The patients with sepsis are in high risk of malnutrition, which could contribute to infection, difficulty in weaning from ventilators. The investigators speculate whether nutrition therapy with high nitrogen could attenuate the malnutrition status and improve the outcome in these sepsis patients. In this prospective Randomized Controlled Trial, the investigators aim to compare high nitrogen intake with conventional nitrogen supply which were recommended in guidelines.

Inclusion Criteria:

• need mechanical ventilation for more than 2 days
• mean blood pressure more than 60mmHg
• predicted ICU stay more than 7 days
• tolerance of parenteral or enteral nutrition

Exclusion Criteria:

• irreversible status of primary disease
• any history of malnutrition before enrollment
• history of steroid cortisol administration
• severe liver dysfunction (Child-Pugh Score C)
• pregnancy
• refuse to enrollment
• re-admission to ICU and has been enrolled during former admission to ICU