For every 100 mL of replacement fluid, add 8 mEq of Na^{+}, 6 mEq of K^{+} and 6 mEq of Cl^{} 
Example 1.
A 12 kg, 94 cm tall child is assessed as being 10% dehydrated (he was about 13 kg a few days ago when he was feeling well). His serum chemistry shows: Na=143, K=4.5, Cl=104, HCO3=18. He is now in stable condition and requires treatment for his isotonic dehydration. Using the caloric method (or the HolidaySegar method which is equivalent in this case), his energy requirement is 1100 kcal/day which translates to 1100 mL/day.

First, figure out the amount of fluid that must be given to make up
the deficit. To determine how much electrolytes to add to this fluid,
divide the fluid volume into two equal portions. The first half is
targeted to replace fluid from the extracellular compartment, so the electrolytes
should be make proportional to expected serum values for Na, K, and Cl,
namely a sodium of 140 mEq/L, potassium of 4 mEq/L and Cl of 100 mEq/L.
The other half is considered to be replacement for the intracellular compartment
where potassium is normally about 160 mEq/L. The other electrolytes
in this compartment are negligible.
Example 2.
The same child as above comes into the ER, but this time, he would like his iv fluid therapy to be calculated on a body surface area basis. Being an obliging pediatrician, you comply. He is older than 6 months, so his total body water is about 60% of body weight. Since he is about 10% dehydrated on a weight basis, he is about 16.6% depleted in terms of total body water (=10%/0.6). Since his normal body water would be 7.2 liters (=60% of 12 kg), he must be depleted by about 1200 mL (=16.6% of 7.2 liters). Maintenance is calculated by the body surface area method. In this case, his surface area is calculated as 0.56 m2. As in the caloric method, his fluid requirements are a combination of
his daily maintenance requirements plus whatever he needs to replace the
deficit:

In cases where the patient has received a bolus of fluid for immediate
volume repletion, this bolus must be subtracted from the above calculations.
Here is another example, using the caloric method of calculation:
Example 3.
A 40 kg girl presents with 12% dehydration (she weighed 45 kg last week).
In the ER, she received a two 20 mg/kg boluses of normal saline.
Calculate fluid replacement therapy using the caloric method:

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