Nutritional physiology refers to the role of food and nutrition in the function of the body. In the critically ill patient there are numerous points at which nutrition affects function, since all fuels, tissues, and mediators ultimately arise from the food consumed by the individual. There are now evidence-based guidelines for the provision of nutrition support in the critically ill patient. Several actions related to feeding improve outcomes such as infection rate, days on mechanical ventilation, days in the critical care unit, and mortality. These actions include the provision of early enteral nutrition, use of tube feedings supplemented with n-3 fatty acids and antioxidants, and reaching minimum targets for energy and protein intake. The minimum target range is an area of debate currently. This chapter will focus on energy balance, protein and nitrogen balance, and the macronutrient requirements of critically ill patients compared to normal. The potential role of nutrients to modulate inflammatory injury in the critically ill patient will also be examined.
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