Hyponatraemia

Hospitalised patients receiving intravenous fluids, particularly fluids that are hypotonic to plasma, should have their serum electrolytes checked on a daily basis and urgently if signs of cerebral oedema occur. This applies particularly to the administration of hypotonic intravenous fluids given in the setting of pain and opioid use, or the post-operative state.

Hyponatraemia may develop in patients taking selective serotonin-reuptake inhibitors or thiazide diuretics. This usually occurs within 2 weeks of starting therapy. Patients should have their serum sodium levels checked if they report any symptoms (e.g., headache, change in balance, mental status changes).

In patients who are actively being treated for hyponatraemia, serum sodium concentration should be tested every 2 hours to guide therapy until stabilisation occurs and hypertonic saline is no longer required. It should then be tested every 8-12 hours for 24 hours, and every 24 hours thereafter to monitor the ongoing rate of correction. Urine output should be monitored as spontaneous diuresis can occur that may lead to overcorrection of the serum sodium concentration. If urine output changes abruptly, serum sodium levels should be reassessed. Following hospital discharge, treatment is generally determined by the underlying condition(s).