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Sodium and potassium requirements

The kidneys are able to regulate body Na content by conserving or excreting Na over a wide range, so a precise intake is not necessary. For example:

1

Minimum sodium requirement

In an effort to lose weight rapidly for an upcoming class reunion, the author goes on a "distilled water only" diet. After a couple of days, what will the daily urinary Na excretion be closest to?

a)
b)
c)
Correct. The kidneys can reduce urinary sodium excretion to negligible amounts if the intake is very low. The minimum daily sodium requirement is therefore very small.Incorrect. Pick another answer.Your answer has been saved.
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2

Maximal sodium excretion

After a week, the author gives up, decides to skip the reunion, heads to the local pizzeria, and proceeds to single-handedly demolish a large pizza with pepperoni, sausage, and anchovies. The total salt content of the pizza is 25 G. Over the next day or two, the author will:

a)
b)
c)
Correct. We all ingest excess on occasion. The kidneys can excrete an acute salt load of up to 25 g without any trouble.Incorrect. Pick another answer.Your answer has been saved.
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More info: The consequences of pizza

It is clear that there is no strict daily Na requirement since, in the normal individual, homeostatic mechanisms will instruct the kidney to conserve or excrete Na and keep total body sodium content within the normal range.

However, based on recommendations made by Holliday and Segar, the daily Na requirement is estimated at 3 mEq/100 ml of water water requirement. Holliday and Segar decided on this number by looking at the Na content of human and cows' milk. So, Na is added to maintenance fluids at a concentration of 3 mEq/100ml or 30 mEq/L. For an adult, this will provide about 75 mEq of Na/day, equivalent to approximately 4.5 G of salt.

Using the same reasoning, the maintenance K requirement is estimated at 2 mEq/100 ml of fluid or 20 mEq/L. Potassium either comes pre-added or can be manually added to any intravenous solution at a concentration of 2 mEq/100 ml or 20 mEq/L to provide the appropriate amount of K for maintenance.

In children who have a condition that might predispose to renal failure, such as dehydration, K is not added to intravenous fluids until the presence of renal function has been established.

Note: K concentration in IV fluids of up to 40 mEq/L is used for correction of hypokalemia. A concentration exceeding 40 mEq/L is irritating to the veins and may be dangerous!

3

Daily Na and K requirements

Using these conventions [Na 3mEq/100 ml; K 2mEq/100 ml], the daily Na and K requirements for a 10 Kg child are:

a)
b)
c)
Correct. Very Good!Incorrect. Try again.Your answer has been saved.
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