Comatose state occurs after water loss when how much blood is lost?

Comatose state occurs after water loss when how much blood is lost?

• A. 1 liter
• B. 3 liters
• C. 5 liters
• D. 7 liters

Answer: (C)

The big idea is that coma from water loss happens when circulating blood volume becomes critically low, so the brain stops getting enough blood and oxygen. In an average adult, total blood volume is roughly five liters, so losing about five liters essentially empties the circulating pool. With almost no blood to circulate, cerebral perfusion falls below what the brain needs, and consciousness is lost, resulting in a coma. Smaller losses don’t push the brain into coma: losing around one liter causes weakness and rapid heartbeat; around three liters produces severe shock and confusion but not necessarily coma; and losing more than the total blood volume isn’t compatible with life. So about five liters best fits the onset of coma in this scenario.

The big idea is that coma from water loss happens when circulating blood volume becomes critically low, so the brain stops getting enough blood and oxygen. In an average adult, total blood volume is roughly five liters, so losing about five liters essentially empties the circulating pool. With almost no blood to circulate, cerebral perfusion falls below what the brain needs, and consciousness is lost, resulting in a coma.

Smaller losses don’t push the brain into coma: losing around one liter causes weakness and rapid heartbeat; around three liters produces severe shock and confusion but not necessarily coma; and losing more than the total blood volume isn’t compatible with life. So about five liters best fits the onset of coma in this scenario.