Support for the Burn Patient

kcal/day

Comments

Adult formulas

Harris Benedict

Men:

66.5 + 13.8 (weight in kg) + 5 (height in cm) − 6.76 (age in years)

Women:

655 + 9.6 (weight in kg) + 1.85 (height in cm) − 4.68 (age in years)

Estimates basal energy expenditure; can be adjusted by both activity and stress factor, multiply by 1.5 for common burn stress adjustment

Toronto Formula

−4343 + 10.5 (TBSA) + 0.23 (calorie intake in last 24 h) + 0.84 (Harris Benedict estimation without adjustment) + 114 (temperature) − 4.5 (number of postburn days)

Useful in acute stage of burn care; must be adjusted daily

Davies and Lilijedahl

20 (weight in kg) + 70 (TBSA)

Often overestimates caloric needs for large injuries

Ireton-Jones

Ventilated patient:

1784 − 11 (age in years) + 5 (weight in kg) + (244 if male) + (239 if trauma) + (804 if burn)

Non-ventilated patient:

629 − 11 (age in years) + 25 (weight in kg) − (609 if obese)

Complex formula that integrates variables for ventilation and injury status

Curreri

Age 16–59: 25 (weight in kg) + 40 (TBSA)

Age >60: 20 (weight in kg) + 65 (TBSA)

Commonly overestimates caloric needs

Pediatric formulas

Galveston

0–1 years:

2100 (body surface area) + 1000 (body surface area × TBSA)

1–11 years:

1800 (body surface area) + 1300 (body surface area × TBSA)

12–18 years:

1500 (body surface area) + 1500 (body surface area × TBSA)

Goal focuses on maintaining body weight

Curreri junior

<1 year: recommended dietary allowance + 15 (TBSA)

1–3 years: recommended dietary allowance + 25 (TBSA)

4–15 years: recommended dietary allowance + 40 (TBSA)

Commonly overestimates caloric needs

Indirect calorimetry is currently the gold standard for energy expenditure measurement, but it is difficult to perform and as such is not practical on a routine basis. Indirect calorimetry measurement calculates oxygen consumption and carbon dioxide production and therefore metabolic rate by measuring the volume of expired gas and the oxygen and carbon dioxide concentration of the inhaled and exhaled gas via a face mask or ventilator. Under or overfeeding can be detected by calculating the ratio of carbon dioxide produced to oxygen consumed, known as the respiratory quotient (RQ) [30]. RQ is dependent on metabolism of specific substrates. Fat is the major energy source during unstressed starvation which gives an RQ of approximately 0.7. Normal metabolism of mixed substrates gives an RQ between 0.75 and 0.90. Overfeeding is characterized by the creation of fat from carbohydrate and leads to an RQ greater than 1.0, which explains why overfeeding can cause difficultly in weaning a patient from the ventilator [32]. It is important to note that despite this concern, one study found that in a group of pediatric burn patients, a high-carbohydrate diet did not result in an RQ over 1.05 or any other respiratory complications but did have the positive effect of decreased muscle wasting [33].

21.6 Nutrient Metabolism

Carbohydrates, lipids, and proteins are the three macronutrients that provide energy and biological building blocks to fuel complex metabolic processes. They provide energy via different pathways, and the ratios of these nutrients must be considered for the burn patient after a caloric goal has been determined.

Carbohydrates are the preferred source of energy for burn patients, and high carbohydrate diets improve wound healing and have a protein sparing effect. In a randomized study of severely burned children, those who were fed a high carbohydrate diet had significantly less muscle protein degradation than those on a high-fat diet [34]. These positive effects are, however, limited by the ability to oxidize and utilize glucose. Glucose administration more than 9 mg/kg/min cannot be oxidized at the upper limit, and therefore, this strategy cannot be used above this range. Unfortunately, this maximum rate can be less than the estimated caloric expenditure, inferring some burned patients may have greater glucose needs than can be given safely. If glucose is given at a higher rate than this, it leads to hyperglycemia, glycosuria, dehydration, conversion of glucose to fat, and respiratory problems [35, 36].

Protein is also an important macronutrient after burn and must be carefully considered in the development of a nutritional support plan. Protein needs are greatly increased in these patients because of the catabolic response to burn, and protein supplementation is vital to meet the ongoing demands and supply substrate for wound healing and immune function and to mitigate the loss of leady body mass [37]. Giving supra-normal protein doses does not decrease catabolism of endogenous protein stores, but it does promote protein synthesis and improved nitrogen balance [38]. Predicted protein requirements are 1.5–2.0 g/kg/day for burned adults and 2.5–4.0 g/kg/day for burned children. Protein should always be provided in addition to considerable calories from carbohydrates and fat; otherwise, the protein will be used only as an energy source instead of as a specific nutrient to provide substrate for wound healing and maintenance of muscle mass. Optimal non-protein to nitrogen ratio is a function of burn size and should be around 150:1 for smaller burn up to 100:1 for larger burns [39]. Despite high rates of protein supplementation, burn patients will experience some loss of muscle protein because of the hormonal and proinflammatory reaction to severe burn.

