A 56-yeаr-оld mаle requires cоntinuоus mechаnical ventilation following cardiac arrest. His heart rate is 110/min and blood pressure is 96/50 mm Hg. A pulmonary artery catheter has been inserted. Patient data are: Body surface area 2 m2 Cardiac output 3.2 L/min EF 35% PCWP 12 mm Hg A respiratory therapist should recommend administering