In hypernatremia there is often a deficit of body water. From knowledge of body weight and serum sodium levels the magnitude of the deficit can be estimated.
Method 1
normal total body water in liters =
= 0.6 * (body weight in kilograms)
current total body water in liters =
= (normal serum sodium in mEq/L) * (normal total body water) / (measured serum sodium in mEq/L)
body water deficit =
= (normal total body water) - (current total body water)
Method 2
current total body water in liters =
= (factor) * (current body weight in kg)
where:
• factor = 0.5 for males; 0.4 for females, the elderly in with cachexia
body water deficit in liters =
= (current total body water in liters) * (((serum sodium in mEq/L) / 140) - 1)
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