Outcome and frequency of sodium disturbances in neurocritically ill patients

Sodium disturbances are frequent and serious complications in neurocritically ill patients. Hyponatremia is more common than hypernatremia, which is, however, prognostically worse. The aim of this study was to analyse outcome and frequency of sodium disturbances in relation to measured serum osmolality in neurologic-neurosurgical critically ill patients. A 5-year retrospective collection of patients (pts) and laboratory data were made from the Laboratory Information System database in the Clinical Biochemistry Department. The criteria for patients' inclusion was acute brain disease and serum sodium (SNa(+)) <135 mmol/l (hyponatremia) or SNa(+) >150 mmol/l (hypernatremia). Hypoosmolality was defined as measured serum osmolality (SOsm) <275 mmol/kg, hyperosmolality as SOsm >295 mmol/kg. We performed analysis of differences between hyponatremia and hypernatremia and subanalysis of differences between hypoosmolal hyponatremia and hypernatremia. From 1,440 pts with acute brain diseases there were 251 (17 %) pts with hyponatremia (mean SNa(+) 131.78 ± 2.89 mmol/l, SOsm 279.46 ± 11.84 mmol/kg) and 75 (5 %) pts with hypernatremia (mean SNa(+) 154.38 ± 3.76 mmol/l, SOsm 326.07 ± 15.93 mmol/kg). Hypoosmolal hyponatremia occurred in 50 (20 % of hyponatremic patients) pts (mean SNa(+) 129.62 ± 4.15 mmol/l; mean SOsm 267.35 ± 6.28 mmol/kg). Multiple logistic regression analysis showed that hypernatremia is a significant predictor of mortality during neurologic-neurosurgical intensive care unit (NNICU) stay (OR 5.3, p = 0.002) but not a predictor of bad outcome upon discharge from NNICU, defined as Glasgow Coma Scale 1-3. These results showed that hypernatremia occurred less frequently than all hyponatremias, but more often than hypoosmolal hyponatremia. Hypernatremia was shown to be a significant predictor of NNICU mortality compared to hyponatremia.