Underfeeding in the critically ill patient is a common observable fact throughout intensive care units. Patients who develop caloric deficit during their stay in the ICU have been shown in previous reports to be associated with increased complications such as increased rate of infections, and nosocomial blood stream infections. Yet, other studies have shown that patients with moderate caloric deficit may be associated with better outcome than patients who receive higher levels of caloric intake.

Therefore, the aim of our study is to establish the exact amount of calories to be delivered by indirect calorimetry individually for each patient. Thereafter, each patient will be randomized to the trophic group (hypocaloric feeding), or to the full energy delivery group.

Inclusion Criteria:

• Anticipated Mechanical ventilation for at least 72 hrs.
• Need for enteral feeding
• men and woman aged 18 or older.

Exclusion Criteria:

• Abdominal surgery with inability to feed enterally.
• FiO2 greater than 80%
• Bronchopleural fistula
• Hemodynamic instability in spite the use of vassopressors.