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Dosage Calculations
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Gravity
Terms in this set (63)
mcg → mg → g → kg
÷ by 1,000
mcg ← mg ← g ← kg
x by 1,000
lb → kg
÷ by 2.2
lb ← kg
x by 2.2
mcL → mL → L → kL
÷ by 1,000
mcL ← mL ← L ← kL
x by 1,000
min → hr
÷ by 60
min ← hr
x by 60
Example: Convert 5,000 mcg to mg.
mcg → mg → g → kg ( ÷ by 1,000 )
5,000 mcg ÷ 1,000 = 5 mg
Example: Convert 44 lb to kg.
lb → kg ( ÷ by 2.2 )
44 lb ÷ 2.2 = 20 kg
Example: Convert 0.003 L to mcL.
mcL ← mL ← L ← kL ( x by 1,000 )
0.003 L x 1,000 = 3 mL
3 mL x 1,000 = 3,000 mcL
Example: Convert 5 hours to minutes.
min ← hr ( x by 60 )
5 hr x 60 = 300 min
Apothecary Weight Conversions
60 mg = 1 grain (gr)
15 gr = 1 g or 1000 mg
Example: Convert 3 grams to grains:
3 X 15 = 45 gr
Example: Convert 45 grains to grams:
45 / 15 = 3 g
Example: Convert 5 gr to milligrams:
5 X 60 = 300 mg
Example: Convert 180 mg to grains:
180 / 60 = 3 gr
In order to convert liters and quarts to ounces, multiply the number of liters by 32.
Example: Convert 6 L to fluid ounces
6L X 32 = 192 oz
If you wish to convert ounces to liters or quarts, divide the number of ounces by 32.
Example: Convert 72 oz to liters
72 / 32 = 2 .25 L or 2 .3 L
If you wish to convert ounces to milliliters, you will multiply the number of ounces by 30.
Liquid Volume: 1 ounce (oz) = 30 mL
Example: Convert 8 oz to milliliters: 8 X 30 = 240 mL
In order to convert milliliters to ounces, you will divide the number of milliliters by 30.
Liquid Volume: 1 ounce (oz) = 30 mL
Example: Convert 360 mL to ounces: 360 / 30 = 12 oz
...
Liquid Volume: 1mL = 15 drops (qtts) or 15 minims
...
Liquid Volume: 1mL = 15 drops (qtts) or 15 minims
If you wish to convert milliliters to drops or minims, just multiply the number of milliliters by 15.
Liquid Volume: 1mL = 15 drops (qtts) or 15 minims
Examples: Convert 15 mL to drops (minims)
15 X 15 = 225 drops (minims)
In the event you are interested in converting drops (minims) to milliliters, divide the number of drops (minims) by 15.
Liquid Volume: 1mL = 15 drops (qtts) or 15 minims
Example: Convert 30 drops (minims) to milliliters
30 qtts / 15 = 2 mL
Given an amount of mass per tablet, how many tablets do you require?
Formula:
(Ordered ÷ Have) = Y (Tablets Required)
Example: Metroprolol (Lopressor), 25 mg PO, is ordered. Metropolol is available as 50 mg tablets. How many tablets would the nurse administer?
(Ordered ÷ Have) = Y (Tablets Required)
(25mg ÷ 50mg) = 0.5 tablets
Example: Potassium chloride is available as 10 mg per tablet. Potassium Chloride (K-Dur), 40 mg, is ordered. How many tablets would the nurse administer?
(Ordered ÷ Have) = Y (Tablets Required)
(40mg ÷ 10mg) = 4 tablets
Given an amount of mass per liquid, how much liquid do you require?
Formula:
(Ordered ÷ Have) x Volume Per Have = Y (Liquid Required)
Example: Phenytoin (Dilantin), 0.1 g PO, is ordered to be given through a nasogastric tube. Phenytoin is available as 30 mg / 5 mL. How much would the nurse administer?
(Ordered ÷ Have) x Volume Per Have = Y (Liquid Required)
Convert 0.1 g to mg.
mcg ← mg ← g ← kg ( x by 1,000 )
0.1 g x 1,000 = 100 mg
(100mg ÷ 30mg) x 5mL = 16.7 mL
Example: Ordered Lasix 40 mg IV push now. Available: 80 mg in 1 mL. How much will the nurse draw up?
