Vasopressors and inotropes

Receptors

• Alpha-adrenergic receptors:
  • Alpha-1 agonists cause vasoconstriction
  • Alpha-2 agonists causes vasodilatation especially of coronary arteries
• Beta-adrenergic receptors:
  • Beta-1 agonists increases HR and cardiac contractility --> increased CO
  • Beta-2 agonists dilate small coronary A's, visceral organ A's, skeletal muscle A's and increase bronchodilation
• Dopaminergic receptors:
  • 7 types of dopamine receptors
  • D4 agonists increase cardiac contractility
  • D1 and D2 agonists increase renal diuresis and naturesis
• Vasopressin receptors:
  • V1 agonists cause vasoconstriction mostly in peripheral arterioles and increased sensitivity to catecholamines

Pressor	Alpha	Beta-1	Beta-2	Notes
Dobutamine	–	++	+	More of an inotrope, really.
Dopamine, moderate	–	+++	+++	Precursor to norepi/epi. Higher risk of tachyarrhythmias than norepi.
Dopamine, high	++	+++	+++	More alpha with high doses.
Epinephrine	+++	++++	+++	Increases lactate.
Norepinephrine	+++	+	–
Phenylephrine	+++	–	–	Beware reflex bradycardia.
Vasopressin	–	–	–	Acts on V1 receptors. Increase SVR and can cause ischemia.
Milrinone				Phosphodiesterase III inhibitor. Avoid in renal failure. Long half-life.

Treatment Algorithms

• Distributive shock: norepinephrine, then add vasopressin or epinephrine, then add dopamine or dobutamine
• Cardiogenic shock
  • If left heart failure and BP can tolerate: Dobutamine
  • If right heart failure and BP can tolerate: Milrinone
• Opioid-induced hypotension: phenylephrine