A 42-year-old woman with severe pancreatitis (APACHE II score 18) is admitted to the ICU. On day 2, she develops hypotension (BP 92/58 mmHg), tachycardia (122/min), and oliguria (urine output 0.3 mL/kg/hr). Skin is cool and clammy. Central venous pressure (CVP) is 3 mmHg. Lactate is 5.8 mmol/L. Echocardiography shows normal ejection fraction and no pericardial effusion. After initial fluid bolus (500 mL), BP remains 95/60 mmHg and CVP rises to 6 mmHg, but lactate increases to 6.2 mmol/L. Which vasopressor is most appropriate at this stage?