Just add water....

JUST ADD WATER.......

Today we talked about a classic internal medicine case: hypernatremia. We divided our approach by etiology into “low total body sodium”, “water losses” and “sodium addition”.

Low Total Body Sodium:
These patients may be divided into renal or extra renal losses. The renal losses include osmotic diuresis (mannitol, glucose, urea). Extra renal losses tend to be sweating and diarrhea. Urine sodium helps to differentiae these two in that urine sodium will be >20mEq/L in an osmotic diuresis while it would be expected to be <10mEq/L with diarrhea and excessive sweating. The recommended treatment approach would be hypotonic saline.

Water Loss (Normal total body sodium):
Again the approach to these patients can be divided into renal and extarenal causes. Renal causes include both nephrogenic and central diabetes insipidus. Extra renal water loss tends to be insensible losses from respiratory tract or skin. Urine sodium is less helpful to differentiate this group as in both cases it will be variable. The treatment of choice is replacement of the water.

Increase total body sodium:
There are a number of causes of increase body sodium including endocrinopathies and exogenous administration (chloride, bicarb, saline admin). Endocrine causes include primary hyperaldosteronism and less commonly Cushings. Urine sodium will tend to be >20 mEg/L in these patients. Treatment is again replacement of the water deficit.

For more information / a slightly different appraoch you can review the NEJM review article: http://content.nejm.org/cgi/reprint/342/20/1493.pdf