Hyponatremia incidence after subarachnoid hemorrhage and association with outcomes: systematic review and meta-analysis

Objective: Hyponatremia after aneurysmal subarachnoid hemorrhage (aSAH) is common, however the incidence, and association with vasospasm, morbidity, and mortality, has yet to be defined. We aimed to identify incidence of hyponatremia after aSAH, and quantify its association with measurable outcomes.

Methods: A PRISMA-compliant systematic review and meta-analysis was conducted (PROSPERO ID CRD42022363472). Articles published in MEDLINE, EMBASE, and Cochrane Library between January 1990-January 2024 were included. Hyponatremia definitions, incidence during admission, and association between vasospasm, length of hospital stay, and poor outcome (Glasgow Outcome Scale three or less) were identified. Pooled incidence rates, binary and continuous outcomes were calculated using random effects meta-analysis models.

Results: In total, 52 studies (10512 patients) were included. Most studies included patients admitted to tertiary neuroscience centers (61.5%, N=32), or critical care units (23.1%, N=11). Sodium of less than 135 mmol/l was the most commonly utilized hyponatremia definition (84.6%, N=44). The pooled incidence of hyponatremia was 37.0% (95% CI 31.7-42.4%). Hyponatremia increased the risk of vasospasm (15 studies, Odds Ratio [OR] 2.93, 95% CI 1.77-4.84), and length of hospital stay (3 studies, 16.4 days vs 8.0 days, Mean Difference [MD] 8.5 [95% CI 4.6-12.4]), but was not associated with poor outcome (10 studies, OR 1.15, 95% CI 0.44-3.02). These findings remained when carrying out sensitivity analysis for different hyponatremia and outcome definitions, bias, and aSAH populations.

Conclusions: Hyponatremia is common in aSAH, may increase the likelihood of vasospasm, but in isolation does not appear to affect overall outcomes. Managing hyponatremia effectively should be a priority for treating clinicians.