Chilean National Triage System: Policy, Clinical Implementation, and Performance Metrics of the 5-Level ESI Framework

Triage, derived from the French verb "trier" (to sort or organize), represents a fundamental practice in modern healthcare designed to optimize patient flow and prioritize care. Its core function is to classify patients rapidly and objectively based on the severity of their condition and the corresponding risk level. By establishing a clear classification, the healthcare system ensures that those presenting with the most serious injuries or acute illnesses receive prompt attention, minimizing adverse outcomes, while also managing resources efficiently.

The practice of triage originated in military medicine, dating back to figures like French military surgeon Baron Dominique Jean Larrey during the 18th century, who developed rapid evaluation methods for wounded soldiers on the battlefield. The systematic interpretation and implementation of triage in civilian hospitals began much later, entering the emergency department (ED) setting in 1964. In Chile, this methodology is integrated across the entire national health network, underscoring its importance in achieving correct prioritization and optimizing resource utilization throughout the public system.

1.2 Global Evolution to 5-Level Acuity Scales

Emergency triage has undergone significant evolution, moving from rudimentary 3-level systems to the more granular and universally adopted 5-level acuity scales. This global shift was necessitated by the increasing complexity of patient presentations and the need for finer discrimination between urgent and non-urgent cases.

Currently, four major 5-level international models dominate global emergency medicine practice: the Australasian Triage Scale (ATS), the Canadian Emergency Department Triage and Acuity Scale (CTAS), the Manchester Triage System (MTS), and the Emergency Severity Index (ESI). The ESI model, developed in the late 1990s, represents a significant operational advancement, segregating patients into five distinct treatment levels based on two primary dimensions: physiological stability/need for immediate life-saving intervention, and the expected quantity of required diagnostic resources.

1.3 Rationale for the 5-Level Structure: Improved Resource Allocation and Clinical Safety

The adoption of a 5-level triage system, such as ESI, is a strategic policy decision aimed at enhancing both clinical safety and operational efficiency, particularly within resource-constrained public systems common in the Latin American context. The enhanced granularity offers superior differentiation compared to older 3-level systems, especially concerning moderate and low-acuity cases (Levels 3, 4, and 5).

Crucially, the ESI methodology requires triage nurses to evaluate expected resource needs—a core element often referred to as Decision Point A or B—to determine the final triage level for stable patients. This capability allows triage nurses to accurately predict the burden a patient will place on the ED, enabling healthcare administrators to better allocate resources and staffing effectively. This predictive approach is vital for managing the chronic congestion often seen in public hospital emergency departments (EDs). By adopting ESI, the Chilean Ministry of Health (MINSAL) gains an objective, quantitative metric—expected resource usage—which transforms triage into a sophisticated mechanism for demand management within the system, directing lower acuity patients away from tertiary resources.

From a clinical safety perspective, the increased definition provided by a 5-level scale helps triage staff more easily identify those patients who cannot wait and need immediate intervention, thereby mitigating the risk of patient deterioration within the waiting room. Furthermore, the implementation of a national, structured 5-level system provides a standard operating procedure that is considered more legally defensible as a prioritization scheme.

Policy and Regulatory Framework in Chile

2.1 MINSAL Mandates: Transition to the 5-Level Categorization System

Chilean health policy, guided by the Ministry of Health (MINSAL), mandates the use of a 5-level risk categorization system in hospital emergency units. This system is often referred to locally as the Selector de Demanda , reflecting its core function as a mechanism for controlling patient flow. Within official hospital protocols, the clinical structure explicitly follows the internationally recognized Emergency Severity Index (ESI) framework, designating levels from ESI 1 to ESI 5, or locally as C1 to C5.

The regulatory foundation for this system is provided through official MINSAL documents, such as the "Orientaciones Técnicas" (Technical Guidelines), which direct the redesign of the Adult Emergency Care Process in Hospital Emergency Units (UEH). This regulatory guidance ensures consistency across the national public health service.

