Provision of nutritional support to critically ill patients can be challenging. Critical care nurses must be aware of which patients require specific nutritional support, when to initiate nutritional support, and by which route to provide nutritional support. Consultation with a dietitian or nutritional support service can help facilitate this process. The key points in addressing these questions are (1) the nutritional status of the patient or the length of time he or she has been without significant nutrient intake, (2) whether the patient has a hypermetabolic condition that warrants the early use of nutritional support, and (3) the function of the patient's gastrointestinal tract. What to feed depends on the physiological state of the patient. Adjusting the nutrient composition of the feeding solution may prevent metabolic complications and may improve the overall outcome for the patient.