(Ordered/Have) x Volume Per Have = Y (Liquid Required)
(40mg ÷ 80mg) x 1mL = 0.5mL
Important IV Terms
gtts:
drops
Important IV Terms
Drop Factor:
Number of drops per volume of IV fluid. Varies depending on the tubing used. Usually measured in gtts/mL.
Important IV Terms
Flow Rate:
Measure of the flow of liquid from an IV. Usually measured in gtts/minute (how many drops are released every minute) or in mL/hour (how many mL flow through each hour). gtts/minute is used for manually regulating an IV while mL/hour is used when utilizing an electronic IV regulator.
Important IV Abbreviations
D:
Dextrose
Important IV Abbreviations
W:
Water
Important IV Abbreviations
S:
Saline
Important IV Abbreviations
NS:
Normal Saline (0.9% NaCl)
Important IV Abbreviations
RL or LR:
Lactated Ringer's
Example: D5W = ?
5% Dextrose in Water
Example: D5 � NS = ?
5% dextrose in 0.225% saline solution
Given a volume of IV fluid and a dosage expressed in percent, what is the mass of a particular dosage?
Formula:
(Concentration% ÷ 100) x Volume (mL) = Y (Dosage Amount in g)
Example: Calculate the amount of dextrose in 1000 mL D5W.
(Concentration% ÷ 100) x Volume (mL) = Y (Dosage Amount in g)
(5% ÷ 100) x 1000 mL = 50 g
Example: Calculate the amount of sodium chloride in 2000 mL NS.
Recall NS is 0.9% NaCl (sodium chloride)
(Concentration% ÷ 100) x Volume (mL) = Y (Dosage Amount in g)
(0.9%/100) x 2000 mL = 18 g
Given a certain amount of liquid and a time period, what is the necessary IV flow rate in mL/hr? Measurement used when IV regulated electronically by infusion pump.
Formula:
(Volume (mL) ÷ Time (hr)) = Y (Flow Rate in mL/hr)
Example: Infuse 250 mL over the next 120 minutes by infusion pump.
Formula:
(Volume (mL) ÷ Time (hr)) = Y (Flow Rate in mL/hr)
Convert 120 minutes to hours.
min → hr ( ÷ by 60 )
120 min ÷ 60 = 2 hr
(250 mL ÷ 2 hr) = 125 mL/hr
Example: Ordered 1000 mL D5W IV to infuse in 10 hours by infusion pump.
Formula:
(Volume (mL) ÷ Time (hr)) = Y (Flow Rate in mL/hr)
(1000 mL ÷ 10 hr) = 100 mL/hr
Given a certain amount of liquid, a time period, and a drop factor (gtts/mL), what is the necessary IV flow rate in gtts/min? Measurement used when IV is regulated manually. Because it is not possible to give a patient a fraction of a drop, it is typical to round answers for these problems up or down to the nearest whole number.
Formula:
(Volume (mL) ÷ Time (min))
x Drop Factor (gtts/mL) = Y (Flow Rate in gtts/min)
Example: Calculate the IV flow rate for 1200 mL of NS to be infused in 6 hours. The infusion set is calibrated for a drop factor of 15 gtts/mL.
Formula:
(Volume (mL) ÷ Time (min))
x Drop Factor (gtts/mL) = Y (Flow Rate in gtts/min)
Convert 6 hours to minutes.
min ← hr ( x by 60 )
6 hr x 60 = 360 min
(1200 mL ÷ 360 min)
x 15 gtts/mL = 50 gtts/min
Example: Calculate the IV flow rate for 200 mL of 0.9% NaCl IV over 120 minutes. Infusion set has drop factor of 20 gtts/mL.
Formula:
(Volume (mL) ÷ Time (min))
x Drop Factor (gtts/mL) = Y (Flow Rate in gtts/min)
(200 mL ÷ 120 min)
x 20 gtts/mL = 33 gtts/min
Given the weight of a child or infant, calculate the necessary amount of fluid per day. Different hospitals may have different policies, but for learning how to perform these pediatric dosage calculations, the following commonly used table of fluid requirements may be used.
...
Weight Range 0-10 kg
Required Daily Fluid = ?
100 mL per kg
Weight Range 10-20 kg
Required Daily Fluid = ?
1,000 mL + 50 mL per each kg above 10 kg
Weight Range 20-70 kg
Required Daily Fluid = ?
1,500 mL + 20 mL per each kg above 20 kg
Weight Range Over 70 kg
Required Daily Fluid = ?
