Vasopressin Infusion Rate Calculation
To deliver 0.03 units/min with vasopressin 20 units in 50 mL normal saline, set the infusion rate at 4.5 mL/hour.
Calculation Method
The concentration of your prepared solution is:
- 20 units ÷ 50 mL = 0.4 units/mL
To achieve 0.03 units/min:
- (0.03 units/min ÷ 0.4 units/mL) × 60 min/hour = 4.5 mL/hour
Clinical Context for Vasopressin Dosing
Standard vasopressin dosing for vasodilatory shock is 0.03 units/min (range 0.01-0.03 units/min), which should not be exceeded except in salvage situations 1, 2.
When to Use This Dose
Add vasopressin at 0.03 units/min when norepinephrine reaches 0.25 mcg/kg/min and hypotension persists, rather than continuing to escalate norepinephrine alone 2.
Vasopressin should be used as an adjunct to norepinephrine, not as monotherapy, in patients requiring vasopressor support to maintain MAP ≥65 mmHg despite adequate fluid resuscitation (minimum 30 mL/kg crystalloid bolus) 1, 2.
For anaphylaxis refractory to epinephrine and fluid resuscitation, the dose range is 0.01-0.04 units/min 1.
Critical Dosing Limitations
Never escalate vasopressin beyond 0.03-0.04 units/min, as higher doses cause cardiac, digital, and splanchnic ischemia without additional hemodynamic benefit 2. The 0.03 units/min dose provides catecholamine-independent vasoconstriction through V1a receptors, complementing norepinephrine's adrenergic effects 2.
Administration Requirements
Central venous access is strongly preferred for vasopressin administration, with peripheral IV as a temporary alternative if central access is unavailable 1.
Place an arterial catheter as soon as practical for continuous blood pressure monitoring 2.
Monitor blood pressure and heart rate every 5-15 minutes during initial titration 2.
Monitoring for Adverse Effects
Watch for signs of excessive vasoconstriction:
- Cold extremities and decreased urine output 2
- Rising lactate levels 2
- Digital or extremity ischemia 3
- Myocardial ischemia 3
Alternative Concentration
If you need to prepare a different concentration, the American College of Cardiology recommends 25 units in 250 mL of D5W or normal saline (0.1 units/mL), which would require 18 mL/hour to deliver 0.03 units/min 1.