Which clinical category of shock is defined by low preload due to decreased circulating blood volume?

• A. Cardiogenic shock
• B. Obstructive shock
• C. Hypovolemic shock
• D. Distributive shock

Answer: (C)

Preload is the volume filling the ventricles at the end of diastole, which depends on venous return. When circulating blood volume drops, venous return falls, end-diastolic volume decreases, and preload is reduced. This directly lowers stroke volume and cardiac output, which is the hallmark of hypovolemic shock caused by actual loss of blood or fluids (such as hemorrhage, dehydration, or severe fluid losses).

The other categories involve different primary problems: cardiogenic shock stems from the heart’s pumping failure, so preload is not simply decreased by volume loss and can even be high due to backup; obstructive shock is due to a physical blockage impairing venous return, reducing preload through obstruction rather than a true loss of volume; distributive shock involves widespread vasodilation and pooling of blood, leading to relative hypovolemia, but not primarily a decrease in circulating volume. The defining link to low preload here is the actual decrease in circulating blood volume.