Hyponatremia and cerebral vasospasm in subarachnoid hemorrhage: a systematic review and meta-analysis

Hyponatremia, defined as serum sodium < 135 mEq/L, is a common complication following aneurysmal subarachnoid hemorrhage (aSAH) and has been implicated in the development of cerebral vasospasm, a significant contributor to delayed cerebral ischemia and poor neurological outcomes. However, the strength and consistency of this association remain unclear. This study aimed to evaluate the relationship between hyponatremia and angiographically or radiologically confirmed vasospasm in patients with aSAH.

A comprehensive search of PubMed, Scopus, Embase, and Medline was conducted through July 2025, adhering to PRISMA guidelines (CRD42024621575). Eligible studies included adult or pediatric patients with aSAH, reported serum sodium levels, and documented vasospasm confirmed by imaging. Data were extracted independently by three reviewers, and methodological quality was assessed using a modified Newcastle-Ottawa Scale. Pooled odds ratios (ORs) with 95% confidence intervals (CIs) were calculated using a random-effects model. Heterogeneity and publication bias were assessed using I² statistics and funnel plots, respectively.

Seven studies comprising a total of 983 patients were included in both the systematic review and meta-analysis. Among these, 403 patients developed vasospasm, with 243 having experienced hyponatremia prior to the event. The pooled analysis demonstrated a significant association between hyponatremia and vasospasm (OR = 2.59; 95% CI: 1.60-4.20; p = 0.0001). Moderate heterogeneity was observed (I² = 53%), and no evidence of publication bias was detected.

Hyponatremia is significantly associated with increased risk of cerebral vasospasm in SAH patients. Serum sodium may suggest potential as a component of risk stratification models. Prospective studies are needed to explore causality and the therapeutic impact of sodium correction on clinical outcomes.