Who invented triage algorithms?

The concept of triage, a system for sorting the sick and wounded based on the immediacy of their need for care, does not spring from a single moment of invention or one singular algorithm. Instead, it represents an evolution of thought, a set of practical decision-making processes honed by necessity in situations where resources—time, personnel, and equipment—are critically scarce. To ask who invented triage algorithms is to ask who first imposed rational order onto chaos, but the most definitive answer points toward a military surgeon who established the foundational system that would later be formalized into the complex, weighted algorithms used today.

# Battlefield Genesis

The recognized father of the modern triage system is Dominique Jean Larrey (1766–1842), a French surgeon who served in Napoleon’s army. Before Larrey’s reforms, battlefield medicine often adhered to a tradition where officers were treated first, followed by the wounded based on the order in which they arrived, irrespective of the severity of their injuries. This meant that soldiers with survivable injuries might perish while waiting for care, while others with less urgent needs were attended to sooner.

Larrey’s crucial innovation, developed during the campaigns of the late 18th and early 19th centuries, was to reject this seniority-based or arrival-based hierarchy. He insisted on prioritizing based purely on the medical condition of the patient. Larrey developed a system of categorization that dictated which wounded soldier would receive attention first, based on the severity of their injury, with the aim of saving the greatest number of lives. This direct, needs-based assessment—the initial "algorithm"—was revolutionary because it placed the immediate medical necessity above all other social or chronological considerations. His system led to the establishment of mobile ambulance services, ensuring that care followed the wounded quickly, rather than forcing the wounded to wait for established hospitals. This focus on rapid extraction and immediate categorization is the historical root of all subsequent triage methods.

# Categorizing Need

Larrey’s original field classifications were foundational. While the exact nomenclature has changed many times across different conflicts and clinical settings, the underlying structure involved sorting patients into groups based on their prognosis and required level of urgency. The general conceptual groupings that emerged from this work, and which persist in various forms today, are often categorized as:

• Immediate (Red Tag): Life-threatening injuries requiring immediate intervention to ensure survival.
• Delayed (Yellow Tag): Serious injuries that can tolerate a delay in treatment without significant additional risk to life.
• Minor (Green Tag): Wounds that are relatively minor and can wait for the care of less critical patients, or can even be self-treated.
• Expectant or Deceased (Black Tag): Those who have sustained such severe injuries that survival is unlikely even with maximum resources, or those who have already succumbed.

The persistent utility of this system lies in its simplicity under duress. It is a rapid triage key, designed for the chaos of the battlefield or a mass casualty incident (MCI) where resources are overwhelmed. The ability to quickly assign one of these designations—an instinctive, rapid-fire algorithm—is what separates effective disaster response from uncoordinated chaos.

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# Evolution to Formal Algorithms

The fundamental principle established by Larrey—prioritizing the greatest good for the greatest number through systematic assessment—translated from the smoky fields of battle to the high-volume environment of the civilian emergency department (ED). However, civilian settings rarely deal with the sheer volume of simultaneous life-or-death scenarios seen in combat. Instead, they manage a continuous flow of varying acuity, requiring more nuanced scoring systems than the simple four-category field sort.

The move from Larrey's field method to what we now call a modern algorithm is the shift from qualitative judgment to a semi-quantitative, standardized measurement tool. An algorithm, in this medical context, is a defined, step-by-step procedure designed to arrive at a consistent outcome, regardless of which clinician performs the assessment. This consistency is vital for resource allocation and tracking patient outcomes.

One of the most widely adopted modern algorithms in the United States is the Emergency Severity Index (ESI). The ESI is a five-level triage algorithm that attempts to balance patient acuity with resource needs, which represents a significant formalization beyond Larrey’s original concept.

# The ESI Algorithm

The ESI algorithm specifically looks at two primary factors simultaneously: the patient's acuity (how sick they are) and the anticipated resources they will consume. It’s a highly structured process that forces the assessor to answer a series of questions sequentially. A patient's assignment drops to a lower level only if they meet the criteria for that lower level and they do not meet the criteria for the level above it.

The five levels, which function as the algorithmic outputs, are defined as follows:

While the ESI is a powerful example of a modern triage algorithm, it is crucial to recognize that it is an adaptation of the core principle. Larrey asked, "Can this person wait?" The ESI asks, "How sick are they, and what does their care path look like?". The original system was a binary filter for immediate survival; the modern system is a predictive tool for resource management within a fixed infrastructure.

It is a noteworthy development that the resource component (Levels 4 and 5) was added to the initial acuity-only models. This reflects an understanding gained through decades of ED overcrowding: simply identifying who needs care isn't enough; one must also predict who will consume significant physician or nursing time. A patient with a simple ankle sprain (low acuity) who demands an immediate MRI and orthopedic consult might be prioritized after a Level 3 patient requiring only a prescription, simply because the latter patient’s overall resource demand is lower and more manageable in the short term. This subtle algorithmic weighting is where modern triage truly diverges from its martial origins.

# Specialized Algorithms

The existence of a single, universal triage algorithm is a misconception. The concept must be adapted based on the population being assessed. For instance, pediatric patients, who may present differently or have conditions that escalate much faster than adults, necessitate specialized algorithms. Pediatric triage systems often incorporate age and weight parameters more heavily than adult systems, as the clinical presentation of distress can be masked or misinterpreted without specific age-related benchmarks.

This specialization confirms that "who invented the algorithm" is a misframing. Instead, we should ask, "What scenario demanded the most rigorous, life-saving, systematic sorting?" The answer always leads back to the battlefield, but the current state of triage algorithms is the result of continuous refinement by clinical bodies seeking consistency across diverse patient needs, whether in a disaster zone, a standard ED, or a pediatric unit.

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# Analysis of Algorithmic Consistency

The true value proposition of any triage algorithm—whether Larrey’s mental checklist or the ESI’s printed matrix—is inter-rater reliability. In the original battlefield setting, Larrey’s authority ensured compliance, but his system relied heavily on his personal judgment and experience. In a modern hospital, where ten different nurses might triage ten patients in an hour, the algorithm serves as a standardized language.

Consider the difference in implementation. Larrey likely judged survivability based on visible hemorrhage or respiration cessation. This is a qualitative assessment. The ESI, by contrast, requires the assessor to check vital signs, look for specific red-flag complaints ("suicidal ideation," "uncontrolled bleeding"), and then quantify the number of resources needed (e.g., "two or more" tests, labs, or imaging studies). This quantification is the algorithmic step that allows for data tracking and quality audits in a way Larrey’s system never could.

If we were to construct a simplified historical-to-modern mapping, it would look like this:

The lasting legacy is not about a specific inventor of code, but about the universal recognition that resources are finite, and prioritizing based on need rather than status or arrival time saves more lives. Any clinician faced with mass casualties today, whether in war or in response to a natural disaster, will revert to the Larrey model instinctively because it is the purest, fastest algorithm for mass survival, whereas routine clinical work demands the complexity of the ESI or similar scored systems to manage the steady state of emergency care. The inventor of the algorithm is, therefore, the situation itself, and Larrey was simply the first to successfully formalize the necessary response to it.