You should be aware with two different values.
1. Normal mentainance
2. Replacement for hypokalemia
Normal mentainance of potassium is usually about 2 to 4 mEq/kg/day for infants and children and 1 to 2 mEq/kg/day for adolescents. Usually we use the 20 meq/l solution as mentainance to achieve this normal requirement. However this could not be enough for some patients such as fluid restricted patients and patients recovering too much medications so that the volume left for the mentainance solution is too little to achive the usually required K with the concentration of 20meq/l. In such situations, we have to increase the concentration more than 20meq/l according to the usual need for the patient. Remember, we still talking mentainance.
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As replacement, we should add more K according to the status of hydration (is the patient dehydrated? and what type of dehydration). Usually the deficit can be calculated using the following formula:
potassium deficit = fluid deficit (L) × 0.4 x 120 mEq/L
You can read more about this from:
1. ACCP Updates in Therapeutics: Pediatric Pharmacy Preparatory Review and Recertification Course, Fluids and electrolytes chapter.
2. The Harriet Lane Handbook, Fluids and electrolytes chapter.