Situation: A 66-year-old man weighing 80 kg is in the coronary care unit after a large anterior myocardial infarction. Six hours after primary percutaneous coronary intervention (PCI), his blood pressure is 78/50 mmHg, his skin is cool and clammy, crackles are heard in both lungs, and his urine output is 15 mL/h. After noradrenaline (norepinephrine) raises his blood pressure, dobutamine 5 mcg/kg/min is ordered. The premixed bag contains dobutamine 500 mg in 250 mL. At what rate should the nurse set the pump? Round to one decimal place.

Concentration: 500 mg ÷ 250 mL = 2 mg/mL = 2,000 mcg/mL. Hourly dose: 5 mcg/kg/min × 80 kg × 60 min = 24,000 mcg/h. Rate: 24,000 ÷ 2,000 = 12.0 mL/h.

Step 1: Identify the drug concentration

The premixed bag contains 500 mg of dobutamine in 250 mL. First, convert the total dose to micrograms because the ordered rate is in mcg/kg/min. Since 1 mg = 1,000 mcg, the bag contains 500,000 mcg. Dividing by the volume gives a concentration of 2,000 mcg/mL.


Step 2: Calculate the ordered hourly dose

The order is 5 mcg/kg/min for a patient weighing 80 kg. Multiply the weight-based dose by the patient’s weight to find the per-minute dose: 5 × 80 = 400 mcg/min. Convert this to an hourly dose by multiplying by 60 minutes: 400 × 60 = 24,000 mcg/h.


Step 3: Determine the infusion rate

Divide the required hourly dose by the drug concentration: 24,000 mcg/h ÷ 2,000 mcg/mL = 12.0 mL/h. The pump should be set at 12.0 mL/h.


The final rate is 12.0 mL/h, which delivers exactly 5 mcg/kg/min of dobutamine to this 80 kg patient.


Clinical context: Why dobutamine after norepinephrine?

This patient is in cardiogenic shock following a large anterior myocardial infarction. The clinical picture—hypotension, cool clammy skin, pulmonary crackles, and oliguria—reflects low cardiac output with elevated left ventricular filling pressure and end-organ hypoperfusion. In the AHA scientific statement on cardiogenic shock, initial vasopressor support with norepinephrine is recommended to restore a minimum perfusion pressure, but dobutamine is then added as an inotrope to improve cardiac contractility and forward flow ^[1].


Key point! Dobutamine is primarily a beta-1 adrenergic agonist. It increases myocardial contractility and stroke volume, which is why it is selected when the blood pressure has been stabilized but cardiac output remains inadequate. It is not a first-line vasopressor for restoring blood pressure in shock.


Watch out! Dobutamine can cause tachycardia and increase myocardial oxygen demand. In a patient with a recent large anterior MI, the nurse must monitor heart rate, rhythm, and for signs of worsening ischemia while the infusion runs.


Why the other options are incorrect

Option	Rate	Error in calculation
2	24.0 mL/h	Used 1,000 mcg/mL instead of 2,000 mcg/mL (forgot to convert 500 mg to 500,000 mcg correctly)
3	96.0 mL/h	Multiplied the per-minute dose by 60 twice or used the wrong weight conversion
4	0.2 mL/h	Divided the per-minute dose (400 mcg/min) by concentration without converting to an hourly rate

In infusion calculations, the most common errors are unit mismatches between mg and mcg, and forgetting to convert minutes to hours. Always write out the units at each step and confirm they cancel correctly before entering the rate on the pump.


Nursing safety check

Before starting the infusion, verify the pump setting with a second nurse, confirm the patient’s actual weight in kilograms, and ensure the dobutamine concentration on the bag label matches the concentration used in the calculation. In cardiogenic shock, frequent reassessment of blood pressure, urine output, mentation, and lung sounds guides titration of both norepinephrine and dobutamine ^[1].