Burns, metabolism and nutritional requirements

Quemaduras, el metabolismo y los requerimientos nutricionales

N. Mendonça Machado¹, A. Gragnani² and L. Masako Ferreira³

¹Student of sensu lato post-graduation course in Surgery. Universidade Federal de São Paulo. São Paulo. Brasil.
²Associate Professor. Plastic Surgery Division. Universidade Federal de São Paulo. São Paulo. Brasil.
³Full Professor. Plastic Surgery Division. Head of Surgery Department. Universidade Federal de São Paulo. São Paulo. Brasil.

ABSTRACT

Objectives: To review the nutritional evaluation in burned patient, considering the literature descriptions of nutritional evaluation and energy requirements of these patients.
Introduction: Thermal injury is the traumatic event with the highest metabolic response in critically ill patients. Various mathematical formulas have been developed to estimate nutritional requirements in burned patient. Indirect Calorimetry is the only method considered gold standard for measuring caloric expenditure.
Methods: A survey of the literature and data was collected based on official data bases, LILACS, EMBASE and PubMed.
Results: The metabolic changes involved in hypermetabolism are designed to supply energy to support immune function, brain activity, wound healing, and preservation of body tissues. Body weight is considered the easiest indicator and perhaps the best to assess the nutritional status. The most common formulas utilized in these patients are the Curreri, Pennisi, Schofield, Ireton-Jones, Harris-Benedict and the ASPEN recommendations. For children is the Mayes and World Health Organization formula. The majority of mathematical formulas overestimate the nutritional needs. The regular use of Indirect Calorimetry supplies adequate nutritional support to the burn patient.
Discussion: The traditional nutritional evaluation considers anthropometry, biochemical markers and estimation of nutritional requirements. The weight provides a basis for decisions that are established in the clinical context. Classic parameters can be adapted to intensive care environment.
Conclusions: The use of Indirect Calorimetry is crucial to ensure the safety of the nutritional support of burn patients and this should be widely encouraged.

RESUMEN

Objetivos: Revisar la evaluación nutricional del paciente quemado, considerando las descripciones bibliográficas de la evaluación nutricional y de los requerimientos energéticos de estos pacientes.
Introducción: la lesión térmica es el acontecimiento traumático con la mayor respuesta metabólica en los pacientes críticos. Se han desarrollado diversas fórmulas matemáticas para estimar los requerimientos nutricionales del paciente quemado. La calorimetría indirecta es el único método de referencia para medir el gasto calórico.
Métodos: se realizó una revisión bibliográfica y una recogida de datos a partir de las bases de datos oficiales LILACS, EMBASE y PubMed.
Resultados: Los cambios metabólicos que implican un hipermetabolismo están diseñados para aportar energía para mantener la función inmunitaria, la actividad cerebral y la curación de las heridas así como la conservación de los tejidos corporales. Se considera que el peso corporal es el indicador más sencillo y quizás el óptimo para evaluar el estado nutritivo. Las fórmulas más frecuentemente empleadas en estos pacientes son Curreri, Pennisi, Schofield, Ireton-Jones, Harris-Benedict y las recomendaciones de ASPEN. En los niños son la de Mayes y la de la Organización Mundial de la Salud. La mayoría de las fórmulas matemáticas sobreestiman las necesidades nutricionales. El uso habitual de la calorimetría indirecta proporciona un soporte nutricional adecuado en el paciente quemado.
Discusión: La evaluación nutricional tradicional considera la antropometría, los marcadores bioquímicos y la estimación de los requerimientos nutricionales. El peso proporciona la base para las decisiones que se establecen en el contexto clínico. Los parámetros clásicos pueden adaptarse al ambiente de los cuidados intensivos.
Conclusiones: el uso de la calorimetría indirecta es crucial para asegurar la seguridad del soporte nutricional de los pacientes quemados por lo que debería potenciarse.

Palabras clave: Quemaduras. Metabolismo. Evaluación nutricional.

