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.

This trial was designed to be a randomized, single-center, double-blind, placebo-controlled trial. A total of 68 elderly patients from two ICUs will be randomly allocated at a 1:1 ratio to the intervention group or the control group. Both groups will receive the ABCDEF (A2F) bundle strategy recommended by guidelines, a multicomponent approach including pain and delirium management, breathing trial practice, analgesic and sedation usage control, family engagement and so on, to prevent delirium. The intervention group will additionally receive aromatherapy lasting for five days. The primary outcome is the prevalence of delirium. Secondary outcomes include the severity and duration of delirium, the length of ICU stay, the duration of physical restraint, the duration of analgesic and sedative medication and the 28-day mortality rate. We will use the CAM-ICU and CAM-S to measure the prevalence and severity of delirium, and analyses of variance (ANOVAs) or repeated-measures ANOVAs and Wilcoxon rank-sum tests to analyze the observation results.

Inclusion Criteria:

• Critically ill patients aged between 60 and 90 years old
• Had an expected total ICU length of stay (LOS) of 72 hours or more
• Admitted to the ICU within 48 hours before screening
• Signed the informed consent form.

Exclusion Criteria:

• Incapacitation preventing the assessment of delirium (i.e., coma, sedation, or active seizures)
• History of psychiatric disorders, dementia, Parkinson's disease, use of antipsychotic drugs, or alcohol dependence
• History of traumatic brain injury or brain infection
• Diagnosis of delirium prior to intervention initiation
• Allergies to medications used in the protocol or current participation in other drug studies
• Inability to communicate in Chinese or English
• Expected to be discharged or deceased within 72 hours of admission.