How to mix vasopressin to achieve an infusion rate of 0.03 units (U) per minute (min)?

Vasopressin Preparation for 0.03 U/min Infusion

To prepare vasopressin for an infusion rate of 0.03 U/min, dilute vasopressin injection (20 units/mL) in normal saline (0.9% sodium chloride) or 5% dextrose in water (D5W) to achieve the target concentration. 1

Standard Preparation Method

The FDA-approved vasopressin preparation instructions recommend:

1. Start with vasopressin injection solution (20 units/mL)
2. Dilute in either:
   • Normal saline (0.9% sodium chloride) OR
   • 5% dextrose in water (D5W)
3. Common dilution methods:
   • Add 100 units (5 mL of 20 units/mL) to 100 mL of diluent = 1 unit/mL
   • Add 100 units (5 mL of 20 units/mL) to 250 mL of diluent = 0.4 units/mL

Infusion Rate Calculation

For a target dose of 0.03 U/min:

• If using 1 unit/mL concentration:

  • Infusion rate = 0.03 U/min × 60 min/hr = 1.8 mL/hr

• If using 0.4 units/mL concentration:

  • Infusion rate = 0.03 U/min × 60 min/hr ÷ 0.4 units/mL = 4.5 mL/hr

Important Clinical Considerations

• Vasopressin is recommended as an adjunct to norepinephrine in shock, not as a first-line agent 2
• The maximum recommended dose is 0.03 U/min (fixed dose) for septic shock 2, 1
• Discard unused diluted solution after 18 hours at room temperature or 24 hours under refrigeration 1
• Inspect for particulate matter and discoloration prior to use 1

Monitoring and Titration

When administering vasopressin:

• Establish arterial line monitoring before starting the infusion 2
• Monitor for hemodynamic response (target MAP ≥65 mmHg) 2
• Monitor for adverse effects, which may include:
  • Decreased cardiac output
  • Cardiac arrhythmias
  • Digital or mesenteric ischemia 3

Common Pitfalls to Avoid

• Using doses higher than 0.04 U/min has not shown increased effectiveness and may be associated with higher adverse effects, including cardiac arrest 4
• Recent evidence suggests no significant difference in hemodynamic response between 0.03 U/min and 0.04 U/min dosing 5
• Failure to monitor urine output, which typically increases with vasopressin administration 4, 6
• Not titrating down vasopressor support once target blood pressure is achieved and maintained 1