Review Question - QID 213373

A 21-year-old G1P0 woman presents to the labor and delivery ward at 39 weeks gestation for elective induction of labor. She requests a labor epidural. An epidural catheter is secured at the L4-L5 space. She exhibits no hemodynamic reaction to lidocaine 1.5% with epinephrine 1:200,000. A continuous infusion of bupivacaine 0.0625% is started. After 5 minutes, the nurse informs the anesthesiologist that the patient is hypotensive to 80/50 mmHg with a heart rate increase from 90 bpm to 120 bpm. The patient is asymptomatic and fetal heart rate has not changed significantly from baseline. She says that her legs feel heavy but is still able to move them. What is the most likely cause of the hemodynamic change?