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Vasopressors and inotropes
The drug is chosen by what is missing: vascular tone (noradrenaline, vasopressin, phenylephrine) or contractility (dobutamine, milrinone) — and in septic shock the first line is noradrenaline with a MAP target of 65.
Why it matters in the exam
The exam asks about the receptors of each drug and its effect on heart rate and blood pressure, the first line in septic shock, when vasopressin and hydrocortisone are added, why phenylephrine causes bradycardia, and why dopamine is no longer recommended. It also asks what to choose under anaesthesia in aortic stenosis or HOCM, and what to give a patient on beta-blockers with a low cardiac output (milrinone).
Noradrenaline acts mainly on alpha-1 and to a lesser extent on beta-1, so it raises blood pressure with hardly any tachycardia. Phenylephrine is pure alpha-1 and so lowers heart rate reflexly — suitable when tachycardia is harmful. Ephedrine acts indirectly (releasing noradrenaline) and loses effect with repeated doses. Dobutamine and milrinone increase contractility and dilate vessels, so blood pressure may fall.
In exam questions first identify the type of shock: distributive (sepsis, anaphylaxis, anaesthesia) with relaxed vessels, cardiogenic with low output, hypovolaemic, or obstructive (tamponade, tension pneumothorax, pulmonary embolism). Only after that distinction is a drug chosen, and in obstructive shock the answer is usually an action — drainage or decompression — not a drug. Remember that all these drugs are given as continuous infusions with continuous blood pressure monitoring, usually through an arterial line.
Key points
- Noradrenaline — first line in septic shock, MAP of 65.
- Vasopressin as an add-on; hydrocortisone in refractory shock.
- Phenylephrine — pure alpha, bradycardia; ephedrine — indirect, tachyphylaxis.
- Dobutamine and milrinone for low cardiac output; milrinone bypasses beta-blockers.
- Dopamine is not recommended in shock.
Summary table
| Drug | Receptor or mechanism | Main use | Note |
|---|---|---|---|
| Noradrenaline | Alpha-1 > beta-1 | First line in septic shock | Can run through a large peripheral vein for a short time |
| Vasopressin | V1 | Added when noradrenaline is 0.25–0.5 mcg/kg/min | Effective even in acidosis; not a catecholamine |
| Adrenaline | Beta-1, beta-2, alpha-1 | Anaphylaxis, cardiac arrest, second line in shock | Raises lactate |
| Phenylephrine / ephedrine | Pure alpha-1 / indirect + direct | Hypotension under anaesthesia | Phenylephrine — reflex bradycardia; ephedrine — tachyphylaxis |
| Dobutamine / milrinone | Beta-1 / PDE3 inhibitor | Low cardiac output | Milrinone bypasses beta-blockade; renally excreted |
Free exam questions
למטופל אישון קטן מימין (miosis) , העפעף נופל באותו צד (ptosis) , והוא גם אינו מזיע בצד ימין (anhidrosis) . נוירולוג נותן למטופל טיפות של hydroxyl amphetamine בעיניים ללא תגובה. הוא מכריז שהמקור האנטומי של הפגיעה ב ”3rd order neuron” . איזה אבחנה יכולה להסביר את כל הקליניקה של המטופל? (the question as examined, in Hebrew)
- א. הרדמה אפידורלית
- ב. אירוע מוחי
- ג. Carotid dissection
- ד. ניתוח Cataract
בבדיקת TEE מייד לאחר תיקון של המסתם המיטרלי מתגלה Systolic Anterior Motion (SAM) של העלה הקדמי של המסתם, הגורמת לחסימה של ה - Left ventricular outflow tract המלווה בקיפוח המודינמי משמעותי. מהו הטיפול התרופתי המיידי המתאים ביותר? (the question as examined, in Hebrew)
- א. מתן Dobutamine
- ב. מתן Nitroglycerin
- ג. מתן Esmolol
- ד. מתן Milrinone
In the full version for subscribers
- A simple algorithm
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- Exam traps
- 5 review cards
- Enough for IMLE
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Sources
- Surviving Sepsis Campaign: International Guidelines for Management of Sepsis and Septic Shock, 2021 — Vasoactive agents and corticosteroids
- Miller's Anesthesia, 9th edition (2020) — Cardiovascular Pharmacology
- Morgan & Mikhail's Clinical Anesthesiology, 7th edition (2022) — Adrenergic Agonists and Antagonists
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-02. The text may contain errors; when in doubt, check the source.