The first thing to say is that a child who is severely unwell due to fluid loss ( ie in shock) should be aggressively resuscitated as per any other form of shock with 20ml/kg boluses of warmed normal saline until organ perfusion is restored.
The next thing to say is that in most cases, rehydration by the oral or naso-gastric route (using a rehydration solution such as Gastrolyte)Â is far more preferable for mild to moderate cases of dehydration than IV fluid replacement.
OK, so that aside. Lets say you are looking after a young girl who has an IV drip in progress. The girl weighs 10 kg and you want to get some idea if the drip is running at the correct rate.
In order to calculate an accurate fluid replacement it is important to plug in an accurate weight. Ideally, you want to obtain a bare weight.
If this is not possible you can make a rough calculation with the following formula: Wt = [ age in years + 4] x 2
maintenance fluid rate:
There are many normograms and calculations to determine a child’s maintenance fluid requirements.Â Most are based on an estimation of the child’s weight, body surface area or amount of expended calories to arrive at an amount to be delivered over 24 hours.
The simple method we are going to look at is known as the 4:2:1 method. This method will give you a quick way of calculating the required mls per hour
- 4 ml/kg/hr for the first 10 kg,
- adding 2 ml/kg/hr for the second 10 kg
- and 1 ml/kg/hr for each kg over 20 kg.
For an 8kg child we calculate 4mls per kg for the first 8kg.
This gives us a total of 32 mls/hr.
For a 15 kg child we calculate 4mls per kg for the first 10kg, and then add 2mls per kg for the next 5 kg.
This gives us a total of 50 mls/hr.
For a 28kg child we calculate 4mls per kg for the first 10kg, and then add 2mls per kg for the next 10kg, and finally add 1ml per kg for the remaining weight.
This gives us a total of 68 mls/hr.
Replacement of deficit:
Remember we have only calculated replacing the child’s usual fluid requirements,Â we also need to consider any acute deficit in hydration caused by such problems as
- Gastroenteritis (a common cause in children)
- Inadequate fluid intake
- Diabetes mellitus
The most accurate way to do this is to compare their current weight with their pre-morbid weight, that is, their weight before they became ill. This is usually not practical and so the less accurate method of clinically assessing their deficit must be used:
*Skin condition is less useful in diagnosis of dehydration in children >2 years of age.
Now, to calculate the estimated deficit in mls:Â multiply the weight(kg) by the deficit%,Â and multiply the answer by 10.
For an 8-kg child with 10% dehydration:
8 kg x 10% x 10 = 800 mls.
This deficit is usually given over 6 to 8 hrs and added to the maintenance rate.
So what of our 10 kg girl?
Well she was estimated to be around 10% dehydrated and had her drip started around 3 hrs ago. You check and find itÂ is running at 140 mls per hour. What do you think about that?
To gauge the effectiveness of any fluid therapy you need to keep a close eye on the child’s vital signs, capillary refill, skin turgor and urine output (we want at least 1ml/kg of urine per hr in children and 2ml/kg/hrÂ in infants). You might like to check out some info on paediatric circulatory assessment.
[Photo credit: jenn jenn]