In adult patients requiring pharmacologic support of arterial pressure, which vasopressor is first‑line for septic shock, cardiogenic shock, anaphylactic shock, neurogenic (spinal) shock, and postoperative/distributive hypotension, and what are the recommended dosing ranges for each?

Vasopressor Selection by Shock Type

Septic Shock

Norepinephrine is the mandatory first-line vasopressor for septic shock, started immediately when hypotension persists after initial fluid resuscitation (minimum 30 mL/kg crystalloid), targeting MAP ≥65 mmHg. 1

Initial Management

• Begin norepinephrine at 0.02–0.05 µg/kg/min via central venous access (or large peripheral vein if central access delayed) 1
• Administer at least 30 mL/kg crystalloid within the first 3 hours before or concurrent with vasopressor initiation 1
• Place an arterial catheter for continuous blood pressure monitoring as soon as practical 1
• Target MAP ≥65 mmHg for most patients; consider 70–85 mmHg in patients with chronic hypertension to reduce need for renal replacement therapy 1

Escalation Protocol for Refractory Hypotension

When norepinephrine reaches 0.1–0.25 µg/kg/min and MAP remains <65 mmHg:

1. Add vasopressin at fixed dose of 0.03 units/min (never as monotherapy; do not exceed 0.03–0.04 units/min except as salvage) 1, 2
2. If still inadequate, add epinephrine starting at 0.05 µg/kg/min, titrating up to 0.3 µg/kg/min 1
3. For persistent hypoperfusion despite adequate MAP, add dobutamine 2.5–20 µg/kg/min when myocardial dysfunction is evident 1
4. For refractory shock after ≥4 hours of high-dose vasopressors, consider hydrocortisone 200 mg/day IV 1

Agents to Avoid in Septic Shock

• Dopamine is strongly contraindicated (Grade 1A): associated with 11% absolute increase in mortality and significantly more arrhythmias (ventricular arrhythmias RR 0.35; 95% CI 0.19–0.66) 1
• Low-dose dopamine for renal protection is strongly discouraged (Grade 1A) 1
• Phenylephrine is not recommended except in three specific situations: (1) norepinephrine-induced serious arrhythmias, (2) documented high cardiac output with persistent hypotension, or (3) salvage therapy when all other agents have failed 1

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Cardiogenic Shock

Norepinephrine is the reasonable first-line vasopressor for cardiogenic shock when blood pressure restoration is needed, due to lower risk of adverse events compared to other catecholamine vasopressors. 3, 4, 5

Initial Strategy

• Start norepinephrine at 0.02–0.05 µg/kg/min, titrating to MAP ≥65 mmHg 1
• Norepinephrine increases MAP through vasoconstriction while maintaining or improving cardiac output via modest β₁-adrenergic cardiac stimulation 1
• Perform bedside echocardiography to distinguish vasodilatory shock (high CO, low SVR) from cardiogenic shock (low CO, high SVR), which require opposite therapeutic strategies 1

When Perfusion Remains Inadequate Despite Adequate MAP

Add dobutamine 2.5–20 µg/kg/min when MAP is adequate but signs of tissue hypoperfusion persist (elevated lactate, low urine output, altered mental status), particularly with myocardial dysfunction 1, 3, 4

Alternative Vasopressor Considerations

• Vasopressin 0.03 units/min may be added to norepinephrine in post-cardiotomy shock or when norepinephrine alone fails to maintain adequate MAP 1, 2
• In right ventricular failure with pulmonary hypertension, vasopressin may be advocated because it maintains cardiac output while selectively increasing diastolic pressure, preventing RV ischemia 1, 5

Agents to Avoid

• Epinephrine may be inferior to norepinephrine in cardiogenic shock, particularly after myocardial infarction, based on recent RCT and meta-analysis data 4, 5
• Phenylephrine should be avoided because it can lower cardiac output through reflex bradycardia and increased afterload 1

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Anaphylactic Shock

Epinephrine is the first-line agent for anaphylactic shock, administered as intramuscular boluses (0.3–0.5 mg IM every 5–15 minutes) for initial treatment. [General Medicine Knowledge]

Refractory Anaphylaxis Requiring Infusion

• If IM epinephrine fails and continuous vasopressor support is needed, epinephrine infusion 0.05–2 µg/kg/min can be used 1
• Norepinephrine may be considered as an alternative if epinephrine causes excessive tachycardia or arrhythmias [General Medicine Knowledge]

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Neurogenic (Spinal) Shock

Norepinephrine is the preferred first-line vasopressor for neurogenic shock because it provides both vasoconstriction and modest cardiac stimulation to counteract the loss of sympathetic tone. [General Medicine Knowledge, 1]

Dosing and Targets

• Start norepinephrine at 0.02–0.05 µg/kg/min, targeting MAP ≥85–90 mmHg (higher than septic shock) to maintain spinal cord perfusion in acute spinal cord injury [General Medicine Knowledge]
• Continuous arterial blood pressure monitoring is essential 1

Alternative Considerations

• Dopamine may be considered in neurogenic shock with bradycardia, as this is one of the few scenarios where dopamine's chronotropic effect may be beneficial 1
• However, dopamine carries higher arrhythmia risk and should be used cautiously 1

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Postoperative/Distributive Hypotension

Norepinephrine is the first-line vasopressor for postoperative distributive hypotension, started after ensuring adequate volume resuscitation. 1

Initial Approach

• Verify adequate intravascular volume with dynamic variables (pulse-pressure variation, stroke-volume variation) or passive leg raise test 1
• Start norepinephrine at 0.02–0.05 µg/kg/min, targeting MAP ≥65 mmHg 1
• Place arterial catheter for continuous monitoring 1

Escalation for Refractory Hypotension

• Add vasopressin 0.03 units/min when norepinephrine reaches 0.1–0.25 µg/kg/min and MAP remains inadequate 1, 2
• Phenylephrine may be used as push-dose rescue (100 µg aliquots) for brief episodes of profound hypotension, though it is not recommended for continuous infusion 1, 6

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Critical Monitoring Parameters (All Shock Types)

Beyond MAP—Tissue Perfusion Markers

• Lactate clearance: obtain baseline and repeat within 6 hours if elevated; aim for normalization 1
• Urine output: maintain ≥0.5 mL/kg/h 1
• Mental status, skin perfusion, and capillary refill: assess regularly 1
• Cardiac output measurement is recommended when pure vasopressors (vasopressin or phenylephrine) are used to verify adequate flow 1

Vasopressor Safety Limits

• Vasopressin must not exceed 0.03–0.04 units/min (except salvage therapy); higher doses cause cardiac, digital, and splanchnic ischemia 1, 2
• Norepinephrine doses above 15 µg/min (approximately 0.2 µg/kg/min in a 70 kg patient) indicate severe shock and warrant addition of second-line agents rather than further escalation 1

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Common Pitfalls to Avoid

• Do not delay norepinephrine while pursuing excessive fluid resuscitation in profound hypotension; early vasopressor use is appropriate when diastolic blood pressure is critically low 1
• Do not focus solely on MAP; incorporate tissue-perfusion markers (lactate, urine output, mental status) into decision-making 1
• Do not use dopamine as first-line therapy in any shock state except highly selected patients with bradycardia and low arrhythmia risk 1
• Do not combine dopamine with norepinephrine or epinephrine due to excessive sympathomimetic stimulation and increased adverse events 1
• Do not use phenylephrine as continuous first-line therapy; it may raise blood pressure while worsening tissue perfusion 1