How should vasopressin be dosed (infusion rate, weight‑based dosing for children, and bolus exceptions) for an adult with vasodilatory or septic shock and for a pediatric patient?

Vasopressin Dosing in Septic and Vasodilatory Shock

Adult Dosing

For adults with septic or vasodilatory shock, vasopressin should be added to norepinephrine at a fixed dose of 0.03 units/minute when norepinephrine alone fails to maintain MAP ≥65 mmHg despite adequate fluid resuscitation (minimum 30 mL/kg crystalloid). 1, 2

Specific Dosing Parameters

• Starting dose: 0.01 units/minute, titrated upward by 0.005 units/minute every 10–15 minutes 1
• Standard maintenance dose: 0.03 units/minute (fixed, not titrated) 3, 1, 2
• Maximum dose: 0.03–0.04 units/minute for routine use; higher doses reserved only for salvage therapy when all other vasopressors have failed 3, 1, 2
• FDA-approved range: 0.01–0.07 units/minute for septic shock; 0.03–0.1 units/minute for post-cardiotomy shock 2

Critical Administration Requirements

• Never use vasopressin as monotherapy—it must always be added to norepinephrine, not used alone 3, 1, 4
• Administer via central venous access with continuous arterial blood pressure monitoring 1, 4
• Target MAP ≥65 mmHg (or 70–85 mmHg in patients with chronic hypertension) 1

Escalation Algorithm

1. First-line: Norepinephrine 0.05–0.1 µg/kg/min after 30 mL/kg crystalloid bolus, targeting MAP ≥65 mmHg 1
2. Second-line: Add vasopressin 0.03 units/minute when norepinephrine reaches 0.1–0.25 µg/kg/min and MAP remains <65 mmHg 1, 4
3. Third-line: Add epinephrine 0.05–0.3 µg/kg/min if MAP target not achieved with norepinephrine plus vasopressin 1, 5
4. Inotropic support: Add dobutamine 2.5–20 µg/kg/min if MAP is adequate but tissue hypoperfusion persists (elevated lactate, low urine output, altered mental status) 1, 5

Pediatric Dosing

Pediatric vasopressin dosing differs fundamentally from adults because children with fluid-refractory septic shock predominantly have low cardiac output, unlike the high-output/low-resistance pattern typical in adults. 3

Pediatric-Specific Considerations

• Vasopressin may be used to counteract hypotension caused by phosphodiesterase inhibitors (milrinone, inamrinone) when excessive vasodilation occurs 3
• No weight-based pediatric dosing is established in guidelines; the 2007 American College of Critical Care Medicine pediatric septic shock guidelines mention vasopressin only as a rescue agent for hypotension-related toxicity from other medications 3
• Dopamine-resistant shock in children commonly responds to norepinephrine or high-dose epinephrine rather than vasopressin 3

Pediatric Vasopressor Hierarchy

• First-line: Dopamine for fluid-refractory hypotensive shock with low SVR (though norepinephrine increasingly preferred) 3
• Second-line: Norepinephrine or epinephrine for dopamine-resistant shock 3
• Inotropic support: Milrinone or inamrinone for low cardiac output/high SVR states (common in pediatric septic shock) 3
• Vasopressin role: Rescue therapy for refractory hypotension, particularly when phosphodiesterase inhibitors cause excessive vasodilation 3

Critical Safety Limits

Exceeding 0.03–0.04 units/minute causes cardiac, digital, and splanchnic ischemia without additional hemodynamic benefit. 3, 1, 2

Dose-Related Toxicity

• Vasopressin follows a sigmoidal dose-response curve; beyond the therapeutic plateau, further escalation produces pathologic vasoconstriction that impairs tissue perfusion 1
• Doses >0.04 units/minute are associated with myocardial ischemia, digital necrosis, mesenteric ischemia, and potential cardiac arrest 2, 6, 7
• The VASST trial demonstrated that patients requiring ≥15 µg/min norepinephrine had significantly elevated mortality; vasopressin should be added at lower norepinephrine thresholds (0.1–0.25 µg/kg/min) rather than escalated beyond safe limits 1

Monitoring Requirements

• Hemodynamic: Continuous arterial blood pressure via arterial catheter 1, 4
• Tissue perfusion: Lactate clearance every 2–4 hours, urine output ≥0.5 mL/kg/h, mental status, capillary refill, skin temperature 1, 4
• Adverse effects: Digital ischemia, decreased urine output despite adequate MAP, rising lactate, cardiac arrhythmias, hyponatremia 1, 2, 6

Common Pitfalls

• Do not titrate vasopressin like other vasopressors—use a fixed dose of 0.03 units/minute 3, 1, 8
• Do not delay norepinephrine initiation while pursuing aggressive fluid resuscitation if life-threatening hypotension (systolic BP <80 mmHg) is present 1, 4
• Do not use dopamine for renal protection—this is strongly contraindicated (Grade 1A recommendation) 1, 4
• Do not use phenylephrine as first-line therapy—it may raise blood pressure while worsening tissue perfusion 1
• Do not withdraw vasopressin before weaning norepinephrine—maintain vasopressin at 0.03 units/minute while gradually reducing norepinephrine by 0.01–0.02 µg/kg/min every 15–30 minutes 4