Vasopressin: Indications and Dosing
Vasopressin should be added as a second-line vasopressor at 0.03 units/minute when norepinephrine doses reach 0.25-0.50 µg/kg/min in septic shock, administered at 40 units as a single dose for refractory cardiac arrest, and infused at 1-1.5 units/minute for acute variceal bleeding.
Septic Shock (Refractory)
When to Initiate
Add vasopressin when norepinephrine requirements exceed 0.25-0.50 µg/kg/min despite adequate fluid resuscitation 1. Recent reinforcement learning data suggests earlier initiation may be beneficial—the optimal strategy appears to be starting vasopressin at median norepinephrine doses of 0.20 µg/kg/min rather than waiting for higher doses 2.
Never use vasopressin as monotherapy for septic shock—it must always be combined with norepinephrine 1, 3.
Dosing Regimen
- Standard dose: 0.03 units/minute (fixed rate, not titrated) 1
- The FDA label indicates a range of 0.01-0.07 units/minute for septic shock 3
- Post-cardiotomy shock may require 0.03-0.1 units/minute 3
- Do not exceed 0.03-0.04 units/minute except as salvage therapy when other vasopressors fail 1
Recent evidence shows no hemodynamic advantage to using 0.04 units/min over 0.03 units/min, so stick with the guideline-recommended 0.03 units/min 4.
Clinical Considerations
Vasopressin works by causing vasoconstriction through V1 receptors and provides a "norepinephrine-sparing effect" 3, 5. Up to one-third of septic shock patients have relative vasopressin deficiency 5.
Factors predicting better response 6:
- Higher norepinephrine doses (≥0.30 µg/kg/min)
- Normal BMI (obesity reduces response)
- Lower lactate levels
- Higher pH
Factors predicting worse response 6:
- Obesity (aOR 0.30)
- Hyperlactatemia (aOR 0.86 per mmol/L increase)
- Longer duration of norepinephrine before vasopressin initiation
Weaning Strategy
When norepinephrine decreases to approximately 0.2 µg/kg/min, withdraw vasopressin in small steps according to MAP response 7. Rebound hypotension occurs in 9% of patients when vasopressin is terminated, particularly if duration was <24 hours 6.
Cardiac Arrest
Dosing for Refractory Arrest
40 units intravenously as a single dose when initial epinephrine and defibrillation fail 8, 9. This is equivalent to epinephrine 1 mg per current ACLS guidelines 8.
Evidence and Limitations
Vasopressin showed similar outcomes to epinephrine for ventricular fibrillation and pulseless electrical activity, but was superior in asystolic arrest 7. The combination of vasopressin followed by epinephrine resulted in higher rates of survival to hospital admission and discharge 7. However, do not use higher doses or other vasopressors beyond standard-dose epinephrine during CPR 8.
The 2023 AHA guidelines maintain vasopressin as an alternative to epinephrine but do not preferentially recommend it, as no definitive mortality benefit has been established 8.
Acute Variceal Bleeding
Dosing Regimen
High-dose vasopressin: 1-1.5 units/minute by continuous infusion 10. This is substantially higher than septic shock dosing.
Clinical Benefits
High-dose vasopressin for variceal hemorrhage reduces 10:
- Postoperative mortality (21% vs 6%)
- Need for emergency operation (40% vs 18%)
- Operative blood loss (1340 vs 793 mL)
The mechanism involves splanchnic vasoconstriction reducing portal pressure and variceal bleeding 11. Terlipressin (a vasopressin analogue) is also effective and may have fewer cardiac side effects 11.
Important Caveat
While high-dose vasopressin increases adverse effects, no significant morbidity occurred in the landmark study 10. However, this indication requires careful monitoring given the substantially higher doses compared to septic shock.
Critical Warnings
Contraindications 3:
- Known allergy to vasopressin or chlorobutanol
Common adverse effects 3:
- Decreased cardiac output
- Bradycardia and tachyarrhythmias
- Hyponatremia
- Ischemia (coronary, mesenteric, skin, digital)
- Can worsen cardiac function
- May cause reversible diabetes insipidus
- Can induce uterine contractions in pregnancy
Drug interactions 3:
- Additive pressor effects with catecholamines
- Indomethacin prolongs vasopressin effects
- Ganglionic blockers increase pressor response
- Drugs causing diabetes insipidus decrease pressor response
Preparation and Administration
Dilute the 20 units/mL vial with normal saline or D5W to either 0.1 units/mL or 1 unit/mL 3. Discard unused diluted solution after 18 hours at room temperature or 24 hours refrigerated 3. Always use an arterial catheter for blood pressure monitoring when vasopressors are required 1.