The Early Nasojejunal Tube to Meet Energy Requirements in Intensive Care (ENTERIC) Study

Inclusion Criteria: ICU patients are eligible for enrolment if they meet all of the following: * Age \> 18 years old * In ICU for \< 48 hours prior to enrolment * Receiving invasive mechanical ventilation (through an endotracheal tube or tracheostomy, but NOT a facemask) with an anticipated need for \> 48 hours of mechanical ventilation * Receiving a continuous infusion of any one of: * morphine \> 2 mg/hour, * fentanyl \> 20 mcg/hour, or * pethidine \> 20 mg/hour * Either a single GRV \> 150 mls (whilst receiving EN via a NG tube) or nasogastric drainage \> 500 mls over 12 hours (whether receiving EN or not) Exclusion Criteria: Patients will be ineligible for enrolment if they meet any of the following: * Previous or recent surgery which has altered the anatomy of the upper gastrointestinal tract (eg. oesophagectomy, gastrectomy, any gastric anastomosis surgery, gastroplasty, pyloroplasty, pancreaticoduodenectomy \[Whipple's procedure\]) * Known gastric malignancy * Known oesophageal varices * Current admission for peptic ulceration * Current mechanical bowel obstruction * Current gastrostomy, jejunostomy, or surgically-placed enteral tube in situ * Contraindication to the use of the nose and mouth for enteral tube insertion (eg. recent facial trauma or surgery) * Receiving nutritional support prior to ICU admission * Severe coagulopathy (defined by platelet count \< 20 and/or international normalized ratio \[INR\] \> 4.0)