What is the dosing formula for inotropes (inotropic agents) used in shock?

Inotropic Agents Dosing Formulas for Shock Management

The standard dosing formulas for inotropes in shock include dobutamine at 2-20 μg/kg/min, dopamine at 3-5 μg/kg/min (inotropic effect) or >5 μg/kg/min (vasopressor effect), norepinephrine at 0.2-1.0 μg/kg/min, and epinephrine at 0.05-0.5 μg/kg/min. 1

First-Line Inotropes and Vasopressors

Norepinephrine

• First-line vasopressor for most shock states, especially in hypotensive patients with adequate fluid resuscitation 1
• Dosing: 0.2-1.0 μg/kg/min IV infusion, titrated to desired blood pressure 1
• Acts on both alpha and beta receptors to provide vasoconstrictive effects while maintaining cardiac output 2

Dobutamine

• First-line inotrope for cardiogenic shock with decreased cardiac output 1
• Dosing: 2-20 μg/kg/min IV infusion without loading dose 1
• Start at 2-3 μg/kg/min and titrate according to clinical response 1
• May require higher doses (up to 20 μg/kg/min) in patients on beta-blocker therapy 1
• Primarily stimulates β1-receptors to produce dose-dependent positive inotropic and chronotropic effects 1

Dopamine

• Dosing is effect-dependent 1:
  • 2-3 μg/kg/min: Dopaminergic effects (limited renal effects)
  • 3-5 μg/kg/min: Inotropic effects (β-adrenergic)

  • 5 μg/kg/min: Vasopressor effects (α-adrenergic)

• Higher doses (>20 μg/kg/min) may cause peripheral, renal, and splanchnic vasoconstriction and ischemia 1

Second-Line Agents

Epinephrine

• Dosing: 0.05-0.5 μg/kg/min IV infusion 1
• For resuscitation: 1 mg IV bolus, repeated every 3-5 minutes as needed 1
• Reserved for persistent hypotension despite adequate cardiac filling pressures and use of other vasoactive agents 1
• For continued shock after volume resuscitation: Start at 0.1 μg/kg/min and titrate up to 1.0 μg/kg/min 1

Vasopressin

• Dosing: 0.01-0.04 units/min as a continuous infusion 3
• For septic shock: Start at 0.01 units/min and titrate up by 0.005 units/min at 10-15 minute intervals 3
• For post-cardiotomy shock: Start at 0.03 units/min 3
• Useful for its norepinephrine-sparing effects 1

Phosphodiesterase Inhibitors

• Milrinone: 25-75 μg/kg loading dose over 10-20 min, followed by 0.375-0.75 μg/kg/min infusion 1
• Enoximone: 0.5-1.0 mg/kg loading dose, followed by 5-20 μg/kg/min infusion 1

Levosimendan

• Optional loading dose: 12 μg/kg over 10 minutes (avoid in hypotensive patients) 1
• Maintenance: 0.1 μg/kg/min, which can be decreased to 0.05 or increased to 0.2 μg/kg/min 1
• Preferable over dobutamine to reverse beta-blockade effects 1
• Not suitable for patients with hypotension (SBP <85 mmHg) unless combined with other inotropes or vasopressors 1

Clinical Considerations and Monitoring

• Titrate all inotropes to the lowest effective dose to achieve adequate organ perfusion 1
• Monitor for adverse effects including tachyarrhythmias, myocardial ischemia, and peripheral tissue ischemia 1
• For extravasation of catecholamines, consider phentolamine (0.1-0.2 mg/kg up to 10 mg diluted in 10 mL of 0.9% sodium chloride) injected intradermally at the extravasation site 1
• ECG monitoring is required during inotrope infusion due to risk of arrhythmias 1
• When weaning dobutamine, gradually taper by steps of 2 μg/kg/min while optimizing oral therapy 1

Shock-Specific Considerations

Cardiogenic Shock

• First-line: Dobutamine 2-20 μg/kg/min for low cardiac output 1, 4
• If hypotensive: Add norepinephrine 0.2-1.0 μg/kg/min 4
• For beta-blocked patients: Consider levosimendan 1, 4

Septic Shock

• First-line: Norepinephrine 0.2-1.0 μg/kg/min after adequate fluid resuscitation 1, 5
• If cardiac dysfunction persists: Add dobutamine 2-20 μg/kg/min 1, 5
• Consider vasopressin (0.01-0.04 units/min) to reduce norepinephrine requirements 3

Distributive Shock

• First-line: Norepinephrine 0.2-1.0 μg/kg/min 1, 2
• If inadequate response: Consider vasopressin 0.01-0.04 units/min 2, 3

Remember that inotropes have a narrow therapeutic window and should be used cautiously, starting from low doses and titrating up with close monitoring 1. They should be viewed as temporary support while addressing the underlying cause of shock 4, 6.