Perioperative Vasopressor Selection

Fast Triage

MAP goal: usually ≥65 mmHg (individualize) First-line in distributive: Norepinephrine Neuraxial hypotension: Phenylephrine Refractory catecholamine-resistant: add Vasopressin

Correct volume deficits and fix the cause first when possible; vasopressors support perfusion—they don’t replace hemostasis or fluids.

Algorithm: Hypotension in Surgical Patients

Step 1

Confirm & Assess

Verify BP (art line if available), check MAP trend, HR, rhythm, SpO₂, ETCO₂.
Look for bleeding, anesthetic depth, neuraxial block, anaphylaxis, PE/tamponade.
Check responsiveness to fluid (PPV/SVV if ventilated; bedside echo if available).

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Step 2

Phenotype the Shock

Distributive: warm extremities, low SVR ± high CO (sepsis, anesthetic depth, neuraxial, vasoplegia, anaphylaxis).

Hypovolemic: blood/volume loss, tachycardia, low preload/CO (bleeding, third-spacing).

Cardiogenic: pump failure, low CO, high SVR (ischemia, stunning, arrhythmia, valvular).

Obstructive: impaired filling/outflow (PE, tamponade, tension PTX).

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Step 3

Select Initial Therapy

Distributive: Start norepinephrine; add vasopressin if escalating or ACE-I/ARB vasoplegia suspected.
Neuraxial hypotension (bradycardia/vasodilation): phenylephrine preferred.
Hypovolemic: prioritize hemostasis & balanced resuscitation; use norepinephrine as a bridge if needed.
Cardiogenic: start inotrope (dobutamine; consider milrinone) ± norepinephrine to maintain MAP.
Obstructive: immediate cause-directed intervention ± norepinephrine for support.
Anaphylaxis: epinephrine first (bolus/infusion per protocol), fluids, airway support; add adjuncts after epi.

At-a-Glance: Receptor Profiles

Agent	α1	β1	β2	V1	Key Clinical Notes
Norepinephrine	+++	++	+	–	First-line in distributive shock; maintains MAP with modest inotropy.
Phenylephrine	+++	–	–	–	Pure α-agonist; ideal for neuraxial/anesthetic vasodilation with tachycardia.
Vasopressin	–	–	–	+++	Fixed-dose adjunct; helpful in vasoplegia & ACE-I/ARB patients.
Epinephrine	++	+++	++	–	Bolus/infusion of choice for anaphylaxis; inotropy + bronchodilation.
Dobutamine	–	+++	++	–	Inotrope for cardiogenic shock; may lower SVR slightly—watch BP.
Milrinone	–	Inotrope	Vasodilator	–	PDE-3 inhibitor; RV failure/post-cardiac surgery or when afterload reduction helps.

Common Dosing & Titration

Agent	Typical Start	Range	Titration	Notes
Norepinephrine	0.02–0.05 mcg/kg/min	0.02–0.5+ mcg/kg/min	Every 2–5 min to MAP	Short t½; watch for digital ischemia at high doses.
Phenylephrine	40–100 mcg IV bolus or 0.25–1 mcg/kg/min infusion	Bolus repeat PRN; 0.1–2 mcg/kg/min	To effect (rate/bolus)	Useful with tachycardia (neuraxial/volatile anesthetics).
Vasopressin	0.03 units/min (fixed)	0.01–0.04 units/min	Usually not titrated	Longer t½; avoid high doses (gut/skin ischemia risk).
Epinephrine	Anaphylaxis: 10–50 mcg IV bolus; infusion 10–20 mcg/min	Bolus to effect; 1–50+ mcg/min	To effect	Arrhythmias, lactate rise; first-line in anaphylaxis.
Dobutamine	2.5 mcg/kg/min	2.5–10+ mcg/kg/min	Every 5–10 min	Watch tachycardia/ischemia; combine with NE if hypotensive.
Milrinone	No bolus; 0.125–0.25 mcg/kg/min	0.125–0.75 mcg/kg/min	Slowly; renal adjust	Vasodilation may drop BP—pair with NE as needed.

Peripheral pressors are acceptable short-term with good IV and hourly checks, but central access is preferred for ongoing infusions. Treat extravasation promptly (e.g., phentolamine per protocol).

Bedside Differentiation: Common Surgical Scenarios

Neuraxial (spinal/epidural) hypotension

Features: vasodilation ± bradycardia.
Phenylephrine first; consider glycopyrrolate if vagal.
Fluids/leg elevation; assess block height and anesthetic dose.

Anesthetic depth / volatile or propofol

Reduce depth if appropriate.
Norepinephrine preferred if vasopressor needed.
Echo if myocardial depression suspected.

Active bleeding / hypovolemia

Hemostasis, balanced blood products ± TXA per protocol.
NE as bridge only; avoid masking volume loss.

ACE-I/ARB vasoplegia or post-CPB

NE + early vasopressin (fixed dose).
Consider adjuncts per institutional pathway if refractory.

Anaphylaxis

Epinephrine first (IV bolus/infusion), high-flow O₂, fluids.
Add H1/H2 blockers and steroid after epi; consider vasopressin if refractory.

Cardiogenic features

Dobutamine (or milrinone) for inotropy; add NE to keep MAP.
Urgent cause-directed therapy (e.g., ischemia, arrhythmia).

Monitoring & Safety

Art line preferred with continuous vasopressors; track MAP and trend.
Watch end-organ perfusion (mental status, urine output, lactate).
Telemetry for β-agonists (arrhythmias); correct K⁺/Mg²⁺/Ca²⁺.
Prevent/monitor extravasation; have phentolamine protocol at hand.
De-escalate promptly as cause resolves; avoid “pressor creep.”

Teaching Reference

Use this guide alongside bedside hemodynamic assessment and institutional protocols. Individualize targets for chronic hypertension and high-risk patients.