Abbreviations: ]]> TBSA: Total Body Surface Area.
ESPEN: European Society for Clinical Nutrition and Metabolism.
NRS: Nutritional Risk Screening.
ASPEN: American Society for Parenteral and Enteral Nutrition.
IC: Indirect Calorimetry.

Introduction

Thermal injury is the traumatic event with the highest metabolic response in critically ill patients.^1,2 This response is proportional to the size of the burn and damage continue years after the incident.³ Pathophysiological changes induce an acute inflammatory response, peripheral resistance to insulin and immunodeficiency.^4,5

The effect of continuous and prolonged secretion of cytokines on metabolism can lead to an unstable and hypercatabolic condition, causing multiple organ failure.⁶

Objective determination of nutritional needs should be accurately evaluated to ensure adequate nutrition for this condition. Knowledge of the patient's profile is essential to prevent under-nutrition or over-nutrition and to minimize the complications of nutritional support.⁷

Methods and materials

A survey of the literature and data was collected utilizing the key words burns, metabolism, nutritional evaluation and intensive care unit based on official data bases from LILACS, EMBASE and PubMed.

Metabolic response to burns injury

The patient essentially exhibits two phases: the first is referred to the ebb stage, in which the patient shows a deficit in plasma volume and insulin levels, initial signs of shock, hypothermia, lowered oxygen consumption and a decrease in overall metabolic rate. After this, the body undergoes hormonal modifications and, the ebb phase evolves to the flow phase. This stage is characterized by an increased concentration of catabolic hormones regulating the metabolic response. An increase in heart rate, body temperature, calorie consumption, proteolysis and neoglycogenesis is observed.⁹ These reactions result of metabolic events aimed at wound healing.¹⁰

Hypermetabolism begins at about the fifth post-burn day and persists for close to twentyfour months, causing loss of lean body mass, reduced bone density and muscle weakness, among other events.^11,12

The intensive use of energy substrates predisposes the patient to malnutrition, which can cause a deficiency in the immune system, infections, an important nitrogen loss, delayed wound healing, prolonged hospital stay and mortality.^13,14

The catabolic state is maintained by the inflammatory events activated by the damaged tissues. The cytokines released from these tissues transform the modified basal metabolism and keep it altered for long periods after acute trauma.¹⁵

Nutrition

Currently the concept that nutritional support plays an indisputable role in treating critically ill patient is well-accepted by scientific and health professional societies.¹⁶ The metabolic changes involved in hypermetabolism are designed to supply energy to support immune function, brain activity, wound healing and preservation of body tissues.¹⁷

Tissue repair, accentuated and persistent muscle catabolism, and wound losses promote an increased protein needs after thermal injury. A clear recommendation is more problematic, although numerous investigators have discussed the increased protein needs of the thermally injured patient.¹⁸

The molecular mechanism of the hypermetabolic response to burn injury is not completely understood. Studies indicate that approximately 60% of the increased metabolic response to burn injury is attributable to an increased protein synthesis, gluconeogenesis, urea production and substrate cycling.¹⁹

Nutritional therapy aims: to offer favorable conditions for the establishment of the therapeutic plan, to offer energy, fluids and nutrients in adequate quantities to maintain vital functions and homeostasis, recover the activity immune system, reduce the risks of overfeeding, ensure offers of protein and energy necessary to minimize the protein catabolism and nitrogen loss.²⁰

Metabolic transformations involving nutrients

Numerous studies have established that hypercatabolic and hypermetabolic states are associated with profound glutamine deprivation. A study conducted by Peng et al. (2005) found that when supplemented at a rate of 0.5 g/kg/day burned patients were capable of reversing the changes made during the burn.²⁴

Hyperglycemia from metabolic perspective results from an increase in hepatic gluconeogenesis and a resistance to the action of insulin to clear glucose into muscle.²⁵

Futile recycling of free fatty acids and triglycerides results of the enhanced lipolysis combined with fat oxidation.²³

