About the Vasopressin Infusion Calculator

This guide provides supplementary clinical information for the Vasopressin Infusion calculator. Vasopressin is an antidiuretic hormone (ADH) analog with potent vasopressor properties, primarily used in critical care settings to increase systemic vascular resistance and blood pressure in patients with vasodilatory shock, such as septic shock. This content is for educational purposes and should not replace clinical judgment or institutional protocols.

Outputs Explained

The calculator provides two primary outputs based on the selected calculation mode:

• Infusion Rate (mL/hr): When you input a desired dose (e.g., 0.03 units/min), the calculator determines the infusion pump rate in milliliters per hour required to deliver that dose accurately, based on the specified drug concentration.
• Current Dose (units/min or units/hr): When you input a current infusion rate (mL/hr), the calculator determines the exact dose of vasopressin the patient is receiving in units per minute or units per hour. This is useful for verifying dosing and during patient handoffs.

How to Use the Calculator

Follow these steps for accurate vasopressin dose and rate calculations:

1. Select Calculation Mode: Choose whether you need to find the Infusion Rate from a known dose or find the Current Dose from a known rate.
2. Enter Drug Concentration: Select from a list of standard concentrations (e.g., 20 units in 100 mL) or choose “Custom” to input the total units of vasopressin and total volume of IV fluid for non-standard preparations.
3. Input Known Value:
   • For Rate Mode: Enter the desired dose and select the appropriate dose unit (units/min or units/hr).
   • For Dose Mode: Enter the current infusion rate from the pump in mL/hr.
4. Patient Weight (Optional): Enter the patient’s weight if desired for documentation. Vasopressin dosing for shock is typically not weight-based.
5. Review Results: The tool will instantly display the calculated result, along with a summary of the inputs used. Always double-check calculations before making clinical changes.

Dosing Overview

Vasopressin dosing in adults with vasodilatory shock is standardized and aims to supplement endogenous levels.

• Indication (Septic Shock): Used as an adjunct to catecholamine vasopressors (e.g., norepinephrine) to raise mean arterial pressure (MAP) to target levels (typically ≥65 mmHg).
• Starting Dose: A common starting infusion rate is 0.01 units/minute.
• Titration: The dose is typically titrated up to a maximum of 0.03 or 0.04 units/minute. Higher doses are associated with increased risk of adverse effects (e.g., cardiac and mesenteric ischemia) without clear benefit and are generally not recommended.
• Administration: Vasopressin is a potent vasoconstrictor and must be administered via a central venous catheter to minimize the risk of severe tissue injury (extravasation).

Switching and Weaning

Vasopressin is not “switched” but rather weaned off as the patient’s hemodynamic status improves. The process is guided by clinical stability and institutional protocols. Typically, the primary catecholamine vasopressor (e.g., norepinephrine) is weaned first. Once the catecholamine dose is low or off, the vasopressin infusion is slowly tapered and discontinued to prevent rebound hypotension.

Infusion Interruption

Unlike medications with long half-lives, a continuous vasopressor infusion has an immediate effect. If the infusion is stopped or interrupted:

• The patient’s blood pressure may drop rapidly.
• Immediately assess the patient and the reason for interruption (e.g., IV line issue, empty bag).
• Correct the issue and restart the infusion as per the last prescribed rate.
• Notify the responsible clinician immediately, as a fluid bolus or adjustment of other vasopressors may be necessary.

Safety Alerts

• Extravasation Risk: Leakage of vasopressin from the vein into surrounding tissue can cause severe vasoconstriction, ischemia, and necrosis. Administer through a central line whenever possible. Monitor the infusion site closely.
• High Dose Warning: The calculator flags doses above 0.1 units/minute as a high dose. Such doses are outside the standard range for septic shock and require careful verification of the order and indication.
• Cardiovascular Effects: May cause arrhythmias, bradycardia, or cardiac ischemia. Continuous cardiac and hemodynamic monitoring is essential.
• Water Intoxication: Due to its antidiuretic effects, vasopressin can cause fluid retention and hyponatremia. Monitor fluid balance, urine output, and serum sodium levels.

Frequently Asked Questions

References

• Evans L, et al. Surviving Sepsis Campaign: International Guidelines for Management of Sepsis and Septic Shock 2021. Crit Care Med. 2021;49(11):e1063-e1143. View on NCBI
• VASOSTRICT® (vasopressin injection) Prescribing Information. Eagle Pharmaceuticals, Inc. Access via FDA.gov
• American Society of Health-System Pharmacists (ASHP). Standardize 4 Safety Initiative: Standard Drug Concentrations. View Resource
• Institute for Safe Medication Practices (ISMP). ISMP List of High-Alert Medications in Acute Care Settings. View on ISMP.org