Vasopressors squeeze the vessels; inotropes squeeze the heart
Mnemonic
“Pressors squeeze, inotropes squeeze the heart”:
| Drug | Receptors | Main effect | Use |
|---|---|---|---|
| Noradrenaline | alpha » beta1 | Vasoconstriction | Septic shock, first line |
| Adrenaline | alpha and beta | Both | Anaphylaxis, cardiac arrest |
| Dobutamine | beta1 > beta2 | Inotropy, vasodilates | Cardiogenic shock |
| Vasopressin | V1 | Vasoconstriction | Adjunct in septic shock |
| Metaraminol, phenylephrine | alpha | Vasoconstriction | Peripheral, anaesthesia |
| Milrinone | PDE3 inhibitor | Inotropy and vasodilatation | Right heart failure |
“Noradrenaline for the vasodilated, dobutamine for the failing pump.”
Choosing follows from the type of shock: distributive shock is a resistance problem so it needs a vasoconstrictor, while cardiogenic shock is an output problem so it needs inotropy, and giving the wrong one worsens the patient.
Most require central access because of the risk of extravasation and tissue necrosis, and all require invasive blood pressure monitoring; metaraminol and dilute phenylephrine are the usual peripheral bridge.
Expansion
| Drug | Main receptors | Main effect |
|---|---|---|
| Noradrenaline | Alpha-1 » beta-1 | Vasoconstriction; first line in septic shock |
| Adrenaline | Alpha and beta | Raises output and resistance; used in anaphylaxis and cardiac arrest |
| Dobutamine | Beta-1 > beta-2 | Inotropy, often with a fall in resistance |
| Dopamine | Dose dependent | Dopaminergic, then beta, then alpha |
| Vasopressin | V1 | Vasoconstriction independent of adrenoceptors |
| Metaraminol / phenylephrine | Alpha-1 | Pure vasoconstriction, with reflex bradycardia |
| Milrinone | Phosphodiesterase-3 inhibition | Inotropy plus vasodilatation, an inodilator |
| Levosimendan | Calcium sensitiser | Inotropy without raising calcium or oxygen demand |
The choice follows from MAP = cardiac output x systemic vascular resistance. Septic shock is a resistance problem, so noradrenaline is first line. Cardiogenic shock is an output problem, so dobutamine or milrinone is added; but if pressure is too low to perfuse the coronaries, a vasopressor is needed first.
Note that vasopressin retains its effect in acidosis, when catecholamine responsiveness falls.