What pressor agent should be started first in cases of shock?

Vasopressor Selection and Timing in Shock

First-Line Vasopressor Choice

Norepinephrine is the mandatory first-choice vasopressor for septic shock and should be started immediately when hypotension persists after initial fluid resuscitation. 1, 2, 3

The evidence strongly supports norepinephrine over all alternatives:

• Norepinephrine reduces mortality by 11% compared to dopamine (absolute risk reduction, number needed to treat = 9), with fewer arrhythmias and adverse events 4
• The Surviving Sepsis Campaign provides a strong recommendation with moderate quality evidence for norepinephrine as first-line therapy 1
• Dopamine should only be considered in highly selected patients with absolute or relative bradycardia and low risk of tachyarrhythmias 1, 2

When to Start Vasopressors

Start norepinephrine early—as soon as hypotension persists despite initial fluid resuscitation, rather than waiting for complete volume repletion. 5

Specific Timing Algorithm:

• Administer at least 30 mL/kg crystalloid bolus before or concurrent with norepinephrine initiation 1, 2, 6
• In severe hypotension (systolic <70 mmHg), start norepinephrine as an emergency measure while fluid resuscitation continues 6
• Early norepinephrine administration increases cardiac output, improves microcirculation, and prevents fluid overload 5
• Profound and prolonged hypotension independently increases mortality, making early vasopressor initiation critical 5

Initial Dosing and Administration

Start norepinephrine at 0.1-0.5 mcg/kg/min (approximately 7-35 mcg/min in a 70 kg adult) via central venous access when possible, targeting a mean arterial pressure (MAP) of 65 mmHg. 1, 2, 6

Administration Requirements:

• Central venous access is strongly preferred to minimize extravasation risk and tissue necrosis 2, 6
• If central access is unavailable, peripheral IV administration can be used temporarily with strict monitoring 2, 6
• Place an arterial catheter as soon as practical for continuous blood pressure monitoring 1, 2

Target Blood Pressure

Target MAP of 65 mmHg in most patients. 1, 2, 3

• Patients with chronic hypertension may require higher targets (80-85 mmHg) 2, 3
• Titrate to both MAP and markers of tissue perfusion: lactate clearance, urine output (>50 mL/h), mental status, and capillary refill 1, 3, 6

Escalation for Refractory Hypotension

When norepinephrine reaches 0.25 mcg/kg/min and hypotension persists, add vasopressin at 0.03 units/minute rather than continuing to escalate norepinephrine alone. 1, 2, 7

Escalation Algorithm:

1. Add vasopressin 0.03 units/minute (maximum 0.03-0.04 units/minute) to raise MAP or decrease norepinephrine requirements 1, 2, 7
2. Never use vasopressin as monotherapy—it must be added to norepinephrine 1, 2
3. Alternative: Add epinephrine (0.1-0.5 mcg/kg/min) if vasopressin is unavailable or additional support is needed 1, 2
4. Consider dobutamine (up to 20 mcg/kg/min) if persistent hypoperfusion exists despite adequate vasopressors, particularly with myocardial dysfunction 1, 2, 3

Vasopressin Dosing Details (FDA-Approved):

• Septic shock: Start at 0.01 units/minute 7
• Post-cardiotomy shock: Start at 0.03 units/minute 7
• Titrate up by 0.005 units/minute at 10-15 minute intervals until target blood pressure is reached 7
• Doses above 0.03-0.04 units/minute should be reserved for salvage therapy due to risk of cardiac, digital, and splanchnic ischemia 1, 2

Agents to Avoid

Do not use dopamine as first-line therapy—it is associated with higher mortality and more arrhythmias compared to norepinephrine. 1, 2, 4

• Dopamine only in highly selected patients with absolute/relative bradycardia and low arrhythmia risk 1, 2
• Never use low-dose dopamine for renal protection—strong recommendation against this practice 1, 2
• Phenylephrine is not recommended except when norepinephrine causes serious arrhythmias, cardiac output is documented high with persistent hypotension, or as salvage therapy 1, 2, 3

Critical Pitfalls to Avoid

• Do not delay norepinephrine waiting for complete volume repletion—early administration is beneficial 5
• Do not use vasopressin as the sole initial vasopressor—always combine with norepinephrine 1, 2
• Do not escalate vasopressin above 0.03-0.04 units/minute—add epinephrine instead 1, 2
• Do not use phenylephrine as first-line—it may raise blood pressure while worsening tissue perfusion 1, 2
• Avoid excessive vasoconstriction—monitor for cold extremities, decreased urine output, rising lactate, and digital ischemia 1, 2

Monitoring Requirements

Continuous arterial blood pressure monitoring is essential for all patients on vasopressors. 1, 2, 3

• Monitor blood pressure and heart rate every 5-15 minutes during initial titration 6
• Assess tissue perfusion markers: lactate, urine output, mental status, capillary refill 3, 6
• Watch for signs of excessive vasoconstriction and organ hypoperfusion 1, 2