Altitude and Delayed Cerebral Ischemia After Aneurysmal Subarachnoid Hemorrhage on the Tibetan Plateau: A Retrospective Cohort Study
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Background
Delayed cerebral ischemia (DCI) is a major driver of poor functional outcome after aneurysmal subarachnoid hemorrhage (aSAH). Virtually all DCI risk factor evidence derives from sea-level populations, with few data examining DCI as a primary endpoint in patients chronically exposed to high-altitude hypoxia.
Methods
This single-center retrospective cohort study at the People’s Hospital of Tibet Autonomous Region included 256 consecutive aSAH patients residing at 2330–4920 m. DCI was adjudicated per 2010 international consensus criteria, with residential altitude and admission hemoglobin prespecified as primary exposures. A prespecified multivariable logistic model (Model A; events-per-variable ≥10) identified independent DCI correlates, with sensitivity analyses across three DCI definitions and internal validation via 2000 bootstrap resamples with calibration assessment.
Results
DCI occurred in 60/256 patients (23.4%). Fisher grade III–IV (aOR 3.38, 95% CI 1.77–6.47) and surgical treatment (aOR 5.22, 95% CI 2.37–11.47) independently predicted DCI. Each 100-m residential altitude increment associated with higher DCI odds but fell just short of significance (aOR 1.08, 95% CI 1.00–1.17; p=0.051), with unstable significance across model specifications (p=0.021–0.157). Admission hemoglobin showed no association (aOR 1.00; p=0.988). Model A demonstrated acceptable discrimination (AUC 0.759, bootstrap 95% CI 0.690–0.828). DCI strongly associated with increased in-hospital mortality (20.0% vs 3.6%) and 1-year functional dependence (mRS ≥3: 47.9% vs 14.8%).
Conclusions
In this high-altitude aSAH cohort, hemorrhage burden and surgical treatment were the dominant DCI correlates, while admission hemoglobin showed no association. Residential altitude demonstrated a suggestive borderline DCI signal most pronounced above ∼4000 m, consistent with a potential threshold rather than linear effect. These hypothesis-generating findings require multicenter prospective validation before clinical application.
