Shock

Shock is a life-threatening condition in which the circulatory system fails to deliver sufficient oxygen and nutrients to the body’s tissues to meet their metabolic needs. Without adequate perfusion, cells switch to anaerobic metabolism, producing lactic acid and ultimately dying. Shock is classified into four main types based on its underlying mechanism, each requiring a different approach to treatment.

Cardiogenic shock occurs when the heart fails to pump effectively enough to maintain adequate cardiac output, causing low blood pressure, poor peripheral perfusion and signs of organ failure. It is a recognised complication of cardiac arrest (due to myocardial stunning), large heart attack, severe heart failure, or critical valve disease. Management involves vasopressors, inotropes, and in severe cases mechanical circulatory support. Hypovolaemic shock results from insufficient circulating blood volume, caused by haemorrhage, severe dehydration, or fluid loss from burns. Treatment is fluid and blood product replacement to restore volume.

Distributive shock occurs when abnormal vasodilation causes blood to pool in peripheral vessels, despite a normal or increased cardiac output. Sepsis is the most common cause, driven by systemic inflammatory response to infection. Anaphylaxis (severe allergic reaction) and neurogenic shock (from spinal cord injury) are other forms. Treatment addresses the underlying cause while restoring vascular tone with vasopressors. Obstructive shock results from a mechanical blockage to blood flow, most commonly pulmonary embolism (blocking the pulmonary circulation), cardiac tamponade (fluid compressing the heart), or tension pneumothorax (air compressing the heart and great vessels). Removing the obstruction is the priority.

In the post-cardiac arrest period, patients commonly experience a combination of cardiogenic shock (from myocardial stunning) and distributive shock (from the systemic inflammatory response of post-cardiac arrest syndrome). Both components require simultaneous management in the intensive care unit. Identification of the shock type guides treatment: echocardiography is invaluable for rapidly distinguishing cardiogenic from other forms.