IV Infusion Rate Calculator
Understanding the Infusion Rate Formula
Calculating the correct infusion rate is a critical nursing skill that ensures patient safety during Intravenous (IV) therapy. Whether you are using an electronic infusion pump or a manual gravity drip, understanding the underlying math helps prevent medication errors.
There are two primary ways to express infusion rates:
- mL/hr: Milliliters per hour (typically used for electronic pumps).
- gtt/min: Drops per minute (typically used for gravity flow tubing).
Formula for mL/hr (Electronic Pump)
When using an infusion pump, the machine regulates the flow. You simply need to program the total volume and the time. The formula is straightforward:
Example: A doctor orders 1,000 mL of Normal Saline to be infused over 8 hours.
Calculation: 1,000 mL ÷ 8 hours = 125 mL/hr.
Formula for gtt/min (Gravity Drip)
When an infusion pump is unavailable, nurses must manually regulate the flow using the roller clamp on the IV tubing. To do this, you must calculate the "drops per minute" based on the tubing's Drop Factor.
The Drop Factor is printed on the IV tubing package and represents how many drops (gtt) it takes to make 1 milliliter (mL). Common factors are:
- Macro Drip: 10, 15, or 20 gtt/mL (used for general hydration).
- Micro Drip: 60 gtt/mL (used for pediatrics or precise medication).
Example: Order is 1,000 mL NS over 8 hours using tubing with a drop factor of 15 gtt/mL.
- Convert hours to minutes: 8 hours × 60 = 480 minutes.
- Multiply Volume by Drop Factor: 1,000 × 15 = 15,000.
- Divide by Time in minutes: 15,000 ÷ 480 = 31.25 gtt/min.
Since you cannot count a fraction of a drop, you would round to the nearest whole number: 31 gtt/min.
Why Accuracy Matters
Inaccurate infusion rates can lead to serious complications. Infusing too fast can cause fluid overload (hypervolemia), leading to heart failure or pulmonary edema. Infusing too slowly can result in dehydration or sub-therapeutic medication levels. Always double-check your calculations and verify the drop factor of the specific tubing you are using.