- A pharmacist receives an order for a dexmedetomidine infusion to run at 1.2 mcg/kg/hr. The patient weighs 180 lbs. The standard concentration is 400 mcg in 100 mL. What is the correct infusion rate in mL/hr?
Answer: 24.5 mL/hr
This question includes a common trap: the patient's weight is given in pounds (lbs) and must be converted to kilograms (kg).
1. Convert weight: 180 lbs ÷ 2.2 lbs/kg ≈ 81.82 kg.
2. Calculate total dose: 1.2 mcg/kg/hr × 81.82 kg ≈ 98.18 mcg/hr.
3. Calculate concentration: 400 mcg / 100 mL = 4 mcg/mL.
4. Calculate rate: 98.18 mcg/hr ÷ 4 mcg/mL ≈ 24.5 mL/hr.
A (12.3 mL/hr) is half the correct rate and may result from a calculation error.
C (36.0 mL/hr) is incorrect.
D (54.0 mL/hr) is the rate calculated if the weight in pounds (180) is incorrectly used as kilograms in the dose calculation: (1.2 mcg/kg/hr × 180 kg × 1 hr) / (4 mcg/mL) = 54 mL/hr. This is a very common mistake.
- A patient's blood pressure is not responding to a norepinephrine infusion that is currently at its maximum protocol dose of 0.5 mcg/kg/min. The patient weighs 80 kg and the infusion concentration is 8 mg in 250 mL. The protocol states 'If at max norepinephrine dose and MAP < 65, notify provider and anticipate order for vasopressin.' What is the current norepinephrine infusion rate in mL/hr?
Answer: 75.0 mL/hr
The question asks for the infusion rate at the maximum dose, which requires a standard dose-to-rate calculation. The information about vasopressin is context for a decision-making scenario but not needed for the calculation.
1. Calculate total dose in mcg/min: 0.5 mcg/kg/min × 80 kg = 40 mcg/min.
2. Convert dose to mcg/hr: 40 mcg/min × 60 min/hr = 2400 mcg/hr.
3. Calculate concentration: 8 mg = 8000 mcg. Concentration = 8000 mcg / 250 mL = 32 mcg/mL.
4. Calculate rate: Rate = Dose / Concentration = 2400 mcg/hr / 32 mcg/mL = 75 mL/hr.
A (37.5 mL/hr) would be the rate for a dose of 0.25 mcg/kg/min (half the max dose).
B (50.0 mL/hr) might be selected if the concentration was incorrectly calculated using 4 mg in the bag.
C (62.5 mL/hr) is incorrect and does not correspond to a common calculation error.
- A vasopressin infusion is ordered to start at 0.03 units/minute. The pharmacy supplies a bag containing 50 units of vasopressin in 250 mL of NS. What is the correct initial rate for the infusion pump in mL/hr?
Answer: 9.0 mL/hr
This problem requires converting a dose from units/minute to a rate in mL/hr.
1. Convert dose to units/hr: 0.03 units/min × 60 min/hr = 1.8 units/hr.
2. Calculate concentration: 50 units / 250 mL = 0.2 units/mL.
3. Calculate rate: Rate = Dose / Concentration = 1.8 units/hr / 0.2 units/mL = 9 mL/hr.
A (3.0 mL/hr) would be the rate for a dose of 0.01 units/min.
B (6.0 mL/hr) would be the rate for a dose of 0.02 units/min.
D (12.0 mL/hr) would be the rate for a dose of 0.04 units/min.
- A patient is receiving an amiodarone maintenance infusion post-bolus. The order is for 0.5 mg/min for 18 hours. The IV bag contains 450 mg of amiodarone in 250 mL of D5W. What is the correct infusion rate in mL/hr?
Answer: 16.7 mL/hr
This is a non-weight-based calculation requiring unit conversions.
1. Convert dose from mg/min to mg/hr: 0.5 mg/min × 60 min/hr = 30 mg/hr.
2. Calculate concentration: 450 mg / 250 mL = 1.8 mg/mL.
3. Calculate rate in mL/hr: Rate = Dose / Concentration = 30 mg/hr / 1.8 mg/mL ≈ 16.7 mL/hr.
The 18-hour duration is information about the order's length but not needed for the rate calculation.
A (12.5 mL/hr) might result from a calculation error, possibly in the concentration.
C (20.8 mL/hr) would be the rate if the concentration was 900mg in 500mL and the dose was 1mg/min.
D (33.3 mL/hr) would be the correct rate for a dose of 1 mg/min with this concentration.
- After the titration, what will the new infusion pump rate be in mL/hr?
Answer: 14.1 mL/hr
This problem requires calculating the current dose, adding the titration dose, and then finding the new rate.
