Overview of nutrition support in burn patients

INTRODUCTION — Nutrition support is the provision of nutrients and any necessary adjunctive therapeutic agents to improve or maintain nutritional status. Nutrition support is fundamental in the management of patients with a moderate-to-severe burn injury.

The primary goal of nutrition support following severe burn injury is to meet the distinctive demands placed upon the body by hypermetabolism. The adverse effects of the hypermetabolic response can result in life-threatening protein-calorie malnutrition. While management of nutritional needs in burn patients has many features in common with the nutritional management of other critically ill surgical patients, the severity, magnitude, and duration of the hypermetabolic response and the ensuing energy requirements for the severe burn patient are far greater.

Nutrition support is administered into the stomach or small intestine (enteral) and/or by intravenous infusion (parenteral). Enteral nutrition, which is administered through a nasogastric, gastric, or intestinal tube, is the preferred method of feeding critically ill patients and an important means of counteracting hypermetabolism. Supplemental parenteral nutrition should only be given to patients in whom enteral feeds are contraindicated, those who do not tolerate enteral feeds, or for patients who do not reach their target nutrient intake in a reasonable time on enteral feedings alone [1]. (See "Nutrition support in intubated critically ill adult patients: Initial evaluation and prescription".)

The unique characteristics of nutritional requirements in the moderate and severe burn patient, including patient selection, initiation, and delivery of nutrition support, are reviewed. Other aspects of burn care are reviewed separately. (See "Overview of the management of the severely burned patient" and "Hypermetabolic response to moderate-to-severe burn injury and management".)

CANDIDATES FOR NUTRITION SUPPORT — Although provision of adequate nutrition is vital in all burn injuries, identification of patients who require coordinated nutrition support is a key component of the comprehensive care of the patient with moderate-to-severe burns (algorithm 1).

Identification of patients who are likely to require coordinated nutrition support presents a challenge because of the heterogeneity of the metabolic response and burn injury patterns. While there is limited evidence to support the decision-making process and the timing of the initiation of nutrition support in the critical care setting, the combined Society of Critical Care Medicine (SCCM) and American Society for Parenteral and Enteral Nutrition (ASPEN) guidelines suggest based on expert consensus that very early initiation of enteral feeds should be targeted in patients with burn injury [1].

Moderate-to-severe burns — Burn patients who are not expected to initiate an oral diet within 6 to 12 hours of sustaining the burn injury are started on nutrition support [2].

Metabolic rate increases proportionally with burn size. A minimum of 15 to 25 percent total body surface area (TBSA) burn injury can initiate a catabolic response that includes impaired immunity and fluid shifts [3,4]. Patients with burns greater than 40 percent TBSA consistently experience hypermetabolism. (See "Hypermetabolic response to moderate-to-severe burn injury and management", section on 'Magnitude'.)

Inhalational injury — Patients who have sustained inhalation injury or who have extensive facial burns, both of which are likely to result in a prolonged ventilator course, usually meet criteria for nutritional support. (See "Inhalation injury from heat, smoke, or chemical irritants".)

Failure to maintain weight — Failure to maintain lean body mass (LBM) and body weight (ie, dry body weight or weight on postburn day five) with oral intake is an accepted indication for nutrition support in burn patients.

Patients with burns that involve 20 to 40 percent of TBSA may not be able to consume sufficient calories to maintain LBM and weight [5,6]. Similarly, patients who require extensive surgery, develop complications of their injury, or have a known nutritional deficiency at the time of admission may not consume adequate calories.

Nutrition support following burn injury is unlikely to redress preexisting conditions but is intended to treat the metabolic demands incurred because of the burn injury [5].

Selected patients with less severe burns — Nutrition support is used selectively in patients with less extensive burn injury (<20 percent) burn injury. Patient groups that may benefit include children, older adults, and patients with obesity. (See "Overview of perioperative nutrition support", section on 'Nutritional assessment in the surgical patient' and "Clinical assessment and monitoring of nutrition support in adult surgical patients".)

