Question

Difficulty: MediumPharmacological and Parenteral Therapies

A nurse is caring for a client in the intensive care unit who is experiencing severe hypotension and weighs 87 kg87\text{ kg}. The healthcare provider prescribes a continuous intravenous (IV) infusion of norepinephrine at 0.05 mcg/kg/min0.05\text{ mcg/kg/min}. The pharmacy dispenses norepinephrine 4 mg4\text{ mg} in 250 mL250\text{ mL} of 5%5\% dextrose in water (D5W\text{D}_5\text{W}). At what rate should the nurse set the IV infusion pump in mL/hr\text{mL/hr}? (Round the answer to the nearest tenth. Do not use a trailing zero.)

Answer: 16.3 mL/hr

Answer

16.3
The correct infusion rate is calculated by first determining the total hourly dose required for the client's specific weight (0.05 mcg/kg/min×87 kg×60 min/hr=261 mcg/hr0.05\text{ mcg/kg/min} \times 87\text{ kg} \times 60\text{ min/hr} = 261\text{ mcg/hr}). Next, the concentration of the IV bag is found by converting milligrams to micrograms (4 mg=4000 mcg4\text{ mg} = 4000\text{ mcg}) and dividing by the total volume (4000 mcg/250 mL=16 mcg/mL4000\text{ mcg} / 250\text{ mL} = 16\text{ mcg/mL}). Finally, dividing the hourly dose by the concentration gives the pump rate (261 mcg/hr÷16 mcg/mL=16.3125 mL/hr261\text{ mcg/hr} \div 16\text{ mcg/mL} = 16.3125\text{ mL/hr}), which rounds to 16.316.3.

Step-by-Step Solution

1
Calculate the prescribed dose per minute based on the client's weight.
0.05 mcg/kg/min×87 kg=4.35 mcg/min0.05\text{ mcg/kg/min} \times 87\text{ kg} = 4.35\text{ mcg/min}
The prescription is weight-based, so the total microgram dose per minute must be determined first.
2
Convert the prescribed dose per minute to the prescribed dose per hour.
4.35 mcg/min×60 min/hr=261 mcg/hr4.35\text{ mcg/min} \times 60\text{ min/hr} = 261\text{ mcg/hr}
IV infusion pumps deliver medication at an hourly rate (mL/hr\text{mL/hr}), requiring the dose to be converted from minutes to hours.
3
Determine the concentration of the dispensed IV solution in mcg/mL\text{mcg/mL}.
4 mg×1000 mcg/mg=4000 mcg4\text{ mg} \times 1000\text{ mcg/mg} = 4000\text{ mcg}. Then, 4000 mcg/250 mL=16 mcg/mL4000\text{ mcg} / 250\text{ mL} = 16\text{ mcg/mL}.
The prescribed dose is in micrograms, so the medication supplied in milligrams must be converted to match the units before calculating the volume.
4
Calculate the final infusion rate in mL/hr\text{mL/hr} and round to the nearest tenth.
261 mcg/hr÷16 mcg/mL=16.3125 mL/hr261\text{ mcg/hr} \div 16\text{ mcg/mL} = 16.3125\text{ mL/hr}. Rounded to the nearest tenth is 16.316.3.
Dividing the required hourly dose by the concentration yields the exact volume needed per hour. Rounding to the nearest tenth is standard for critical care infusions.

Key Concept

Weight-based continuous intravenous (IV) medication calculation and infusion pump programming.

Alternative Method

Dimensional analysis can be used to solve this in a single equation: X mL/hr=(250 mL/4 mg)×(1 mg/1000 mcg)×(0.05 mcg/1 kg×1 min)×(87 kg/1)×(60 min/1 hr)=16.3125 mL/hrX\text{ mL/hr} = (250\text{ mL} / 4\text{ mg}) \times (1\text{ mg} / 1000\text{ mcg}) \times (0.05\text{ mcg} / 1\text{ kg} \times 1\text{ min}) \times (87\text{ kg} / 1) \times (60\text{ min} / 1\text{ hr}) = 16.3125\text{ mL/hr}.
Estimated Time:2m 0s
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