Determinants of successful initial burn treatment are early aggressive resuscitation (including nutrition), control of infection, and early closure of the burn wound. In general, the primary goal of nutritional support is to provide an adequate energy supply and the nutrients necessary to support life and function. Dietary nutrients must be ingested, digested, absorbed, and processed before the garnered substrates are used, stored, or expended for energy. Aggressive, early enteral feeding provides maximal benefits to the patient by alleviating catabolism and improving outcomes (43, 44). In contrast, the use of oral alimentation alone in patients with burns covering 40% of the TBSA resulted in a 25% decrease in preadmission body weight within 21 days after injury (13). However, overcompensation in the form of excess calories or protein is ineffective and is associated with increased complications such as hyperglycemia, carbon dioxide retention, and azotemia (45). Thus, the primary goal of nutritional support is to meet the unusual metabolic needs of severely burned patients adequately, to promote wound healing, increase resistance to infection, and attenuate the persistent loss of muscle protein that is characteristic of burn injury while avoiding exacerbation of existing complications.

Current clinical practice is to administer nutrition enterally whenever possible, given the strong evidence provided by preclinical and clinical studies, as well as by clinical comparison of oral feedings with gastric or small bowel tube feedings (25, 44). Enteral nutrition (EN), in particular, was shown to decrease bacteremia (related to translocation of bacteria from the intestines), reduce sepsis, maintain motility of the gut, and preserve first-pass nutrient supply to the liver in an animal model of severe burn injury (43). In patients in whom EN is not applicable (e.g., those with prolonged ileus or intolerance to EN), parenteral nutrition (PN) should be used to maintain appropriate macronutrient and micronutrient intake (see the chapters on EN and PN). PN remains of critical importance in patients with burns in whom appropriate dietary support cannot be achieved or in those whose total caloric requirements cannot be fully supplied by EN alone.

In addition to the nutritional route of administration, a major determinant of outcome for severely burned patients is timing, because any delays in resuscitation lead to poorer outcomes (46). In the short term, the significant gut mucosal damage present after burn injury leads to increased bacterial translocation secondary to abnormal
gut barrier function and a decreased ability to absorb nutrients (47, 48). Accordingly, optimal nutritional support for the severely burned patient is best accomplished by early (within 12 hours after injury) initiation of EN (49). Multiple studies in animal models supported this recommendation and demonstrated that early institution of EN could significantly modulate the hypermetabolic responses to severe burns, as described earlier (43, 44). Specifically, these studies showed that by 2 weeks after burn, animals given early continuous EN (by tube, within 2 hours after burn) had significantly lower metabolic rates than animals fed 3 days after burn; this finding points to the benefits of delivering feedings into the gut lumen as soon as possible (43). Early EN significantly reduced catecholamine levels and supported gut mucosal integrity in these models (50).

In human studies, early continuous EN delivered appropriate calculated caloric requirements (based on the resting energy expenditure) by postburn day 3, attenuated the hypermetabolic response, and significantly decreased circulating levels of catecholamines, cortisol, and glucagon (50, 51). Intestinal hypoperfusion (ileus) secondary to delays in resuscitation can be reversed by reperfusion or adequate resuscitation. Postburn ileus spares the small bowel and primarily affects the stomach and colon (52). Patients with severe burn injury can be safely enterally fed in the duodenum or jejunum within 6 hours after burn, whether or not they have total gastroduodenal function (53). Thus, nasojejunal or nasoduodenal feeding must be administered early to facilitate the full resuscitation of the severely burned patient.

Currently, resting energy requirements of burned patients are commonly estimated using equations that incorporate body mass, age, and gender. Traditionally, the performance of these equations has been weighed against measured resting energy expenditure (MREE) (obtained through indirect calorimetry), even though the accuracy and precision of MREE is not well established in burns. Furthermore, investigations have shown that MREE requires a correcting factor of +20% to 40% to maintain adequate body weight (54, 55). Validation and agreement analysis of formulas such as the Harris-Benedict, Schofield HW, Curreri, and World Health Organization formulas have shown that although these formulas are based on patient-specific factors such as age, gender, weight, and burn size, they may significantly overestimate caloric requirements in patients with burns, thus increasing the risk of overfeeding and its subsequent deleterious effects (54, 56). After considering the significant expense of acquiring and maintaining the equipment for bedside indirect calorimetry, more researchers and facilities have sought to identify new and more accurate equations to ensure that the equipment is useful and beneficial. The adapted Toronto equation may be one such equation because the calculated results very closely matched the MREEs of 10 adult patients (56). The hope is that, as further testing of these formulas and indirect calorimetry itself continues, the ideal method to quantify the required nutritional support in burn adults and children will be refined (2, 57, 58). Although imperfect, measurement of resting energy expenditures using the current method of indirect calorimetry can still provide a value close to actual caloric requirements (2, 54, 57). Goran et al (57) found that feeding patients with 1.2 times MREE preserves body weight, with a 10% loss in LBM and gains in fat deposition (54, 58). This finding further underscores the need for improvement in meeting nutritional needs because preservation of LBM should be the primary goal of nutritional support in patients with severe burns.

The major energy source for patients with burns should be carbohydrates, which serve as fuel during wound healing, thereby sparing protein from oxidation for energy and allowing the protein to be more appropriately used (e.g., protein synthesis by the liver, for wound healing). Critically ill burned patients are estimated to have caloric requirements that far exceed the body’s ability to assimilate glucose, which has been reported to be 5 mg/ kg/minute or approximately 7 g/kg/day (2240 kcal for an 80-kg man) (59, 60, 61). However, providing a limited amount of dietary fat diminishes the need for carbohydrates and ameliorates glucose tolerance.