Calculating IV Drip Rates
Microdrip and Macrodrip
Regardless of the method, it is important to know how to calculate the correct IV flow rate. When calculating the flow rate, determine which IV tubing you will be using (microdrip or macrodrip), so you can use the proper drop factor in your calculations. The drop factor is the number of drops in 1 mL of solution, and is printed on the IV tubing package.
Macrodrip and microdrip refers to the diameter of the needle where the drop enters the drip chamber.
Macrodrip tubing delivers 10 to 20 gtts/mL and is used to infuse large volumes or to infuse fluids quickly. Microdrip tubing delivers 60 gtts/mL and is used for small or very precise amounts of fluid, as with neonates or pediatric patients.
If you simply need to figure out the mL per hour to infuse, take the total volume in mL, divided by the total time in hours, to equal the mL per hour. For example, if you have 1,000 mL NS to infuse over 8 hours, take 1,000 divided by 8, to equal 125 mL/hr. To calculate the drops per minute, the drop factor is needed. The formula for calculating the IV flow rate (drip rate) is total volume (in mL) divided by time (in min), multiplied by the drop factor (in gtts/mL), which equals the IV flow rate in gtts/min.
Let’s try an example. The provider has ordered 1,000 mL Lactated Ringers to infuse over 8 hours. You have a macrodrip tubing with a drop factor of 15 gtts/mL. Calculate how many gtts/min to set as the IV flow rate.
Using the formula, 1,000 mL divided by 8 times 60 (since we have 8 hours times 60 min/hr), then multiply by 15 gtts/min to equal 31.2, rounded to 31 gtts/min.
Here’s a tip: when the IV tubing is microdrip, 60 gtts/mL, the drops per min will be the same as the mL per hour. For example, you have 500 mL to infuse over 12 hours with a microdrip set. The total volume (500 mL) divided by the total time in hours (12) equals 41.6, rounded to 42 mL per hour. The drops per minute would be calculated as total volume, divided by time (in minutes), multiplied by the drop factor of 60 gtts/min, which also equals 41.6, rounded to 42 drops per minute.
Let’s look at an example of an IV piggyback medication.
Ancef 1 gm in 100 mL normal saline to be infused over 30 minutes. You have macrodrip tubing with a drop factor of 10 gtts/mL. Calculate how many gtts/min to set as the IV flow rate.
Use the formula, with 100 mL divided by 30 min, multiplied by 10 gtts/min, which equals 33.3, rounded to 33 gtts/min. If you need to set this up on an IV infusion pump, use the formula, volume (mL) divided by time (min), multiplied by 60 min over 1 hour, this equals the IV flow rate in mL/hr. Using this formula, 100 mL divided by 30 min, times 60 min in 1 hr, equals 199.9, rounded to 200 mL/hr.
Once the infusion has started, monitor closely to be sure it is infusing at the correct rate and check the patient’s IV site for signs of infiltration or inflammation.
Thank you for watching this video about calculating IV drip rates!