The effects of morphine on venous tone in patients with acute pulmonary edema.

“There is no doubt that morphine is the analgesic of choice in severe, ischaemic chest pain. It is also extremely effective in relieving the dyspnoea associated with acute left ventricular failure and pulmonary oedema. However, the concept of a 'medical phlebotomy' has not been proven and the benefits of morphine are likely to lie more in its central sympatholytic and anxiolytic properties.”

“A certain vasodilation has been described after morphine administration, but the evidence for this mechanism is relatively poor and morphine-induced anxiolysis may possibly be the most important factor of morphine in pulmonary oedema and therefore some authors have suggested benzodiazepines as an alternative treatment.”

“The useful action of morphine in relieving distressing cardiac dyspnoea is not adequately explained by systemic venous blood pooling. These results suggest that the effects of morphine on the central nervous system are more important.”