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Approach to undifferentiated shock
Shock is inadequate oxygen delivery to the tissues; in the emergency department it is sorted into four mechanisms — hypovolaemic, cardiogenic, obstructive and distributive — by simple examination and bedside ultrasound, and the cause is treated while the patient is stabilised.
Why it matters in the exam
Shock questions are almost always built on a hypotensive patient, and the correct answer requires recognising the mechanism from clues: neck veins, limb temperature, breath sounds and POCUS. A standard distractor is large-volume fluid for a patient in cardiogenic or obstructive shock, where the problem is not volume.
Candidates are also asked about the tools: a shock index (heart rate divided by systolic pressure) above 1, lactate above 2 mmol/L, urine output below 0.5 mL/kg per hour, and the choice of noradrenaline as the first vasopressor with a mean arterial pressure target of 65 mmHg.
Typically the question shows a confused patient with tachycardia, hypotension and a raised lactate, and asks you to choose between more fluid, a vasopressor, imaging or an invasive procedure. Combine three simple findings — neck veins, limb temperature and lung sounds — with the bedside ultrasound picture, and the shock can be assigned to one of the four mechanisms within minutes.
Key points
- Four mechanisms: hypovolaemic, cardiogenic, obstructive, distributive.
- Neck veins, limb temperature and POCUS point to the mechanism.
- A shock index above 1 and lactate above 2 mmol/L are warning signs even with a normal blood pressure.
- Fluids in small boluses with reassessment; noradrenaline first, MAP target 65 mmHg.
- Obstructive shock is treated by relieving the obstruction, not by fluid alone.
Summary table
| Type | Examination clues | POCUS | First treatment |
|---|---|---|---|
| Hypovolaemic (bleeding, dehydration) | Cold limbs, flat neck veins | Small collapsing IVC, hyperdynamic heart | Stop bleeding, blood or fluids |
| Cardiogenic | Cold limbs, full neck veins, crackles | Poor left ventricular function, B-lines | Treat the cause (PCI), noradrenaline, dobutamine |
| Obstructive (tamponade, tension pneumothorax, massive PE) | Full neck veins, clear lungs | Pericardial fluid, dilated right ventricle, absent lung sliding | Pericardiocentesis, needle decompression and a drain, thrombolysis |
| Distributive (sepsis, anaphylaxis, neurogenic, adrenal) | Warm limbs, wide pulse pressure | Hyperdynamic heart, small IVC | Fluids, noradrenaline; adrenaline in anaphylaxis; hydrocortisone in adrenal crisis |
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Sources
- Surviving Sepsis Campaign: International Guidelines for Management of Sepsis and Septic Shock, 2021 — Haemodynamic management
- ESICM task force consensus on circulatory shock and haemodynamic monitoring, 2014 — Definitions and initial approach
- Tintinalli's Emergency Medicine: A Comprehensive Study Guide, 9th edition (2020) — Approach to shock
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.