In adult ICU patients with hypotension or shock, which vasopressor(s) should be selected for septic/vasodilatory shock, cardiogenic shock, anaphylactic shock, and refractory shock, taking into account heart rate, cardiac output, and arrhythmia profile?

Vasopressor Selection by Shock Type in Adult ICU Patients

Septic/Vasodilatory Shock

Norepinephrine is the mandatory first-line vasopressor for septic shock, initiated immediately when MAP <65 mmHg persists after administering at least 30 mL/kg crystalloid within the first 3 hours. 1

Initial Management

• Start norepinephrine at 0.02–0.05 µg/kg/min via central venous access (peripheral acceptable while awaiting central line) and titrate to MAP ≥65 mmHg 1, 2
• Place an arterial catheter as soon as practical for continuous blood pressure monitoring 3, 1
• Target MAP of 65 mmHg for most patients; increase to 70–75 mmHg in chronic hypertensives 1, 2

Escalation Protocol for Refractory Hypotension

• Add vasopressin 0.03 units/min (fixed dose, not titrated) when norepinephrine reaches 0.1–0.2 µg/kg/min without achieving target MAP 1, 2
• Vasopressin should never be used as monotherapy—only as adjunct to norepinephrine 1
• Do not exceed vasopressin 0.03–0.04 units/min except as salvage therapy; higher doses cause cardiac, digital, and splanchnic ischemia 3, 1

Third-Line Options

• Add epinephrine (0.05–2 µg/kg/min) if MAP remains inadequate despite norepinephrine plus vasopressin, particularly when myocardial dysfunction is present 1, 2
• Add dobutamine (2.5–20 µg/kg/min) when MAP is adequate but persistent hypoperfusion exists (elevated lactate, low ScvO₂ <70%, oliguria), especially with documented low cardiac output 3, 1

Agents to Avoid

• Dopamine is strongly contraindicated as first-line therapy—it increases mortality by 11% absolute risk and causes significantly more arrhythmias compared to norepinephrine 1
• Never use low-dose dopamine for renal protection (Grade 1A recommendation against) 3, 1
• Phenylephrine should be avoided except in three narrow circumstances: (1) norepinephrine-induced serious arrhythmias, (2) documented high cardiac output with persistent hypotension, or (3) salvage therapy when all other agents have failed 1, 4

Special Consideration: Tachycardia

• In septic shock patients with tachycardia, norepinephrine remains the first-choice vasopressor because it causes less tachycardia than dopamine or epinephrine 4
• Phenylephrine is not recommended even in tachycardic patients unless norepinephrine causes serious arrhythmias 4

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Cardiogenic Shock

Norepinephrine is the appropriate first-line vasopressor for cardiogenic shock when hypotension persists despite adequate preload, targeting MAP ≥65 mmHg. 5, 6

Initial Strategy

• Start norepinephrine at 0.1–0.5 µg/kg/min via central access, titrating to MAP ≥65 mmHg 1
• Norepinephrine increases MAP through vasoconstriction while maintaining cardiac output via modest β₁-adrenergic stimulation 3, 5

Inotropic Support

• Add dobutamine (2.5–10 µg/kg/min) when evidence of low cardiac output persists despite adequate MAP and filling pressures 3, 2
• Dobutamine is the first-choice inotrope for measured or suspected low cardiac output with adequate left ventricular filling pressure 3
• Monitor for increased myocardial oxygen demand and arrhythmias when combining dobutamine with high-dose catecholamines 1

Alternative Inotropes

• Low-dose epinephrine or dopamine may be used for inotropic support, but high doses carry excessive risk of adverse events 5
• Epinephrine increases myocardial oxygen consumption more than norepinephrine, making it less safe in patients with potential cardiac ischemia 1

Critical Pitfall

• In cardiogenic shock with preexisting heart failure, norepinephrine may increase myocardial oxygen requirements but this does not contraindicate its use 1
• Continue chronic beta-blockers unless acute hemodynamic decompensation or signs of low cardiac output are present 1

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Anaphylactic Shock

Epinephrine is the definitive treatment for anaphylactic shock, not norepinephrine, though norepinephrine may be added for refractory hypotension after epinephrine. 7

Primary Management

• Administer epinephrine as the first-line agent for anaphylaxis-induced vasodilatory shock 7
• If hypotension persists after epinephrine and fluid resuscitation, norepinephrine may be added as a vasopressor 7

Escalation

• Follow the same escalation protocol as septic shock if refractory hypotension develops: add vasopressin 0.03 units/min to norepinephrine 1

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Refractory Shock (All Types)

When norepinephrine plus vasopressin fail to achieve target MAP, add epinephrine as the third vasopressor or consider angiotensin II for rapid rescue in profound hypotension. 1, 8

Third-Line Vasopressor Options

• Epinephrine (0.05–2 µg/kg/min) is the preferred third agent when norepinephrine plus vasopressin are inadequate 1, 2
• Angiotensin II may be administered for rapid resuscitation in profoundly hypotensive patients unresponsive to standard catecholamine vasopressors, particularly in vasoplegic shock 1, 8

Adjunctive Therapies

• Hydrocortisone 200 mg/day IV for shock reversal if hypotension remains refractory to vasopressors after at least 4 hours of high-dose therapy 3, 1
• Consider adding dobutamine (up to 20 µg/kg/min) if persistent hypoperfusion exists despite adequate MAP, particularly when myocardial dysfunction is evident 3, 1

Monitoring Beyond MAP

• MAP ≥65 mmHg alone is insufficient—assess tissue perfusion using lactate clearance (repeat within 6 hours if elevated), urine output ≥0.5 mL/kg/h, mental status, skin perfusion, and capillary refill 3, 1

Critical Pitfall: Excessive Vasopressin

• Patients receiving norepinephrine ≥15 µg/min already have severe shock and should receive additional vasopressin, but never exceed vasopressin 0.03–0.04 units/min 1
• Doses above 0.03–0.04 units/min are associated with cardiac, digital, and splanchnic ischemia 3, 1

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Heart Rate and Arrhythmia Considerations Across All Shock Types

Bradycardia

• Dopamine may be considered only in highly selected patients with absolute or relative bradycardia and low risk of tachyarrhythmias 3, 1
• This is the only acceptable indication for dopamine in modern critical care 1

Tachycardia and Arrhythmias

• Norepinephrine causes significantly fewer arrhythmias than dopamine (53% risk reduction for supraventricular arrhythmias, 65% for ventricular arrhythmias) 1
• Epinephrine increases the risk of serious cardiac arrhythmias, particularly when combined with norepinephrine due to additive sympathomimetic effects 1
• If norepinephrine causes serious arrhythmias, phenylephrine may be substituted as a pure α-agonist 1, 4

Cardiac Output Monitoring

• When cardiac output is documented to be high but blood pressure remains low, phenylephrine may be considered as it provides pure vasoconstriction without inotropic effects 1, 4
• Cardiac output measurement is desirable when pure vasopressors (vasopressin, phenylephrine) are instituted to ensure adequate flow is maintained 3