🧮 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 line on the whiteboard and a colleague double-checks. Vasoactive drips are double-checked for the same reason insulin is.
📌 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): Squeeze vessels to raise blood pressure in shock after fluids are given, titrated by pump (dopamine in mcg/kg/min) to a mean arterial pressure of 65 or more through a central line; watch for tachycardia and arrhythmias, and infiltrate phentolamine if the drug extravasates.
✅ 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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