When to start vasopressin in a patient on norepinephrine (noradrenaline) for distributive shock?

When to Start Vasopressin in a Patient on Norepinephrine for Distributive Shock

Vasopressin should be added to norepinephrine when the norepinephrine dose reaches 0.25-0.5 μg/kg/min for more than 2-6 hours and the target mean arterial pressure (MAP) of 65 mmHg is not achieved. 1, 2

Initial Vasopressor Management

• Norepinephrine is the first-line vasopressor of choice for distributive shock, with an initial target MAP of 65 mmHg 3, 1
• Adequate fluid resuscitation should ideally precede or accompany vasopressor therapy, though vasopressors may be needed early in severe shock 3
• An arterial catheter should be placed as soon as practical for all patients requiring vasopressors 3, 1

When to Add Vasopressin

• Vasopressin should be added as a second-line agent when norepinephrine alone is insufficient to maintain the target MAP 1, 4
• The most common trigger for adding vasopressin is a norepinephrine dose of 0.25-0.5 μg/kg/min for more than 2-6 hours 2
• Vasopressin should not be used as the single initial vasopressor for treatment of distributive shock 3, 5

Vasopressin Dosing Protocol

• The recommended dose of vasopressin is 0.01-0.03 units/minute when added to norepinephrine 5, 4
• The maximum recommended dose is 0.03-0.04 units/minute for standard therapy 3, 5
• Higher doses (>0.04 units/minute) should be reserved for salvage therapy when other vasopressors have failed to achieve target MAP 3, 4

Benefits of Adding Vasopressin

• Adding vasopressin can help achieve target MAP or decrease norepinephrine dosage 3, 1
• Vasopressin may reduce the incidence of supraventricular arrhythmias compared to high doses of norepinephrine alone 4
• Vasopressin may reduce the need for renal replacement therapy compared to escalating norepinephrine doses 6

Pharmacology and Mechanism

• Vasopressin causes vasoconstriction by binding to V1 receptors on vascular smooth muscle 7
• Vasopressin is relatively deficient during sepsis, making exogenous administration physiologically rational 8, 9
• Vasopressin acts on different vascular receptors than norepinephrine (α1-adrenergic), providing a complementary mechanism of action 7, 8

Monitoring and Discontinuation

• Continuous arterial blood pressure monitoring is essential for patients receiving vasopressors 1, 4
• Vasopressin should be tapered when the target MAP is achieved and maintained 4, 2
• Discontinuation should be progressive rather than abrupt, typically after the norepinephrine dose has been lowered below a predefined threshold 2

Cautions and Contraindications

• Monitor for potential adverse effects including digital or skin ischemia and non-occlusive mesenteric ischemia 2
• The pressor effect of vasopressin reaches its peak within 15 minutes and fades within 20 minutes after stopping the infusion 7
• Push-dose vasopressin (1 unit IV bolus) may be considered for transient hypotension while preparing continuous infusions, though this is not standard practice 10