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Haemodynamic Shock Quiz
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Which mechanism best explains the development of distributive shock?
- A Profound peripheral vasodilation leading to a marked reduction in total peripheral resistance You picked ✓
- B Acute loss of circulating blood volume due to haemorrhage or dehydration You picked ✕
- C Obstruction to cardiac filling or outflow resulting in reduced cardiac output You picked ✕
- D Primary failure of ventricular contraction causing blood to back up into the venous circulation You picked ✕
- E Chronic hypertension causing adaptive thickening of the arterial wall You picked ✕
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The answer is A: Profound peripheral vasodilation leading to a marked reduction in total peripheral resistance
Explanation
Why A is correct
See Understanding Shock. Option A is correct because distributive shock is shock caused by a fall in total peripheral resistance from profound vasodilation of the peripheral blood vessels. The mean arterial blood pressure depends on the cardiac output multiplied by the total peripheral resistance (MaBP = CO x TPR). If the resistance falls massively because the vessels are widely dilated, the blood pressure falls even though the circulating volume is normal and the heart is pumping. The blood is distributed in a larger vascular space, so the tissues are not perfused properly, and the lack of oxygen can lead to organ failure. The two types are septic shock, in which toxins and inflammatory mediators from an infection cause the vasodilation, and anaphylactic shock, in which histamine and other mediators released in an allergic reaction do so. The other categories are cardiogenic, obstructive and hypovolaemic shock.
- Definition: distributive shock is a fall in total peripheral resistance from profound vasodilation.
- Blood pressure: mean arterial pressure is the cardiac output multiplied by the total peripheral resistance, so low resistance lowers the pressure even with a normal volume and a pumping heart.
- Types: septic shock and anaphylactic shock.
A neat way to sort the types is to ask whether the problem is the pump, the pipes or the volume.
Why the other options are incorrect
- B. Acute loss of circulating blood volume due to haemorrhage or dehydration: Acute loss of circulating volume from haemorrhage or dehydration is hypovolaemic shock. In distributive shock the volume is normal. Your answer
- C. Obstruction to cardiac filling or outflow resulting in reduced cardiac output: Obstruction to cardiac filling or outflow is obstructive (mechanical) shock, as in tamponade or pulmonary embolism. The vessels are not primarily dilated in that condition. Your answer
- D. Primary failure of ventricular contraction causing blood to back up into the venous circulation: Primary failure of ventricular contraction describes cardiogenic shock. Blood backs up behind a failing pump, which is a different mechanism. Your answer
- E. Chronic hypertension causing adaptive thickening of the arterial wall: Adaptive thickening of the arterial wall in chronic hypertension is a long-term change. It does not explain acute hypotension and poor tissue perfusion. Your answer
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More questions from this set. Start the quiz to answer them and see each explanation.
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1
Which physiological response initially helps to partially restore circulating volume during early hypovolaemic shock?
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2
A previously healthy adult presents with acute hypovolaemia following several days of severe vomiting. Initially, their blood pressure is maintained despite reduced circulating volume. Which physiological mechanism most directly explains this early maintenance of blood pressure?
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