Two specific amino acids have been studied and found to play unique roles after burn. Glutamine provides direct energy for lymphocytes and enterocytes and is crucial for preserving small bowel integrity and sustaining gut-associated immune function [40, 41]. It also portends some degree of cellular protection after stress via increased production of heat shock proteins, and it is a precursor of an important antioxidant, glutathione [42, 43]. Supplementation of 25 g/kg/day of glutamine has shown to reduce mortality and length of stay in burn patients [44, 45]. Arginine is another important amino acid with significant effects on the immune system. Arginine supplementation in burn patients led to improvement in wound healing and immune responsiveness; however, data from critically ill nonburn patients suggest that it is potentially harmful [46–49]. For this reason, arginine supplementation is not currently recommended in burn patients, but further investigations are underway.

Lipids are necessary to prevent essential fatty acid deficiency, but fat supplementation is only recommended in limited doses [50]. Lipolysis and lipid mobilization are increased after burn, while at the same time, utilization of lipids as an energy source is decreased [51, 52]; most free fatty acids are not used and lead to lipid accumulation in the liver. Increased fat intake has also been shown to worsen immune function, and because of these effects, burn patients should have no more than 15% of their calories from lipids. Many forego lipid emulsions completely for patients receiving parenteral nutrition for less than 10 days. The composition of administered fat must also be considered. Many of the commonly used enteral formulas contain omega-6 fatty acids which create proinflammatory cytokines during metabolism. Lipids with a high proportion of omega-3 fatty acids do not promote proinflammatory mediators and have been associated with improved immune response, less hyperglycemia, and improved outcomes [53, 54]. Omega-3 fatty acids are a component of “immune-enhancing diets” because of these effects. Most formulas have an omega 6:3 ratio ranging from 2.5:1 to 6:1, but the “immune-enhancing diets” have a ratio closer to 1:1. The optimal composition and volume of fat in the diet of burn patients is still controversial and deserves further investigation.

21.7 Micronutrients

Vitamins and trace elements supplementation is also crucial after burn, as these are important for immunity and wound healing. Reduced levels of vitamins A, C, and D, Fe, Cu, Se, and Zn have been found to impair wound healing and skeletal and immune functions [55–57]. Vitamin A improves epithelial growth and accelerates wound healing. Vitamin C supports in the formation and cross-linking of collagen [58]. Vitamin D is important in maintaining bone density, and the levels are often deficient after burn, leading to bone demineralization and even spontaneous fractures [59]. Other trace elements including Fe, Cu, Se, and Zn are vital for cellular and humoral immunity, but they are lost in significant amounts with exudative burn wound losses [55]. Zn is needed for protein synthesis, wound healing, lymphocyte function, and DNA replication [60]. Se promotes cell-mediated immunity, and Fe is a cofactor for oxygen-carrying proteins [61, 62]. Cu is vital for collagen creation and wound healing, and its deficiency has been associated with arrhythmias and immune dysfunction in burn patients [63]. These micronutrients are therefore important to supplement [64, 65]. Table 21.2 shows the recommended micronutrient supplementation for burned patients.

Table 21.2

Recommended micronutrient supplementation

Age, years	Vit A, IU	Vit D, IU	Vit E, IU	Vit C, IU	Vit K, μg	Folate, μg	Cu, mg	Fe, mg	Se, μg	Zn, mg
0–13
Nonburned	1300–2000	600	6–16	15–50	2–60	65–300	0.2–0.7	0.3–8	15–40	2–8
Burned	2500–5000			250–500		1000	0.8–2.8		60–140	12.5–25
≥13
Nonburned	200–3000	600	23	75–90	75–120	300–400	0.9	8–18	40–60	8–11
Burned	10,000			1000		1000	4		300–500	25–40

21.8 Enteral and Parenteral Formulas

A multitude of enteral formulas with varied amounts of substrates and micronutrients are commercially available. Table 21.3 includes a few of the commonly used formulas, but it is far from exhaustive. A formula with a high carbohydrate concentration should be used as glucose in the preferred energy source for burn patients [33, 66]. Parenteral formulas typically consist of 25% dextrose, 5% crystalline amino acids, and maintenance electrolytes. Essential fatty acids are supplemented with infusions of 250 mL of 20% lipid emulsions three times per week, although some clinicians forego this supplementation in courses of parenteral nutrition that are less than a week [67, 68].

Table 21.3

Selected adult enteral nutrition formulas [79]

Formula	kcal/mL	Carbohydrate, g/L (% calories)	Protein, g/L (% calories)	Fat, g/L (% calories)	Comments
Impact	1.0	130 (53)	56 (22)	28 (25)	IED with arginine, glutamine fiber
Crucial	1.5	89 (36)	63 (25)	45 (39)	IED with arginine, hypertonic
Osmolite	1.06	144 (54)	44 (17)	35 (29)	Inexpensive, isotonic
Glucerna	1.0	96 (34)	42 (17)	54 (49)	Low carbohydrate, for diabetic patients
Nepro	1.8	167 (34)	81 (18)	96 (48)	Concentrated, for patients with renal failure