Pharmacy Calculations: IV Flow Rates - PTCB CPhT PTCE Math Pharmacy Technician NAPLEX Test Prep
Summary
This video explains intravenous (IV) flow rates, defined as volume per unit of time for medication delivery. It covers how IV administration sets work, the concept of drop factors (drops per milliliter) for gravitational drip chambers, and details two methods for solving flow rate calculations: fractions with cancelling units and equivalent fractions using ratio and proportion. Several examples are provided to demonstrate calculating milliliters per hour, milliliters per minute, drops per minute, and infusion time, including considerations for specific medications like vancomycin.
Key Insights
Calculate drops/minute: 500 mL over 6 hours with a 60 gtts/mL set equals 83 gtts/min.
Example 3: Order is 500 mL D5W over 6 hours. Drip rate is 60 gtts/mL. What is the flow rate in drops/minute? Convert 6 hours to minutes (6 hrs * 60 min/hr = 360 min). Using Method 1: (60 gtts/mL) * (500 mL / 360 min) = 83.33 gtts/min, rounded to 83 gtts/min. Using Method 2: First find total drops: (60 gtts/mL) * (500 mL / 1 mL) = 30,000 gtts. Then divide by total minutes: (30,000 gtts / 360 min) = 83.33 gtts/min, rounded to 83 gtts/min.
Calculate drops/minute with macro set: 1 L over 6 hours with a 10 gtts/mL set equals 28 gtts/min.
Example 4: Order is 1 Liter D5W over 6 hours. Use a 10 gtts/mL IV set. How many drops/minute? Convert 1 L to mL (1 L = 1000 mL). Convert 6 hours to minutes (6 hrs * 60 min/hr = 360 min). Using Method 1: (1000 mL / 360 min) * (10 gtts / 1 mL) = 27.77 gtts/min, rounded to 28 gtts/min. Using Method 2: First find total drops: (1000 mL) * (10 gtts / 1 mL) = 10,000 gtts. Then divide by total minutes: (10,000 gtts / 360 min) = 27.77 gtts/min, rounded to 28 gtts/min.
Sections
Introduction to IV Flow Rates
Define IV flow rate, which is volume delivered per time via IV route.
A flow rate is the volume per time that a medication is delivered by intravenous or IV route to a patient. It is also known as a drip rate or infusion rate. The formula is Flow Rate = Volume / Time. Volume can be in liters, milliliters, or drops, and time can be in hours or minutes. Common units include milliliters per hour or drops per minute.
Explain types of IV administration sets: gravitational drip chambers and electronic pumps.
IV administration sets deliver IV solutions and connect to the IV bag. They function either via a gravitational drip chamber or an electronic infusion pump. Electronic pumps can be set at various rates, while gravitational systems use different drop factors which are crucial for flow rate calculations.
Define drop factor (drip factor) as drops per milliliter.
A drop factor, also known as a drip factor, is the number of drops required to equal one milliliter of volume. The units are drops per mL (or gtts/mL).
Distinguish between macro and micro IV sets based on drop factor.
IV sets are categorized as macro sets or micro sets. Macro sets have a larger volume per drop (e.g., 10 drops/mL), meaning fewer drops are needed for 1 mL. Micro sets have a smaller volume per drop (e.g., 60 drops/mL), requiring more drops to equal 1 mL.
Methods for Solving Flow Rate Calculations
Flow rate calculations use conversions and ratio/proportion methods.
Flow rate calculations can be solved using conversion factors and ratio and proportion methods. It's important to know common conversions for volume, time, and dosage.
Common IV calculation conversions include Liters to mL, Hours to Minutes, Grams to milligrams, and milligrams to micrograms.
Common conversions for flow rate calculations include: 1 Liter = 1000 milliliters, 1 hour = 60 minutes, 1 gram = 1000 milligrams, and 1 milligram = 1000 micrograms.
Method 1: Set up fractions that cancel units, then multiply.
Method 1 involves setting up fractions strategically so that like units cancel out, leaving only the desired units. The fractions are then multiplied to obtain the answer. For example, converting 5 hours to minutes: (60 minutes / 1 hour) * (5 hours / 1) = 300 minutes.
Method 2: Set up equivalent fractions, cross-multiply, then divide.
Method 2 involves setting up equivalent fractions. You cross-multiply the numerators and denominators and then divide to solve for the unknown variable (x). For example, converting 5 hours to minutes, setting up (60 minutes / 1 hour) = (x minutes / 5 hours), then (60 * 5) / 1 = 300 minutes.
