What symptom indicates severe hypovolemic shock?

Little urine output is a significant symptom indicating severe hypovolemic shock because it reflects the body’s response to a critical reduction in blood volume. In severe hypovolemic shock, the circulatory system lacks sufficient blood to maintain normal physiological functions, which prompts the kidneys to conserve water and reduce urine output as a compensatory mechanism. This process is part of the body's effort to divert blood flow to vital organs and maintain blood pressure.

In contrast, other symptoms such as headache and fatigue can be associated with various conditions and are not specific indicators of hypovolemic shock. Increased thirst may occur as the body signals for fluid replacement, but it does not directly indicate the severity of hypovolemic shock as effectively as minimal urine output does. Therefore, among the listed symptoms, little urine output is the most critical sign of severe hypovolemic shock, as it indicates the body is struggling to cope with the significant loss of fluid and blood volume.