Triage as a formal system dates to the Napoleonic Wars of the late eighteenth and early nineteenth centuries, when a French military surgeon named Dominique Jean Larrey began sorting wounded soldiers by medical urgency rather than by rank or social status. The word itself comes from the French “trier,” meaning to sort or select, and Larrey’s innovation was radical for its time: the worst injuries got treated first, whether the patient was a general or a conscript. But the practice has far older roots in battlefield medicine, and its evolution from a wartime improvisation to the structured system that greets you in every modern emergency room spans more than two centuries of trial, error, and ethical argument.
Larrey and the Napoleonic Battlefield
Before Larrey, wounded soldiers were typically left on the battlefield until fighting stopped, sometimes waiting hours or days for care. Officers received attention before enlisted men. Larrey, who served as surgeon-in-chief to Napoleon’s Grande Armée, upended both customs. He established a categorical rule for sorting war casualties: treatment was determined by the severity of injury and the urgency of the needed care, regardless of the patient’s rank or nationality.1PubMed. “To afford the wounded speedy assistance”: Dominique Jean Larrey and Napoleon That last part is easy to overlook, but it was genuinely revolutionary. Larrey treated enemy soldiers alongside his own, applying a principle of medical need that military medicine had never formalized.
Larrey also pioneered what he called “flying ambulances,” lightweight horse-drawn carriages designed to reach the wounded during battle rather than after it. The combination of rapid transport and need-based sorting created the scaffolding of what we now call triage. His system was imperfect by modern standards, built more on a surgeon’s experienced eye than on any formal protocol, but the underlying logic persists in every emergency department today: who needs help right now, who can wait, and who is beyond help.
The American Civil War and Jonathan Letterman
The next major leap happened half a century later during the American Civil War, under a Union Army surgeon named Jonathan Letterman. The sheer scale of Civil War casualties, with tens of thousands wounded in single battles, exposed the inadequacy of ad hoc battlefield medicine. Letterman built what amounted to a system: an organized ambulance corps, a structured evacuation plan, and a formal triage process that sorted the wounded before they ever reached a field hospital.2PubMed Central. The Life and Legacy of Dr. Jonathan Letterman (1824-1872): The Father of Modern Battlefield Medicine He also pushed for improvements in military camp sanitation, recognizing that disease killed far more soldiers than enemy fire.
Letterman’s contribution was organizational as much as medical. Where Larrey had the insight that urgency should determine treatment order, Letterman built the bureaucratic and logistical infrastructure to make that principle work at scale. His system influenced military medicine for generations and earned him the title “Father of Modern Battlefield Medicine.”
From the World Wars to Korea
The treatment of war wounds has been an ancient practice, but since the nineteenth century, mortality from combat injuries dropped steadily as military surgeons developed systems for moving the wounded quickly from the front line to hospitals equipped to treat them.3PubMed Central. Warfare Injuries: History, Triage, Transport and Field Hospital Setup in the Armed Forces World War I formalized triage further out of grim necessity. Casualty clearing stations near the front lines became the places where medical officers made rapid sorting decisions, categorizing the wounded into groups: those who needed immediate surgery, those who could be transported to rear hospitals, and those whose injuries were so severe that treatment was unlikely to help. The volume of wounded soldiers, sometimes arriving in waves of hundreds after a single artillery barrage, forced these decisions to become more systematic and less reliant on individual judgment.
World War II and the Korean War accelerated the trend. During Korea, the United States introduced Mobile Army Surgical Hospitals, placing surgical teams close enough to the front that critically wounded soldiers could reach an operating table within hours. Innovations including helicopter evacuation, whole blood transfusions, and antibiotic treatments reduced the mortality rate among soldiers who reached treatment to roughly 3%.4PubMed Central. Lessons from foreign military surgeons in the Korean War: advancing trauma care and preparing for future conflicts That number reflected not just better surgery but better triage. Getting the right patient to the right facility at the right time became as important as what happened in the operating room.
Vietnam and the Helicopter Revolution
The Vietnam War made helicopter evacuation routine rather than exceptional, and the effect on survival was dramatic. Rapid transport by air was associated with unprecedented survival among critically injured patients.5Panamerican Journal of Trauma, Critical Care & Emergency Surgery. Tactical Evacuation of Casualties by Military Helicopters: Present and Future Aspects A wounded soldier in Vietnam could go from the battlefield to a surgical facility in under an hour, a timeline unimaginable in earlier conflicts. This speed compressed the triage decision window. Medics in the field had to make faster sorting calls because the helicopter was coming whether or not they were ready.
Vietnam also highlighted a problem that still haunts triage: the gap between a field medic’s assessment and the surgical team’s priorities. A soldier triaged as urgent in the field might arrive at a hospital already overloaded with other urgent cases. The war pushed military medicine to think harder about coordination between triage points, not just the sorting decision at each individual station.
