Indeed in the critically ill patient nutritional status plays a key role in recovery. Critically ill patients are often malnourished, which causes wide spread organ dysfunction and increases peri-operative morbidity and mortality rates.Nutritional repletion has been shown to be effective in improving wound healing, restoring immune competence and reducing morbidity and mortality in critically ill patients. Assessing the level of nutritional deficit of a patient is clearly the first step in deciding the degree of nutritional support required. The two main routes for providing nutritional support in critically ill patients are enteral nutrition (EN) and parenteral nutrition (PN). In all clinical situations, if the gut is functioning then it should be used as the route of feeding. EN is being preferred because of decreased risk of infection, ease of administration, decreased cost and no need for central venous access and improved gastrointestinal function. If EN is contraindicated or cannot be established then PN may be required. It is generally not necessary if the patient is likely to be able to recommence enteral feeding within a few days, unless the patient is already severly wasted or malnourished. Multiple complications may occur with nutritional support, some of which occur in both EN and PN like nutritionally associated hypercapnia and vitamin deficiencies, others are confined with EN only (like diarrhea and abdominal distention) or with PN only (like catheter complications as pneumothorax).