Nutrition support for the burn patient

er to institute and experienced more frequent interruptions [20, 21]. Either route can be used successfully provided that this issue is incorporated into an overall plan for nutritional management.

Application: In the patient presented above, a naso-enteric feeding tube was placed on the morning following admission (24 hours after injury) under fluoroscopic guidance and carefully secured. Enteral nutrition (see below for a discussion of formulas) was started at a low rate, and increased gradually over the next 48 hours, so that the patient achieved goal-rate nutrition by 72 hours post-burn. We also elected to give a single enteral dose of erythromycin as a “pro motility” agent to help reduce gastric ileus and promote passage of the enteral tube into the small intestine [22].

Determining nutritional demands

Initiation of nutritional support requires estimation of a caloric goal in ICU patients[3]. This estimation can prove particularly challenging in burns because of the profound hypermetabolic response that the body mounts in response to significant burn injury. Malnutrition is associated with the development of pneumonia in critically ill patients and is known to impair wound healing. Without appropriate management, the protein-calorie malnutrition that results from burn hypermetabolism may be life threatening.

Further, although adequate nutrition is desired, care must be taken not to provide calories in excess of the patient’s needs. Overfeeding has been shown to result in fat accretion in burn patients and may contribute to difficulties with glycemic control and ventilator weaning. Estimated energy demands provide an appropriate starting point for nutritional support in major burns, with revision occurring based upon metabolic characteristics and patient tolerance of enteral feeds.

What is an appropriate initial nutrition plan for this patient?

Energy expenditure in burn patients is a heterogeneous metabolic process and the protean manifestations of burn hypermetabolism make determination of energy and protein requirements particularly dif-

ficult. However, several algebraic formulas are widely used for determination of initial assessment of energy needs. Estimation of basal energy expenditure (BEE) using the Harris-Benedict equation or kcal/ Kg formulas are used at most American Burn Association verified burn centers [23]. The baseline estimate acquired using the Harris-Benedict equation is usually multiplied by a factor of 1.2 to 1.4 to allow for the hypermetabolism associated with the burn injury. Although more varied methods are used in children, two methods are used most commonly to estimate caloric needs. The first of these is the recommended dietary allowances (RDA), recently revised and known as the Dietary Reference Index (DRI) [24]. This is a widely-used standard formula for estimating nutritional requirements. A burn-specific formula, the Galveston formula, is also widely used in pediatric burn care. Together, the RDA/DRI and/ or Galveston formulas are the routine methods of estimating energy requirements used in over 70% of US burn centers [23]. Of note, the previously used Curreri formula appears to have fallen out of favor for both adult and pediatric burns, likely because of the marked overestimation of energy demands demonstrated by this formula[25, 26]. Table 1 shows each of the more commonly used formulas and includes additional comments on many of these formulas, including information on the accuracy of each formula versus measured energy demands using indirect calorimetry (IDC) when that data is available.

The primary pitfall of these commonly used formulas for caloric demands in burned adults and children is that they frequently overestimate patients’ resting energy expenditure (REE) [3, 25, 26]. Feeding more than 1.2 times REE has been shown to increase fat accretion and does not improve maintenance of lean body mass in acute burn patients [27]. Therefore, although these formulas typically provide an appropriate method for initial estimates, measurement of energy expenditure by IDC provides a more precise representation of the burn patient’s energy expenditure over time.

Estimation of caloric needs in the obese burn patient should use ideal body weight in any algebraic formula calculations; otherwise, these equations result in substantial overfeeding. Although the concept of “permissive underfeeding” in the obese currently predominates the ICU nutrition literature, the bene-

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Table 1. Commonly used algebraic formulas for caloric needs in nutritional support

ADULT FORMULAS	Formula	Daily caloric estimates for	Comments
		25 year-old male, 85 kg,
		180 cm, 48% TBSA
Harris-Benedict [111]	Men: 66.5 + 13.8 (Weight in Kg)	Baseline = 1,946 kcal	Estimates basal energy expend-
	+ 5 (Height in cm) – 6.76 (Age in	If factor 1.5 = 2,918 kcal	iture (BEE). Best stress adjust-
	years)		ment is a factor of 1.5; results in
	Women: 655 + 9.6 (Weight in		a % calorie variance of 19 24%
			from measured REE (MREE)
	Kg) + 1.85 (Height in cm) – 4.68
			(p = NS). [26]
	(Age in years)
Kcal/Kg	35 kcal/kg	2,975 kcal	Variance of 23 ± 36% from
(Common use) [26]			MREE (p = NS) [26]
Curreri [112]	Age 16–59: 25 kcal/ kg/ day	4,045 kcal	Variance of 35 ± 35% from
	+ 40 kcal/ %TBSA burn/ day		MREE (p = 0 001)[26] Now
	Age 60: 20 kcal/kg/day		rarely used because of marked
			tendency to over-estimate
	+ 65 kcal/ %TBSA burn/ day
			calories.
PEDIATRIC FORMULAS	Formula	Daily caloric estimates for	Comments
		a 15-month old male,
		11 kg, 0.9 m2 BSA
DRI [113]	On-line calculator	899 kcal/day	Varies according to age, weight,
		If factor 1.2 = 1,078 kcal/	and activity level. Includes
		day	allowances for growth and
		If factor 1.4 = 1,258 kcal/	activity.
		day
Galveston [114–116]	0–1 Years: 2 100 kcal/m2/day		Like the Curreri formula, the
	+ 1 000 kcal/m2 TBSA burn/day		Galveston formula was created
	1–11 Years: 1 800 kcal/m2/day	2,182 kcal/day	with the goal of maintaining
	+ 1 300 kcal/m2 TBSA burn/day		body weight.
	12–18 Years: 1 500 kcal/m2/day
	+ 1 500 kcal/ m2 TBSA burn/day
Curreri Junior [117]	1 Year: RDA + 15 kcal/ %TBSA		Now rarely used because of
	burn		marked tendency to over-esti-
	1–3 Years: RDA + 25 kcal/ %	2,099 kcal	mate calories.
	TBSA burn
	4–15 Years: RDA + 40 kcal/ %
	TBSA burn

