Final answer:
The nurse should first start an IV infusion to stabilize the patient's circulatory system as they are exhibiting signs of hypovolemic shock, with low blood pressure and weak pulses.
Step-by-step explanation:
The nurse should prioritize actions based on the ABCs (Airway, Breathing, and Circulation) and the patient's immediate needs. With a blood pressure of 68/31 mm Hg and weak bilateral leg pulses, this patient is exhibiting signs of hypovolemic shock. Before obtaining consent or assessing with a Doppler, the nurse should start an IV infusion to address the shock by administering fluids or medications as needed. This intervention can provide rapid support to the circulatory system. While bruit and pulsation at the umbilicus may suggest an abdominal aortic aneurysm, stabilizing the patient's hemodynamics is the first priority before further assessment or surgery can be safely pursued.