Question

Difficulty: HardPharmacological and Parenteral Therapies

A nurse is caring for a client with a hypertensive crisis. The provider prescribes a continuous intravenous (IV) infusion of sodium nitroprusside at 3 mcg/kg/min3 \text{ mcg/kg/min}. The client weighs 176 lbs176 \text{ lbs}. The medication is supplied as 50 mg50 \text{ mg} of sodium nitroprusside in 250 mL250 \text{ mL} of 5% Dextrose5\% \text{ Dextrose} in water (D5WD_5W). At what rate should the nurse set the IV infusion pump in mL/hr\text{mL/hr}? (Round the answer to the nearest whole number.)

Answer: 72 mL/hr

Answer

The correct infusion rate is 72 mL/hr.
To solve this calculation correctly, multiple conversions are required. First, the client's weight of 176 lbs176 \text{ lbs} is converted to 80 kg80 \text{ kg}. The total per-minute dose is 80 kg×3 mcg/kg/min=240 mcg/min80 \text{ kg} \times 3 \text{ mcg/kg/min} = 240 \text{ mcg/min}. This equals 14,400 mcg/hr14,400 \text{ mcg/hr} (240×60240 \times 60). Converting to milligrams gives 14.4 mg/hr14.4 \text{ mg/hr} (14,400÷1,00014,400 \div 1,000). The concentration of the supplied bag is 50 mg/250 mL=0.2 mg/mL50 \text{ mg} / 250 \text{ mL} = 0.2 \text{ mg/mL}. Dividing the hourly dose by the concentration (14.4÷0.214.4 \div 0.2) yields exactly 72 mL/hr72 \text{ mL/hr}.

Step-by-Step Solution

1
Convert weight to kilograms
176 lbs÷2.2 lbs/kg=80 kg176 \text{ lbs} \div 2.2 \text{ lbs/kg} = 80 \text{ kg}
The prescribed dose is weight-based in kg.
2
Calculate dose per minute
80 kg×3 mcg/kg/min=240 mcg/min80 \text{ kg} \times 3 \text{ mcg/kg/min} = 240 \text{ mcg/min}
To determine the total micrograms the client receives each minute.
3
Calculate dose per hour
240 mcg/min×60 min/hr=14,400 mcg/hr240 \text{ mcg/min} \times 60 \text{ min/hr} = 14,400 \text{ mcg/hr}
Infusion pumps are set in mL/hr, requiring an hourly dose.
4
Convert dose to milligrams
14,400 mcg/hr÷1,000 mcg/mg=14.4 mg/hr14,400 \text{ mcg/hr} \div 1,000 \text{ mcg/mg} = 14.4 \text{ mg/hr}
The supplied medication is measured in milligrams, so the units must match.
5
Calculate the infusion rate in mL/hr
14.4 mg/hr÷(50 mg/250 mL)=14.4 mg/hr÷0.2 mg/mL=72 mL/hr14.4 \text{ mg/hr} \div (50 \text{ mg} / 250 \text{ mL}) = 14.4 \text{ mg/hr} \div 0.2 \text{ mg/mL} = 72 \text{ mL/hr}
To find the final volume to be infused per hour based on the drug's concentration.

Key Concept

Weight-based continuous intravenous (IV) infusion calculations requiring multi-step unit conversions.
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