Unit 48

Calculating Intravenous

Flow Rates

Basic Principles of Calculating Intravenous Flow Rates

• Intravenous (IV) fluids are fluids injected directly into a vein.

• They are used to replace body fluids or electrolytes, administer medications, or keep a vein open (KVO) for future use.

Basic Principles of Calculating Intravenous Flow Rates

• The type of IV solution used is determined by what is needed in blood and body fluids to ensure a normal balance of fluid and electrolytes.– If too many electrolytes are present and body

fluids must be diluted, a hypotonic solution is administered.

Basic Principles of Calculating Intravenous Flow Rates

– If the IV is used to expand the volume of body fluids while maintaining normal balance, an isotonic solution such as 0.9% NS is ordered.

– If electrolytes must be replaced after being lost through conditions such as vomiting and diarrhea, a hypertonic solution is used.

Basic Principles of Calculating Intravenous Flow Rates

• The physician orders the type, amount, and flow rate for an IV solution or medication.

• The flow rate determines how much of the fluid enters the vein in a specific period of time. – It is calculated as drops per minute (gtt/min).

Calculating IV Flow Rates

• By knowing the drop factor, the amount or volume of IV solution, and the time period for infusion, the correct IV flow rate can be calculated. – The flow rate is always calculated in drops

per minute or gtt/min.

Calculating Infusion Time

• Infusion time is the total time required for a specific volume of an IV solution to infuse at a given flow rate.

• By knowing the total amount or volume of IV to infuse and the number of milliliters (mL) infusing per hour, it is easy to determine total infusion time.

Calculating IV Fluid Volume

• By knowing the amount of time, the flow rate in gtt/min, and the calibration or drop factor in gtt/mL, you can determine how much IV solution will be absorbed in the specific period of time.

• The same formula used to calculate flow rate can be used to calculate IV fluid volume.

Automated Infusion Pumps

• In many health care agencies, IV solutions are regulated electronically by IV infusion pumps.

• The pumps are programmed for a specific flow rate.

• Alarms sound when this flow rate is interrupted.

• A common type of electronic infusion pump is a patient-controlled analgesia (PCA).

Calculating Intravenous Flow Rates

• Example: A bag of 0.9% NS (normal saline) is infusing at the rate of 20 gtt/min. The infusion set is calibrated for a drop factor of 15 gtt/mL.

• How many mL of solution will infuse during an 8-hour shift? – First change 8 hours to minutes: 1 hour = 60

minutes; 8 hours = 480 minutes– Now insert information into the formula:

Calculating Intravenous Flow Rates

• Fill in the formula:

• Therefore, 640 mL of the solution will infuse in the 8-hour period.

Practical Problem

• An IV of lactated Ringer’s is to run at 50 mL per hour. The drop factor of the infusion set is 15 gtt/mL.

• What is the flow rate?

Practical Problem

• Set up and solve the formula:

• The flow rate is 12.5 (which may be rounded to 13) drops per minute.