Measuring the compensatory reserve to identify shock
Shock is classically defined as inadequate tissue perfusion,1–4 and associated with clinical markers such as low systolic blood pressure (<90 mm Hg), elevated heart rate (>120 bpm), increased respiration rate (>20 breaths per minute), decreased pulse pressure, cold and clammy skin, altered mental state (e.g., disorientation, confusion), and elevated blood lactate (>2–3 mmol/L) or base deficit (< −4 mmol/L).5,6 However, these signs do not change until the later stages of hemorrhage and thus waiting until a clinically significant change can impede early diagnosis of shock when interventions could be most effective. The tendency for measuring these traditional vital signs that are easy to obtain and understand (e.g., blood pressure) but provide information of little value during the early stages of compensatory shock, rather than using technologically more advanced but meaningful measures has been defined as “tangible bias.”7 The century-long perpetuation of this bias in monitoring patients in the prehospital emergency medical setting has enabled the inability of our emergency medical community to identify shock in its earliest compensatory stages when the application of lifesaving interventions would be most effective. The emergence of new computer technologies that are based on advanced machine-learning principles and signal processing of large amounts of data has now made it possible to escape the “tangible bias” created by currently used medical monitoring technologies by providing real-time assessments of global tissue oxygenation status in individual patients (precision medicine). Within this context, the objectives of this article are to (1) describe why current physiologic monitoring is inaccurate; (2) introduce and define a new paradigm named the compensatory reserve; (3) demonstrate the usefulness of measuring the compensatory reserve with clinical examples; and (4) identify future applications of compensatory reserve monitoring, including the prehospital phase of resuscitation.