architectural layout, but by a sequence of processes: rapid access to clinical assessment, immediate availability of diagnostics, multidisciplinary integration and structured discharge criteria. The transition from outpatient surgery to AEC is therefore primarily a methodological shift rather than a functional one. In both cases, the focus lies on risk management through selection, standardization and continuity of care, rather than through indiscriminate increases in infrastructural complexity.

Origin and development of Ambulatory Emergency Care

The Ambulatory Emergency Care model originated in the United Kingdom within the National Health Service as a structured response to systemic challenges that emerged progressively from the early 2000s. Increasing emergency department overcrowding, rising costs associated with inpatient care and difficulties in ensuring timely clinical pathways for patients with low- to medium-complexity acute conditions highlighted the unsustainability of a hospitalization-centered approach.
In this context, the NHS initiated an organizational reflection aimed at separating the need for urgent clinical assessment from the need for inpatient hospitalization, laying the groundwork for care models capable of delivering rapid clinical decisions without automatic admission. AEC developed as a structured evolution of this approach, integrating principles already established in outpatient surgery and day services with the specific requirements of emergency care.
The role of the Royal College of Emergency Medicine was instrumental in formalizing the model, defining its clinical, organizational and operational criteria and promoting AEC as a stable component of emergency services. In the UK, AEC is now considered an organizational standard, integrated into emergency department pathways and measured through performance indicators related to same-day management, safety and clinical outcomes.
Building on the UK experience, Ambulatory Emergency Care has also been adopted in other healthcare systems facing similar challenges. In Nordic countries, high levels of hospital–community integration have facilitated the use of outpatient emergency pathways to ensure continuity of care and optimize patient flows. In extra-European contexts such as Australia and Canada, comparable models have been developed to address geographic dispersion, bed capacity pressure and the need to optimize access to acute care.
In recent years, the concept of Ambulatory Emergency Care has also spread across continental Europe, adapting to healthcare systems with different organizational and regulatory frameworks. While implementation varies significantly between countries, there is convergence around the core principles of the model: rapid clinical assessment, immediate access to diagnostics, multidisciplinary integration and the possibility of safe same-day discharge. In this sense, AEC represents not a rigidly exported model, but a set of organizational principles adapted to local regulatory and structural contexts.

The adoption of outpatient and AEC models has a direct impact on traditional operating room design. Full-spec operating rooms are designed to accommodate high variability in case mix, including high-risk scenarios and lengthy procedures, resulting in stringent requirements for HVAC systems, redundancy, medical gases, technological integration and ancillary spaces.
By contrast, outpatient surgical units and procedure rooms associated with AEC models can be designed with requirements proportionate to the authorized case mix. At the European level, there is no single prescriptive standard defining these environments; instead, reference is made to technical standards (such as ISO 14644 for controlled environment classification), national guidelines and local authorization requirements. This performance-based approach allows greater design flexibility, while requiring clear definition of operational limits and permitted procedures.

European regulation and focus on the Italian context

At the European level, regulation of surgical and procedural environments is fragmented. The European Union primarily intervenes through horizontal regulations such as the Medical Device Regulation (MDR), while structural and organizational requirements remain within national competence.
In Italy, the historical reference is Presidential Decree of 14 January 1997 on minimum requirements, supplemented by policy guidance from the State–Regions Conference and regional regulations that define in detail the characteristics of operating rooms, outpatient surgical units and day surgery facilities. This regulatory fragmentation represents one of the main barriers to uniform adoption of AEC models across Europe, while simultaneously allowing local adaptation to healthcare system and territorial characteristics.

Technological equipment and devices: a risk-based approach

From an equipment perspective, the difference between an operating room and an outpatient surgical unit cannot be expressed as a rigid list of devices that must be “present” or “absent” . The appropriate approach, consistent with European regulation and clinical evidence, is risk-based. Low-complexity procedures performed under local anesthesia or sedation do not necessarily require the same infrastructure and equipment as major interventions under general anesthesia. This principle is central to AEC models as well, where technological availability is oriented toward rapid decision-making rather than the management of extreme scenarios. Design and outfitting must therefore be aligned with the authorized risk profile, avoiding both over- and under-equipping.

Economic impact and sustainability

From an economic standpoint, the difference between outfitting a high-spec operating room and an outpatient surgical unit or AEC procedure room is significant, particularly with respect to HVAC systems, surface areas, validation processes and operating costs. Bottom-up analyses show that infrastructural complexity has a substantial impact on both CAPEX and OPEX.
Although no uniform European benchmarks exist, design experience indicates that, for an equivalent level of clinical safety within the authorized case mix, outpatient-based approaches can lead to substantial reductions in investment and operating costs.

The primary limitation to the widespread adoption of AEC models in Europe is not clinical or technological, but regulatory and cultural. The absence of a harmonized EU-level definition of Ambulatory Emergency Care and outpatient surgical units creates authorization uncertainty and heterogeneous implementation. Nevertheless, convergence around principles of appropriateness, sustainability and safety suggests that these models represent a structural direction for the future evolution of European healthcare systems.