Triage, derived from the French verb trier meaning “to sort,” is a fundamental process in emergency medicine and disaster response. It is the systematic method of prioritizing patients based on the severity of their condition and their likelihood of survival, aiming to provide the greatest good for the greatest number of people. This system originated in military settings, notably with French surgeon Baron Dominique Jean Larrey during the Napoleonic Wars. Rapid assessment and categorization are paramount in emergency situations to ensure that those with life-threatening injuries receive immediate intervention. Triage expanded into civilian hospitals beginning in the mid-20th century to manage patient flow in emergency departments.
Why the Number of Triage Levels Varies
The number of triage levels used is not consistent across all hospitals or countries. The specific scale adopted depends on the local healthcare system’s resources, the clinical complexity of the environment, and the national standard. Historically, many emergency departments utilized a simpler three-level system, which categorized patients as emergent, urgent, or non-urgent.
Three-level systems were often less precise, leading to inconsistencies in classifying patients with moderate injuries. This variability spurred the development of more granular scales, such as four-level and five-level systems. The Australasian Triage Scale (ATS) and the Canadian Triage and Acuity Scale (CTAS) are prominent examples of five-level systems used internationally.
Five-level scales are now widely considered the standard for emergency department triage due to their increased reliability in assessing patient acuity. These scales, including the Emergency Severity Index (ESI), introduce more distinct categories. This helps minimize the “under-triage” of high-risk patients and allows emergency departments to more accurately allocate staff and resources.
Understanding the Five-Level Emergency Severity Index (ESI)
The Emergency Severity Index (ESI) is the most common five-level triage algorithm used in the United States. It classifies patients based on the urgency of their condition and the anticipated number of resources required. ESI Level 1, or Resuscitation, is reserved for patients who require immediate life-saving intervention, such as those experiencing cardiac arrest or severe respiratory failure. These patients are seen immediately, as their condition presents an imminent threat to life or limb.
ESI Level 2, or Emergent, is assigned to high-risk patients who are in severe pain or who could rapidly deteriorate, but do not require an immediate life-saving procedure. Conditions like stroke symptoms, chest pain, or significant difficulty breathing often fall into this category, requiring prompt intervention within ten minutes. The distinction between Level 1 and Level 2 hinges on the need for immediate, hands-on, life-saving action.
For stable patients who do not meet the criteria for Level 1 or 2, the ESI assessment focuses on the likely use of hospital resources. Resources are defined as diagnostic tools or interventions, such as laboratory tests, X-rays, CT scans, sutures, or intravenous fluids and medications. ESI Level 3, or Urgent, is assigned to patients whose vital signs are stable but who are anticipated to require multiple resources (two or more interventions or tests).
ESI Level 4, or Less Urgent, is for patients expected to need only one resource, such as a single X-ray for a minor fracture. Level 5, or Non-Urgent, is for patients anticipated to require no resources at all, or only administrative services. Simple procedures like applying a splint or receiving oral medications are specifically not counted as “resources” in the ESI model.
Triage in Disaster Settings
Triage procedures change significantly when resources are overwhelmed, such as during a mass casualty incident (MCI) or a disaster. In these field settings, the goal shifts from providing definitive care to maximizing the overall number of survivors. This is accomplished using a rapid, simpler categorization system like Simple Triage and Rapid Treatment (START).
The START method is a four-category system that uses color-coded tags to quickly classify victims:
- Immediate (Red): For patients with life-threatening injuries who can still be saved with rapid intervention.
- Delayed (Yellow): For those with serious injuries whose treatment can be postponed without immediate threat to life.
- Minor (Green): Assigned to the “walking wounded” with superficial injuries who require minimal care.
- Deceased/Expectant (Black): For those whose injuries are so severe that survival is unlikely given the limited resources, or those who have already died.
The field triage process focuses on a rapid assessment of respiration, perfusion, and mental status (RPM) to determine priority for transport, not for complex treatment at the scene.