The purpose of the study is to compare continuous versus intermittent strategy for enteral nutrition. The study will examine if there is a difference in achieving nutritional delivery goals, tolerance and number of complications of enteral nutrition.

The study will commence following the Approval by The Ethics Research Committee. All patients admitted to our ICU from the 1st of June 2018 to the 31st of May 2019 will be enrolled after fulfilling the inclusion criteria and in the absence of any exclusion criteria. Informed consent will be requested. Enteral nutrition will be administered via nasogastric of orogastric tube. Patients will be randomised in 2 groups. In the group of patients receiving continuous feeding will be enteral nutrition administered via enteral feeding pump for at least 16 hours par day. In the group of patients receiving intermittent feeding will be enteral nutrition administered as 30-60minutes lasting bolus via enteral feeding pump 6 times per day. Following the administration of the bolus the patient will be placed for 30 minutes in semi-upright sitting position. Enteral nutrition requirement and composition will be standardised with the adoption of international guidelines. In 5 subsequent days from the enteral nutrition commencement will be examined if there is a difference in achieving energy and protein targets, tolerance and number of complications of enteral nutrition in between both groups. As achievement of energy and protein targets will be considered at least 80% of calculated values. The tolerance of enteral nutrition will be evaluated by the clinical examination of the abdomen, presence of diarrhoea, vomiting and the gastric residual volume of at least 0,5 liter. As the complications of enteral nutrition will be regarded the aspiration of gastric contents and ventilator associated pneumonia. Nutritional status parameters will be analysed. the length of hospital stay, ICU length of stay and 28-day mortality will be also monitored.

Inclusion Criteria:

• age between 18 - 80 years
• indication of enteral nutrition with nasogastric or orogastric tube
• Nutrition Risk in the Critically Ill (NUTRIC) score ≥5
• Body mass index between 18 - 50
• mechanical ventilation expected for at least 72 hours

Exclusion Criteria:

• upper gastrointestinal tract surgery in previous medical history
• bowel obstruction
• bowel ischemia
• acute pancreatitis
• severe diarrhoea (>1l/24hours)
• gastrointestinal bleeding
• short bowel syndrome
• malabsorption syndrome in previous medical history
• ongoing enteral nutrition on admission to ICU