dopamine for shock?
February 23, 2009 8:35 PM   Subscribe

Neurologic Drug Filter: I've been reading for a while and am quite tired so I'm hoping my exhaustion is not resulting in my going on mefi and asking a totally stupid question. So here goes.... If the activation of domaminergic receptors result in the vasodilation of the blood vessels in places like the heart and kidneys, why is one of the clinical uses of dopamine shock and hypotension? I'm a little confused by this. It would seem if dopamine results in vasodilation, you would not want to give it to someone hypotensive or in shock. Any ideas?
posted by GlowWyrm to Science & Nature (4 answers total) 1 user marked this as a favorite
Best answer: The effects of dopamine are dose-dependent. See first paragraph here for an explanation.
posted by Asherah at 8:48 PM on February 23, 2009

Best answer: According to my pharmacology textbook, at moderate doses dopamine also stimulates beta-1 receptors, which increases cardiac output (the opposite of how beta-blockers reduce blood pressure). At high doses, it stimulates alpha-1 receptors as well, causing vasoconstriction and further increasing blood pressure. The book also says dopamine is not so good at correcting serious hypotension, and that hypovolemia should be corrected before beginning dopamine therapy for the best results. (IANAD, and I am probably in the same brain fog of pharmacology studying as you. I just looked this up because I have a test on this next week and couldn't remember the answer.)
posted by vytae at 8:48 PM on February 23, 2009

Response by poster: Ah so it depends on the dose. That does sound familiar now that you mention it. Thanks a lot for the help. I appreciate it.
posted by GlowWyrm at 9:00 PM on February 23, 2009

Best answer: Dopamine has mixed effects on multiple receptor subtypes. Depending on the recipient and the dosage used, classical teaching is that there is indeed a dose dependent response. At very low doses it tends to cause relative vasodilation in vascular beds with dopaminergic receptors (the kidneys). There was a time when folks used to use low dose dopamine infusions on patients with acute renal failure in the hopes of improving renal blood flow and saving the kidneys for this reason. This practice however has fallen out of favor as a growing body of evidence demonstrated that while dopamine did potentially improve urine output, it ultimately had no significant impact on mortality or morbidity in critically ill patients.

At higher dosages dopamine exerts a beta adrenergic effect leading to increased cardiac output, and at still higher dosages it tends to have an alpha-1 predominant effect leading to peripheral vasoconstriction. These effects are overlapping at many typically used dosages. Primarily, the alpha-agonistic effects help maintain blood pressure by reversing the vasodilatory effects of distributive shock (ie sepsis). Some favor dopamine particularly in the setting of hypotension of potentially mixed (cardiogenic and distributive) or unclear etiology, or in patients with known cardiac dysfunction who present with septic shock given it's effects on both cardiac output and peripheral vascular tone.
posted by drpynchon at 9:09 PM on February 23, 2009 [2 favorites]

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