IV Flow Rate Calculation

Your patients must receive the correct amount of fluids or medications over a specific period. This requires understanding how to calculate the IV flow rate: the speed at which the IV fluid is administered. The flow rate is typically measured in drops per minute (gtts/min). This skill can be strengthened by practicing the individual parts and then gradually trying the bigger formula. By mastering this skill, you can provide accurate and effective care in emergency situations without making errors.

Drip Sets

Drip Sets and Their Use

The two most common types of automated devices to deliver IV medication are: Macrodrip IV Set ("10-drop set"): This set delivers larger drops and is used for patients who need fluids quickly. These sets can vary, such as 10, 12, 15, or 20 drops per milliliter (gtt/mL), but 10 gtt/mL is common. It takes 10 drops in a macro drip set to deliver 1 ml of solution. Microdrip IV Set ("60-drop set"): This set delivers smaller drops and is used for precise fluid administration. It typically delivers 60 drops per milliliter (60 gtt/mL). It takes 60 drops in a micro drip set to deliver 1 ml of solution.

Drip Rate Formula Explained:

To calculate the drip rate (gtts/min), you'll need three pieces of information:

1. Volume to be Infused (mL): This is the total amount of fluid you need to give the patient.
2. Time (min): This is the amount of time over which the fluid should be given.
3. Drop Factor (gtts/mL): This is a characteristic of the IV tubing you're using, which tells you how many drops make up one milliliter of fluid.

Here's the formula:

Drip Rate (gtts/min) = Volume to be Infused (mL) Time (min) × Drop Factor (gtts/mL)

Breaking It Down:

 

1. Calculate the Rate of Infusion:

   • First, determine how much fluid you need to give per minute. This is done by dividing the total volume of fluid by the total time. For example, if you need to give 500 mL over 2 hours (which is 120 minutes), you'd do:

   $\frac{500 \text{ mL}}{120 \text{ min}} = 4.17 \text{ mL/min}$

2. Adjust for the Drop Factor:

   • Next, multiply this rate by the drop factor. If your IV tubing has a drop factor of 20 gtts/mL, you'd do:

   $4.17 \text{ mL/min} \times 20 \text{ gtts/mL} = 83.4 \text{ gtts/min}$

 

This means you should set the IV to deliver 83-84 drops per minute.

 

When and Why to Use These Calculations

 

• Emergency Situations: In cases where a patient needs fluids quickly (e.g., shock or dehydration), knowing how to calculate the drip rate ensures the patient receives the necessary volume promptly. You can always call med control to verify dosages and treatments, but by being quick with the skill and the math, you can make fast and accurate medication decisions for your patient.
• Precise Medication Delivery: For medications that require accurate dosing (e.g., antibiotics or pain management), using the correct drip rate makes sure that the patient gets the right amount over the specified time.

 

Alternate Formulas

 

In addition to the primary drip rate formula, there are other formulas suited for specific scenarios in medical practice.

 

mL/hr Calculation:

 

This formula is often used when a medication order specifies the volume of fluid to be administered over a certain number of hours via pump. It's straightforward and commonly used for continuous IV infusions.

 

$\text{Flow Rate (mL/hr)} = \frac{\text{Order (mL)}}{\text{Time (hr)}}$

 

Example Scenario: If you need to administer 1000 mL of saline over 8 hours, the flow rate would be:

 

$\frac{1000 \text{ mL}}{8 \text{ hr}} = 125 \text{ mL/hr}$

 

This means the IV pump should be set to deliver 125 mL per hour.

 

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Weight-Based Infusion Rate:

 

This formula is used for medications that require dosing based on the patient's weight. It's particularly common in pediatric and critical care settings.

 

$\text{Flow Rate (mL/hr)} = \frac{\text{Order (mg/kg/hr)} \times \text{Weight (kg)} \times \text{Set (mL)}}{\text{Concentration (mg/mL)}}$

 

Example Scenario: For a medication order of 5 mg/kg/hr for a patient weighing 70 kg with a concentration of 1 mg/mL, and a set delivering 1 mL per hour:

 

$\text{Flow Rate (mL/hr)} = \frac{5 \times 70 \times 1}{1} = 350 \text{ mL/hr}$​

 

Simple Volume-Time Formula:

 

This formula is used when calculating the flow rate for a set fluid volume to be administered over a specific period. It's useful for intermittent IV infusions.

 

$\text{Flow Rate (mL/hr)} = \frac{\text{Volume (mL)}}{\text{Time (hr)}}$

 

Example Scenario: If you need to give 500 mL over 4 hours, the flow rate would be:

 

$\frac{500 \text{ mL}}{4 \text{ hr}} = 125 \text{ mL/hr}$

 

This formula simplifies the process of determining how fast to run an IV infusion to meet a specific volume and time requirement.