Hypernatremia is common only in patients that cannot choose the fluids they take in (OK and in diabetes insipidus patients) – this pertains to practically all our stroke unit patients. So we review the physiology and pathophysiology of sodium and osmolality (-larity) derangements to develop a practical plan.
The plan is
- get a history and do a physical examination
- get Na, K, Cl, osmolality in serum and urine, urea and uric acid in serum and urine
- know where to look up the formulas of total body water, free water deficit
- know where to find the algorithm that uses the above data to compute what is the matter.
Much more important than the algorithm is prevention. This means that all patients that are on nasogastric tubes need to be offered free water to choose whether they want it (unless they have DI, in which case that doesn’t help).