Moving Into Civilian Emergency Rooms
For most of its history, triage was exclusively a military tool. Civilian hospitals did not think about emergency care in the same way, partly because emergency departments as we know them barely existed before the mid-twentieth century. The rise of emergency medicine as a distinct specialty in the 1960s changed that, but the transition was not smooth. Urban teaching hospitals, which had established their own triage systems and ambulatory care facilities, actually resisted the formalization of emergency medicine as a separate discipline, delaying its development.6Oxford Academic. The Rise of Emergency Medicine in the Sixties: Paving a New Entrance to the House of Medicine
The resistance seems counterintuitive now, but it made political sense at the time. Existing hospital departments viewed emergency medicine as an encroachment on their turf. Surgeons, internists, and pediatricians had long handled emergencies that fell within their domains, and a new specialty that claimed all of emergency care as its own was threatening to established hierarchies. Triage in civilian hospitals eventually became standardized not because of top-down mandates but because the growing volume of emergency department visits made it unavoidable. By the 1990s, most major emergency departments used some form of structured triage to sort incoming patients.
How Modern Hospital Triage Works
The most widely used triage system in U.S. emergency departments today is the Emergency Severity Index, or ESI, a five-level scale. Level 1 is immediate, life-threatening. Level 5 is minor, a patient who needs few or no resources. A study validating version 3 of the ESI found strong agreement between nurses’ triage assignments and the “true” ESI level, with admission rates tracking closely with acuity: about 80% of Level 1 patients were admitted to the hospital, compared with roughly 5% of Level 5 patients.7PubMed. Reliability and validity of scores on The Emergency Severity Index version 3 The system also predicted who would end up in intensive care, with around 40% of Level 1 patients requiring ICU admission versus essentially none at Levels 4 and 5.
A broader systematic review found that across multiple studies, the ESI showed good reliability and solid accuracy for predicting mortality and ICU admission, with lower rates of both under-triage and over-triage compared with other triage systems.8African Journal of Emergency Medicine. Systematic Review of Emergency Severity Index (ESI) triage tool’s utility in predicting mortality and critical care unit admission in Emergency Departments That said, accuracy improved substantially when the ESI score was combined with additional clinical information, which suggests the five-level score is a useful starting point but not the whole picture.
One persistent challenge is getting consistent triage scores across different types of providers. When paramedics in the field used the ESI to triage patients and their ratings were compared against emergency nurses’ assessments, agreement was only moderate.9PubMed. Emergency medical services triage using the emergency severity index: is it reliable and valid? The gap was not about competence; it reflected the reality that triage involves judgment calls about how sick someone looks, how they are likely to deteriorate, and what resources they will need. Different clinicians weigh those factors differently, and doing so under time pressure makes disagreement inevitable.
Mass Casualty and Disaster Triage
Hospital triage handles a steady stream of patients one at a time. Mass casualty events, natural disasters, bombings, building collapses, and pandemics, overwhelm that approach. Disaster triage protocols evolved to handle situations where the number of victims vastly exceeds available medical resources.
The most familiar disaster triage method is START (Simple Triage and Rapid Treatment), which sorts victims into four color-coded categories based on whether they can walk, whether they are breathing, and a few other quick assessments. Green means minor injuries. Yellow means delayed but not immediately life-threatening. Red means immediate treatment needed. Black means deceased or injuries incompatible with survival. The entire assessment takes under a minute per patient, which is the point: when 200 people are injured, you cannot spend fifteen minutes evaluating each one.
Children present a particular challenge because their physiology differs from adults’. A modified version of START called JumpSTART was developed specifically for pediatric patients in disaster settings.10Prehospital and Disaster Medicine. JumpSTART Triage Protocol in Disaster Pediatric Patients: A Systematic Literature Review Children have different baseline vital signs, different injury patterns, and different psychological responses to trauma, all of which can mislead responders using adult-oriented protocols. JumpSTART adjusts the assessment thresholds accordingly, though research on its real-world performance remains limited because large-scale pediatric disaster events are, thankfully, uncommon.
The Ethical Tensions Built Into Triage
Triage forces a question that medicine usually tries to avoid: when you cannot treat everyone, who gets priority? Two competing philosophies have shaped how different systems answer that question. The egalitarian model, which dominates everyday emergency medicine, says you treat the sickest first regardless of any other consideration. The utilitarian model, which tends to surface during mass casualty events, says you allocate resources to save the greatest number of lives overall, even if that means bypassing someone who is very sick but unlikely to survive.11PubMed. Triage and equality: an historical reassessment of utilitarian analyses of triage
In theory, these models coexist. In practice, the boundary between them is blurry and contested. Conventional triage guidelines mandate treatment based solely on medical necessity, regardless of non-medical considerations.12PubMed Central. When do caregivers ignore the veil of ignorance? An empirical study on medical triage decision-making That is the egalitarian principle, and it works well when resources are tight but not catastrophically scarce. When resources are truly exhausted, however, utilitarianism tends to take over. Current disaster triage protocols are largely utilitarian because the efficient use of limited resources prevents the greatest overall disability and death.13University of Western Ontario Medical Journal. Distributive justice in disaster triage: Utilitarianism competes with egalitarianism, autonomy, and the physician-patient relationship That means the most severely injured patient, the person who under normal circumstances would receive maximum attention, might be placed in the black category during a disaster because treating them would consume resources needed to save three others.
