Elderly critically ill patients in the intensive care unit (ICU) are at risk of delirium, which is primarily characterized by acute consciousness impairment and perceptual, cognitive, and memory impairment, resulting in excess death, care expenditures, and acquired dementia, depression and anxiety, which severely affect the prognosis of critically ill patients. However, there are currently no effective pharmacological strategies for preventing delirium. Inhalation aromatherapy has been proven to benefits the sleep disorder, anxiety or depression and lavender oil is one of the most used essential oils. Therefore, we hypothesized that the use of lavender would reduce the incidence rate of delirium in ICU patients.