Some have found the Critical Care Intravenous Infusion Drug Handbook to be helpful. I have not used it. I agree with Okami that your pharmacist is a good resource. Also with multiple pressors on the same pt. It is helpful to consult the intensivist.
If a pt. has epinephrine, norepinephrine, vasopressin, and milrinone - the milrinone is not a pressor but often lower BP while increasing cardiac output. Epinephrine increases pressure and cardiac output but has undesired dysrhythmia effects. So knowing your pt.s cardiac output, CVP, PA pressures, and heart details (Valves,LVED, etc,) and goals is essential. Sometimes the cardiac surgeon or intensivist has a plan so I just ask, which one do you want me to titrate first. If it doesn't mesh with my thoughts I just ask them to educate me as to why and we discuss.