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Scene Size-Up

Category: Patient Assessment Sources: raw/supplemental/patient-assessment-sequence.md, raw/nremt/psychomotor-skills.md Last updated: 2026-04-03

Overview

Scene size-up is the first step in every patient contact and happens before you touch the patient. The goal is to gather situational awareness — identify hazards, understand what happened, and determine what resources you need. If the scene is not safe, do not enter.

Key Points

  • BSI/PPE first: Gloves are the absolute minimum. Add eye protection, gown, or mask based on anticipated exposure risk (blood, vomiting, airborne illness).
  • Scene safety: Look for hazards before approaching — traffic, violence, downed power lines, structural instability, smoke, hazmat. If the scene becomes unsafe after entry, exit.
  • MOI vs NOI: Determine whether the call is trauma (mechanism of injury) or medical (nature of illness). This drives the entire assessment path downstream.
  • Number of patients: Count patients before committing resources. One critical patient may need all your attention; three patients may require mutual aid immediately.
  • Additional resources: Request before you need them — ALS upgrade, fire, law enforcement, additional units. It is faster to cancel a response than to call for one late.
  • C-spine consideration: High-energy MOI (MVC, fall from height, diving, penetrating trauma near spine) triggers manual spinal stabilization immediately.

Why MOI vs NOI Is the Fork in the Road

The MOI vs NOI determination is not a checkbox — it is the single decision that defines the entire downstream assessment strategy. Getting it wrong at this step means performing the wrong exam, missing the right injuries, and potentially walking a patient to the ambulance who needed a rapid trauma assessment and a surgeon.

Trauma: MOI determines what you search for before you find it

Trauma injures by energy transfer. When a 70 kg person hits a windshield at 60 mph, kinetic energy (½mv²) is transferred from the body to whatever it strikes. The energy doesn't disappear — it deforms, tears, and compresses tissue according to predictable physics. High-speed MVCs produce characteristic injury patterns: head and face from windshield contact, chest from the steering column, abdomen from the lap belt, femur from the dashboard. Ejection adds secondary impacts with unpredictable distribution.

This is the key insight: knowing the mechanism lets you predict injury patterns before you find them. A 25-year-old who was ejected from an ATV at speed has a cervical spine injury, a traumatic brain injury, a pneumothorax, and internal abdominal hemorrhage until you prove otherwise — even if they are awake and complaining only of shoulder pain. The MOI tells you where the energy went. Your exam confirms or rules out what the physics predicted.

High-energy MOI triggers: rapid full-body trauma assessment, spinal precautions, ALS upgrade, expedited transport. Not because you've found these injuries yet — because you haven't yet ruled them out, and missing them kills.

Medical: NOI means pathology is invisible without history

Medical complaints have a fundamentally different search strategy because the pathology is internal, invisible, and doesn't announce itself in the physical environment. You can look at a trauma scene and read the mechanism. You cannot look at a patient with chest pain and see their coronary artery occluding.

For NOI, the history IS the mechanism. The patient's SAMPLE history tells you what system is involved, how fast it is progressing, what prior conditions affect it, and which medications are already influencing the presentation. Without history, you have no basis for a focused physical exam — and without a focused exam targeted at the right system, you will find nothing useful.

This is also why medical patients who have both an NOI and an MOI (the diabetic who fell, the stroke patient who hit their head) require both strategies: treat the NOI as the underlying cause, perform the trauma assessment for the secondary MOI.

The practical consequence

The assessment path is not symmetric: - Trauma + high MOI → rapid full-body exam → load and go → treat en route - Medical + NOI → focused history → focused physical exam targeted at the complaint → stabilize before transport in many cases

Misclassifying a high-MOI patient as a focused medical exam means you never examine the abdomen of the patient with a splenic laceration who is telling you about his shoulder pain.

Assessment Relevance

Scene size-up feeds every decision that follows. MOI vs NOI determines whether you perform a rapid trauma assessment or a focused medical exam in the secondary assessment. Significant MOI triggers spinal precautions and alters your transport priority. Patient count determines triage if MCI criteria are met.

Standard flow into the next step: size-up complete → move to primary-assessment.

Procedures

  1. Don BSI/PPE before approaching.
  2. Scan the scene from a distance before committing to approach.
  3. Identify hazards and mitigate or stage safely.
  4. Determine MOI (trauma) or NOI (medical).
  5. Count patients visible; look for additional victims.
  6. Request additional resources if patient count or acuity warrants.
  7. Apply manual c-spine stabilization if MOI suggests spinal injury.

NM Protocol Notes

  • NM EMS follows standard scene safety doctrine. In rural San Juan County, common hazards include agricultural equipment, oil field operations, and remote terrain.
  • NM law requires EMS providers to stage and wait for law enforcement clearance on scenes involving violence or potential weapons.
  • Hazmat incidents: stage uphill and upwind; NM uses NIMS/ICS command structure.

NREMT Relevance

Scene size-up is the opening step on both the Trauma and Medical patient assessment/management skills sheets. Examiners look for: - Verbalizing BSI/PPE before any patient contact - Verbalizing scene safety assessment - Correctly identifying MOI vs NOI - Verbalizing number of patients - Verbalizing need for additional resources when indicated - Verbalizing c-spine consideration based on MOI

Failure to verbalize BSI is a critical failure on many skill stations. Say it out loud, every time.

Sources

  • raw/supplemental/patient-assessment-sequence.md — Section 1: Scene Size-Up
  • raw/nremt/psychomotor-skills.md — Patient Assessment/Management (Trauma and Medical)