Answer :
Final answer:
The most likely diagnosis for the 15-year-old boy who hit his head on the bottom of the swimming pool and subsequently has no sensation or motor function below the nipple line is neurogenic shock.
Explanation:
Neurogenic shock occurs when there is a disruption in the normal functioning of the nervous system, specifically the spinal cord. This can lead to a loss of coordination and control of the body below the affected area. In this case, the trauma to the head and subsequent loss of sensation and motor function suggest a spinal cord injury. The vital signs provided, including a low blood pressure and low oxygen saturation, also support the diagnosis of neurogenic shock.