Shock: The Four Types Explained
Shock is one of those words students hear constantly and often struggle to define. It is not the same as low blood pressure, and it is not the same as feeling shaken after an accident. Shock means the body's tissues are not getting enough oxygen to meet their needs. Recognising it early, and working out which type you are dealing with, changes what you do next. This guide breaks shock into four types that are much easier to remember under pressure.
Pathophysiology
What shock actually is
Shock is a state of circulatory failure in which oxygen delivery to the tissues is inadequate. Without enough oxygen, cells switch to anaerobic metabolism, which produces far less energy and generates lactic acid. If this continues, cells start to fail, then organs, and eventually the whole body.
A simple way to understand it is to think of the circulation as a plumbing system with three parts: the pump (the heart), the pipes (the blood vessels) and the fluid (the blood). Shock happens when one or more of these fails, or when something blocks the flow.
Shock is not low blood pressure. It is not enough oxygen reaching the tissues, and blood pressure is often the last thing to fall.
The four types
Hypovolaemic: not enough fluid in the system. The most common cause in trauma is haemorrhage, but severe vomiting, diarrhoea and burns can also cause it.
Distributive: the pipes become too wide and leaky, so blood pools and pressure falls. Causes include sepsis, anaphylaxis and spinal cord injury, known as neurogenic shock.
Cardiogenic: the pump fails. Causes include a large heart attack, severe heart failure and dangerous arrhythmias.
Obstructive: something physically blocks blood flow into or out of the heart. Causes include tension pneumothorax, cardiac tamponade and a large pulmonary embolism.
Compensation, then collapse
In early shock, the body fights back. The heart rate rises, breathing quickens and blood vessels in the skin and gut constrict to protect the brain and heart. This is compensated shock, and blood pressure may still be normal. When these mechanisms are exhausted, blood pressure falls and the patient decompensates. Left untreated, shock becomes irreversible as organ damage accumulates.
Assessment and Treatment
Recognising early shock
Look for the body's compensation, not just the blood pressure:
A rising heart rate and respiratory rate.
Pale, cool, clammy skin and a prolonged capillary refill.
Anxiety, restlessness or confusion, as the brain receives less oxygen.
Reduced urine output.
A narrowing pulse pressure, as the diastolic pressure rises with vasoconstriction.
Some patients hide shock well. Children and fit young adults can maintain a normal blood pressure until very late, then deteriorate suddenly. Older people and patients on medications such as beta blockers may not mount a fast heart rate. Distributive shock may present with warm, flushed skin early on rather than cool, pale skin.
In practice: a young adult after a fall with a heart rate of 125, a capillary refill of four seconds and a normal blood pressure is in compensated shock. The normal blood pressure is not reassuring. It is the body working very hard to stay normal.
Treating the cause
General priorities apply to every type: manage the airway and breathing, give oxygen if saturation is low, keep the patient warm, monitor closely and transport early with clear notification to the receiving hospital. Beyond that, treatment depends on the type:
Hypovolaemic: control bleeding first, then replace volume according to your guidelines. In uncontrolled haemorrhage, many guidelines aim for adequate perfusion rather than a normal blood pressure.
Distributive: treat the cause, such as adrenaline in anaphylaxis or early recognition and escalation in sepsis, with fluids and further support as your guidelines direct.
Cardiogenic: be cautious with fluids, as a failing heart can be overloaded. Early ECG, specialist notification and transport to an appropriate centre are key.
Obstructive: relieve the obstruction, such as decompressing a tension pneumothorax. Fluids alone will not fix a blocked circulation.
Conclusion
Shock is inadequate oxygen delivery to the tissues, and it falls into four types: hypovolaemic, distributive, cardiogenic and obstructive. Recognise it early through tachycardia, tachypnoea, poor perfusion and a changing mental state, and do not wait for the blood pressure to fall. Work out the type, because the right treatment for one can be the wrong treatment for another.
References
Vincent JL, De Backer D. Circulatory shock. N Engl J Med. 2013;369(18):1726.
Shock. StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing.
American College of Surgeons Committee on Trauma. Advanced Trauma Life Support (ATLS) Student Course Manual. 10th ed. Chicago: American College of Surgeons; 2018.
Singer M, Deutschman CS, Seymour CW, et al. The Third International Consensus Definitions for Sepsis and Septic Shock (Sepsis-3). JAMA. 2016;315(8):801.
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Disclaimer: This article is general education for students. It is not medical advice, and it does not replace your service's clinical practice guidelines, your educators or your local protocols.
