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Difficulty: MediumAnte/Intra/Postpartum and Newborn Care

A nurse is caring for a client at 3131 weeks of gestation who is experiencing preterm labor. The healthcare provider prescribes a continuous intravenous infusion of magnesium sulfate at a rate of 3 g/hr3\text{ g/hr} for fetal neuroprotection. The pharmacy dispenses a premixed IV bag containing 20 g20\text{ g} of magnesium sulfate in 500 mL500\text{ mL} of sterile water. At what rate in mL/hr\text{mL/hr} should the nurse set the intravenous infusion pump? (Record your answer as a whole number.)

Answer: 75 mL/hr

Answer

75
To determine the correct infusion rate, first find the concentration of the medication. Divide the total amount of the drug (20 g20\text{ g}) by the total volume of the IV fluid (500 mL500\text{ mL}) to get 0.04 g/mL0.04\text{ g/mL}. Next, divide the prescribed dose (3 g/hr3\text{ g/hr}) by the concentration to find the correct rate of 75 mL/hr75\text{ mL/hr}. Alternatively, dimensional analysis can be used: (500 mL/20 g)×(3 g/1 hr)=1500/20=75 mL/hr(500\text{ mL} / 20\text{ g}) \times (3\text{ g} / 1\text{ hr}) = 1500 / 20 = 75\text{ mL/hr}.

Step-by-Step Solution

1
Determine the concentration of the magnesium sulfate solution.
20 g/500 mL=0.04 g/mL20\text{ g} / 500\text{ mL} = 0.04\text{ g/mL}
Establishing the amount of medication per milliliter of IV fluid is required to calculate the correct fluid delivery rate.
2
Calculate the infusion rate in mL/hr\text{mL/hr}.
3 g/hr÷0.04 g/mL=75 mL/hr3\text{ g/hr} \div 0.04\text{ g/mL} = 75\text{ mL/hr}
Dividing the prescribed hourly dose by the concentration yields the volume of fluid that must be infused each hour.

Key Concept

Intravenous medication dosage calculation for continuous infusions during preterm labor.
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Topics

Ante/Intra/Postpartum and Newborn Care

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