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🧮 剂量计算 · 第5课，共5课 · 7 min

mcg/kg/min：三步换算

mcg/kg/min: The Three-Step Conversion

🫀 Dopamine以5 mcg/kg/min用于一名80 kg的患者，输液袋为400 mg在250 mL中。三项换算横亘在医嘱与输液泵设置之间，而考试要求你完成全部三项。

🫀 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.

💡 核心要点

每分钟剂量，乘以60得到每小时剂量，与输液袋的单位保持一致，再除以浓度。写下每一步及其单位。

Dose per minute, times 60 for the hour, matched to the bag's units, divided by the concentration. Write every step with its unit.

🧠 为什么重要

步骤1：求出每分钟剂量：mcg/kg/min × kg。5 × 80 = 400 mcg/min。步骤2：换算为每小时：× 60 = 24,000 mcg/hr，然后如果输液袋以mg计，则换算为mg：÷ 1,000 = 24 mg/hr。步骤3：求出输液袋的浓度：400 mg ÷ 250 mL = 1.6 mg/mL。然后mL/hr = 24 ÷ 1.6 = 15 mL/hr。反向问题会给出输液泵速度并询问剂量：15 mL/hr × 1.6 mg/mL = 24 mg/hr = 24,000 mcg/hr ÷ 60 = 400 mcg/min ÷ 80 kg = 5 mcg/kg/min。单位就是一切：mcg与mcg保持一致，mg与mg保持一致，并写下每一步。血管活性药物的输注尽可能通过中心静脉导管进行，使用专用输液泵，滴定至平均动脉压等目标，且不通过该导管进行推注或冲管。

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.

🏥 真实场景

📝 医嘱：norepinephrine 0.1 mcg/kg/min，患者70 kg，输液袋4 mg在250 mL中。0.1 × 70 = 7 mcg/min；× 60 = 420 mcg/hr = 0.42 mg/hr；输液袋为4 ÷ 250 = 0.016 mg/mL；0.42 ÷ 0.016 = 26.25，所以是26.3 mL/hr。护士在工作表上写下每一步及其单位。在不看那份计算的情况下，一位同事根据医嘱和输液袋标签单独计算速度。两人在设置输液泵之前比较结果。血管活性药物滴注接受这种独立双重核查，原因与insulin相同：两者都是高警示药物。

📝 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.

📌 要点总结

  • mcg/kg/min × kg = mcg/min；× 60 = mcg/hrmcg/kg/min × kg = mcg/min; × 60 = mcg/hr
  • 使单位与输液袋一致，然后除以浓度Match units to the bag, then divide by concentration
  • 高警示输注要接受独立双重核查High-alert infusions get an independent double check

📖 本课术语

血管升压药（norepinephrine、dopamine） (Vasopressors (norepinephrine, dopamine)): 在补液期间或之后收缩血管以升高休克患者的血压（脓毒性休克首选norepinephrine），通过输液泵滴定至平均动脉压65或以上；首选中心静脉通路，但可短期通过粗大的近端外周IV开始使用。

✅ 自我测试

Dopamine 400 mg在250 mL中，以5 mcg/kg/min开具给一名体重60 kg的患者，输液泵速度是多少？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?
  1. 7.5 mL/hr
  2. 15 mL/hr
  3. 18 mL/hr
  4. 11.25 mL/hr

答案: D · 11.25 mL/hr

5 × 60 = 300 mcg/min；× 60 = 18,000 mcg/hr = 18 mg/hr；浓度1.6 mg/mL；18 ÷ 1.6 = 11.25 mL/hr。18 mL/hr是将以毫克计的每小时剂量误认为速度，跳过了除以1.6 mg/mL浓度这一步。

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. 18 mL/hr is the hourly dose in milligrams mistaken for the rate, skipping the division by the 1.6 mg/mL concentration.

一名患者接受dobutamine 500 mg在250 mL中，输注速度为12 mL/hr，该患者体重100 kg，正在输送的剂量是多少？A client receives dobutamine 500 mg in 250 mL at 12 mL/hr. The client weighs 100 kg. What dose is being delivered?
  1. 8 mcg/kg/min
  2. 4 mcg/kg/min
  3. 10 mcg/kg/min
  4. 2 mcg/kg/min

答案: B · 4 mcg/kg/min

浓度2 mg/mL；12 × 2 = 24 mg/hr = 24,000 mcg/hr ÷ 60 = 400 mcg/min ÷ 100 kg = 4 mcg/kg/min。2 mcg/kg/min是将12 mL/hr当作12 mg/hr得出的，跳过了2 mg/mL的浓度。

Concentration 2 mg/mL; 12 × 2 = 24 mg/hr = 24,000 mcg/hr ÷ 60 = 400 mcg/min ÷ 100 kg = 4 mcg/kg/min. 2 mcg/kg/min comes from treating 12 mL/hr as 12 mg/hr, skipping the 2 mg/mL concentration.

对于持续血管加压药输注，哪种做法是合适的？Which practice is appropriate for a continuous vasopressor infusion?
  1. 如果输液泵正在使用，则将输液袋以重力方式悬挂输注Hang the bag by gravity if the pump is in use
  2. 通过同一导管给予IV推注药物，以节省通路Give IV push medications through the same line to save access
  3. 每次滴定后快速冲洗导管Flush the line rapidly after each titration
  4. 在专用输液泵上运行输注，并滴定至医嘱目标Run the infusion on a dedicated pump and titrate to the ordered target

答案: D · 在专用输液泵上运行输注，并滴定至医嘱目标

血管活性药物需要专用、由输液泵控制的导管；通过该导管推注或冲管会输送非预期的剂量。

Vasoactive drugs need a dedicated, pump-controlled line; boluses or flushes through that line deliver unintended doses.

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