Foundations II Dosage Calculations

1
Foundations IIDosage Calculations

• Fermin Renteria, MNSc, APN, CPNP

2
IV Calculations

• Will generally see large volumes ordered in
  mL/hr, i.e. infuse D5½NS 20mEq KCl at125 mL/hr
• mL/hr flow rates are generally used for IV pumps
• Must convert to gtt/min when no pump used
• Most common conversion is mL/hr to gtt/min
• IV tubing is calibrated in gtt/mL
• Macrodrip tubing is common 10, 15, or 20 gtt/mL
• Microdrip tubing ALWAYS 60 gtt/mL
• DO NOT use the oral volume conversion of
  15gtt/mL, the tubing calibration will always be
  given to you in the problem
• Example problem D5½NS 20mEq KCl to infuse at
  125 mL/hr. The tubing has a drop factor of
  20gtt/mL. Calculate the flow rate in gtt/min

3
IV Calculations

• Small volumes (usually 100 ml or less) can be
  ordered to infuse over less than 1 hour, i.e. 100
  mL to be infused over 40 minutes
• Need to convert mL/min to gtt/min
• This means only 1 conversion is necessary mL to
  gtt
• To calculate completion time from ordered flow
  rate, i.e. 500 mL ordered to run at 40 mL/hr
• Divide ordered volume by flow rate
• 500 ml x 1 hr 12.5 hr
• 40mL

4
IV Calculations

• Heparin infusions
• Heparin is most commonly ordered in U/hr
• Heparin is available in U/mL solutions
• Calculating gtt/min flow rate is same process as
  for other IV fluids
• A heparin solution of 40,000 U/1000 mL D5W is
  ordered to infuse at a rate of of 1000U/hr. A 15
  gtt/mL set is used.
• 1000U x 1 hr x 1000 mL x 15 gtt
• 1 hr 60 min 40,000 U 1 mL
• To calculate U/hr infusing when given mL/hr
  infusing, begin with ordered flow rate and
  convert
• An IV of 1000 mL D5W containing 40,000 U of
  heparin has been ordered to infuse at 30 mL/hr.
  Calculate the U/hr infusing.
• 30 mL x 40,000 U
• 1 hr 1000 mL

5
Keys to Success

• Use the drug math text, text CD-ROM, and lecture
  notes to understand concepts.
• Use the drug math text CD-ROM for practice
  working problems.
• Use the practice tests on the drug math website.
• Prepare and take each test early in the exam time
  frame to help decrease stress/pressure.
• Be prepared, well-rested, and ready to do your
  best when you take a drug math test.

6
Keys to Success

• ALWAYS begin with medication order
• Label everything
• Cross off as conversions are made
• Final label must be on top
• Read the question carefully
• THINK about your answer
• DO NOT put labels in answer box, the computer
  will count it wrong
• You must ask the staff to keep your scratch
  paper, be sure your name is on it and that it is
  readable