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 other electrolytes in this compartment are negligible. 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.
Maintenance is calculated by the body surface area method.
In this case, his surface area is calculated as 0.56 m2. The two methods for calculating replacement fluids agree well in terms of concentration of electrolytes per liter of replacement fluid. However, the caloric method predicts a total fluid requirement about 250 mL greater than the surface area method. These differences are minor compared to the total fluid volume, so this discrepancy does not cause problems. In cases where the patient has received a bolus of fluid for immediate volume repletion, this bolus must be subtracted from the above calculations.