In the previous study, the investigators obtained the cutoff value of Bispectral Index to detect early deep sedation in patients with mechanical ventilation. Bispectral Index monitoring can be used as an adjunct tool in screening and confirming deep sedation during the early period of mechanical ventilation. In present study, validation test will be carried out to clarify the sensitivity and specificity of obtained cutoff value in screening deep sedation in patients with mechanical ventilation.

Inclusion Criteria:

• Adult patients are intubated and ventilated within the previous 24 hours, are administered with continuous or intermittent intravenous sedatives and/or analgesics, and are expected to receive mechanical ventilation and sedation for longer than 24 hours

Exclusion Criteria:

• Age under 18 or over 65 years;
• Continuously infusion of muscle relaxants;
• Diagnosed or suspected brain diseases, which including brain trauma, intracranial hemorrhage, stroke, brain tumors, hypoxic-ischemic encephalopathy, epilepsy and meningitis;
• Diagnosed conditions that resulted in a decrease level of consciousness, which including hypoxemia with partial pressure of oxygen in arterial blood less than 60 mmHg, hypotension with systolic blood pressure less than 90 mmHg, hypoglycemia with blood glucose concentration less than 4.1 mmol/L, anemia with hemoglobin concentration less than 70 g/L, and body temperature below 36 °C.

Adult patients admitted to 3 ICUs in University Affiliated Hospital will be screened daily and enrolled consecutively.