Vasopressors & Inotropes in Shock
When a patient's blood pressure collapses and their organs start to starve, the drugs that pull them back are the same adrenaline-like molecules from the autonomic section — now running through an IV line in intensive care. But choosing the right one is everything: the drug that saves a patient in septic shock could harm one in cardiogenic shock. It all comes down to WHY the circulation failed.
A patient with a severe infection crashes: despite litres of intravenous fluid, their blood pressure keeps falling, their skin mottles, and their kidneys stop making urine — septic shock. The team starts an infusion of noradrenaline through a central line, and the pressure climbs back to a level that perfuses the brain, heart, and kidneys. That drip is buying time while antibiotics fight the infection. Which drug to run, and how fast, depends entirely on what kind of shock this is — so the first question in any collapsing circulation is 'why?'
Match the drug to the shock
Shock has different causes, each needing a different fix. Shock means the circulation can't perfuse the tissues, and it comes in types. In hypovolaemic shock (bleeding or fluid loss) the tank is empty — the treatment is fluids or blood, not a drug to squeeze the vessels. In distributive shock (sepsis, anaphylaxis) the vessels are pathologically dilated — here you need a VASOPRESSOR to constrict them back and raise pressure. In cardiogenic shock the pump itself is failing — here you need an INOTROPE to boost contractility. So vasopressors and inotropes are not interchangeable: give a pure vasoconstrictor to a failing heart and you make it pump against even higher resistance; give an inotrope to an empty tank and you flog a heart with nothing to pump. Cause first, drug second.
The drugs, by receptor
Most of these drugs act on the adrenergic receptors from the autonomic section. Noradrenaline (norepinephrine) is a powerful alpha-1 vasoconstrictor (with some beta-1) — the first-line vasopressor for septic shock, tightening the dilated vessels. Adrenaline (epinephrine) hits alpha and beta together — first-line for anaphylactic shock and used in cardiac arrest and refractory shock. Dobutamine is a beta-1 agonist that boosts the heart's contractility — the classic inotrope for cardiogenic shock and low-output states. Vasopressin works through a different, non-adrenergic receptor to constrict vessels and is added in septic shock when noradrenaline alone isn't enough. Phenylephrine is a pure alpha-1 vasoconstrictor, and milrinone is an 'inodilator' (boosts contractility while dilating vessels). Nearly all are given through a central line in an intensive-care setting.
This is the autonomic receptor map, applied at the bedside of the sickest patients. Want to raise a dangerously low blood pressure by constricting dilated vessels? Choose an alpha-1 agonist (noradrenaline, phenylephrine). Want to make a failing heart pump harder? Choose a beta-1 agonist (dobutamine). Want both at once in a dying patient? Adrenaline hits everything. Knowing which receptor produces which effect — straight from the autonomic articles — lets you pick the right pressor for the right shock instead of memorizing a list.
- Shock type dictates therapy: fluids for hypovolemic, vasopressors for distributive, inotropes for cardiogenic.
- Noradrenaline (α1) is first-line vasopressor in septic shock.
- Adrenaline (α+β) = anaphylaxis, cardiac arrest, refractory shock.
- Dobutamine (β1) is the inotrope for cardiogenic shock; vasopressin is an add-on pressor in sepsis.
- Most are given via a central line in intensive care.
- Giving a vasopressor instead of fluids/blood in hypovolemic shock. Fill the tank first.
- Using a pure vasoconstrictor in cardiogenic shock. It raises afterload on a failing heart.
- Running potent vasopressors through a small peripheral vein — tissue damage if it leaks.
- Treating shock without finding and fixing the cause. The drugs only buy time.
Which is the first-line vasopressor for septic shock?
- Shock type decides the drug: fluids (hypovolemic), vasopressors (distributive), inotropes (cardiogenic).
- Noradrenaline (α1) first-line in sepsis; adrenaline (α+β) for anaphylaxis/arrest.
- Dobutamine (β1) is the inotrope for cardiogenic shock; vasopressin is a non-adrenergic add-on.
- It's the adrenergic receptor map applied in the ICU — and always fix the underlying cause.
- Katzung BG. Basic & Clinical Pharmacology — Adrenoceptor agonists (vasopressors & inotropes).
- Surviving Sepsis Campaign guidelines — Vasopressor & inotrope selection in shock.
- Brunton LL, et al. Goodman & Gilman's The Pharmacological Basis of Therapeutics — Catecholamines & sympathomimetics.
- Marino PL. The ICU Book — Vasopressors & inotropic therapy.
- Whalen K. Lippincott Illustrated Reviews: Pharmacology — Adrenergic agonists in shock.
