How Does Triage Work? Deciding Who Waits When Everyone Cannot Be Treated

The practice and the word come from Napoleonic military surgery, where a surgeon established the principle of treating the wounded by severity rather than by rank, which was a radical assertion of equality at the time. Military triage developed the core insight that the goal in a mass casualty situation is different from the goal in a clinic: not the best outcome for each individual treated in sequence, but the best outcome for the group given what is available. That produces the counterintuitive feature that the most severely injured may receive the lowest priority, because the time and resources required to attempt saving them would cost the lives of several others with survivable injuries. That category, generally labelled expectant, means comfort care rather than abandonment and is the hardest part of the system for both clinicians and families, and it applies only when resources genuinely cannot meet demand. Crucially, everyday emergency department triage is not this. It is a sorting by urgency where everyone will be treated, and only the order changes, which is a different ethical situation entirely and is why the same word covering both causes confusion.

Several formal schemes exist, differing in setting and in what they measure:

• •Everyday emergency department scales, typically five levels from immediately life-threatening to non-urgent, which set target times to be seen rather than deciding who is treated
• •Mass casualty field systems using simple physiological checks that a responder can perform in under a minute, assessing walking ability, breathing, circulation and responsiveness, and assigning a colour
• •The colour convention of red for immediate, yellow for delayed, green for minor and black for deceased or expectant, marked with tags or tape
• •Reverse triage, used where an event has produced many walking wounded, prioritising getting the minor cases out of the way and out of the treatment area
• •Secondary triage at the receiving hospital, which reassesses everyone because field categorisation is deliberately crude and conditions change
• •Crisis standards of care, formal frameworks activated when demand exceeds capacity across a whole system, which shift decision-making from individual clinicians to protocols and committees

Allocating scarce treatment forces an explicit choice of principle, and the candidates conflict. Maximising lives saved counts each life equally. Maximising life-years saved favours the young, which some regard as fair because a younger person has had less of a life and others regard as age discrimination. Prioritising those with the best prognosis is efficient and disadvantages people with disabilities and chronic conditions, a concern raised sharply during pandemic planning when several draft protocols were criticised or withdrawn for using criteria that systematically deprioritised disabled people. Random selection by lottery treats everyone equally and ignores information that could save more lives. Priority to key workers is defended instrumentally, on the grounds that treating them returns capacity to the system, and criticised as privileging a class. First come first served appears neutral and advantages those with better access. Most published frameworks combine several principles with explicit weightings, and the significant procedural commitments are that criteria be published in advance, applied by people not treating the patient, and subject to appeal.

Failures are well documented and mostly predictable. Over-triage, meaning classifying too many as urgent, floods the receiving hospitals and paradoxically increases mortality by diluting attention, and studies of terrorist incidents have identified it as a recurring problem. Under-triage misses serious injuries, particularly internal bleeding in patients who initially look well. Field systems are validated poorly because the events are rare and chaotic, and the evidence base for choosing between them is thinner than their widespread adoption suggests. Decisions made under pressure are affected by who is visible, who is loud and who arrives first, rather than by who is sickest, and children and distressed relatives distort prioritisation in ways responders acknowledge. Psychological consequences for staff making expectant decisions are significant and moral injury is a recognised outcome. The most effective mitigation is preparation, since protocols decided calmly in advance, rehearsed, and applied by designated people protect both patients and clinicians from having to invent an ethical framework in the middle of the worst hour of their career.

Sorting a group to do the most good overall is a different goal from treating each patient as well as possible, which is why the most severely injured can receive the lowest priority when resources genuinely cannot meet demand. Everyday hospital sorting is not that, since everyone is treated and only the order changes. Principles conflict, with life-years saved and best prognosis disadvantaging older and disabled people, so frameworks are published in advance and applied by people not treating the patient.