The Effect of Hyponatremia and Sodium Variability on Outcomes in Adults with Aneurysmal Subarachnoid Hemorrhage

BACKGROUND: Hyponatremia is common in patients with subarachnoid hemorrhage, but its effect on outcomes remains contentious. Fluctuation in sodium has been reported to negatively affect perioperative outcomes in general surgical patients, but not specifically in patients with a subarachnoid hemorrhage. The primary aim was to describe the relationship between 1) hyponatremia and 2) sodium fluctuations during intensive care and neurologic outcome at hospital discharge. METHODS: Adults with aneurysmal subarachnoid hemorrhage between January 2012 and September 2013 were retrospectively reviewed. Data were collected for admission to day 14 of intensive care or death. Severity of illness was assessed by Hunt and Hess grade and simplified acute physiology score. Hyponatremia was defined as any measurement <135 mEq/L. Sodium variability was categorized as a maximum change of < 6, 6-12, or >12 mEq/L during intensive care. Neurologic outcomes at discharge were assessed by modified Rankin Scale. The relationship between sodium and outcome was assessed by ordinal logistic regression. RESULTS: A total of 198 patients were included. After adjustment for Hunt and Hess grade, severity of systemic illness, patient age, surgical intervention, and whether or not the hyponatremia was treated with additional sodium, hyponatremia was not associated with worse neurologic outcomes. More patients with sodium variability of 6-12 and >12 mEq/L had cerebral infarction than those with variability < 6 mEq/L and had modified Rankin Scale scores of 2-3 and 4-6, respectively (P = 0.001). CONCLUSIONS: Sodium fluctuation, not hyponatremia, is associated with worse neurologic outcome in patients with aneurysmal subarachnoid hemorrhage. This is in contradistinction to current teaching and warrants further examination.