A 72-year-old man with a history of COPD presents with increasing confusion, fever and productive cough. Blood pressure is 88/50 mm Hg, heart rate 118 beats/min, respiratory rate 30 breaths/min and oxygen saturation 90% on room air. Laboratory tests show lactate 3.9 mmol/L. After 30 mL/kg crystalloid, his blood pressure remains 82/48 mm Hg. According to the Surviving Sepsis Campaign, which vasopressor is preferred as first-line therapy?