The Importance of Being Precise in Calculations for Our Careers Discussions

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Discussion Prompts: Discussion IIA
Chapter 5 is critically important, and the calculations that you perform in this chapter have no room for error. These are the sorts of calculations you will encounter on a regular basis in a health-science career.
(1) In your own words and in the context of your anticipated career, explain the importance of getting the correct answers to these sorts of problems.
(2) Construct a new problem (that differs in some way [even if only in the numbers] from the problems in the book or problems already posted here). Post both an original problem and a solution. I will consider using problems that are posted here as quiz problems, so you should use each other’s questions as extra practice.
Please use this space to respond to the two discussion prompts I provide and for any questions you have about course content from Chapter 5. If you have an answer to a question that someone else has posted, please share your answer here. This is an opportunity to help each other.
For help responding to a post, click here.
Please remember course norms when posting to this discussion. Be polite and respectful. Use full sentences and proper English spelling and grammar. 
I will not generally post replies immediately in part because I want to give everyone a chance to post answers to questions here. 
NOTE: This is a graded discussion. You are expected to participate in the discussion of this material. You should post to this discussion board at least 6 times (including your responses to the discussion prompts). 
———–
I will count four things as “good” posts:

(1) Appropriate responses to the discussion prompts,
(2) (Nontrivial) Questions about the material that have not already been asked,
(3) Answers to questions that have not already been answered, and
(4) Posts that contribute to the sense of community and the sharing of information. Note that (4) is a fairly broad category, and I will be fairly generous when considering your posts, but the final decision for whether a post is deserving of points is mine. 

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Chapter 5
Drug Dosages and
Intravenous Calculations
Objectives
▪
▪
▪
▪
Interpret drug orders and labels
Calculate drug orders
Identify and calculate medication volumes
Calculate the volume of reconstituted
medication in powdered form
▪ Perform intravenous and intramuscular
calculations
© 2010 Delmar, Cengage Learning.
2
Objectives (cont’d.)
▪ Perform titration calculations
▪ Calculate drug dosages based on body
weight
▪ Calculate drug dosages based on BSA using
formulas and the West Nomogram chart
© 2010 Delmar, Cengage Learning.
3
Interpreting Drug Orders
▪ Physicians use
short-hand
notations to
prescribe drugs
© 2010 Delmar, Cengage Learning.
4
Interpreting Drug Labels
▪ Labels give information such as:
•
•
•
•
Dosage strength
Brand name (or generic name)
Manufacturer
How to administer (orally, sublingually, injection,
or other)
• Drug form (e.g., tablet, capsule, liquid)
• Expiration date
© 2010 Delmar, Cengage Learning.
5
Interpreting Drug Labels (cont’d.)
▪ What is the drug?
▪ What is the total volume?
▪ What is the strength?
© 2010 Delmar, Cengage Learning.
6
Dosage Calculation Methods
▪ Dosage formula:
• .
▪ Proportions:
• .
▪ Dimensional analysis
© 2010 Delmar, Cengage Learning.
7
Dosage Calculation Methods (cont’d.)
▪ An order for 75 mg of phenytoin is given
• Only 100 mg are available
• How many tables should be given?
▪ Dosage formula:
• .
▪ Proportions:
• .
© 2010 Delmar, Cengage Learning.
8
Dosage Calculation Methods (cont’d.)
▪ Dimensional analysis:
• .
© 2010 Delmar, Cengage Learning.
9
Parenteral Dosage Calculations
▪ Administered through a non-gastrointestinal
route (e.g. syringe)
Figure 5.1 A 3-mL syringe
Figure 5.2 A 1-mL syringe
© 2010 Delmar, Cengage Learning.
10
Parenteral Dosage Calculations
(cont’d.)
▪ 0.25 mg of a medication by IM injection is
ordered
• In stock is a vial labeled 0.5 mg in 2 mL
• What volume should be administered?
▪ Dosage formula:
• .
© 2010 Delmar, Cengage Learning.
11
Parenteral Dosage Calculations
(cont’d.)
▪ Proportions:
• .
▪ Dimensional Analysis:
• .
© 2010 Delmar, Cengage Learning.
12
Reconstitution of Solutions
▪ 300 mg Zithromax IV is ordered
• In stock is a vial of powdered Zithromax that
states:
– “Constitute to 100 mg/mL with 4.8 mL of Sterile Water
for Injection”
– Single-dose vial contains 500 mg
▪ Dosage formula:
• .
© 2010 Delmar, Cengage Learning.
13
Reconstitution of Solutions (cont’d.)
▪ Proportions:
• .
© 2010 Delmar, Cengage Learning.
14
Reconstitution of Solutions (cont’d.)
▪ Dimensional analysis:
• Express:
© 2010 Delmar, Cengage Learning.
15
Intravenous Flow Rates
▪ Rate of flow: number of drops (gtt) that flow
into patient per minute
• .
• Drop factor: number of drops it takes to produce
1 cc
• Amount of solution: total amount of solution
administered
• Time: time it takes for solution administration
© 2010 Delmar, Cengage Learning.
16
Intravenous Flow Rates (cont’d.)
▪ An IV bag contains 1,000 mL solution
• Drop factor is 90 gtt/mL
• Flow rate is 125 gtt/min
• Find infusion time:
© 2010 Delmar, Cengage Learning.
17
Intravenous Flow Rates (cont’d.)
▪ Dimensional analysis:
• .
© 2010 Delmar, Cengage Learning.
18
Titration of Intravenous Medications
▪ Four-step process:
•
•
•
•
If order has different units than strength of
solution, convert the strength
Determine lower limit by using lower range
given together with patient’s weight
Use step 1 result to convert lower limit in step 2
into units of milliliters per hour
Use step 3 result together with ratio of upper
titration range to lower titration range, to find
upper limit
© 2010 Delmar, Cengage Learning.
19
Titration of Intravenous Medications
(cont’d.)
▪ IV line was ordered to titrate between 2 and
4 mcg/kg/min
• Patient weighs 60 kg
• IV solution contains 60 mg of drug in 300 mL
solution
• Determine rate of flow in milliliters per hour
© 2010 Delmar, Cengage Learning.
20
Titration of Intravenous Medications
(cont’d.)
▪.
© 2010 Delmar, Cengage Learning.
21
Titration of Intravenous Medications
(cont’d.)
▪ Using dimensional analysis:
• .
© 2010 Delmar, Cengage Learning.
22
Dosages Based on Weight
▪ Convert patient’s weight to kilograms
▪ Find dose (range) for body weight
• Example: 400 mg/kg/day for 99 lbs
– How many milligrams a day?
– How many every 6 hours?
© 2010 Delmar, Cengage Learning.
23
Dosages Based on BSA
▪ Formulas:
• .
• West Nomogram: common chart used to
estimate BSA
– See Figure 5.3
© 2010 Delmar, Cengage Learning.
24
Summary
▪ Physicians use short-hand notations
▪ Drug labels contain a lot of information
▪ Dosages can be calculated using formulas,
proportions and dimensional analysis
▪ Many parenteral dosages and reconstitution
of solutions can be determined by using:
© 2010 Delmar, Cengage Learning.
25

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Being Precise

Patient medication

labels of medications

precise calculations

proper conversions

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