Blood Volume & Loss: Why Losing 5 Pints Is Fatal

Total blood volume ≈ 70 mL/kg (≈5 L / 10.5 pints in 70 kg adult). Losing 5 pints (≈2.4 L) = Class III hemorrhage (30–40% volume loss).

Hemorrhage Classes

Class	% Volume Lost	Volume (70 kg)	Signs
I	<15%	<750 mL	Minimal (HR normal)
II	15–30%	750–1500 mL	Tachycardia, cool skin, anxiety
III	30–40%	1500–2000 mL	↓BP, confusion, oliguria, delayed cap refill
IV	>40%	>2000 mL	Shock, unconscious, anuria, fatal without resuscitation

5 pints (2.4 L) ≈ 48% loss → Class IV, lethal without immediate massive transfusion.

Physiology

• Compensation: tachycardia, vasoconstriction, fluid shift from interstitium.
• Decompensation: tissue hypoxia → lactic acidosis → organ failure.