IV Drip Rates – A Practice Pharmacology Math Problems SHOW ALL OF YOUR WORK IV Volume Problems 1. Dr. Kathy Terr ordered an IV to run at 50 cc per hour. The tubing has a drop factor of 20 drops/mL. How many drops per min should the IV run at?
The correct answer and explanation is:
To calculate the IV drip rate, we use the following formula: Drip rate (gtt/min)=(Volume to be infused (mL/hr)×Drop factor (gtt/mL)60 minutes)\text{Drip rate (gtt/min)} = \left( \frac{\text{Volume to be infused (mL/hr)} \times \text{Drop factor (gtt/mL)}}{60 \text{ minutes}} \right)
Given data:
- IV flow rate = 50 cc/hr (1 cc = 1 mL, so 50 mL/hr)
- Drop factor = 20 drops/mL
- Time = 60 minutes
Now, substitute the values into the formula: Drip rate=(50×2060)\text{Drip rate} = \left( \frac{50 \times 20}{60} \right) =100060= \frac{1000}{60} =16.67 gtt/min= 16.67 \text{ gtt/min}
Since the drip rate must be a whole number, we round to 17 gtt/min.
Explanation:
In pharmacology and nursing, calculating IV drip rates is critical to ensure that patients receive the correct amount of fluids or medication over a given period. The drop factor (gtt/mL) varies depending on the IV tubing used, and it is essential to consider this when determining the flow rate.
In this case, the drop factor is 20 gtt/mL, which is a common macrodrip tubing used in adult patients. The physician prescribed an infusion rate of 50 mL per hour, meaning the IV pump must be set to deliver this volume over 60 minutes.
To manually regulate an IV, healthcare professionals use gravity infusion and count the number of drops per minute. Since the pump runs on a drop factor of 20 gtt/mL, it means that every 1 mL of fluid corresponds to 20 drops in the IV chamber.
After applying the formula, we calculated 16.67 gtt/min, which we rounded to 17 gtt/min. This means that the IV tubing should be adjusted to ensure 17 drops fall per minute from the IV chamber into the patient’s vein.
Accurate IV calculations prevent over-infusion (which can cause fluid overload or toxicity) or under-infusion (which can result in ineffective treatment). Nurses often double-check calculations using the formula and adjust the drip rate accordingly.
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