2.2 Official Terminology: Understanding "Selector de Demanda" and ESI Integration

The coexistence of the terms "Selector de Demanda" and ESI reflects the operational and policy objectives of the system. While "Categorización" or "Selector de Demanda" serves as the general umbrella term for the process of demand control , the specific clinical criteria and methodological approach are anchored in the ESI framework.

The standardized electronic data capturing mechanism within the hospital system—the Digital Assisted Urgency (DAU) system—requires registration in the electronic categorization profile using the ESI framework. This consistent use of ESI nomenclature across digital platforms confirms that ESI is the official national standard for data structure and reporting acuity, even if local protocols are called the "Selector de Demanda." By mandating ESI data reporting, MINSAL ensures that national quality monitoring and international benchmarking remain possible, supporting quality improvement efforts through comparable data across the network.

2.3 Integration with the National Health System: Primary Care and Guaranteed Care

The triage system plays a critical role in managing patient flow across the three primary layers of emergency and urgent care: Hospital Emergency Units (UEH), Services of Primary Emergency Care (SAPU), and High-Resolution Services (SAR).

A key strategic goal of the Chilean public health policy is to use the 5-level system to actively manage demand and prevent the saturation of high-complexity hospital EDs. Patients categorized as C4 (Low complexity) or C5 (Lowest complexity) are explicitly identified as potentially resolvable in primary care facilities (SAPU or SAR). For these lower categories (C4 and C5), health entities are required to establish articulated strategies to guarantee and improve opportunity for access to necessary complementary services, such as general, specialized, or priority external consultation, and diagnostic support.

The functional success of this system relies heavily on the triage nurse acting as a crucial gatekeeper for hospital resources. While this role is vital for optimal resource utilization, ensuring that hospital capacity is preserved for ESI 1, 2, and 3 patients, it introduces tension. If the primary care system (SAPU/SAR) is inadequate or inaccessible, patients will continue to present at hospital EDs, leading to long waits for C4/C5 patients and potential patient dissatisfaction. The effectiveness of the ESI adaptation is thus intrinsically linked to the operational robustness and accessibility of the entire primary care network. Furthermore, while the Explicit Health Guarantees (GES) system dictates maximum resolution times for a defined set of health problems, errors in classification (e.g., misplacing a GES-covered patient onto a non-prioritized waiting list) can have catastrophic consequences, emphasizing the importance of accurate classification throughout the network.

Operational Breakdown of the 5-Level Chilean Triage Scale (C1–C5 / ESI 1–5)

The Chilean 5-level system (C1–C5), derived from the ESI model, defines acuity based on clinical severity, predicted resource consumption, and mandatory time-to-attention benchmarks. These benchmarks serve as crucial internal quality indicators (IQIs) for monitoring system performance.

3.1 Category 1 (C1/ESI 1): Immediate Life-Threat/Resuscitation

This category represents the highest level of risk. The clinical condition is defined as an Emergencia vital (vital emergency), where the patient requires immediate, life-saving intervention.

• Clinical Criteria: Patients are unstable and require immediate attention (0 minutes). Examples include cardiopulmonary arrest, severe traumatic injuries resulting in unresponsiveness, extreme difficulty breathing, or severe trauma leading to loss of consciousness.

• Time Benchmark: Attention must be provided immediately upon arrival (0 minutes).

• Operational Note: These patients are rapidly transferred to a designated resuscitation area (Box de Reanimación), which requires structural capacity for handling high-acuity interventions, typically considering at least two patient spaces.

3.2 Category 2 (C2/ESI 2): High Risk/Emergent

C2 denotes a condition of Alta complejidad (High complexity) where the patient presents with symptoms that are time-sensitive or pose a high risk of deterioration, requiring immediate professional assessment.

• Clinical Criteria: Symptoms are severe, such as disorientation, acute confusion, intense pain, or moderate respiratory distress. Immediate physician involvement in care is considered critical.

• Time Benchmark: Attention is required "a la brevedad" (as soon as possible). Although the maximum time is not explicitly stated in all public documentation, international ESI standards typically mandate clinical intervention within 10 to 15 minutes of triage.

