Hyponatraemia: Ask the right questions

Asking the right questions in these two cases helped to identify their dangers and to plan the right treatment. In both patients hyponatraemia was truly hypotonic (low serum osmolality). In the first patient, hyponatraemia was acute and symptomatic, warranting hypertonic saline for cerebral edema. In the second patient hyponatraemia was likely chronic, but she was mildly symptomatic. Therefore, a moderate rise in serum sodium was established with hypertonic saline, followed by a gradual correction to prevent osmotic demyelination. In both patients vasopressin was elevated (high urine osmolality) due to their medication (risperidone and the thiazide diuretic, respectively). Finally, both patients did not have signs of a low effective arterial blood volume and therefore had no indication for treatment with isotonic saline.