1. Calculate concentration: 500 mg / 250 mL = 2 mg/mL, which is 2000 mcg/mL.
2. Calculate current dose rate: The pump is at 10 mL/hr. 10 mL/hr × 2000 mcg/mL = 20,000 mcg/hr.
3. Convert current dose to mcg/kg/min: (20,000 mcg/hr ÷ 60 min/hr) ÷ 68 kg ≈ 4.9 mcg/kg/min.
4. Determine the new dose: The protocol requires an increase of 2 mcg/kg/min. New dose = 4.9 + 2 = 6.9 mcg/kg/min.
5. Calculate the new total dose in mcg/hr: 6.9 mcg/kg/min × 68 kg × 60 min/hr ≈ 28,152 mcg/hr.
6. Calculate the new rate in mL/hr: 28,152 mcg/hr ÷ 2000 mcg/mL ≈ 14.1 mL/hr.
A simpler way: Calculate the volume increase for the titration. Titration dose = 2 mcg/kg/min. Total titration dose = 2 mcg/kg/min 68 kg = 136 mcg/min. Convert to mg/hr = 136 mcg/min 60 min/hr / 1000 mcg/mg = 8.16 mg/hr. Convert to mL/hr = 8.16 mg/hr / 2 mg/mL = 4.08 mL/hr. New rate = 10 mL/hr + 4.08 mL/hr = 14.08 mL/hr, which rounds to 14.1 mL/hr.
A (4.1 mL/hr) represents only the calculated increase in rate, not the new total rate.
B (10.0 mL/hr) is the current rate before the required titration.
D (18.2 mL/hr) would be the result of a significant calculation error, possibly increasing the dose by 5 mcg/kg/min instead of 2.
- A patient with a hypertensive crisis is started on a sodium nitroprusside infusion. The order is to titrate by 0.2 mcg/kg/min every 5 minutes to a target MAP of 90 mmHg. The patient weighs 70 kg. The current dose is 0.5 mcg/kg/min, and the MAP is 110 mmHg. What is the new dose after one titration?
Answer: 0.7 mcg/kg/min
Sodium nitroprusside is a vasodilator, so to lower the blood pressure (MAP 110 > target 90), the infusion rate must be increased. The question tests understanding of the drug's action in the context of titration.
1. Determine titration direction: The patient is hypertensive (MAP 110), so the vasodilator dose needs to be increased.
2. Apply titration amount: The protocol states to titrate by 0.2 mcg/kg/min.
3. Calculate new dose: Current dose (0.5 mcg/kg/min) + titration amount (0.2 mcg/kg/min) = 0.7 mcg/kg/min.
A (0.3 mcg/kg/min) is incorrect. This would be a decrease in the dose, which would worsen the hypertension.
B (0.5 mcg/kg/min) is the current dose, not the new dose after titration.
D (1.0 mcg/kg/min) would be the dose after multiple titrations, not just one.
- An order is written to titrate a milrinone infusion by +0.05 mcg/kg/min. The patient weighs 65 kg and the infusion bag has a concentration of 20 mg in 100 mL. By how many mL/hr should the nurse increase the infusion rate?
Answer: 1.0 mL/hr
This question asks for the change in rate (Δ rate), not the new total rate.
1. Calculate the dose change in mcg/min: 0.05 mcg/kg/min × 65 kg = 3.25 mcg/min.
2. Convert the dose change to mcg/hr: 3.25 mcg/min × 60 min/hr = 195 mcg/hr.
3. Calculate the infusion concentration: 20 mg = 20,000 mcg. Concentration = 20,000 mcg / 100 mL = 200 mcg/mL.
4. Calculate the change in rate: Δ Rate = Δ Dose / Concentration = 195 mcg/hr / 200 mcg/mL = 0.975 mL/hr, which rounds to 1.0 mL/hr.
B (1.6 mL/hr) would be the increase for a titration of 0.08 mcg/kg/min.
C (2.5 mL/hr) is incorrect; it might result from using the wrong weight or making a decimal error.
D (3.3 mL/hr) might be the result if the concentration was assumed to be 10mg in 100mL.
- Based on the information on the pump screen, at what rate in mL/hr is the infusion currently programmed to run?
Answer: 60 mL/hr
This question tests the fundamental relationship Rate = Volume / Time, requiring a conversion of the time unit.
1. Convert time to hours: 2 hr 30 min = 2.5 hours.
2. Calculate rate: Rate = Total Volume / Total Time = 150 mL / 2.5 hr = 60 mL/hr.
A (50 mL/hr) would be the rate if the time remaining was 3 hours.
C (75 mL/hr) would be the rate if the time remaining was 2 hours.
