['Hypertonic saline therapy is often used in critically ill subarachnoid hemorrhage (SAH) patients for indications ranging from control of intracranial hypertension to managing symptomatic hyponatremia. The risk factors for developing acute kidney injury (AKI) in this patient population are not well defined.', 'To study the role of serum sodium in developing AKI (based on the AKIN definition) in the SAH population admitted to a large academic neurocritical care unit.', 'This is an IRB-approved, retrospective cohort study of patients admitted to a tertiary neuro intensive care unit. We included adult (age ≥ 18 years) SAH patients admitted to the neuro intensive care unit for at least 72 h. Development of AKI after admission to the ICU was defined using the AKIN serum creatinine criteria between 72 h and 14 days following admission. A Cox proportional hazards survival model with multiple time varying covariates was developed to evaluate the effect of maximum sodium exposure on the risk of AKI. Sodium exposure was captured as the running maximum of daily maximum serum sodium concentration (mEq/L). Sodium exposure was used as a surrogate for hypertonic saline therapy.', 'The final cohort of patients included 736 patients admitted to the neuro intensive care unit between 2006 and 2012. The number of patients who developed AKI was 64 (9 %). These patients had an increased length of stay (15.6 ± 9.4 vs. 12.5 ± 8.7 days). The odds of death were more than two fold greater among patients who developed AKI (odds ratio 2.33 95 % CI 1.27, 4.3). Sodium exposure was significantly associated with the hazard of developing AKI, adjusting for age, sex, preexisting renal disease, diabetes mellitus, radiocontrast exposure, number of days on mechanical ventilation, and admission Glasgow Coma Scale score. For each 1 mEq/L increase in the running maximum daily serum sodium, the hazard of developing AKI was increased by 5.4 % (95 % CI 1.4, 9.7).'] Is hypernatremia a significant risk factor for acute kidney injury after subarachnoid hemorrhage : a retrospective analysis?