Correction: Detective Nephron: An Electrolyte Mystery

Correction: Kidney News regrets an error in the March Detective Nephron column in which text was incorrectly repeated on the first page. The corrected text appears here.

Nice Glom (the new medical student) enters the room along with L.O. Henle to present a case.
Nephron What do you have for me today Henle?
Henle looks at Glom
Glom I have a 65-year-old man with a serum sodium concentration of 112 mEq/L.
Nephron Hyponatremia! My favorite electrolyte disorder. What is the first question you need to ask?
Henle Whether the patient has symptoms?
Nephron Exactly. Given the severity of this hyponatremia, we need to know if we need to treat immediately with hypertonic saline to avoid life-threatening cerebral edema. Severe symptoms such as seizures and coma indicate significant cerebral edema and require the use of NaCl 3% 100 mL IV bolus, which you could repeat twice if symptoms persist. Moderate symptoms such as confusion indicate a lesser degree of cerebral edema but still significant enough to be dangerous and also require the use of NaCl 3% but in slow infusion. Remember, severely symptomatic or moderately symptomatic hyponatremia are medical emergencies and need to be treated with hypertonic saline.
Henle I interviewed the patient and did a full neurological exam. The patient is asymptomatic.
Nephron (upset) That is not entirely true, is it? Evidence has emerged over the last several years suggesting that all hyponatremias are symptomatic to a degree. Even mild chronic hyponatremia in the range of 125 to 135 mEq/L is not only associated with increased mortality but also increased morbidity in the form of subtle attention deficits, gait disturbances, falls, fractures, and osteoporosis.
Glom I did not know that.
Nephron (smiling) Are you familiar with the concept of regulatory volume decrease or RVD?
Henle & Glom (looking at each other) No.