Why Norepinephrine is Better than Dopamine for Shock

Spoon Feed
Norepinephrine and dopamine were equal with regard to mortality in shock, except for the subgroup with cardiogenic shock, in which the dopamine group fared worse. There were twice as many dysrhythmias in the dopamine group, largely atrial fibrillation.

Why does this matter?
For years, both norepinephrine and dopamine were recommended as first line agents for patients in shock.  Dopamine must be used at higher doses to see additive alpha agonist effect, whereas norepinephrine has much stronger alpha agonist effect at lower doses.  The AHA formerly recommended dopamine first line for cardiogenic shock.  Now norepinephrine is recommended first line in patient with undifferentiated shock (Surviving Sepsis 2016).

Pump you up
This was a multi-center RCT of 1679 patients with mixed forms of shock requiring pressors who were treated with either norepinephrine vs. dopamine.   Patients were well matched and were given fluid prior to starting pressors.  They found that there was no difference in 28-day mortality (which was very high, almost 50% per group).  But 24% had cardiac arrhythmia in the dopamine group vs. 12% in the norepinephrine group, largely attributable to atrial fibrillation (86%).  In subgroup analysis, there was higher mortality in the cardiogenic shock group.  This study was instrumental in the current recommendations to start norepinephrine as the first line agent for shock.

Source
Comparison of dopamine and norepinephrine in the treatment of shock.  N Engl J Med. 2010 Mar 4;362(9):779-89. doi: 10.1056/NEJMoa0907118.

Another Spoonful
Journal Watch has an excellent review of this article.