Key points

Introduction

Burn injury is a serious and life-threatening condition. Approximately 486,000 people in the United States undergo treatment of burn injuries each year, with about 40,000 of those injured requiring hospitalization and roughly 3275 cases resulting in death. Major burn patients are arguably the sickest population in the hospital, characterized by a severe inflammatory response, high oxidative stress, and a prolonged hypermetabolic and catabolic response.

Nutrition is vital to the health and recovery of burn patients. Massive fluid shifts immediately following injury, hypermetabolism as early as 24 hours postburn (lasting for up to 2 years), increased risk for loss of lean body mass, and potentially damaging free radial production all indicate the need for targeted and often aggressive medical nutrition therapy to improve clinical outcomes following major burns. Although underfeeding can lead to muscle wasting and delays in wound healing, overfeeding can have equally serious complications, such as hyperglycemia, fatty liver, and prolonged ventilator dependency. Understanding the physiologic response to burn stress, recognizing the increased risk for nutritional deficit, and applying evidence-based medical and nutritional treatment guidelines are key factors in supporting the recovery of patients postburn injury.

Introduction

Burn injury is a serious and life-threatening condition. Approximately 486,000 people in the United States undergo treatment of burn injuries each year, with about 40,000 of those injured requiring hospitalization and roughly 3275 cases resulting in death. Major burn patients are arguably the sickest population in the hospital, characterized by a severe inflammatory response, high oxidative stress, and a prolonged hypermetabolic and catabolic response.

Nutrition is vital to the health and recovery of burn patients. Massive fluid shifts immediately following injury, hypermetabolism as early as 24 hours postburn (lasting for up to 2 years), increased risk for loss of lean body mass, and potentially damaging free radial production all indicate the need for targeted and often aggressive medical nutrition therapy to improve clinical outcomes following major burns. Although underfeeding can lead to muscle wasting and delays in wound healing, overfeeding can have equally serious complications, such as hyperglycemia, fatty liver, and prolonged ventilator dependency. Understanding the physiologic response to burn stress, recognizing the increased risk for nutritional deficit, and applying evidence-based medical and nutritional treatment guidelines are key factors in supporting the recovery of patients postburn injury.

Overview of burns

Burns are characterized 1 of 3 ways: superficial (first degree), partial thickness, divided into superficial and deep (second degree), and full thickness (third degree). Superficial burns involve only the epidermis and can heal without intervention in about 3 to 4 days. Topical treatments like aloe lotion can be of benefit for symptomatic relieve. Partial-thickness burns involve damage to both the epidermal and the dermal layers of the skin, with superficial burns involving papillary dermis with sparing the skin appendages and deep burns involving the reticular dermis with loss of the skin appendages. They can be very painful (superficial) and typically require 3 or more weeks to heal. Supportive measures like bacitracin and petroleum-based dressing application are beneficial for superficial, whereas deep second-degree burns benefit from excision and grafting. Full-thickness burns involve damage to the epidermis and dermis, including the skin appendages and free nerve endings and are therefore not painful to the touch. Full-thickness burns require surgical intervention, such as wound debridement and skin grafting, to heal.

Major burn injuries can be defined as injuries with greater than 20% burned total body surface area (TBSA), and severe burns can be defined as greater than 40% TBSA. Early massive capillary leaks and fluid shifts can lead to hypovolemic shock and need for aggressive resuscitation in these patients. Physiologic changes can include a 10- to 50-fold increase in catecholamines and corticosteroids, which can last up to up to 9 months postburn ; an increase in energy expenditure and metabolic rate, which can still be at 120% 6 months postburn; an increase in cardiac work with an increase in myocardial consumption, which can be increased into the rehabilitation phase. Other changes can include lipolysis, liver dysfunction, severe muscle catabolism with net protein loss, insulin resistance, increase in cytokine levels, and decrease in sex hormones and endogenous growth hormone release. The increased metabolism and hyperdynamic circulation can lead to fatality if untreated.

Severity of the physical response to burns depends on many factors, including burn size and depth, gender, age, presence of inhalation injury, timeliness of medical treatment, and other comorbid conditions present. Complications following burn injury vary in severity. Negative outcomes are also associated with inadequate nutritional care. Insufficient intake of calories and protein can lead to a loss of lean muscle mass, which can induce immune dysfunction, impair wound healing, and increase mortality at 10%, 20%, and 40% loss, respectively.

Laboratory testing

There has been a historic link between low serum hepatic proteins, including serum albumin (A), serum prealbumin (PA), and transferrin (T) and the presence of malnutrition. However, current evidence shows that, in hospitalized patients, serum levels of these proteins have a more positive correlation with inflammation, stress, and mortality. Levels may be falsely increased by dehydration, blood, and intravenous A infusion, severe renal failure, corticosteroid and oral contraceptive use, and falsely low with fluid resuscitation, hepatitis and hepatic failure, dialysis, hyperthyroidism, pregnancy, hyperglycemia, infection, inflammation, and generalized stress. A, PA, and T alone poorly reflect malnutrition or the adequacy of calorie/protein intake and should alone not be used as indicators of nutritional status or adequacy of nutrition support therapy. Using other laboratory values such C-reactive protein in addition to serum protein values will help assess the inflammatory impact on serum protein levels.

