Prof: What is the first line therapeutic strategy for those in shock?
Student: Administration of intravenous fluids.
Prof: That is right. But what if the blood pressure remains low in spite of fluid resuscitation?
Student: Give vasoconstrictors.
Prof: Right again. What are the vasoconstrictors commonly used for shock?
Student: Dopamine, Dobutamine and Norepinephrine.
Prof: Which is better - dopamine or norepinephrine?
Student: I am not sure.
Prof: Vasoconstrictors differ in their degree of alpha adrenergic, beta adrenergic and dopaminergic effects. Dopamine and norepinephrine (noradrenaline) both have alpha and beta adrenergic effects but norepinephrine stimulates alpha adrenergic receptors more than beta adrenergic receptors. Stimulation of alpha receptors will bring up the blood pressure more effectively but at the cost of reduced splanchnic and renal blood flow. Dopamine also stimulates dopaminergic receptors which norepinephrine does not. Stimulation of dopaminergic receptors helps to improve blood flow to the internal organs and kidney but has a deleterious effect on the hypothalamic pituitary axis because it results in reduced prolactin and growth hormone levels. So you can see that there are good and bad points for both norepinephrine and dopamine. A study was published in the March 2010 issue of the New England Journal of Medicine which compared the effect of these two vasoconstrictor agents in shock. You can read the article HERE. You can see from it that both these agents are good as initial therapy for shock. But based on this study it would be preferable to use norepinephrine rather than dopamine for cardiogenic shock.
