OBJECTIVE: Symptomatic vasospasm (SVS) affects the outcomes of patients with subarachnoid hemorrhage (SAH) and often requires endovascular treatment. Hyponatremia is a predictor of SVS
however, no guidelines have recommended an absolute serum sodium value for SVS prevention. This study aimed to identify factors that influence SVS in patients with low-grade SAH and determine a specific threshold of serum sodium level that predicts SVS. METHODS: We conducted a multicenter, retrospective study of 216 patients with aneurysmal SAH grades I-III (World Federation of Neurological Societies scale). Patients were divided into the endovascular treatment-needed vasospasm (etVS) group (n = 29) and non-etVS group (n = 187). The minimum serum sodium level (minNa) was determined in the initial 2 weeks after SAH onset. RESULTS: The minNa of the etVS group (median 132 mmol/L) was significantly lower compared to that of the non-etVS group (median 136 mmol/L) (p <
0.002). The receiver operating characteristic curve revealed that a threshold minNa of 133 mmol/L predicted the development of etVS (sensitivity 0.797 and specificity 0.552), and the area under the curve was 0.703 (95% confidence interval [CI]: 0.591-0.815). The odds ratios for etVS in patients with a minNa ≤128 mmol/L and 129-132 mmol/L were 6.79 (95% CI: 2.24-20.51) and 2.96 (95% CI: 0.90-9.73), respectively, when compared to those with a minNa 133-136 mmol/L. CONCLUSION: Serum sodium levels were a predictor of etVS in patients with low-grade SAH. This is the first study to identify a threshold of serum sodium level for predicting etVS, aiding clinicians in setting a management goal for SVS prevention.