Calories

Calculating precise energy (calorie) requirements can be challenging for clinicians. An ebb-and-flow response is often seen in burn injuries, where an initial reduction of metabolic rate occurs followed by hypermetabolism that can last for weeks. Energy expenditure typically begins to increase about 72 hours postburn, peaks in 5 to 7 days, and can remain elevated for up to 2 years. Factors that may impact energy expenditure postburn include wound closure, surgical procedures, initiation of nutrition support, physical therapy, certain medications, sepsis, and ambient temperature. Size of the burn is also a key determinant of caloric need. For burns greater than 10% TBSA, resting metabolic rate will likely be close to or at the normal range. However, patients with major burn injury are as much as double baseline, with a subsequent rate decline.

The 2 most common methods used to estimate calorie needs are IC and mathematical calculations. Both methods have pros and cons that must be considered.

Indirect calorimetry (IC) is a respiratory test that calculates actual resting energy expenditure (REE) by measuring the exchange of oxygen and carbon dioxide by the lungs by using IC to measure calorie needs, factors that may impact energy expenditure measured, resulting in a more reliable estimation of calorie needs. It is important to note that IC only provides a measurement of energy expenditure for the time frame testing was completed, which is typically at rest. To compensate, measured REE should be multiplied by 1.2 to 1.3. Although IC has long been coined the “gold standard” in estimating energy needs, financial cost often prohibits its use. IC adds cost to both the facility and the patient, including an upfront cost to purchase the machine and employ trained staff as well as a procedural cost to the patient.

Mathematical calculations are a lower-cost alternative to IC and more readily available, although multiple studies have indicated that mathematical equations are less accurate in estimating caloric need because burn patients have highly variable energy expenditure. Inaccuracy can lead to underfeeding as well as massive overfeeding, which can lead to fatty liver infiltration and increased rate of infection. Numerous static equations exist and are used to calculate needs based on height, weight, stress, activity, and variety of other variables ( Table 1 ).

Protein

According to the American Society of Parenteral and Enteral Nutrition (ASPEN), critically ill patients are at an increased risk for protein loss related to increases in protein turnover rates, synthesis, breakdown, and oxidation. Current literature recommends providing protein at 1.5 to 2 g per kilogram of body weight per day in the critically ill adult burn population. Higher protein intakes (>2.2 g/kg) do not result in a higher net protein synthesis. For morbidly obese critically ill patients, ideal body weight should be used to calculate protein requirements. To ensure optimal protein utilization, calorie intake should also be adequate, with protein comprising no more than 20% to 25% of estimated caloric needs.

Carbohydrates

Sufficient carbohydrate intake is similar to that of non-burned individuals at 55% to 60% of total energy requirements. Because burn patients have higher than usual energy needs, precaution should be taken to avoid excessive carbohydrate load, which can induce hyperglycemia and shock liver. Although excessive carbohydrate is unlikely via oral or enteral route due to digestive limitations and capacity, it is likely to occur via the parenteral route. The maximum intravenous carbohydrate infusion rate for adults is 5 to 7 mg/kg/d, with excess of 7 mg/kg/d increasing risk of shock liver and hyperglycemia.

Lipid

Nonburned individuals require a maximum of 30% of energy from lipid, with less than 10% of lipid calories from saturated fatty acids for cardiovascular health. There is no evidence to support increasing lipid consumption postburn injury. Total lipid intake from all sources should be accounted for to avoid overfeeding, including lipid emulsions included with intravenous medications such as propofol.

Fluid

Adequate fluid resuscitation is an important part of the postburn recovery process. Localized edema is common in smaller burns, and patients with larger burns may experience whole body edema. Although total body water may remain unchanged, circulating fluid is reduced and requires replacement. The Parkland Formula recommends 4 mL lactated Ringers/kg per % TBSA burned, with half of total volume given over the first 8 hours, and the remaining half of total volume given over the next 16 hours. Fluid intake should always be titrated to maintain adequate urine output, which has been shown the best measurement available for adequate tissue perfusion in burns. The use and titration of lactated Ringers solution according to the urine output for burns up to 40% without inhalation injury is a safe and well-tested method. In patients with larger burns (>40%), inhalation injuries, or preexisting heart disease, and in geriatric patients, the use of a lower volume aided by colloid can be beneficial.

Nutrition therapy

Three options exist for route of nutrition therapy: oral, enteral, and parenteral. Oral route with high protein foods and small, frequent feedings is always preferred, if the patient is able to consume adequate intake per the aforementioned guidelines. For instance, when the patient is unable to eat or unable to consume adequate intake (defined as at least 60% of estimated energy requirement), enteral (EN) and/or parenteral nutrition (PN) should be considered ( Fig. 1 ).

Decision tree. GI, gastrointestinal; NPO, nothing by mouth; PO, orally.