A patient weighing 80 kg has to be administered dopamine as an intravenous infusion through a Micro-drip set at the rate of 10 micrograms/kg/minute. 400 milligrams of dopamine is mixed in 500 ml of Normal saline. If 60 Microdrops = 1 millilitre, the calculated drop rate will be

Appeared in: NHM UP Staff Nurse - 2017

Explanation

The calculation requires finding the total required dose per minute for the patient's weight, which is 800 mcg/min (10 mcg/kg/min × 80 kg).
Next, the concentration of the IV solution is determined. With 400 mg (400,000 mcg) in 500 ml, the concentration is 800 mcg/ml.
The required volume per minute is then calculated by dividing the required dose by the concentration (800 mcg/min ÷ 800 mcg/ml), which equals 1 ml/min.
Finally, the drop rate is found by multiplying the volume per minute by the microdrip set's drop factor (1 ml/min × 60 microdrops/ml), resulting in 60 microdrops/minute.

Option A: A rate of 30 microdrops/minute would deliver only half the required dose (400 mcg/min).
Option C: A rate of 90 microdrops/minute would deliver 1.5 times the required dose (1200 mcg/min).
Option D: A rate of 120 microdrops/minute would deliver double the required dose (1600 mcg/min).

Clinical Relevance

Nursing practice connection: Use the key finding related to IV Drip Rate Calculation to guide bedside assessment, documentation, and the next nursing action.
Accurate drug calculation is a critical nursing skill to ensure patient safety and prevent medication errors, which can have severe or fatal consequences.
Vasoactive drugs like dopamine have a narrow therapeutic index, meaning small deviations in dosage can lead to significant adverse effects (e.g., severe hypertension, arrhythmias) or therapeutic failure. Double-checking calculations is essential.
What if the order was to be run through a macrodrip set with a drop factor of 15 gtt/ml? The volume per minute (1 ml/min) remains the same, but the drop rate would change to 1 ml/min × 15 gtt/ml = 15 drops/minute.

How to Approach the Question

First, identify all the given variables: patient weight (80 kg), drug dose (10 mcg/kg/min), drug preparation (400 mg in 500 ml), and drip set factor (60 microdrops/ml).
The goal is to find the 'drop rate' in microdrops/minute. This requires a multi-step approach.
Step 1: Calculate the total dose needed per minute based on the patient's weight.
Step 2: Calculate the concentration of the drug in the IV bag (mcg per ml). Be careful with unit conversions (mg to mcg).
Step 3: Use the results from steps 1 and 2 to determine how many ml need to be infused per minute.
Step 4: Use the result from step 3 and the given drop factor to calculate the final drop rate.

Concept Tested & Keywords

Concept Tested: IV Drip Rate Calculation
Stem keywords: dopamine, intravenous infusion, Micro-drip set, 10 micrograms/kg/minute, 80 kg, drug calculation
Lead-in keywords: calculated drop rate

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E6 Pharmacology Nurses Shanbhag 3e pp. 56-58, 57-59, 54-56

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