Shock — Types, Pathophysiology & Management

The Concept — What Shock Actually Is

Shock is a state of acute circulatory failure in which the delivery of oxygen to the tissues is inadequate to meet their metabolic needs. The single most important idea to grasp is that shock is about tissue perfusion, not blood pressure — a patient can be in established shock with a still-normal blood pressure. When cells are starved of oxygen they switch to anaerobic metabolism, producing lactic acid; if perfusion is not restored, this progresses to cell death, organ failure and, ultimately, death. Everything else follows from thinking about what determines oxygen delivery.

Oxygen delivery depends on cardiac output (heart rate × stroke volume) and the oxygen content of the blood. Stroke volume in turn depends on preload (the volume returning to the heart), contractility (the pump), and afterload (the vascular resistance). Shock arises whenever one of these fails — and that gives us a logical classification.

Classification — BY the Mechanism That Fails

Pathophysiology & Stages — WHY Early Shock Hides

Understanding the stages explains the clinical signs. In the compensated stage, baroreceptors detect the falling pressure and trigger a sympathetic response: the heart speeds up (tachycardia) and the peripheral vessels constrict to divert blood to vital organs. This is why an early-shock patient is tachycardic with cool, clammy skin, a prolonged capillary refill and reduced urine output — yet a still-normal blood pressure. The body is holding the pressure up by squeezing. In the decompensated stage, these mechanisms are exhausted, so blood pressure finally falls, perfusion worsens and acidosis deepens. If this continues, the irreversible stage supervenes — widespread cell death and multi-organ failure that no longer respond to treatment.

Clinical Features

The typical picture is tachycardia, a weak thready pulse, cool/pale/mottled clammy skin, prolonged capillary refill (> 2 s), tachypnoea, oliguria and altered mental state (anxiety → confusion → drowsiness), with hypotension appearing late. One important exception is early distributive (septic or anaphylactic) shock, where widespread vasodilatation makes the patient warm, flushed and bounding ('warm shock') before they eventually become cold as it decompensates.

Management — Restore Perfusion, Treat the Cause

Resuscitation follows the ABC approach. Secure the airway and give high-flow oxygen; insert two large-bore IV cannulae (wide and short cannulae allow the fastest flow); and attach full monitoring. Then two things happen in parallel — restore the circulation and identify/treat the cause:

• Hypovolaemic/distributive shock — rapid fluid resuscitation with isotonic crystalloid boluses, reassessing after each; give blood for haemorrhage.
• Cardiogenic shock — fluids are given cautiously (the failing pump is easily overloaded); inotropes support contractility.
• Distributive/refractory shock — vasopressors (noradrenaline first-line) restore vascular tone once volume is replaced.
• Obstructive shock — relieve the obstruction (needle/tube decompression of a tension pneumothorax, pericardiocentesis for tamponade).
• Treat the cause definitively — stop the bleeding, give antibiotics and achieve source control for sepsis, adrenaline for anaphylaxis.

Response is judged not by blood pressure alone but by improving perfusion: a falling heart rate, warming peripheries, urine output above 0.5 mL/kg/hour, restored mental state and a clearing lactate.

Distinguishing the Types at the Bedside

• Although the initial resuscitation is similar, reading the clinical pattern points to the type and therefore the definitive treatment.
• Hypovolaemic shock gives cold peripheries with an obvious source of loss (bleeding, vomiting, burns) and a low CVP.
• Cardiogenic shock also has cold peripheries but with signs of a full circulation — a raised CVP/JVP, basal crackles, a gallop — because the problem is the pump, not the volume.
• Distributive (septic/anaphylactic) shock is classically warm and vasodilated early with a low CVP.
• Obstructive shock shows a high CVP with specific signs — tracheal deviation and absent breath sounds (tension pneumothorax), or muffled heart sounds (tamponade).

Complications of Prolonged Shock

If perfusion is not restored quickly, sustained tissue hypoxia damages every organ: the kidneys develop acute tubular necrosis (acute kidney injury), the lungs develop acute respiratory distress syndrome (ARDS), the gut mucosal barrier breaks down (allowing bacterial translocation and worsening sepsis), the clotting system may tip into DIC, and ultimately multi-organ dysfunction syndrome (MODS) supervenes. This cascade is precisely why early recognition and rapid restoration of perfusion — before the compensated stage fails — saves lives.

Shock is defined by inadequate perfusion, not by blood pressure alone.

• Shock = acute circulatory failure with inadequate tissue oxygen delivery; it is about perfusion, not blood pressure.
• Types (by mechanism): hypovolaemic (commonest), cardiogenic, distributive (septic/anaphylactic/neurogenic), obstructive.
• Compensated stage keeps BP normal by tachycardia + vasoconstriction → cool clammy skin, prolonged CRT, oliguria; hypotension is a late sign.
• ABC + high-flow O2 + two large-bore cannulae; restore volume (crystalloid/blood) + treat the cause; inotropes/vasopressors for cardiogenic/refractory.
• Judge response by perfusion — heart rate, urine output >0.5 mL/kg/h, mental state, lactate clearance.