Nutritional evaluation

Assessment is used to identify patients who would benefit from nutritional support and suggests a design for that therapy.²⁶ In general, the same methods are used for other patients to conduct an assessment of nutritional status of critically ill patients, such as anthropometric and biochemical markers. However, nutritional assessment is limited in the burned patient.²⁷

Most nutritional assessment tools available in a clinical setting are confounded by the physiological elements of the inflammatory response. Despite their limitations, many of markers of nutritional status when used collectively can help in daily monitoring of nutritional support.²¹

Nutritional risk is defined as "the chances of a better or worse outcome from disease or surgery according to actual or potential nutritional and metabolic status" by the European Society for Clinical Nutrition and Metabolism (ESPEN), Nutritional Risk Screening (NRS) 2002.^28,29 (table I).

According to the study by Hart et al. (2000) the five most significant variables in determining the magnitude of the catabolic response to severe burn were admission weight, percentage of TBSA burned, metabolic rate expressed as the percentage of the predicted energy expenditure, time from burn to the primary excision of the wound and burn sepsis.³⁰

Anthropometric variables

Body compartments and evolution of hydration status in burn patients invalidate anthropometric variables for nutritional evaluation.³¹ Body weight is considered the easiest indicator and perhaps the best to assess the nutritional status.³² Moreover, presence of edema are common.²⁷

The anatomical point for the anthropometry measurements may be inaccessible and surgical procedures require days of bed rest. Semiologic analysis is important to detect the signs of depletion and some situations must be constantly monitored (table II).

Energy requirements

The size of the burn will proportionally influence the hypermetabolic response, inflammation, catabolism, changes in body composition, hormone production and organic dysfunction.^3,33

The increase in energetic expenditure significantly contributes to the development of malnutrition and predicts that all adult patients with over 20% of TBSA must receive specific and individualized nutritional support.³⁴

The majority of mathematical formulas overestimate the nutritional needs of burn patient.¹¹ It is difficult for a single formula to define individual nutritional needs with satisfactory precision, since all the factors involved in affecting metabolism are very complex. Predetermined equations to estimate energy expenditure are not recommended.^35,36

Between 1970 and 1980 the most frequently used formula for estimating the nutritional needs of burn patients was developed by William Curreri.^37,38 In 1976, Pennisi created a more comprehensive formula, designed for adults and children, estimating both the energetic needs in calories and protein needs in grams.³⁹ Other formulas developed for critically ill and burn patients include Toronto,⁴⁰ Schofield,⁴¹ Ireton-Jones,⁴² Harris-Benedict,^43,44 and the American Society for Parenteral and Enteral Nutrition (ASPEN) recommendations.⁴⁵ The most widely formulas used in children are those of Harris and Benedict, Mayes and the World Health Organization⁴⁶ (table III).

In order to compare the energy requirements suggested by the formulas most commonly used in adults, it was hypothesized a case of burn, and all formulas were employed. Hypothetically, was taken as reference for the use of formulas to a patient following conditions: 30 years old, weighing 72 kg, height 170cm, 40% of TBSA, bedridden, with eight days of burning, body temperature of 37^oC, breathing spontaneously and with average intake of 2.000 calories per day (fig. 2).

Over-nutrition predisposes the patient to hyperglycemia, overload of the respiratory system, steatosis and hyperosmolarity. When dealing with under-nutrition, the patient could suffer from malnutrition and subsequent reduction of immunocompetence, prolonged dependency on mechanical ventilation and delay in the healing processes, increased risk of infection, morbidity and mortality.⁴⁶

In 1783, a study on the physiology of breathing -Mémoire sur la Chaleur, published by Lavoisier and Laplace for a periodical on the study of heat, generated the initial concepts of energy metabolism. The study explained the relationship between the inspired oxygen and the heat lost by the body.⁴⁸

With respect to the study of energy metabolism, Indirect Calorimetry (IC) is the only research method considered gold standard for measuring caloric expenditure.⁴⁹ Identifying the patient's metabolic rate is essential to prevent deficits in energetic equilibrium. The regular use of IC supplies adequate nutritional support to the burn patient and is useful in the early detection of under-nutrition and over-nutrition.^50,51

Due to its high cost, the use of IC for nutritional evaluation occurs mainly for research and few professionals have access to it. In the past 33 years, about 111 scientific articles reporting on burn injuries and IC have been published. The rate of publications over the last three decades follows an irregular pattern.