• Examples: Severe chest pain accompanied by pallor and profuse sweating, or patients responsive only to painful stimuli or unresponsive on the AVPU scale, signaling a sudden change in level of consciousness.

3.3 Category 3 (C3/ESI 3): Urgent/Medium Complexity

This is the largest category in many 5-level systems, representing Mediana complejidad (Medium complexity). Patients are generally physiologically stable but often require multiple diagnostic studies or complex evaluations that demand significant ED resources.

• Clinical Criteria: The patient is stable but their clinical condition is expected to require two or more different types of resources, such as specialized laboratory testing, imaging (CT scan or ultrasound), specialty consultation, or observation.

• Time Benchmark: Clinical attention must be initiated before 1 hour and 30 minutes (90 minutes). This stringent benchmark acts as a sensitive barometer for system capacity.

• Examples: Crisis hipertensivas (hypertensive crises), either an elevation or drop in blood pressure, or patients presenting with multiple contusions.

3.4 Category 4 (C4/ESI 4): Non-Urgent/Low Complexity

C4 patients are classified as Non-Urgent or Baja complejidad (Low complexity). These individuals are stable, without immediate risk of clinical deterioration, and their condition is typically one that could appropriately be managed outside of the hospital setting.

• Clinical Criteria: The patient requires only minimal resources, typically one resource (e.g., a simple X-ray, basic blood work, or a single consultation). Their condition is often deemed suitable for primary care management.

• Time Benchmark: The permissible waiting time for clinical attention can reach up to 3 hours.

• Examples: Simple gastrointestinal complaints or uncomplicated respiratory ailments.

3.5 Category 5 (C5/ESI 5): Non-Urgent/General Attention

C5 represents the lowest acuity level, categorized as Atención General (General Attention).

• Clinical Criteria: The patient is stable, presents no risk of clinical deterioration, and is expected to require zero resources in the ED. Their treatment and study can often be resolved on an ambulatory basis without the immediate necessity of diagnostic exams or imaging in the urgency setting.

• Time Benchmark: Waiting time is determined entirely by the existing demand for assistance. Wait times are variable and are often the longest in the department, potentially exceeding 3 hours.

The existence of mandated maximum wait times (90 minutes for C3 and 3 hours for C4) serves as a critical measure of operational quality. Consistent breaches of these standards signal deficiencies in ED capacity, resource availability, or treatment box allocation. Given that ESI places a high degree of dependence on resource prediction to distinguish between C3 and C4, the accuracy of the triage nurse in estimating future needs is paramount. Errors at this boundary—misclassifying a C3 patient as C4—directly increases the risk of clinical deterioration beyond the permissible 90-minute safety window.

Contextual Adaptations and Clinical Nuances

4.1 The Challenge of Triage Specificity: Pediatric and Obstetric Populations

Effective triage necessitates specialized criteria for vulnerable populations, as generalized adult criteria fail to account for unique physiological, emotional, or clinical indicators in pediatric and obstetric patients. For instance, obstetric triage requires specific consideration of pregnancy criteria, such as gestational age, specific symptoms of pregnancy and childbirth, and the assessment of maternal and fetal well-being, which fundamentally differs from general adult assessment.

International guidelines, such as the Australasian Triage Scale (ATS), specifically incorporate detailed protocols for complex areas including mental health, pediatrics, and obstetrics. The Chilean system must, therefore, incorporate these specialized adaptations to maintain clinical integrity across all demographics.

4.2 Adaptation Requirements in Chilean Public Hospitals

The physical and operational structure of public hospitals in Chile introduces unique challenges to triage implementation. The local adaptation, the "Selector de demanda," is unique in that it accounts for specialized services—gynecological, obstetric, and pediatric—which are often physically distant from the main Adult Emergency Unit and typically operate their own separate demand selector systems.