D (100 mL/hr) would be the rate if the time remaining was 1.5 hours.
- A patient is receiving an infusion of propofol at 15 mL/hr. Two hours later, the rate is increased to 20 mL/hr. After another three hours, the rate is decreased to 18 mL/hr, which is maintained for one hour before the infusion is discontinued. What is the total volume of propofol infused over the entire 6-hour period?
Answer: 108 mL
This question requires calculating the volume infused during three distinct time periods and then summing them.
1. Period 1: 15 mL/hr for 2 hours = 15 × 2 = 30 mL.
2. Period 2: 20 mL/hr for 3 hours = 20 × 3 = 60 mL.
3. Period 3: 18 mL/hr for 1 hour = 18 × 1 = 18 mL.
4. Total Volume: 30 mL + 60 mL + 18 mL = 108 mL.
A (53 mL) is incorrect and may result from adding the rates (15+20+18) instead of the volumes.
B (98 mL) is incorrect; this may result from a calculation error in one of the periods.
D (113 mL) is incorrect and may result from misreading the time frames, for example, running the 20 mL/hr rate for 4 hours instead of 3.
- A patient is receiving a diltiazem infusion at 10 mL/hr from a bag with a concentration of 125 mg in 125 mL D5W. The pharmacy sends a new, more concentrated bag containing 125 mg in 100 mL D5W. To maintain the same dose of diltiazem in mg/hr, the nurse should adjust the infusion pump to what new rate?
Answer: 8.0 mL/hr
The key is to maintain the same dose (mg/hr) when the concentration (mg/mL) changes.
1. Calculate the current dose: The initial concentration is 125 mg / 125 mL = 1 mg/mL. The dose is 10 mL/hr × 1 mg/mL = 10 mg/hr.
2. Calculate the new concentration: The new bag's concentration is 125 mg / 100 mL = 1.25 mg/mL.
3. Calculate the new rate: To deliver the same 10 mg/hr dose with the new concentration, the rate must be adjusted: Rate = Dose / Concentration = 10 mg/hr / 1.25 mg/mL = 8 mL/hr.
B (10.0 mL/hr) is incorrect. Keeping the rate the same would increase the drug delivery to 12.5 mg/hr (10 mL/hr × 1.25 mg/mL).
C (12.5 mL/hr) is incorrect. This error often comes from multiplying by the concentration change instead of dividing (10 mL/hr × 1.25 = 12.5 mL/hr).
D (15.0 mL/hr) is an incorrect calculation without a clear logical basis.
- A 100 kg patient is ordered to start a lidocaine infusion at 2 mg/min following a bolus. The standard pharmacy concentration is 2 g of lidocaine in 500 mL of D5W. At what rate in mL/hr should the nurse set the infusion pump?
Answer: 30 mL/hr
This calculation requires converting units and is not weight-based, making the patient's weight extraneous information.
1. Convert dose to mg/hr: The ordered dose is 2 mg/min. To find the hourly dose, multiply by 60: 2 mg/min × 60 min/hr = 120 mg/hr.
2. Calculate concentration: The bag contains 2 g, which is 2000 mg. The concentration is 2000 mg / 500 mL = 4 mg/mL.
3. Calculate the rate: Rate = Dose / Concentration = 120 mg/hr / 4 mg/mL = 30 mL/hr.
A (15 mL/hr) would be the rate for a dose of 1 mg/min.
C (45 mL/hr) would be the rate for a dose of 3 mg/min.
D (60 mL/hr) would be the rate for a dose of 4 mg/min, or if the concentration was miscalculated as 2 mg/mL.
- What is the new infusion rate in mL/hr after making the required adjustment?
Answer: 37.0 mL/hr
This problem involves titrating a dose that is not weight-based.
1. Calculate the concentration: 25 mg / 250 mL = 0.1 mg/mL.
2. Calculate the current dose in mg/hr: 12 mL/hr × 0.1 mg/mL = 1.2 mg/hr.
3. Determine the new dose: The protocol requires an increase of 2.5 mg/hr. New dose = 1.2 mg/hr + 2.5 mg/hr = 3.7 mg/hr.
4. Calculate the new rate in mL/hr: New Rate = New Dose / Concentration = 3.7 mg/hr / 0.1 mg/mL = 37 mL/hr.
A (14.5 mL/hr) is incorrect; it results from adding the dose change (2.5) directly to the rate (12), failing to account for concentration.
B (22.0 mL/hr) is incorrect and may result from miscalculating the initial dose or the required rate.
C (25.0 mL/hr) is the rate that would deliver exactly 2.5 mg/hr (2.5 mg/hr ÷ 0.1 mg/mL), but this is the change in dose, not the new total rate.
