Shock is a state of acute circulatory failure in which inadequate oxygen delivery to the tissues leads to cellular dysfunction and, if untreated, multi-organ failure and death. It is not simply hypotension — shock is defined by tissue hypoperfusion, which can exist even when blood pressure still appears normal during the early, compensated stage. Recognizing shock before the pressure falls is the central nursing skill the NCLEX-RN tests. Shock is classified into four main types by underlying mechanism: - Hypovolemic: inadequate intravascular volume (hemorrhage, burns, severe dehydration) - Distributive: maldistribution of blood flow despite normal or elevated volume (septic, anaphylactic, neurogenic) - Cardiogenic: pump failure (MI, cardiomyopathy, dysrhythmia) - Obstructive: mechanical obstruction to flow (cardiac tamponade, tension pneumothorax, massive pulmonary embolism) Shock also progresses through stages — compensated (the body maintains pressure through sympathetic vasoconstriction, tachycardia, and renal fluid conservation), then progressive or decompensated (overt hypotension, organ hypoperfusion, and metabolic acidosis), and finally refractory (irreversible). For the NCLEX-RN, the priority is to recognize the type, identify the stage, and implement the correct intervention for that type — for example, rapid...