Basics in IV Fluids Calculation

Here’s a few basic calculation stuff…

Standard IV set delivers either 15 drops or 20 drops per ml.

Simple maths first. I will use the 15 drops per ml as a guide.

1ml = 15 drops

1L = 1000ml = 15000 drops

1L/hr = 15000 drops/60 mins = 250 drops/min

250 drops/min = 250 drops/60 secs = 4 drops/sec

In summary, 4 drops/sec from a 1L solution bag given intravenously completes 1L of fluid in an hour.

So, in order to give 2L of fluids within an hour in an emergency setting, the rate of drops is doubled to compensate for the amount given. 8 drops/sec. Pure mathematics.

The average of amount an adult needs is about 2.5 – 3.0 litres of water per day.

  • 1.5L is lost from urine output.
  • 1.0L is lost from breathing, sweating and gut movement.
  • ≈ 0.5L for additional losses. (giving a bit more is better than giving lesser)

Info from MayoClinic. http://www.mayoclinic.com/health/water/NU00283

Therefore, for a relatively well person, if he is to be put on an IV drip (nil by mouth of course…), he needs 3.0L of fluids/24 hours. The calculation is as below.

24 hours = 3000ml

1 hour = 125ml

1 min = 125ml/60min = 2ml/min

1ml = 15 drops

2ml/min = 30 drops/min = 0.5 drop/sec

You can’t possible have a 0.5 drops rite… so just multiply it by 2 loh. Which means 1 drop/2 secs.

In summary, by giving 1 drop over 2 secs for 24 hours in a patient who is NBM, you will complete a total of 3L of fluids in a day.

If we are to prepare a patient (relatively fit) for surgery and to fast him/her for a day, this is the rate of fluids that we should be giving. If patient needs to go for a surgery within 6 hours of admission, it’s just the same. Taken into account that the patient has been eating normally before admission.

In order for the nurses (or whoever is setting up the drip) to understand, this is what should be written on the case notes:

IV 1L of 0.9% saline (or 5% dextrose). Run at 125ml/hr (1 drop/2 secs).

Why a litre and not 3? There’s no point in writing 3L when you do only have 6 hours. 125ml x 6hr is only 750ml. Therefore, just use a 1L bag would be sufficient.

Fluid Therapy for the Needy

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21 thoughts on “Basics in IV Fluids Calculation

  1. well eric, actualy i want to thank you for this IV COMPUTATION, it help me a lot, now i understand much better.. i am a nursing student and we will be taking this topic early this morning, and im happy that i’ve learn from you in just a single moment viewing you posted note…

    thanks a lot eric… and i hope i can see more info in relation with science like this from you, i know your notes can help me to understand those certain things…

    heres my email if you have time to send some to me… i posted it into you private info response table

    Godbless eric!!! and more power to you!!!

  2. thanks that was a nice one.
    i have an query with regard to IV fluid duration.how could we calculate the duration of iv fluids in general when it cannot be simplified easily.For eg if there is an IV order of 7 pints in 24 hours. how can we calculate the time duration of each pint,
    thanks.

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