Inclusion Criteria:  ages between 18 and 80 years; expected stay in the ICU of > 72 h; patients diagnosed with sepsis or septic shock; informed consent was signed by the patient or relatives;  Exclusion Criteria:  at terminal stage of disease; primary brain injury (such as traumatic brain injury, stroke, cardiac arrest, intracranial infection, epilepsy, Alzheimer's disease, Parkinson disease and meningitis etc.); acute mental deterioration secondary to non-septic metabolic disorders with organ dysfunction (hepatic encephalopathy, pulmonary encephalopathy, severe electrolyte imbalance, severe blood glucose disorders etc.); history of craniocerebral surgery; psychiatric illness; use of psychiatric medications; impaired hearing; participated in other clinical trial; pregnant or lactating women; expected death within 72 h after admission.