Shock is defined as hypoperfusion of vital organs, i.e. not meeting the metabolic demands of vital organs including the heart and the brain.

Traditionally, pre-hospital care teams have relied on bedside measures of tissue perfusion to diagnose shock, e.g. blood pressure and heart rate. However, the best indicators of shock are plasma pH, end-tidal PCO₂, lactate and base excess. With point-of-care testing and capnography in pre-hospital care, it may now be possible for the pre-hospital team to access these vital pieces of information on the scene. This will allow more accurate assessment of the state of shock of a patient.