Exsanguination is defined as:

Exsanguination refers specifically to a severe loss of blood, often to the extent that it can threaten life. This term is commonly used in medical contexts to describe a condition where bleeding is so significant that the body's ability to function is compromised due to insufficient blood volume. In clinical settings, rapid identification and response to exsanguination is crucial to prevent shock and other serious health complications.

The other options do not accurately define exsanguination: excessive fluid retention pertains to an accumulation of fluids in the body, severe anemia indicates a deficiency of red blood cells or hemoglobin, while high blood pressure refers to the force of blood against the walls of arteries. None of these concepts encapsulate the essence of significant blood loss that exsanguination denotes.