The aim of this study is to perform a prospective, randomized, controlled blinded study in critically patients to assess the necessity for measuring daily resting energy expenditure as a guide for nutritional support. Our hypothesis is that tight caloric control will reduce the rate of new infections.

Study Design :Multi-center, randomized, single blinded, controlled study. Study Population: newly-admitted, adult mechanically ventilated ICU patients.

Study objectives

To evaluate the effect of tight caloric control in critical patients on:

• The rate of acquired nosocomial infections (Ventilated associated pneumonia, Catheter related infections, Urinary tract infections)
• Mortality rates, length of stay in the ICU and in hospital, length of ventilation and incidence of non-infectious complications.

Primary endpoint:

Rate of nosocomial infections (for definitions see appendage 1) acquired after 48 to 72 hours following admission.

Secondary endpoints

• Metabolic control: glucose concentration, insulin administration, rate of hypoglycemic events.
• Success of tight caloric control: accumulative and maximum negative energy balance.
• Organ function: SOFA score.
• Rate of non-infectious complications: requirement for surgery or occurrence of pressure sores.
• Length of ICU stay and of assisted ventilation (LOS and LOV)
• ICU survival rate.
• Patient status and disposition on day 28 or at hospital discharge.
• 3 & 6 months survival.

Inclusion Criteria:

1. Mechanically-ventilated adults(Male or Female)admitted to general ICU within the first 48 hours of ICU admission.
2. Age ≥ 18 years;no upper age limit.
3. Expected stay in ICU> 3 days: [SAPS II (18) > ICU median or high-level of nursing care implemented or per clinical impression of attending physician]
4. Medical and abdomino/thoracic surgery patients, as well as multiple trauma patients with Glasgow Coma Score ≥ 10.

Exclusion Criteria:

1. Pregnancy.
2. DNR order.
3. Readmission in the ICU during the same hospitalization/transfer from other ICU.
4. Admission for postoperative monitoring.
5. Respiratory instability: SpO2 <90% or need for ventilator adjustments during the preceding hour or hyperventilation (Respiratory rate > 35/min)
6. Bicarbonate infusion, loss of bicarbonate (diarrhea, ureterosogmoidostomy or use of acetazoloamide, ultrafiltration).
7. Aerosolization with nitric oxide or heliox, tracheal insufflations or visible leaks in chest drainage system.
8. FiO2 80% or patients requiring prone position
9. Chronic/acute liver failure:Child-Pugh class C
10. Brain injury for various reasons with Glasgow Coma Scale below 10.
11. Cardiac surgery patients.
12. Patients in the hospital for more than 7 days.
13. Contra indication to use enteral nutrition.
14. Participation in a clinical study with an investigational drug within one month prior to the start of this clinical trial.
15. Ethical issues that will influence subject eligibility.