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.