Severe hyponatraemia in elderly patients: cause for concern.

Abstract An increased incidence of severe hyponatraemia in an orthopaedic unit led to an investigation into the possible causes. Routine perioperative administration of 'hypotonic' intravenous fluid to an elderly population emerged as the most important aggravating factor. Care is necessary in prescribing intravenous fluid regimens in order to avoid potentially serious complications.