Scene Size-Up

Scene size-up — 4 components

The scene size-up is the first part of patient assessment, but it does not end when you reach the patient. Scenes are dynamic, so the size-up continues throughout the call. It has four components: scene safety, Standard Precautions, the nature of the call (the mechanism of injury (MOI) or the nature of the illness), and the number of patients together with the resources they will need.

Never assume a scene is safe, even when police, fire, or other units are already there. Always do your own size-up. It begins before the ambulance stops, and you keep observing as you approach and again before you exit the vehicle.

Approaching a collision — danger zone distances

When you approach a motor vehicle collision, the hazards present determine how far from the wreck you park. The table below sets out the danger-zone distance for each hazard.

Table 11.1Approaching a collision — danger zone distances

Violence and crime scenes are a hazard of a different kind. Never enter a violent scene to provide care. The warning signs are fighting or loud voices, weapons that are visible or have been used, signs of alcohol or drug use, an unusual silence, and a known history of prior violence at that address.

Standard Precautions (BSI)

Standard Precautions, also called body substance isolation (BSI), are the measures you take to keep a patient's body substances from reaching you. Body substances include blood, saliva, and all other body fluids, and they enter the body through cuts and other openings in the skin or through the eyes, nose, and mouth. The high-risk situations are bleeding, coughing, sneezing, and direct contact such as mouth-to-mouth. The infection risk runs both ways: the patient can infect you, and you can infect the patient.

The protection you choose depends on the situation. Gloves and eyewear are appropriate for trauma with suspected bleeding. A mask and eyewear are added when you are suctioning or the patient is spitting blood. An N-95 or HEPA respirator is worn when tuberculosis (TB) or another airborne disease is suspected.

Nature of the call — mechanism of injury

The mechanism of injury (MOI) is the force or forces that caused an injury. Certain mechanisms are commonly associated with certain injuries: falls and collisions with bone and joint injury, fire and explosion with burns, and gunshots with penetrating soft-tissue injury. Knowing the mechanism therefore tells you what to look for before you have found it.

Maintaining a high index of suspicion means staying aware of possible injury even when there are no obvious signs of it. Never assume there is no injury just because the mechanism seems minor.

Motor vehicle collisions

Every motor vehicle collision (MVC) is really 3 collisions: (1) the vehicle hits an object, (2) the occupant's body hits the interior of the vehicle, and (3) the organs hit the inside of the body. Airbags deploy once only. The powder they release is nontoxic and should not be mistaken for smoke, but the bags themselves can cause abrasions and fractures, and they can turn loose objects into projectiles.

The type of collision predicts the pattern of injury, as the table below shows.

Table 11.2Motor vehicle collisions

Falls & penetrating/blunt trauma

In a fall, consider the height, the surface struck, the part of the body that hit it, and anything that interrupted the fall. The 2021 national field triage guideline uses one threshold for every age: a fall from more than 10 feet (3 m). The adult figure used to be taught as 20 feet, and the 2011 guideline used a multiple of a child's height; it came down because injuries were being missed below it. For a child aged 5 or under or an adult aged 65 or over, a low-level fall with a significant head strike is a risk factor to weigh under EMS judgment, and so is anticoagulant use in any fall. A patient who has fallen that far should go to a trauma center.

Penetrating trauma is classified by the velocity of the object. Low-velocity wounds, such as those from knives, are localized, although the blade may have moved inside the body. Medium-velocity wounds come from handguns and shotguns. Arrows, like knives, are low-velocity. High-velocity wounds, from rifles, can cause damage almost anywhere. A bullet injures in two ways: along its direct path, and by cavitation, in which the pressure wave creates a temporary cavity larger than the bullet itself.

In blunt-force trauma the energy travels through the body, so organs can rupture or hemorrhage while the external signs stay subtle. The MOI is your main clue that something serious has happened inside.

Number of patients & resources

Actively scan the scene for additional patients, such as passengers and pedestrians. If there are more patients than you can handle, call for more ambulances immediately rather than waiting to see how things develop. Call for extra help early: once you are involved in patient care it is easy to forget, and by then it may be too late for help to arrive in time.