Septic patients in Intensive Care Unit always need mechanical ventilation and conscious-sedation. But the recommended dose 0.2-0.7μg/kg/h could not run well because of wide range. The purpose of this study is to find the effective dose of dexmedetomidine adult septic patients of mechanical ventilation .

Inclusion Criteria:

Age: between 18 years mechanical ventilation RASS≥2 A diagnosis of sepsis within 48 hours

Exclusion Criteria:

Cardiac disease Cardiac rhythm abnormalities liver dysfunction coma severe hypotension muscle relaxant users

Primary Outcome Measures:

Dose of dexmedetomidine

Secondary Outcome Measures:

RASS score Requirement for rescue intervention, RASS will be recorded per hour.

Inclusion Criteria:

• intubated patients RASS≥2 A diagnosis of sepsis within 48h

Exclusion Criteria:

• Cardiac disease Cardiac rhythm abnormalities liver dysfunction coma severe hypotension muscle relaxant users