EMT · Scene Size-Up and Safety · 6 min read
Mechanism of Injury, Nature of Illness and Scene Clues
- Distinguish between mechanism of injury (MOI) and nature of illness (NOI), and apply an index of suspicion to anticipate unseen traumatic or medical conditions.
- Analyze physical damage, impact vectors, and energy levels in motor vehicle collisions, falls, penetrating trauma, and blast events to guide triage and assessment.
- Evaluate environmental clues, physical evidence, and scene safety hazards to guide clinical decisions, request necessary resources, and report findings accurately.
Foundations of MOI, NOI, and the Index of Suspicion
When arriving at any emergency, an EMT must rapidly evaluate what caused the patient's condition. The mechanism of injury refers to the physical forces applied to the body that cause trauma, such as the impact of a motor vehicle crash or a fall from a ladder. In contrast, the nature of illness describes the medical condition or disease process causing the patient's symptoms, such as an asthma flare-up or an infection. Dispatch information and the patient's chief complaint often suggest the nature of illness, which EMTs refine through a careful history and physical assessment.
Trauma and medical problems frequently overlap rather than occurring in isolation. Trauma patients may have an underlying medical emergency that precipitated the traumatic event, such as a driver who suffers a sudden seizure or cardiac event before crashing into a tree. Conversely, medical patients may sustain secondary traumatic injuries if their illness causes a sudden fall or collision. For example, a person who faints while standing may strike their head on a hard floor.
To provide high-quality care, EMTs maintain an index of suspicion, which is the rescuer's concern for potentially serious, unseen injuries based on the mechanism of injury, scene findings, and patient assessment. An apparently minor mechanism of injury can cause catastrophic internal injuries in elderly patients due to physiologic frailty. Identifying a concerning mechanism of injury or nature of illness early guides the decision to call for specialized or additional resources promptly.
Common mistakes
- Assuming that visible entrance and exit wounds trace a straight line through the body, which overlooks internal projectile deflection and cavitation.
- Ruling out internal head or chest trauma simply because a vehicle's airbags deployed successfully during a collision.
- Assuming an unresponsive patient in a room with empty pill bottles or alcohol containers has suffered an intentional toxic ingestion without assessing for underlying medical emergencies.
- Failing to recognize that an apparently minor fall in an elderly patient can produce catastrophic internal trauma due to physiologic frailty.
Key points
- Mechanism of injury (MOI) describes physical forces producing trauma, while nature of illness (NOI) describes medical diseases; maintain an index of suspicion as both can occur simultaneously.
- High-energy blunt trauma clues include passenger compartment intrusion, spider-webbed windshields, deformed steering wheels, rollover vectors, and vehicle ejection.
- Fall severity depends on height, landing surface, and initial impact point; current national field-triage guidance lists falls over 10 feet at any age as a mechanism criterion, while shorter falls still require assessment for serious injury.
- Penetrating trauma severity correlates with projectile velocity and cavitation; blast injuries are categorized into primary (shockwave), secondary (shrapnel), tertiary (body propelled), and quaternary (burns/smoke/crush).
- Scene findings like prescription bottles, medical IDs, and home oxygen provide clues but do not confirm diagnoses, while multiple symptomatic patients indicate environmental hazards such as carbon monoxide.
- Always assess for scene hazards like unsecured firearms or non-deployed airbags, evaluate for spinal motion restriction, and thoroughly document environmental clues for hospital handoff.
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