Nutrition in the critically ill patient.

Critically ill patients are hypermetabolic and have increased nutrient requirements. Although it is assumed that nutritional support is beneficial in this group of patients there are no well designed clinical trials to test this hypothesis. The rationale for nutritional support, therefore, is based upon clinical judgement. Although it is not known how long a critically ill patient can tolerate what is effectively starvation, the loss of lean tissue which occurs in catabolic patients (20-40 g nitrogen/day) suggests that depletion to a critical level may occur after 14 days. Total parenteral nutrition given to malnourished patients with gastrointestinal cancer for 7 to 10 days before surgery has been shown to decrease complications by about 10%. Wound healing and normal immune responses are dependent upon adequate nutrient intake, and it seems reasonable, therefore, to commence feeding as soon as possible. Earlier feeding may decrease length of stay and complication rates in both critically ill patients and following surgery. It has been shown in randomised controlled trials of both enteral and parenteral feeding in the critically ill, that current regimens are sub-optimal. Calorie intake was shown to be often considerably in excess of metabolic requirements alone, and variable study design has made comparisons impossible. Despite the lack of knowledge regarding even the most simple of nutritional requirements in these patients, the administration of specific micronutrients and specialised supplements has attracted attention. Again, many of these more recent studies are limited because of poor study design.