Children — Children are quite vulnerable to the metabolic demands and consequences of a burn injury [7]. They have greater basal metabolic requirements than adults per unit of weight because of energy needed to sustain growth and activity. Children also mount a hypermetabolic response to burns comparable to the response seen in adults but have relatively limited energy reserves when compared with adults.

Oral intake in burned children may prove particularly challenging because of pain and anxiety, as well as the inability of younger children to comprehend the importance of adequate oral intake. The psychological aspects of nutrition coupled with the deleterious effects of acute protein-calorie malnutrition mean that enteral nutrition support should be started in children earlier and with less severe injuries when compared with adults [8].

Older adults — Older adult patients with burn injuries provide a particular challenge for nutrition management for a variety of reasons and may benefit from nutrition support. Older adult patients have a higher incidence of malnutrition (age- and disease-related wasting and/or undernourishment) at the time of injury, which may result in poorer outcomes unless nutritional status is effectively addressed [9]. (See "Geriatric nutrition: Nutritional issues in older adults".)

In general, weight increases with age up to the age of 60; thereafter, there is a progressive loss of lean body mass with a relative increase in fat mass. Weight declines as maintenance of weight becomes increasingly difficult in the advanced years of life. The decrease in lean body mass, which may decline by up to 45 percent by the eighth decade of life, comes mostly from the loss of skeletal muscle. Infiltration of muscle tissue or replacement with fat is associated with functional decline, poorer physical function, and reduced strength. These changes in body composition may affect nutritional needs and wound healing.

Under normal circumstances, older adults have a decreased resting metabolic rate and may not generate an increase in measured metabolic rate in response to a burn injury. Additionally, decreased appetite; changes in sight, smell, and taste; poor dentition; and social factors make eating more challenging. Finally, because of underlying organ dysfunction consequent to aging or true medical comorbidities, limitation of some macronutrients (eg, protein, fat) and micronutrients (eg, potassium, glucose) may be appropriate in the older adult burn patient.

Obesity — Determining the nutritional needs in patients with obesity and burn injury adds another nuance to their care. Metabolic syndrome and diabetes mellitus are more common in these patients, and glycemic control can be difficult. (See 'Glycemic control' below and "Metabolic syndrome (insulin resistance syndrome or syndrome X)".)

The presence of obesity often leads to a misconception that the patient is well nourished when, in fact, the converse is often true. Despite their extensive fat stores, patients with obesity can demonstrate markedly low lean body mass (LBM), which is referred to as sarcopenic obesity [10,11]. Patients with sarcopenic obesity have morbidity and mortality rates following surgery that are more in line with their LBM measurements than with their actual or ideal body weight. In an effort to improve the nutrition of critically ill patients with sarcopenic obesity, some have suggested a hypocaloric, high-protein feeding regimen [10,12]. However, for burn patients, given the hypermetabolic state that accompanies injury, a strategy that is hypocaloric is likely not safe without further research into its effects on healing [12]. Patients with obesity typically have decreased muscle mass, and the hormonal response of hypermetabolism limits the body's ability to use fat stores as an energy source [5]. (See "Hypermetabolic response to moderate-to-severe burn injury and management".)

TIMING OF NUTRITION SUPPORT

Initiation — Providing nutrition support is essential in the successful management of the burn patient [13,14]. The safety and efficacy of initiating enteral feedings in burn patients has been established, as is a trend toward decreased infection rates and decreased calorie deficits [15-17]; however, the optimal timing of initiating nutrition support is debated. Early enteral nutrition may help to attenuate the hypermetabolic response to burn injury. In a meta-analysis, provision of early nutrition support was not associated with any detrimental effect [18]. Similar lengths of hospital stay, infection, and mortality were found for early (within 24 hours) compared with late (after 24 hours) initiation of enteral nutrition. A study of mechanically ventilated medical and surgical patients reported that patients who received enteral nutrition within three days of initiation of mechanical ventilation had lower in-hospital mortality, fewer ventilator days, shorter hospital length of stay, and lower hospitals costs [19]. Similar results were found in a systematic review and meta-analysis of early enteral nutrition in pediatric burn patients [20]. Pediatric patients who received early enteral nutrition had shorter length of stay and less weight loss. Thus, in the hemodynamically stable patient with moderate-to-severe burn injury (>20 percent total body surface area [TBSA]), we suggest initiating nutrition support in the form of enteral feeding as early as possible.

