Hyponatremia, hypernatremia: a physiological approach.
Natremia belongs to the toolbox of the practicing intensivist. It is an indicator of the hydration status, which is an item that must be continuously monitored in critically ill patients. Hyponatremia is not rare (1% to 2% of hospitalised patients), and hypernatremia is about 10 times less frequent while hypernatremia always indicates hypertonicity, hyponatremia is not equivalent to hypotonicity. Diagnosis depends on the history, clinical examination and basic biochemical data. It should be kept in mind that obtaining urine samples is as important as plasma samples in this respect. The first step consists in confirming that hyponatremia is hypotonic. The second step is to assess the renal response to hypotonicity. Hypotonic hyponatremia will be considered in association with hypovolemia, euvolemia or hypervolemia. The constitution of a hyperosmolar state requires an inadequate water intake The main goal of the treatment is not to normalize numbers (they must always be checked first), but to treat symptoms. Tolerance must always be appreciated. The mathematical formulas proposed are of interest for a better understanding, but should not be followed strictly.
Offenstadt
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Medical Intensive Care Unit, Hôpital Saint-Antoine, Paris, France. georges.offenstadt@sat.aphp.fr
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