Numeracy for Nursing Practice

IV Infusions: Calculating a Flow Rate in mL/hr

• IV Infusions: Calculating a Flow Rate in mL/hr

  Calculating a flow rate in ml/hr requires us to learn a second formula: Volume = Rate x Time.

  This can be reduced to the mnemonic VRT (Very Rarely Troubled!)

  Nurses need to be able to calculate any one of the three elements of the formula from the other two:

  • Volume - for calculating how much fluid should be left in a bag after a given amount of time
  • Rate - for setting a flow rate im ml/hr
  • Time - for calculating how long an infusion will take

  You may already be happy with transposing the 3 elements of the VRT formula - in which case, stick with it! If not, then the 3 permutations are as follows:

  1.Volume = Time x Rate

  2.Rate = Volume ÷ Time

  3.Time = Volume ÷ Rate

  Some people find a more visual representation easier to remember. The presentation below introduces a useful triangle menmonic for remembering the formula. If you can remember that 'the bag goes up high', then you will easily be able to construct the rest of the triangle. Remember to cover up the element that you wish to calculate.

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    Using the VRT Formula File

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    This presentation originally formed part of a Skills Lab Scenario Workshop undertaken by the 2nd Year BSc Adult Nursing cohort in May/June 2013. The 2 mnemonics plus examples should help you to remember, understand and apply this formula to a variety of calculations.

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    VRT Mnemonic Page

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    Test Yourself URL

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    Test your VRT skills with this page from Queen's University Belfast - clicking on this link will open the resource in a new window.