ObjectiveTo analyze whether hypernatremia within 48 hours after cardiac surgery will increase the incidence of delirium which developed 48 hours later after surgery (late-onset delirium).MethodsWe conducted a retrospective analysis of 3 365 patients, including 1 918 males and 1 447 females, aged 18-94 ( 60.53±11.50) years, who were admitted to the Department of Cardiothoracic and Vascular Surgery of Nanjing First Hospital and underwent cardiac surgery from May 2016 to May 2019.ResultsA total of 155 patients developed late-onset delirium, accounting for 4.61%. The incidence of late-onset delirium in patients with hypernatremia was 9.77%, the incidence of late onset delirium in patients without hypernatremia was 3.45%, and the difference was statistically different (P<0.001). The odds ratio (OR) of hypernatremia was 3.028 (95% confidence interval: 2.155-4.224, P<0.001). The OR adjusted for other risk factors including elderly patients, previous history of cerebrovascular disease, operation time, cardiopulmonary bypass time, lactate, hemoglobin≥100 g/L, prolonged mechanical ventilation, left ventricular systolic function, use of epinephrine, use of norepinephrine was 1.524 (95% confidence interval: 1.031-2.231, P=0.032).ConclusionHypernatremia within 48 hours after cardiac surgery may increase the risk of delirium in later stages.