fits and dangers of this practice have not yet been clearly established in patients with burn injury [28–30]. The physiologic principles of permissive underfeeding rely upon fat oxidation to mobilize peripheral energy stores in these patients, a pairing of metabolic processes that are known to be deranged in patients with significant burns.

Ratios for carbohydrate, protein, and fat intake must also be considered once a caloric goal has been

established. Carbohydrates may limit loss of lean body mass by stimulation of protein synthesis, meaning that carbohydrates should be the primary energy source in the hypermetabolic burn patient [31]. In addition, glucose serves as the primary metabolic fuel for wound healing. However, glucose administration rates in excess of 7 mg/kg/min cause hyperglycemia with the attendant complications of impaired wound healing, conversion of excess calories

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to fat, and elevated rates of carbon dioxide production [32]. Optimal nutrition support in burns consists of at least 50% carbohydrate calories, with glucose administration occurring at rate of 5–7 mg/kg/ min [33].

Protein requirements are also heterogeneous in burn patients and must be carefully considered in the development of a nutrition care plan. Protein demands in burn injury are increased due to the catabolic response to injury as well as the need for protein for wound healing and immune function. While healthy, uninjured individuals synthesize protein at a rate of 4 grams/ kg/ day, burn patients may induce protein synthesis rates of nearly twice that [34]. Administration of nutritional support with 1.5–2 grams/ kg/ day of protein balances protein synthesis and breakdown in the course of burn hypermetabolism [35]. The calories provided by protein are usually calculated as part of the total energy support of the patient. However, this protein should always be provided in addition to significant energy in the form of carbohydrate and fat calories; otherwise, the protein will be used entirely as an energy source rather than as a specific nutrient to provide substrate for wound healing and support of muscle mass. For that reason, the amount of protein contained in various nutrients is often expressed as the ratio of nonprotein calories to nitrogen (NPCal:N2). The optimal NPCal:N2 for burn patients has long been recognized to be a function of burn size [36], but is almost always a lower ratio than in unstressed patients.

Administration of nutrition support with lipid content in excess of 15% impairs immune function [37]. Lipids are necessary as a source of free fatty acids and for carriage of lipid-soluble vitamins, and some lipid calories are helpful in avoiding requirements for excessive quantities of glucose. Enhanced lipolysis occurs in burn hypermetabolism with the rate of free fatty acid oxidation being nearly double that measured in healthy volunteers [34]. This enhanced lipolysis may result in increased recycling of free fatty acids or increased total body fat stores. Optimal lipid content for burn nutrition support is therefore less than 15%, at least during the initial highly catabolic phase [33, 38, 39]. However, as will be shown below, few commercially-available enteral products fulfill this requirement. Patients given PN may be better off if fat is withheld entirely for short

periods and given as little as once weekly [40], and this practice is recommended when instituting PN [3] even though this may contribute to aggravated glucose intolerance.

Demands for vitamins and trace minerals are increased in all critically ill patients, and this demand is marked in burn patients because of exudative losses that occur in the absence of the skin barrier. Use of micronutrient supplementation has increased remarkably over the last 20 years and now represents a widespread practice in burn nutrition. All centers that responded to a recent survey on nutrition care practices indicated daily use of a multivitamin supplement [23]. However, no evidence-based guidelines currently exist for additional micronutrient supplementation in burns [5].

Vitamins A and C are routinely supplemented in many burn centers and therefore merit consideration. Both of these vitamins show decreased levels following burn injury and demonstrate responsiveness to supplementation [41]. Vitamin A has multiple functions relevant to burn care, including prevention of free radical damage, maintenance of immune function, and assistance in wound epithelialization. Vitamin C also has antioxidant function and plays a critical role in collagen cross-linking and, therefore, wound healing. One group has recommended supplementation in burn patients with 1000 IU of Vitamin A and 500 mg of Vitamin C daily [42]. Clinicians should be mindful of the potential for toxicity with high doses of Vitamin A. High doses of Vitamin C, in contrast, seem to have no toxic effects with excess simply being excreted in urine.

Burned patients, especially children, are known to suffer bone demineralization, predisposing them to spontaneous fractures [43], and contributing to growth retardation. Reasons for this are multifactorial, including increased glucocorticoid production, reduced production of parathyroid hormone, and impaired synthesis of Vitamin D [44, 45].

Klein et al. have provided a detailed description of the events responsible for demineralization of bone following burn injury, the reduction in parathyroid hormone production, and the subsequent deficiency of 1,25 dihydroxyvitamin D. In addition, skin from burned patients cannot synthesize Vitamin D correctly and burn patients are encouraged to avoid sun exposure on the skin [46]. As a consequence,

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