Why do we use morphine in acute pulmonary edema?

Pulmonary vasodilate: To acutely dilate pulmonary vasculature.

Good question: The growing body of evidence derived from clinical studies suggest that its efficacy may be simply from the decrease of anxiety that accompanies shortness of breath. Reducing catacholemines and secondary vasoconstriction in this condition is indeed beneficial, but this effect can be more safely addressed with benzodiazepines - less incidence of respiratory depression.