Guidelines from the Society of Critical Care Medicine (SCCM) and American Society for Parenteral and Enteral Nutrition (ASPEN) support early enteral nutrition initiation, within four to six hours of injury for all critically ill burn patients, if possible [1]. The recommendations from European Society for Clinical Nutrition and Metabolism (ESPEN) recommend early enteral nutrition for moderate-to-severe burn patients who will not or cannot initiate oral nutrition within 6 to 12 hours of injury [2]. Consultation with a dietitian experienced in the nutritional care of burn patients can prove exceptionally helpful in all aspects of the nutritional care of these patients. (See "Nutrition support in intubated critically ill adult patients: Initial evaluation and prescription".)

For hemodynamically unstable patients, nutrition support should be started as soon as the perfusion of the intestine is thought to be adequate. Care must be taken when delivering full feeds in the setting of marked hemodynamic instability or with high vasopressor requirements due to the risk of causing nonocclusive mesenteric ischemia. In spite of this, the use of enteral nutrition in patients on low or decreasing doses of vasopressors can be safely accomplished [21]. (See "Nonocclusive mesenteric ischemia", section on 'Risk factors'.)

Cessation — There has been little research into the optimal diet for patients in the acute postburn phase; however, it is suggested that they continue to receive adequate nutrition following discharge [22]. It is known that the hypermetabolic state of burn injury can persist for over a year and that in addition to therapies that attenuate the hypermetabolic response, patients may benefit from increased caloric intake and increased consumption of protein during this time period. Patients should monitor their weight closely, and those who are not able to maintain their weight with their normal diet may benefit from supplementation. (See "Hypermetabolic response to moderate-to-severe burn injury and management", section on 'Attenuation of the hypermetabolic response'.)

DELIVERY OF NUTRITION SUPPORT

Route of delivery — Enteral nutrition, rather than parenteral nutrition, is generally preferred in burn patients who require nutrition support. Early enteral nutrition has been associated with improved function of the gastrointestinal tract, less ischemia/reperfusion injury, and reduced intestinal permeability in burn patients receiving enteral nutrition compared with a parenteral route [23]. In a small trial that included 82 burn patients, mortality was higher and the incidence of infectious complications, especially pneumonia, was increased in patients randomly assigned to parenteral nutrition compared with enteral nutrition [24]. In a review of 67 burn patients, septic and metabolic complications were also increased in patients who received parenteral nutrition [25]. Those who received enteral nutrition support had fewer hypoglycemic events, electrolyte abnormalities, pulmonary complications, sepsis, and mortality.

Enteral nutrition support can be delivered into the stomach or small intestine. In many burn centers, postpyloric feeding is preferred over gastric feeding and may be recommended if a patient has a particularly high risk for aspiration or has demonstrated intolerance for gastric nutrition support [1,2]. The practice at our burn center is to place a feeding tube at the bedside in all patients with moderate-to-severe burn injury as soon as is clinically possible (algorithm 1), usually within 24 hours of admission. Once access is established, feedings are initiated at a low rate and increased to an established goal rate over 12 to 18 hours. We provide early gastric feedings if the tube cannot be easily advanced past the pylorus.

The effectiveness of gastric versus postpyloric nutrition support remains an area of controversy in burn care. Many burn centers safely and successfully use only gastric feedings or use a combination of gastric and enteric feedings.

●Advantages of gastric nutrition support include the ease of tube placement, time to initiation of nutrition, and the decreased incidence of diarrhea. The main problem with nutrition support delivered into the stomach is that many moderate-to-severe burn patients require multiple operative procedures, frequently requiring suspension of gastric feedings perioperatively to decrease the risk of aspiration. Among critically ill patients (unselected), a meta-analysis of 15 randomized trials found similar mortality, intensive care unit length of stay, and ventilator days for a gastric versus postpyloric feeding route; however, postpyloric feeding was associated with reduced risk of pneumonia (relative risk 0.75, 95% CI 0.60-0.93) and improved nutrient intake (percent goal rate received: 11 percent, 95% CI 5 to 16 percent) [26].