This tension is not abstract. It plays out every time a natural disaster or pandemic forces hospitals into crisis mode, and historical experience shows that utilitarian triage tends to collapse under public scrutiny even when it saves more lives overall.11PubMed. Triage and equality: an historical reassessment of utilitarian analyses of triage People accept the logic in the abstract but reject it when the person being triaged to a lower priority is someone they love.
COVID-19 and Crisis Standards of Care
The COVID-19 pandemic thrust triage ethics into public consciousness in a way that no previous event had for most people alive today. When ventilators ran short in spring 2020, hospitals had to decide not just who would receive one but whether to take a ventilator away from one patient and give it to another with better odds of surviving. That debate became a focal point for arguments about whether the primary goal of triage should be saving the most lives or addressing health equity concerns rooted in long-standing social disparities.14PubMed Central. The fairness of ventilator allocation during the COVID-19 pandemic
Simulations of New York City’s ventilator allocation guideline during the spring 2020 surge illustrated the stakes. Over a simulated fifteen-day crisis period, roughly a quarter of the crisis cohort had their ventilator access rationed. Among those whose ventilators were rationed, about 44% would have survived had they stayed on a ventilator, while only about 35% of those who received a reallocated ventilator survived to discharge.15JAMA Network Open. Simulation of New York City’s Ventilator Allocation Guideline During the Spring 2020 COVID-19 Surge In other words, reallocation helped some patients but was far from a clean solution, and every ventilator taken from one person and given to another carried real risk for both.
Artificial Intelligence in Triage
The newest frontier in triage involves machine learning models that process patient data at the moment of arrival to predict who is likely to deteriorate. One model built to predict critical outcomes in the emergency department achieved strong discrimination, outperforming the conventional triage scale used at the study site.16Scientific Reports. Development and internal validation of an AI-based emergency triage model for predicting critical outcomes in emergency department A systematic review of machine learning models that predicted hospital admission from emergency department triage data found that the best-performing models showed good accuracy, though the overall literature had inconsistent methodology and uneven risk-of-bias assessments.17Mayo Clinic Proceedings: Digital Health. Predicting Inpatient Admissions From Emergency Department Triage Using Machine Learning: A Systematic Review
These tools are promising but nowhere near replacing human judgment. Most have only been tested retrospectively on existing records, not prospectively in busy emergency departments where patients arrive confused, combative, or unable to communicate their symptoms. The appeal is obvious: an algorithm does not get tired at hour fourteen of a shift, does not carry implicit biases about who “looks sick,” and can integrate dozens of data points simultaneously. But triage is also a human interaction. A skilled triage nurse notices things a model cannot easily capture, like the patient who insists they are fine but whose skin color says otherwise, or the anxious parent whose description of a child’s symptoms suggests something the chief complaint alone would miss.
The Legal Landscape Around Triage Decisions
Triage decisions carry legal weight, and that weight increases dramatically during emergencies. Hospitals face legal requirements for emergency preparedness, and the changing legal landscape during declared states of emergency requires real-time decision-making about issues including negligence, discrimination, and criminal culpability that may surface during or after medical triage.18Cambridge University Press. Emergency Legal Preparedness for Hospitals and Health Care Personnel In normal operations, an emergency department that turns away or under-triages a patient who later dies faces potential malpractice liability. During a declared disaster, legal protections for healthcare workers may expand, but those protections vary by jurisdiction and are often untested in court.
The tension between legal protection and accountability became acute during the pandemic. Healthcare workers making ventilator allocation decisions wanted clear legal frameworks that would shield them from liability for choices made under impossible conditions. Many states issued crisis standards of care that provided some legal cover, but the specifics varied widely, leaving individual providers uncertain about where the boundary lay between protected clinical judgment and actionable negligence.
The Psychological Cost of Sorting Lives
One aspect of triage that gets far less attention than protocols and algorithms is what it does to the people making the decisions. Triage, at its core, requires a clinician to look at a suffering person and decide that someone else needs help more. In routine emergency department work, that decision is manageable because resources are usually sufficient to treat everyone eventually. In mass casualty events and pandemics, it means consciously choosing not to treat patients who might otherwise survive.
The concept of moral injury, borrowed from military psychology, has entered healthcare discussions to describe what happens when clinicians are forced to act in ways that violate their own moral code. During the COVID-19 pandemic, the term gained particular relevance as nurses and physicians confronted situations where patients suffered unnecessarily and where providers felt they could not do enough.19PubMed Central. Moral injury in healthcare professionals: A scoping review and discussion Moral injury is distinct from burnout. Burnout is exhaustion from overwork. Moral injury is the deep emotional wound that comes from being forced to participate in something you believe is wrong, even when you understand intellectually why the system demanded it.
The irony is hard to miss. Triage was invented to bring order and fairness to chaotic, resource-scarce situations. It succeeded at that goal. But the very act of imposing order on who lives and who dies carries a psychological price for the person holding the sorting card, a cost that the system has only recently begun to acknowledge and has barely begun to address.