When using fractions, ensure units to be cancelled are on opposite sides of the fraction bar.
For units to cancel in Method 1, one unit must be in the numerator and the corresponding unit must be in the denominator. To form a fraction with a single unit, a '1' can be placed in the denominator or numerator.
In Method 2, ensure units in the numerators match and units in the denominators match across the equivalent fractions.
When setting up equivalent fractions in Method 2, the units in the numerators of both fractions must be the same, and the units in the denominators of both fractions must also be the same.
Example Calculations
Calculate mL/hour: 1200 mL over 8 hours equals 150 mL/hour.
Example 1: Order is 1200 mL Normal Saline over 8 hours. How many mL/hour? Using Method 1: (1200 mL / 8 hours) * (1 hour / 1) = 150 mL. Using Method 2: (1200 mL / 8 hours) = (x mL / 1 hour), so (1200 * 1) / 8 = 150 mL.
Calculate mL/10 minutes: 1200 mL over 8 hours equals 25 mL/10 minutes.
Example 2: Order is 1200 mL Normal Saline over 8 hours. How many mL/10 minutes? Convert 8 hours to minutes (8 hrs * 60 min/hr = 480 min). Using Method 1: (1200 mL / 480 min) * (10 min / 1) = 25 mL. Using Method 2: (1200 mL / 480 min) = (x mL / 10 min), so (1200 * 10) / 480 = 25 mL.
Calculate drops/minute: 500 mL over 6 hours with a 60 gtts/mL set equals 83 gtts/min.
Example 3: Order is 500 mL D5W over 6 hours. Drip rate is 60 gtts/mL. What is the flow rate in drops/minute? Convert 6 hours to minutes (6 hrs * 60 min/hr = 360 min). Using Method 1: (60 gtts/mL) * (500 mL / 360 min) = 83.33 gtts/min, rounded to 83 gtts/min. Using Method 2: First find total drops: (60 gtts/mL) * (500 mL / 1 mL) = 30,000 gtts. Then divide by total minutes: (30,000 gtts / 360 min) = 83.33 gtts/min, rounded to 83 gtts/min.
Calculate drops/minute with macro set: 1 L over 6 hours with a 10 gtts/mL set equals 28 gtts/min.
Example 4: Order is 1 Liter D5W over 6 hours. Use a 10 gtts/mL IV set. How many drops/minute? Convert 1 L to mL (1 L = 1000 mL). Convert 6 hours to minutes (6 hrs * 60 min/hr = 360 min). Using Method 1: (1000 mL / 360 min) * (10 gtts / 1 mL) = 27.77 gtts/min, rounded to 28 gtts/min. Using Method 2: First find total drops: (1000 mL) * (10 gtts / 1 mL) = 10,000 gtts. Then divide by total minutes: (10,000 gtts / 360 min) = 27.77 gtts/min, rounded to 28 gtts/min.
Calculate infusion time: 1.5g Vancomycin at 10 mg/min rate takes 150 minutes or 2.5 hours.
Example 5: Order is Vancomycin 1.5 grams to be given at 10 mg/min. How long will it take? Note: Vancomycin has a maximum rate to prevent flushing syndrome. Convert grams to milligrams: 1.5 g * 1000 mg/g = 1500 mg. Using Method 1: (1 min / 10 mg) * (1500 mg / 1) = 150 minutes. Convert to hours: 150 min / 60 min/hr = 2.5 hours. Using Method 2: First find total milligrams: (1000 mg / 1 g) = (x mg / 1.5 g), so x = 1500 mg. Then use the rate: (1500 mg / x min) = (10 mg / 1 min), so x = (1500 * 1) / 10 = 150 minutes, or 2.5 hours.
Recognize that extraneous information may be present in calculations, like total volume for time calculation.
In Example 5 with Vancomycin, the given volume of 500 mL was not needed to calculate the infusion time based on the provided rate and total dose. It's important to identify and use only the necessary information.
Summary and Key Takeaways
Reiterate definition of flow rate and its aliases.
A flow rate is the volume per time that a medication is delivered by intravenous route, also called a drip rate or infusion rate.
Emphasize the role of drop factors in IV calculations.
IV sets have different drop factors (drops per milliliter) that are used in flow rate calculations, especially with gravitational drip chambers.
Highlight the two primary methods for solving flow rate problems.
Flow rate calculations can be solved using Method 1 (cancelling units with fractions) or Method 2 (equivalent fractions with cross-multiplication and division).
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