This structural segmentation requires nurses to be highly specialized at each specific entry point. More significantly, this physical distance demands robust inter-departmental referral protocols to ensure continuity of care when a patient initially categorized in one selector needs immediate transfer to another. For example, a high-acuity obstetric emergency presenting to the general adult ED requires a seamless and immediate shift of care jurisdiction, highlighting a potential structural weakness in the network that the ESI protocol must explicitly manage.

4.3 Resource Mapping and Clinical Pathway Triggers

The 5-level system provides significant benefits in terms of automated decision support and facility planning. The assigned triage level, particularly when combined with the chief complaint, can be used to trigger automated clinical guidelines. For example, assigning ESI Level 2 to a patient with chest pain can automatically initiate a clinical guideline specific to potential cardiac ischemia.

Furthermore, the ESI categorization, especially the predicted resource use for C3 patients, is integral to the planning and design of hospital emergency facilities. It determines the necessary allocation of treatment boxes, observation spaces, and specialized areas, such as gynecobstetric boxes and reanimation cups.

4.4 Cultural and Systemic Considerations in Latin American Healthcare Delivery

Successfully implementing ESI in the Chilean context requires more than mere translation; it demands cultural and systemic adaptation. While cultural differences exist between regions (e.g., Chile's lower individualism score compared to the US) , clinical adaptation focuses on ensuring the scale remains reliable, valid, and acceptable within the local healthcare reality. The effectiveness of the system is ultimately tied to public comprehension and trust in the prioritization process. High waiting times for C4 and C5 patients, though clinically justified by the low-risk categorization, must be managed through effective communication, as these prolonged delays can lead to patient dissatisfaction and strain the provider-patient relationship.

Performance, Validity, and Reliability of the Chilean Triage System

Impact on Patient Outcomes and System Throughput

The adoption of structured, 5-level triage systems globally has been demonstrably linked to improved clinical outcomes. Evidence from low- and middle-income country (LMIC) settings indicates a positive association between the introduction of formalized triage and a reduction in both ED mortality and waiting times. Specifically, studies transitioning to a 5-level system have recorded substantial reductions in ED mortality rates. Efficient triage reduces overall resource utilization and significantly decreases Emergency Department Length of Stay (ED LOS). These findings affirm the fundamental value of using a systematic, acuity-based scale to manage high-volume, high-acuity environments.

Comparative Performance Analysis: ESI vs. Alternative Triage Systems

When comparing the Emergency Severity Index (ESI) against other global standards, such as the Manchester Triage System (MTS), both scales demonstrate validity in correlating acuity level with outcomes like resource use and hospitalization rates.

A crucial operational distinction lies in patient allocation. Comparative studies suggest that ESI tends to classify a substantially higher proportion of patients into the middle category, ESI Level 3, compared to MTS (e.g., 70% versus 34% in a comparison study). This means that in Chile, the bulk of the patient population entering the hospital ED is likely categorized as C3, placing immense pressure on the 90-minute time-to-attention benchmark. Furthermore, while all structured systems are preferable to informal triage, studies show variability in undertriage rates (missing high-acuity patients), suggesting that continuous evaluation is necessary regardless of the chosen model.

Validation Status and Reproducibility of Local Adaptations

While the core ESI model is internationally recognized for its validity and reliability , a significant issue specific to the Chilean context is the status of the local adaptation. Academic reviews explicitly state that the validity and reproducibility of the specific Selector de demanda protocol are not known with certainty and have not been formally evaluated.

This absence of formal, contextual validation creates a substantial policy vulnerability. The local system has been modified to account for Chilean public hospital architecture (separate selectors for specialties) and specific language/clinical practices. Without rigorous, local empirical studies—measuring the system’s ability to predict local outcomes (mortality, hospitalization, resource use) among the Chilean patient population—the protocol relies solely on the generic efficacy of ESI. Relying on unvalidated local rules means that MINSAL lacks the necessary scientific evidence to defend the safety and reliability of its specific adapted protocol, should a critical case arise where triage accuracy is questioned. Therefore, closing this validation gap is a matter of urgent scientific and political priority.