●If gastric nutrition support is not tolerated, postpyloric feeding may be better tolerated since the majority of gastrointestinal motility disorders in the critically ill seem to occur in the antral-pyloric region of the stomach [26]. While placement of a postpyloric tube is technically more difficult than placement of a gastric tube and there is a greater risk of dislodgment with the intestinal tube, the minimally lower risk of pneumonia with postpyloric feedings and the ability to continue using them during patient repositioning, wound care, and even through operative procedures provides a slight advantage over gastric feeding in severe burns [26]. Various methods can be used to place feeding tubes beyond the pylorus. (See "Inpatient placement and management of nasogastric and nasoenteric tubes in adults", section on 'Tube placement'.)

Parenteral nutrition is appropriate only in those burn patients who have persistent intolerance to enteral feeds and who are unable to attain adequate protein and calorie intake on enteral nutrition or those who suffer with burns or other injuries that limit access to the stomach or small intestines [5,7,27,28]. Feeding intolerance is identified by abdominal distention, ileus, high gastric residuals, or intractable diarrhea following initiation of enteral nutrition. Our threshold for initiating of parenteral nutrition in burn patients is persistent feeding intolerance for more than 48 to 72 hours. (See "Postoperative parenteral nutrition in adults".)

Data suggest that supplementation of enteral nutrition with parenteral nutrition in burn patients is associated with increased mortality [23,24]. A randomized trial of 39 patients with greater than 50 percent TBSA burn found that aggressive high-calorie feeding with a combination of enteral and parenteral nutrition was associated with significantly higher mortality than enteral feedings alone (63 and 26 percent, respectively). Intravenous supplementation decreased the amount of enteral calories tolerated by burn patients [23].

Nutritional demands and formulas — Various formulations and equations (eg, Harris Benedict, Curreri) and other methods (eg, indirect colorimetry) have been developed to estimate energy requirements of adult and pediatric burn patients [29-34]. Indirect calorimetry remains the standard for estimating energy expenditure in patients who are critically ill [35]. These are reviewed separately. (See "Postoperative parenteral nutrition in adults" and "Nutritional demands and enteral formulas for adult surgical patients", section on 'Determining caloric requirements'.)

The Curreri formula is widely used for estimating the total caloric needs of the burn patient [24,29,32,36]. The two factors used in this formula, percent TBSA and body weight prior to the burn, estimate the energy requirements by linear regression analysis based on the number of calories required to prevent weight loss during the first few weeks postburn. The formula was based on nine adult patients. It does not consider sex, age, activity, or ventilatory status. The Curreri formula overestimates the caloric needs of burn patients when compared to metabolic expenditure as measured by calorimetry [29-31]. The overestimation may be related to the changes in burn care since the formula was developed. Early wound closure, higher ambient temperature, improvements in infection control, and pain management all reduce the hypermetabolic response to the burn injury. (See "Nutritional demands and enteral formulas for adult surgical patients", section on 'Curreri formula'.)

High-fat feeding may increase complications, including hyperlipidemia, hypoxemia, fatty liver infiltration, higher incidence of infection, and higher postoperative mortality [37-39]. The livers of burn patients secrete less very low-density lipoprotein (VLDL), and this contributes significantly to triglyceride accumulation in the liver [40-43]. Thus, the extent to which exogenous lipids can be used as an energy source after burn injury is considerably limited.

Glycemic control — Nutritional management includes avoidance of hyperglycemia, which is associated with higher morbidity and mortality in moderate-to-severe burn patients. The ideal target glucose range is uncertain, but a moderate target glucose level similar to the treatment target for of other critically ill patients seems prudent [44]. Treatment of hyperglycemia in patients with critical illness is discussed separately. (See "Glycemic control in critically ill adult and pediatric patients".)

