A 68-year-old woman with hypertension (on amlodipine) and diabetes mellitus type 2 undergoes epidural anesthesia for hip arthroplasty. The anesthesiologist inserts the epidural catheter at L3-L4 and administers 15 mL of 0.75% ropivacaine. Thirty minutes into surgery, the patient develops severe hypotension (BP 65/40), bradycardia (HR 42 bpm), and the surgeon notices the patient is not responding to surgical stimulation. What is the most appropriate immediate management?