A 45-year-old woman is found unconscious after a motor vehicle collision. What is most likely causing her low blood pressure and increased heart rate?

In the scenario provided, the woman is found unconscious after a motor vehicle collision, which raises concerns about potential traumatic injuries. When assessing her low blood pressure and increased heart rate, one of the most common physiological responses to significant trauma, particularly involving hemorrhage, is the body's attempt to compensate for blood loss.

Bleeding into the chest or abdomen can lead to significant internal bleeding, which decreases the overall blood volume available for circulation. When the blood volume drops, the body responds by increasing the heart rate to maintain adequate perfusion to vital organs, while also causing a drop in blood pressure due to insufficient circulating volume.

This combination of low blood pressure and increased heart rate indicates a state of shock, which is typically associated with hemorrhagic events following traumatic incidents like motor vehicle collisions. In this case, internal bleeding is the most likely cause, as it directly leads to the cardiovascular symptoms observed in the patient.

While other conditions could cause low blood pressure and increased heart rate, such as dehydration or cardiac arrest, the context of an unconscious patient following a collision makes internal bleeding the most probable cause due to its acute onset and relationship to trauma.