Inter-Rater Reliability (IRR) Assessment

Inter-Rater Reliability (IRR), the consistency with which different health professionals assign the same triage level to the same patient scenario, is a universal challenge in triage systems. Studies across various models often report IRR ranging from poor to moderate.

Agreement levels are typically highest for extreme acuity levels (C1 and C2 / ESI 1 and 2), where physiological signs (e.g., trauma, cardiac arrest) leave little room for subjective interpretation. However, inconsistency in assignment remains problematic for medium and low-acuity cases. Variability in triage assignment requires targeted interventions to establish a common clinical language and standardized assessment criteria shared among triage nurses and ED physicians.

The operational implication of moderate IRR, particularly in Chile, is significant. Since the ESI framework heavily loads patients onto Level 3 and the time constraint for C3 is strict (90 minutes) , inconsistencies in distinguishing C3 from C4 (which relies on subtle resource prediction) can lead to either unnecessary resource consumption (over-triage) or clinically risky delays (under-triage). Therefore, training resources must be strategically focused on standardizing the resource estimation steps necessary for accurate C3/C4 differentiation, where the risk of operational failure is highest.

Strategic Recommendations for Optimization and Standardization

Based on the analysis of policy implementation, operational constraints, and identified validation gaps, the following strategic recommendations are proposed for optimizing the Chilean Triage System:

Enhancing Training and Calibration Programs

To address variability in triage assignments and bolster the legal defensibility of the system, mandatory and recurrent calibration programs must be implemented for all triage personnel (nurses and supervisory physicians).

1. Focus on Resource Differentiation: Training must be heavily weighted toward accurately assessing resource consumption, as this is the primary determinant separating C3 from C4 patients under the ESI model. Misclassification in this area has the greatest potential to compromise the 90-minute safety benchmark for urgent cases.

2. Standardized Clinical Language: Establish a national curriculum that formalizes the common clinical language and criteria used during triage, ensuring consistent interpretation between nurses and ED physicians.

3. Context-Specific Flow Training: Training protocols must explicitly cover the necessary steps for managing patient flow across the physically separated specialized selectors (pediatric, obstetric, gynecological) to mitigate the structural risks associated with decentralized triage points.

Policy Recommendations for Standardizing Time-to-Attention Metrics

The national policy must clearly define all operational time thresholds to ensure public accountability and internal quality control.

1. Formalizing C2 Time Standard: While C1 is immediate, the mandatory time-to-attention for C2 (High Risk) must be formally established and rigorously enforced across all UEH facilities, aligning with international best practices (e.g., 10 or 15 minutes).

2. Primary Care System Strengthening: To ensure the C4/C5 diversion strategy is effective, MINSAL must strengthen the capacity and accessibility of Primary Care Emergency Services (SAPU/SAR). Unless these services are perceived as reliable alternatives, patients will continue to overload hospital EDs, leading to chronic breaches of the C4/C5 wait time standards.

3. Rigorous Throughput Measurement: Implement mandatory, standardized tracking of key throughput metrics, including time-to-clinical decision and overall ED Length of Stay (LOS), correlating these metrics directly with the assigned ESI level to pinpoint and eliminate operational bottlenecks.

Future Research Agenda: Closing the Validation Gap

The most critical long-term requirement is the rigorous scientific validation of the locally adapted system.

1. Mandatory Validation Studies: MINSAL must fund and prioritize dedicated studies to assess the internal consistency, construct validity, and, most importantly, the predictive validity of the Selector de demanda against hard clinical outcomes (mortality, intensive care unit admission, hospitalization, and local resource intensity) within the specific operational parameters of the Chilean public health environment.

2. National Reproducibility Measurement: Comprehensive inter-rater reliability (IRR) studies must be conducted across diverse hospital types (teaching, rural, municipal) to accurately quantify the national variability in triage assignment and provide empirical data for targeted training and scale refinement.

3. Data-Driven Refinement: The results of these validation studies should be used to empirically refine the local decision pathways and criteria, ensuring the Chilean Triage Scale is not only conceptually based on ESI but is also optimally adapted and scientifically proven to function safely and efficiently within the Latin American context.