Insulin administration appears to have dual effects: a reduction of proinflammatory effects of glucose by restoration of euglycemia and a proposed additional insulin-mediated anti-inflammatory effect [45]. During the acute burn phase, insulin improves muscle protein synthesis, accelerates donor-site healing time, attenuates the acute phase response, reduces losses in lean body mass, and reduces infection and mortality rates [46-54]. The anti-inflammatory effects of insulin potentially neutralize the proinflammatory actions of glucose [51]. Maintaining optimal glucose levels using a continuous insulin infusion can be challenging in burn patients. Burn patients require frequent operations and dressing changes, which intermittently halts enteral nutrition, leading to variability glucose levels [55]. Insulin resistance can also develop during the acute phase and persist for three years in pediatric burn patients [56]. Metformin, a biguanide, counters the two main metabolic processes that underlie burn injury-induced hyperglycemia by inhibiting gluconeogenesis and augmenting peripheral insulin sensitivity [57-61]. In a trial that randomly assigned 44 severely burned patients to metformin or insulin, metformin controlled blood glucose as well as insulin but with less hypoglycemia (15 versus 6 percent), and it also improved insulin sensitivity (measured by oral glucose tolerance test at discharge) [62].

Another approach to treating hyperglycemia in burn patients without increasing the risk of hypoglycemia is incretin-based therapies. The incretins include glucose-dependent insulinotropic peptide (GIP) and glucagon-like peptide-1 (GLP-1). Exogenous GLP-1 reduces glucose concentration in patients with type 2 diabetes after major surgery [63] and in those who are critically ill without diabetes and receiving enteral nutrition [64]. In a trial that included 24 severely burned patients, exenatide, a synthetic peptide that possesses incretin-mimetic actions including suppression of glucagon secretion and activation of GLP-1, significantly decreased the amount of exogenous insulin required to maintain glucose levels between 80 and 140 mg/dL (4.4 to 7.8 mmol/L) [65]. The GLP-1 analogue tested in this trial appears to be safe and reliably modulated glucose in these patients.

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Nutrition support (parenteral and enteral nutrition) in adults".)

SUMMARY AND RECOMMENDATIONS

●Nutrition support – Nutrition support represents an important cornerstone in the management of patients with burn injury. Candidates for nutrition support are patients with moderate-to-severe burns, inhalational injury, patients who fail to maintain weight, and selected patients with less extensive burns who are at risk for undernutrition. (See 'Introduction' above and 'Candidates for nutrition support' above.)

●Candidates – The primary goal of nutrition support following severe burn injury is to meet the distinctive demands placed upon the body by hypermetabolism. The severity, magnitude, and duration of the hypermetabolic response and the ensuing energy requirements are greater for those with burn injury compared with other patient populations. Adjuvant approaches, including early wound closure, higher ambient temperature, improvements in infection control, and pain management, all reduce the hypermetabolic response to the burn injury. (See 'Candidates for nutrition support' above.)

●Initiation – In the hemodynamically stable patient who otherwise will not be able to consume sufficient oral calories, we suggest early initiation of nutrition support within 24 hours of the burn injury (Grade 2C). We further suggest enteral nutrition as the first-line nutrition support in burn patients who cannot consume all required calories orally (Grade 2C). (See 'Initiation' above and 'Delivery of nutrition support' above.)

●Delivery of nutrition support

•Enteral nutrition support – To accomplish early delivery enteral nutrition support, our preference is use of feeding tube placed into the stomach. Using a postpyloric tube, which is technically more difficult to place, may delay feeding. However, the ability to feed through sepsis and operative procedures with a postpyloric tube provides a slight advantage over gastric feeding in patients with severe burn injury. We avoid the combination of enteral and parenteral nutrition support. (See 'Delivery of nutrition support' above.)

•Parenteral nutrition support – For burn patients with persistent intolerance to enteral feeds (eg, abdominal distention, high residuals, diarrhea) who are unable to attain adequate protein and calorie intake or in those who suffer with burns or other injuries that limit access to the stomach or small intestines, parenteral nutrition is appropriate. Our threshold for initiating of parenteral nutrition in burn patients is persistent feeding intolerance for more than 48 to 72 hours. (See 'Route of delivery' above.)

ACKNOWLEDGMENT — The UpToDate editorial staff acknowledges Amalia Cochran, MD, FACS, FCCM, who contributed to an earlier version of this topic review.