MICU intern's survival guide vasopressors
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-In-Chief: Priyamvada Singh, M.D. [2]
Overview
Shock is a common condition that interns have to encounter in the MICU. Some important ideas to keep in mind while managing shock are: determine the type of shock as the treatment is different for different shocks, norepinephrine can be used as a first line vasopressor in any shock and fluid resuscitation is an important first line management in all type of shocks except cardiogenic shock.
Norepinephrine
Mechanism of action
Acts on both alpha1 (vasoconstriction of blood vessels) and beta1 receptors (increases cardiac output).
Indications
- Septic shock
- Cardiogenic shock - Recent studies have shown that norepinephrine may be better than dopamine in cardiogenic shock due to a decreased risk of tachyarrhythmias.
- In cases where the type of shock is unclear, norepinephrine can be tried as a first line agent.
Doses
- 1-30 mcg/min.
Dopamine
Mechanism of action
- Acts on alpha1 (vasoconstriction of blood vessels), beta1 (increases cardiac output) and dopamine receptors (scattered throughout the body).
- Its action is dose dependent. At low doses it predominantly acts on cardiac receptors (1-10 mcg/min) with less vasoconstriction activities. At higher doses it has both vasoconstriction and cardiac activities.
Indications
- Cardiogenic shock
- Septic shock - second line treatment for septic shock
Side-effects
- Arrhythmogenic. Avoid in patients prone to arrhythmias.
- Doses
- 1-20 mcg/min.
Vasopressin
Mechanism of action
- Acts by stimulating V1 (vasopressin) receptors in vascular and GI smooth muscles causing contraction. It also has anti-diuretics effect.
Indications
- Septic shock - second line treatment for septic shock
Side-effects
- Coronary and splanchnic vasoconstriction. Avoid in NSTEMI (can use in mild troponin leaks but avoid if Trops high 5-10) and gut ischemia.
Doses
- .03units/min (only vasopressor which is not titrated).
Phenylephrine
Mechanism of action
- Acts only on alpha1 receptors (vasoconstriction). No action on cardiac receptors and is cardiac neutral.
Indications
- Used in neurogenic shock
- Third or fourth line vasopressor in septic shock (refractory to norepinephrine, dopamine, and vasopressin).
Side-effects
- Can cause reflex bradycardia but not tachycardia.
Doses
- 20-300 mcg/min
Dobutamine
Mechanism of action
- Acts on Beta1 (increases cardiac output) and Beta2 receptor (vasodilatation). Thus, it increases cardiac output but increases the risks for hypotension too.
Indications
- Cardiogenic shock
- Low output septic shock.
Side-effects
- Tachyarrhythmias (B1 effect)
- Hypotension (B2 effect)
- In cases of hypotension with dobutamine add another vasopressor with alpha effects (norepinephrine or dopamine) with dobutamine.
Doses
- 2.5 to 20mcg/kg/min (usually titrated by doctors and not ICU nurses)