fluids, requirement for

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Help for sleepless parents

fluids, requirement for

Maybe it has crossed your mind - "Hey, I don't know how much fluid my child needs to drink in a day." I know - I get this uneasy feeling every time I put a child in the hospital and have to write IV orders. Here is how we calculate daily fluid requirements:

First, learn the metric system. (Rats. I thought I didn't need that after high school.)
Next, determine your childs weight in kilograms. Divide the weight in pounds by 2.2, or multiply it by 0.45, or do like I do and just take half the weight in pounds and call it kilograms. Close enough.
The easy-to-remember fluid requirement rule is
- 100 cc per kilogram for the first ten kilograms
- 50 cc per kilogram for the next ten kilograms
- then 10 cc per kilogram for each kilogram thereafter

Example #1 - 20 pound child:

That is about 10 kilograms
100 cc of fluid per kilogram for each of the 10 kilos equals 1,000 cc of fluid - which is 33 ounces or about one quart. (Remember, a cc and an ml - cubic centimeter or milliliter - are the same)

Example #2 - 12 pound child:

That is about 6 kilograms (OK, OK, 5.448 kilograms)
100 cc of fluid per kilogram for each of the 6 kilos equals 600 cc of fluid - which is 20 ounces

Example #3 - 44 pound child:

That is about 22 kilograms
100 cc of fluid per kilogram for each of the first 10 kilos equals 1,000 cc of fluid
Then 50 cc per kilogram for each of the next 10 kilos makes 500 cc
And 10 cc per kilogram for each of the last 2 kilos makes 20 cc
Grand total: 1,000 + 500 + 20 = 1,520 cc or about 50 ounces

I know this sounds awfully imprecise, but the body works it out just fine. We have a saying in medicine: "The dumbest kidney is smarter than the smartest doctor."

Now, remember again, this is only basal requirements (see below). If, for example, the body temperature is elevated one degree Celsius (there is that darn metric system again - 1.8 degrees Fahrenheit), for a whole day, increase the fluid requirements by 10%. But don't trouble yourself with this degree of detail; doctors rarely do.

The beauty part is - if you know the fluid requirements, now you know the caloric requirement too! It turns out that for what we call basal metabolism (just running the machine at idle, not walking around, no sports, no allowance for growth, or any other reason to rev up the body machinery), a human burns a calorie for each cc of fluid metabolized, and vice versa.

I admit there is little practical utility in everyday life for this arcane knowledge, but it just might help you someday.

The more precise formula is 100 kcal/kg for an infant 3 to 10 kg; 1000 kcal plus 50 kcal/kg for a child from 10 to 20 kg; 1500 kcal plus 20 kcal/kg over 20 for weights >20 kg. On average, ~40 mL/100 kcals/24 h will replace insensible losses and ~60 mL/100 kcals/24 h will replace urinary losses.

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