When to use inotropes (inotropic agents) versus vasopressors (vasoconstrictor agents) in critical care situations?

When to Use Inotropes vs Vasopressors in Critical Care

Use vasopressors first when hypotension (MAP <65 mmHg) persists despite adequate fluid resuscitation; add inotropes only when signs of tissue hypoperfusion persist despite adequate MAP and there is evidence of low cardiac output or myocardial dysfunction. 1, 2

Initial Approach: Vasopressors for Hypotension

Vasopressors are indicated when adequate fluid resuscitation fails to maintain MAP ≥65 mmHg. 1, 2 The fundamental principle is that adequate fluid resuscitation should ideally be achieved before vasopressors are used, though early vasopressor use as an emergency measure is frequently necessary in severe shock, particularly when diastolic blood pressure is critically low. 1

First-Line Vasopressor Choice

• Norepinephrine is the first-choice vasopressor for all types of shock (septic, cardiogenic, neurogenic) when fluid resuscitation fails to maintain adequate blood pressure. 1, 2, 3
• Target MAP of 65 mmHg initially, though this should be adjusted higher in patients with pre-existing hypertension or atherosclerosis. 1, 2
• Early vasopressor use reduces the incidence of organ failure. 1, 2
• All patients requiring vasopressors should have an arterial catheter placed as soon as practical for continuous monitoring. 1, 2, 3

Second-Line Vasopressor Options

If norepinephrine alone fails to achieve target MAP:

• Add vasopressin (0.01-0.04 U/min) to raise MAP or decrease norepinephrine requirements. 1, 3
• Add or substitute epinephrine when additional agent is needed. 1, 3, 4
• Dopamine should only be used as an alternative in highly selected patients with low risk of tachyarrhythmias and absolute or relative bradycardia. 1, 3

When to Add Inotropes

Inotropes are indicated when signs of tissue hypoperfusion persist despite adequate fluid resuscitation AND adequate MAP from vasopressor therapy. 1, 2 This is a critical distinction—do not use inotropes to treat hypotension alone.

Specific Indications for Inotropic Support

• Evidence of myocardial dysfunction with elevated cardiac filling pressures and low cardiac output. 1, 2, 3
• Mixed venous oxygen saturation (SvO₂) <70% despite adequate MAP and fluid resuscitation. 1
• Persistent signs of hypoperfusion: elevated lactate, poor skin perfusion, decreased mental status, or oliguria despite adequate blood pressure. 1
• Approximately 20% of adults with sepsis develop cardiac failure characterized by persistently low cardiac index despite adequate volume expansion. 1

First-Line Inotrope Choice

• Dobutamine (up to 20 μg/kg/min) is the first-choice inotrope for patients with measured or suspected low cardiac output in the presence of adequate left ventricular filling pressure and adequate MAP. 1, 2, 5
• The combination of dobutamine and norepinephrine stimulates both α1 and β2 adrenergic receptors and is recommended as first-line treatment for patients with low cardiac output and hypotension. 1, 3
• Titrate inotrope therapy to targeted responses: improvements in SvO₂, myocardial function indices, and reduction in lactate levels. 1, 3

Alternative Inotrope Options

• Milrinone may cause less tachycardia than dobutamine and can be considered in patients with cardiogenic shock, particularly those on beta-blockers. 6, 7
• Low-dose epinephrine or dopamine may be used for inotropic support, but high doses carry excessive risk of adverse events. 8

Critical Pitfalls to Avoid

• Never use vasopressors as a substitute for adequate fluid resuscitation in hypovolemic states. 2, 6
• Do not target supranormal cardiac index levels—this strategy is not recommended and may be harmful. 1, 2
• Routine use of inotropes is not recommended—indication cannot be based on isolated cardiac output measurement alone. 1
• Avoid phenylephrine as first-line therapy—it should be reserved only for specific circumstances such as when norepinephrine causes serious arrhythmias or as salvage therapy. 1, 3

Monitoring Requirements

• Supplement blood pressure endpoints with assessment of regional and global perfusion: blood lactate concentrations, skin perfusion, mental status, and urine output. 1
• When using pure vasopressors, cardiac output measurement targeting maintenance of normal or elevated flow is desirable. 1
• Continuously monitor ECG, blood pressure, oxygen saturation, urine output, arterial blood gases, and serum lactate. 6

Shock-Specific Considerations

Septic Shock

• Norepinephrine first-line for hypotension. 1
• Add dobutamine if myocardial depression with persistent hypoperfusion despite adequate MAP. 1

Cardiogenic Shock

• Norepinephrine for hypotension after rapid volume assessment. 6
• Dobutamine (2.5-10 μg/kg/min) for low cardiac output with ventricular dysfunction. 6
• Consider milrinone as alternative inotrope if tachycardia is problematic. 6, 7

Neurogenic Shock

• Norepinephrine is first-choice vasopressor. 3
• Add dobutamine when signs of hypoperfusion persist despite adequate MAP and fluid resuscitation. 3