2,500 mL (adult requirement)
Example: An infant weighs 4 kg. What is the required amount of fluid per day in mL?
0-10 kg = 100 mL per kg
4 kg x 100 mL/kg = 400 mL
Example: An infant weighs 30.8 lb. What is the required IV flow rate in mL/hr to maintain proper fluid levels?
Convert 30.8 lb to kg.
lb → kg ( ÷ by 2.2 )
30.8 lb ÷ 2.2 = 14 kg
10-20 kg = 1,000 mL + 50 mL per each kg above 10kg
14 kg - 10 kg = 4 kg (There are 4 kg over 10 kg).
1,000 mL + (50 mL/kg x 4 kg) = 1,200 mL/day
This is now an ordinary IV Flow Rate - mL Rate Question. The required volume is 1,200 mL and the time is one day.
(Volume (mL) ÷ Time (hr)) = Y (Flow Rate in mL/hr)
(1,200 mL ÷ 24 hr) = 50 mL/hr
Given the weight of a patient and a dosage specified in terms of weight, calculate the necessary dosage. These problems are a type of pediatric dosage calculations.
Formula:
Weight in Kg * Dosage Per Kg = Y (Required Dosage)
Example: A doctor orders 200 mg of Rocephin to be taken by a 15.4 lb infant every 8 hours. The medication label shows that 75-150 mg/kg per day is the appropriate dosage range. Is this doctor's order within the desired range?
Formula:
Weight in Kg * Dosage Per Kg = Y (Required Dosage)
Convert 15.4 lb to kg.
lb → kg ( ÷ by 2.2 )
15.4 lb ÷ 2.2 = 7 kg
7 kg * 75 mg/kg = 525 mg (Minimum Desired Dosage)
7 kg * 150 mg/kg = 1,050 mg (Maximum Desired Dosage)
24 hours in one day and the medication is ordered every 8 hours.
24 hrs / 8 hrs = 3 times per day doctor ordered medication
200 * 3 = 600 mg ordered per day
600 mg is within the desired range of 525-1,050 mg
Yes doctor has ordered a dosage within the desired range.
Example: Solumedrol 1.5 mg/kg is ordered for a child weighing 74.8 lb. Solumedrol is available as 125 mg / 2mL. How many mL must the nurse administer?
Formula:
Weight in Kg * Dosage Per Kg = Y (Required Dosage)
Convert 74.8 lb to kg.
lb → kg ( ÷ by 2.2 )
74.8 lb ÷ 2.2 = 34 kg
34 kg * 1.5 mg/kg = 51 mg
This is now an ordinary Mass/Liquid For Liquid Question. 51 mg is ordered and the medication is available as 125 mg / 2 mL.
(Ordered ÷ Have) * Volume Per Have = Y (liquid Required)
(51 mg ÷ 125 mg) * 2 mL = 0.82 mL
Give an order in quantity of mass per time, determine the necessary IV flow rate in mL/hr based on the given mass per volume. These types of problems are often used in critical care nursing.
Formula:
(Ordered Per Hour ÷ Have) * Volume (mL) = Y (Flow Rate in mL/hr)
Example: Give patient 500 mg of dopamine in 250 mL of D5W to infuse at 20 mg/hr. Calculate the flow rate in mL/hr.
Formula:
(Ordered Per Hour ÷ Have) * Volume (mL) = Y (Flow Rate in mL/hr)
(20 mg/hr ÷ 500 mg) * 250 mL = 10 mL/hr
Example: Aggrastat at 12.5 mg in 250 mL is prescribed to be infused at a rate of 6 mcg/kg/hr in a patient who weighs 100 kg. At what flow rate in mL/hr will you set the pump?
Formula:
(Ordered Per Hour ÷ Have) * Volume (mL) = Y (Flow Rate in mL/hr)
The first step is to convert the order per time to the amount required for this particular patient. This is a Dosage By Weight Question. 100 kg is the weight in kg and 6 mcg/kg/hr is a dosage in terms of kg.
Weight in Kg * Dosage Per Kg = Y (Required Dosage)
100 kg * 6 mcg/kg/hr = 600 mcg/hr
Convert 600 mcg/hr to mg/hr.
mcg → mg → g → kg ( ÷ by 1,000 )
600 ÷ 1,000 = 0.6 mg/hr
(0.6 mg/hr ÷ 12.5 mg) * 250 mL = 12 mL/hr
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