🧮 Dosage Calculations · Lesson 5 of 5 · 7 min
mcg/kg/min: The Three-Step Conversion
🫀 Dopamine at 5 mcg/kg/min for an 80 kg client in a bag of 400 mg in 250 mL. Three conversions stand between the order and the pump setting, and the exam makes you do all three.
💡 Key idea
Dose per minute, times 60 for the hour, matched to the bag's units, divided by the concentration. Write every step with its unit.
🧠 Why it matters
STEP 1: find the dose per minute: mcg/kg/min × kg. 5 × 80 = 400 mcg/min. STEP 2: convert to the hour: × 60 = 24,000 mcg/hr, then convert to mg if the bag is in mg: ÷ 1,000 = 24 mg/hr. STEP 3: find the concentration of the bag: 400 mg ÷ 250 mL = 1.6 mg/mL. Then mL/hr = 24 ÷ 1.6 = 15 mL/hr. The reverse question gives the pump rate and asks for the dose: 15 mL/hr × 1.6 mg/mL = 24 mg/hr = 24,000 mcg/hr ÷ 60 = 400 mcg/min ÷ 80 kg = 5 mcg/kg/min. Units are everything: keep mcg with mcg and mg with mg, and write every step. Infusions of vasoactive drugs run through a central line when possible, on a dedicated pump, titrated to a target such as mean arterial pressure, with no boluses or flushes through that line.
🏥 In the real world
📝 Order: norepinephrine 0.1 mcg/kg/min, client 70 kg, bag 4 mg in 250 mL. 0.1 × 70 = 7 mcg/min; × 60 = 420 mcg/hr = 0.42 mg/hr; bag is 4 ÷ 250 = 0.016 mg/mL; 0.42 ÷ 0.016 = 26.25, so 26.3 mL/hr. The nurse writes each step, with its unit, on a worksheet. Without seeing that work, a colleague calculates the rate separately from the order and the bag label. The two compare results before the pump is programmed. Vasoactive drips get this independent double check for the same reason insulin does: both are high-alert medications.
📌 Takeaways
- mcg/kg/min × kg = mcg/min; × 60 = mcg/hr
- Match units to the bag, then divide by concentration
- High-alert infusions get an independent double check
📖 Terms in this lesson
Vasopressors (norepinephrine, dopamine): Constrict vessels to raise blood pressure in shock during or after fluids (norepinephrine first in septic shock), titrated by pump to a mean arterial pressure of 65 or more; a central line is preferred, but they can start short term in a large proximal peripheral IV.
✅ Test yourself
Dopamine 400 mg in 250 mL is ordered at 5 mcg/kg/min for a client who weighs 60 kg. What is the pump rate?
- 7.5 mL/hr
- 15 mL/hr
- 18 mL/hr
- 11.25 mL/hr
Answer: D · 11.25 mL/hr
5 × 60 = 300 mcg/min; × 60 = 18,000 mcg/hr = 18 mg/hr; concentration 1.6 mg/mL; 18 ÷ 1.6 = 11.25 mL/hr.
A client receives dobutamine 500 mg in 250 mL at 12 mL/hr. The client weighs 100 kg. What dose is being delivered?
- 8 mcg/kg/min
- 4 mcg/kg/min
- 10 mcg/kg/min
- 2 mcg/kg/min
Answer: B · 4 mcg/kg/min
Concentration 2 mg/mL; 12 × 2 = 24 mg/hr = 24,000 mcg/hr ÷ 60 = 400 mcg/min ÷ 100 kg = 4 mcg/kg/min.
Which practice is appropriate for a continuous vasopressor infusion?
- Hang the bag by gravity if the pump is in use
- Give IV push medications through the same line to save access
- Flush the line rapidly after each titration
- Run the infusion on a dedicated pump and titrate to the ordered target
Answer: D · Run the infusion on a dedicated pump and titrate to the ordered target
Vasoactive drugs need a dedicated, pump-controlled line; boluses or flushes through that line deliver unintended doses.
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