Review of investigation and management of severe hyponatraemia in a hospital population

The purpose of this study was to assess retrospectively the prevalence of s evere hyponatraemia in a hospital population and its laboratory investigati on, treatment and clinical outcome. Over a 6-month period 47 patients (27 w omen and 20 men) were found to have a plasma sodium concentration of less t han or equal to 120 mmol/L (this number made up less than 0.17% of all plas ma sodium requests over that time period). The mean patient age was 75+/-16 years and the average hospital stay was 37+/-45 days (1-179 days). Patient mortality was 51% (women 57% and men 43%). The mean initial plasma sodium concentration was 116+/-4.5mmol/L, rising af ter therapeutic intervention to a mean of 130+/-4.2mmol/L. The mean plasma sodium correction rate was 4.7+/-4.3mmol/L/24h (0.9-17.5 range). Twelve per cent of the patients had their plasma sodium raised at a rate of greater t han 10 mmol/L/24 h after their initial presentation. Two patients may have had symptoms and signs suggestive of cerebral oedema/cortical dysfunction: in one patient the sodium concentration was raised at a rate of 9.5 mmol/L/ 24 h and in the other at 12.0 mmol/L/24 h. Sixty-one per cent of the patients had a chest infection, 44% were on diure tics, 28% had congestive cardiac failure, 28% were post-operative (9% ortho paedic procedures), 19% had carcinoma and 9% were on a selective serotonin re-uptake inhibitor. Regarding laboratory investigations, 56% had liver fun ction tests, 41% had thyroid function tests, 36% had plasma osmolality dete rmination, 36% had urinary electrolytes including urinary osmolality and <2 % had tests to exclude hypoadrenalism.