A 22-year-old man stung by a wasp develops widespread urticaria, stridor, and a blood pressure of 70/40 mmHg. Central venous pressure is near zero and the heart is hyperdynamic on bedside echo. The haemodynamic profile of this shock state is characterised by:
- A High systemic vascular resistance with normal cardiac output
- B Low systemic vascular resistance with markedly reduced effective circulating volume from capillary leakage ✓
- C Normal systemic vascular resistance with primary pump failure
- D High systemic vascular resistance with elevated pulmonary capillary wedge pressure
Correct answer: B. Low systemic vascular resistance with markedly reduced effective circulating volume from capillary leakage
Explanation
Anaphylaxis releases histamine and other mediators that cause profound arteriolar vasodilation and increase capillary permeability, so plasma shifts into the interstitium, preload collapses, and the empty hyperdynamic heart reflects compensatory tachycardia against low afterload. The near-zero CVP confirms the low preload state. High SVR profiles belong to cardiogenic and late haemorrhagic shock, not distributive anaphylactic shock.
Reference: Guyton and Hall Textbook of Medical Physiology, 14th ed.
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