creation date: 2026-11-07 15:28
tags: Pharmacology
Vasopressors & Inotropes
Background
Vasopressors and inotropes are medications used for to induce vasoconstriction or increase cardiac contractility, respectively. These are used in patients with shock or severe hypotension.
Catecholamine receptors relevant to their function are:
- Alpha-1: causes vasoconstriction
- Beta-1: increases heart rate, increases contractility
- Beta-2: bronchodilation, vasodilation
Vasopressors / Vasoconstrictors
Norepinephrine
Mechanism of Action
- Acts mostly on alpha receptors (vasoconstriction)
- Some beta effect at higher doses
Side Effects
At very high doses:
- Tachycardia
- Arrhythmia
Additional Considerations
- Common first option
- Titrate to MAP >65
Phenylephrine
Mechanism of Action
- Pure alpha action
Side Effects
- Tachyphylaxis if given over days
Additional Considerations
- Effective for preventing hypotension when administering induction agents
- Often a “pocket pressor”, given as a bolus into a NS bag
- Mix 10 mg in 100 mL NS bag = 100 mcg/mL, then give 1-2 mL
Vasopressin
Mechanism of Action
- Direct vasoconstrictor (not catecholamine pathway)
Side Effects
Additional Considerations
- Used as hormone replacement to treat vasopressin deficiency in shock
- No evidence of mortality benefit in septic shock but can reduce other vasopressor needs
Inodilators
Inotrope plus vasodilation
Dobutamine
Mechanism of Action
- Beta-1 (contractility) and beta-2 (afterload reduction)
Side Effects
- May lower BP due to vasodilation
Additional Considerations
- Use caution in low BP
- Titrate to capillary refill, extremity temperature, and SpO2 waveform (clinical features)
Milrinone
Mechanism of Action
- Non-catecholamine pathway
- Reduces pulmonary vascular resistance (used for RV failure and pulmonary hypertension)
Side Effects
Additional Considerations
- Very long half-life - cannot undo vasodilation in hypotension
Inoconstrictors
Inotrope plus vasoconstriction
Epinephrine
Mechanism of Action
- Mixed alpha (vasoconstriction) and beta (contractility)
Side Effects
Additional Considerations
- Can be good option for unsure cause (eg. mixed CO/SVR)
- Downside is cannot titrate the contractility and vasoconstriction separately
Dopamine
Mechanism of Action
- Mixed alpha (vasoconstriction) and beta (contractility)
Side Effects
Additional Considerations
- Increased mortality with septic shock - only used in prehospital as they come premixed