Microdrop IV Infusion Rate Calculation
For an IV infusion rate of 110 mL/hour using microdrop (microdrip) tubing, you will order 110 microdrops per minute (μgtts/min).
Calculation Method
Microdrop tubing has a standardized drop factor of 60 drops/mL, which simplifies the calculation significantly 1.
The formula is: drops per minute = (Volume in mL × Drop factor) ÷ Time in minutes 1.
For 110 mL/hour with microdrop tubing: (110 mL × 60 drops/mL) ÷ 60 minutes = 110 microdrops/min 2, 1.
Key Clinical Principle
With microdrop tubing (60 drops/mL), the drops per minute numerically equals the mL per hour, making bedside calculations straightforward 2, 1.
This 1:1 relationship exists because: mL/hour × 60 drops/mL ÷ 60 minutes = mL/hour (the 60s cancel out) 1.
Important Considerations for Accuracy
Electronic infusion pumps are strongly preferred over gravity drip methods for critical medications requiring precise administration, as gravity-driven micro-drip infusion can vary widely (up to 2.9-fold) depending on catheter size, fluid column height, and carrier flow rates 1, 3.
When using gravity-driven micro-drip under "wide-open" flow conditions (continuous fluid column rather than discrete drops), drug delivery becomes unpredictable and dependent on extrinsic factors 3.
For vasoactive drugs like epinephrine or norepinephrine infusions, mechanical pumps should be used instead of gravity-driven micro-drips to enhance precision and safety 2, 3.