The two most reliable indicators of shock in a TFC setting are an altered mental status in the absence of head injury and an absent or weak radial pulse.

In an effort to conserve oxygen for vital functions and organs, the body will begin to shunt blood from the periphery to its core (heart, lungs, kidneys, etc.). The result is that peripheral pulses will diminish and disappear prior to central pulses, like the carotid or femoral pulses. Additionally, the physical distance from the heart to those pulse assessment sites is greater, and with borderline blood pressures, the flow of blood at that level may not be detectable by checking for a pulse.

Likewise, although the core functions of the brainstem may be maintained, the flow to the cortex of the brain that controls fine motor function and determines the level of responsiveness may be compromised. The result of this is a decreased ability to respond properly to commands and, ultimately, an altered level of consciousness.

In the field setting, these are the two most reliable indicators of shock, especially when used over time to monitor for potential progression (either deterioration or improvement).