Nutritional support

The introduction of nutritional support cannot suppress hypermetabolic and hypercatabolic responses produced by a burn. Nevertheless, simply providing enteral nutrients in the first 24 hours postburn, reduces the caloric deficit.⁵⁴

A study designed to compare the benefits of enteral nutrition when provided in different amounts was verified that the mortality of patients in the group receiving enteral nutrition in the proportion of 30 kcal/kg/day or more had lower mortality rates.^32,55

In general rule critically ill adults require around 2 g of protein/kg/day or approximately 15% to 20% of total caloric intake in 24 hours.⁵⁶ The nutrients often used for Pharmacological nutrition in burned patients are glutamine, arginine and omega-3. These components, when supplied in quantities 2-7 times higher than those commonly eaten by healthy people, appear to have a beneficial effect on the pathophysiological changes induced by burns.⁵⁷

Discussion

Nutritional support has become a major focus in the care of severely burned patients to overcome clinical events.⁵⁵ Malnutrition is an increasing problem in critically ill adults and can have a profound impact on outcomes. Given the ongoing challenges associated with nutrition screening, assessment, and support processes, this situation is perhaps not surprising. There is an unacceptably high prevalence of malnutrition in critically ill adults.⁵²

Nutrition support may reduce morbidity and mortality after severe thermal injury, but excessive caloric and protein intakes cannot overcome the catabolic response to critical illness.¹⁸

Some patients do not exhibit the expected hypermetabolic response from their wounds. There are other individual factors that interfere with this response and advance the patient's progress to hypometabolism. The chief factors responsible for this unusual response are: the use of analgesia and sedatives, the presence of malnutrition, hypothyroidism, shock or hemodynamic instability, cellular bio-energetic failure, hypothermia and advanced hepatitis.⁵⁸

This unusual response of some patient's causes an increase in the risk of developing clinical complications related to over-nutrition, because this picture is "masked" by typical hypermetabolism of burn patients. Accurate determination of resting energy expenditure is necessary in patients receiving nutritional support to ensure that their energy needs are met and to avoid the complications associated with over or underfeeding.⁵⁹

In clinical practice, the burned patient is constantly exposed to periods of fasting, mostly due execution of examinations or surgical procedures. However, what differs this from other patients in intensive care is the constant need to make bandages. The frequency of these procedures can be daily and also require fasting. Moreover, it is widely described in literature that some inflammatory markers induced anorexia in patients submitted to metabolic stress.^60,61

Keeping patients "fasted" to avoid aspiration complications when attempting extubation and a variety of other reasons generally delay enteral feeding. Several studies and reviews have shown that only about 75% of prescribed nutrients are actually delivered, with substantial variability.⁶²

Even in a simple fasting, as a prolonged fasting, the body of an average adult loses about 60 to 70 g of protein (240 to 280 g of muscle tissue) per day. In severe trauma or sepsis, this loss can reach 150 to 200 g (600 to 1,000 g of muscle tissue) per day.²⁷

The constant development of nutritional assessment reveals a promising future for the discipline. The results of these investigations will allow professionals in the field to broaden knowledge and devise new treatment strategies, improving the quality of care. Nutrition occupies a central role in our lives and for this reason it should be approached seriously, especially in pathological states.

Conclusion

There are lists of possible markers for nutritional assessment, but a minimum set of standards should be established. The use of IC is crucial to ensuring the safety of the nutritional support of burn patients and this should be widely encouraged.

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Correspondence:
Alfredo Gragnani.
Rua Napoleão de Barros 737,
14^o andar, Vila Clementino. ]]> CP: 04024-002 São Paulo. Brasil.
E-mail: alfredogf@ig.com.br

Recibido: 12-II-2011
Aceptado: 5-IV-2011.