Converting Norepinephrine from mcg/kg/min to mL/hour
To convert norepinephrine from mcg/kg/min to mL/hour, use this formula: mL/hour = (dose in mcg/kg/min × patient weight in kg × 60 min/hour) ÷ concentration in mcg/mL.
Standard Concentration Preparation
The most commonly used concentration is 16 mcg/mL, prepared by adding 4 mg of norepinephrine to 250 mL of D5W 1. This is the standard adult concentration recommended by guidelines.
An alternative concentration of 10 mcg/mL can be prepared by adding 1 mg of norepinephrine to 100 mL of saline, which is sometimes used in anaphylaxis scenarios 2, 1.
Step-by-Step Conversion Process
Step 1: Determine Your Variables
- Ordered dose: The prescribed dose in mcg/kg/min
- Patient weight: In kilograms
- Concentration: In mcg/mL (typically 16 mcg/mL for standard preparation)
Step 2: Apply the Formula
mL/hour = (mcg/kg/min × kg × 60) ÷ mcg/mL
Step 3: Practical Examples
Example 1 - Standard concentration (16 mcg/mL):
- Ordered dose: 0.1 mcg/kg/min
- Patient weight: 70 kg
- Calculation: (0.1 × 70 × 60) ÷ 16 = 26.25 mL/hour
Example 2 - Alternative concentration (10 mcg/mL):
- Ordered dose: 0.1 mcg/kg/min
- Patient weight: 70 kg
- Calculation: (0.1 × 70 × 60) ÷ 10 = 42 mL/hour
Typical Dosing Ranges
The usual starting dose for norepinephrine is 0.1-0.5 mcg/kg/min, with titration up to 2 mcg/kg/min in most cases 1. However, doses as high as 5 mcg/kg/min may occasionally be necessary in refractory shock 2.
For the standard 16 mcg/mL concentration in a 70 kg patient:
- 0.1 mcg/kg/min = 26 mL/hour
- 0.5 mcg/kg/min = 131 mL/hour
- 1.0 mcg/kg/min = 263 mL/hour
- 2.0 mcg/kg/min = 525 mL/hour
Critical Considerations for Obese Patients
Use actual body weight for dosing calculations, but be aware that obese patients (BMI ≥30) require lower weight-based doses than non-obese patients to achieve the same blood pressure response 3. The non-weight-based absolute dose (in mcg/min or mg/hour) is similar between obese and non-obese patients 3, 4.
Weight-based dosing in obese patients may lead to higher cumulative doses and prolonged infusion duration without improving time to goal MAP 4. Consider using ideal body weight or a dosing cap in severely obese patients to avoid excessive dosing.
Pediatric Conversions
For pediatric patients, the "Rule of 6" provides a simplified approach: multiply 0.6 × body weight (kg) to get the number of milligrams, then dilute to 100 mL of saline. With this preparation, 1 mL/hour delivers 0.1 mcg/kg/min 2, 1.
Standard pediatric dosing ranges from 0.1-1.0 mcg/kg/min, starting at the lowest dose and titrating to effect 2, 1.
Common Pitfalls to Avoid
Concentration errors: Always verify whether your preparation is 16 mcg/mL (4 mg in 250 mL) or 10 mcg/mL (1 mg in 100 mL), as this dramatically changes the infusion rate 2, 1.
Unit confusion: Ensure you're working in consistent units (mcg vs mg, minutes vs hours) throughout the calculation.
Extravasation risk: Regardless of the calculated rate, always use central venous access when possible, as norepinephrine can cause severe tissue necrosis with extravasation 2, 1. If extravasation occurs, infiltrate phentolamine 5-10 mg diluted in 10-15 mL saline at the site immediately 2, 1.
Inadequate volume resuscitation: Never start norepinephrine without first addressing hypovolemia with crystalloid boluses (minimum 30 mL/kg), as vasoconstriction in hypovolemic patients causes severe organ hypoperfusion 1.