About This Calculator

The Norepinephrine Infusion Calculator is a clinical support tool designed to assist healthcare professionals in accurately determining infusion rates and dosages. Norepinephrine is a potent vasopressor used in critical care settings to manage hypotension, particularly in cases of septic shock. This calculator helps streamline the administration process by converting between desired dose and infusion rate based on patient weight and drug concentration.

Outputs Explained

Based on the inputs provided, the calculator generates the following key outputs:

• Infusion Rate (mL/hr): When calculating by dose, this is the primary result, indicating the speed at which the infusion pump should be set to deliver the desired medication dose.
• Dose (mcg/kg/min or mcg/min): When calculating by rate, this output shows the actual dose the patient is receiving at the current infusion rate. This is useful for charting and clinical assessment.
• Titration Table: An optional table is generated to show a range of doses and their corresponding infusion rates centered around the calculated value. This aids in rapid dose adjustments at the bedside.

How to Use the Calculator

Follow these steps to perform a calculation:

1. Select Calculation Mode: Choose whether you want to calculate the Rate (mL/hr) from a known dose or calculate the Dose from a known rate.
2. Enter Patient Weight: Input the patient's weight and select the appropriate unit (kg or lbs). Weight is required for weight-based dosing (mcg/kg/min).
3. Select Drug Concentration: Choose from standard premixed concentrations (e.g., 4 mg in 250 mL) or select "Custom Concentration" to input the specific amount of norepinephrine (mg) and total fluid volume (mL).
4. Choose Dose Unit: Select whether the dose is weight-based (mcg/kg/min) or non-weight-based (mcg/min).
5. Input Dose or Rate: Depending on the mode selected in Step 1, enter either the desired dose or the current infusion rate.
6. Calculate: The result will be displayed instantly, along with the input parameters used for the calculation.

Dosing Overview

Norepinephrine administration requires careful titration to achieve the desired hemodynamic effect (e.g., target Mean Arterial Pressure) while minimizing adverse effects.

• Initial Dose: For adults with septic shock, a common starting dose is 0.02 to 0.05 mcg/kg/min.
• Titration: The dose is typically titrated every 3-5 minutes by increments of 0.02 to 0.05 mcg/kg/min to achieve the target blood pressure.
• Maintenance Dose: The effective dose range is wide and patient-dependent, but often falls between 0.02 and 3 mcg/kg/min.
• Concentration: Standard concentrations include 16 mcg/mL (4 mg in 250 mL) and 32 mcg/mL (8 mg in 250 mL). Higher concentrations may be used in cases of fluid restriction.

Switching and Tapering

Tapering (weaning) from norepinephrine should be done gradually once the underlying cause of shock is resolving and the patient is hemodynamically stable. Abrupt discontinuation can lead to severe rebound hypotension.

• Weaning Protocol: The infusion rate should be slowly decreased, with frequent blood pressure monitoring to ensure stability.
• Adding Other Vasopressors: In refractory shock, other agents like vasopressin or epinephrine may be added. This allows for a potential reduction in the norepinephrine dose (a "pressor-sparing" effect), which may mitigate some side effects like tachyarrhythmias.

Infusion Interruption

Since norepinephrine has a very short half-life (approximately 2-3 minutes), any interruption in the infusion will cause a rapid drop in blood pressure. It is critical to ensure the infusion line is secure, the infusion pump is functioning correctly, and a new bag is ready before the current one runs out.

Safety Alerts

• Extravasation: Norepinephrine is a potent vasoconstrictor and can cause severe tissue necrosis if it leaks out of the vein. Administration through a central venous catheter is strongly recommended. The infusion site must be monitored closely.
• Antidote for Extravasation: If extravasation occurs, the site should be infiltrated with an alpha-adrenergic blocker like phentolamine as per institutional protocol.
• Continuous Monitoring: Patients on norepinephrine require continuous monitoring of blood pressure (ideally via an arterial line), heart rate, and perfusion status.
• Volume Status: Ensure the patient is adequately fluid-resuscitated before and during norepinephrine therapy, as it is not a substitute for volume replacement.

Frequently Asked Questions

References

1. U.S. Food and Drug Administration. (2022). LEVOPHED (norepinephrine bitartrate) injection, for intravenous use Prescribing Information. Retrieved from FDA.gov
2. Evans, L., et al. (2021). Surviving Sepsis Campaign: International Guidelines for Management of Sepsis and Septic Shock 2021. Critical Care Medicine, 49(11), e1063-e1143. Retrieved from PubMed
3. Richards, J. R., & Trecartin, A. E. (2023). Norepinephrine. In StatPearls. StatPearls Publishing. Retrieved from NCBI StatPearls
4. Myburgh, J. A., & Mythen, M. G. (2013). Resuscitation fluids. The New England journal of medicine, 369(13), 1243–1251. Retrieved from NEJM.org