e2 Abstract The abdomen is both a primary source of disease condi tions that require care in the intensive care unit (ICU) and a sec ondary source of additional pathophysiology for children in the ICU[.]
e2 Abstract: The abdomen is both a primary source of disease conditions that require care in the intensive care unit (ICU) and a secondary source of additional pathophysiology for children in the ICU being treated for other conditions Early recognition of the acute abdomen and the judicious use of medical and surgical intervention can be key to a successful outcome in critically ill children with abdominal disease or injury Key words: acute abdomen, neutropenic enterocolitis, abdominal compartment syndrome, ischemic bowel, volvulus 99 Nutrition of the Critically Ill Child BEN D ALBERT AND NILESH M MEHTA PEARLS • Provision of individually tailored optimal nutrition is an important goal of pediatric critical care • Malnutrition is prevalent in the pediatric intensive care unit (PICU) and is associated with increased physiologic instability and resource utilization • Failure to accurately estimate or measure energy expenditure during critical illness may result in unintended underfeeding or overfeeding Indirect calorimetry is the gold standard for energy expenditure assessment and helps guide energy prescription • Protein catabolism and nitrogen loss are characteristic features of the metabolic stress response to critical illness, resulting in net negative protein balance and loss of lean body mass Accurate measurement of muscle mass and efforts to preserve it during critical illness may improve functional outcomes • Failure to deliver optimal energy and protein has been associated with poor outcomes in critically ill adults and children The precise amount and timing of nutrient delivery during acute illness must be individualized and is an important area of investigation • Enteral nutrition (EN) is the preferred mode of nutrient delivery in patients in the PICU with a functioning gastrointestinal tract Early EN has been associated with positive outcomes in critically ill patients • The gastric route is preferred for enteral nutrition Postpyloric (small bowel) feeding may be considered for patients at risk of aspiration or when gastric feeding is not feasible or has not been tolerated • Use of EN algorithms and the presence of a dedicated dietitian in the PICU may decrease the barriers to EN and improve nutrient delivery • Parenteral nutrition (PN) is associated with mechanical, infectious, and metabolic complications and should be used in carefully selected patients for whom EN is contraindicated, not tolerated, or has failed to provide adequate nutrition Delaying the initiation of PN and attempting EN delivery during the early phase of critical illness is prudent Timing of PN initiation during acute critical illness may need to be individualized Malnutrition is prevalent in critically ill children at the time of admission to the pediatric intensive care unit (PICU).1,2 Further nutritional deficiencies during their illness course are often incurred due to the burden of illness or suboptimal nutrient intake and may result in poor outcomes Safe provision of optimal nutrients during hospitalization is an important goal of pediatric critical care The prediction, estimation, and measurement of true energy expenditure in PICU patients can be challenging, resulting in unintended underfeeding or overfeeding Although underfeeding has long been recognized as a problem, a significant proportion of critically ill children are at risk of being overfed.3 A number of barriers impede the delivery of prescribed nutrients to the critically ill child and result in a delay or failure to achieve the prescribed energy and protein goal Although the complexities of critical care or the nature of illness frequently conflicts with nutrient provision, many perceived barriers to bedside nutrient delivery may be avoidable This chapter will review some of the evidence-based and consensus statements around procedures for assessment of a critically ill child in the PICU and the approach to optimal and safe nutrient delivery in this group Malnutrition in the Pediatric Critically Ill Patient Critical illness increases metabolic demand on the host in the early stages of the stress response, when nutrient intake may be limited (see also Chapter 80) As a result, children admitted to the PICU are at risk of deteriorating nutritional status and anthropometric changes with increased morbidity.1 This effect is more pronounced in a subgroup of patients who are already malnourished or at risk of malnutrition on admission The prevalence of malnutrition in children admitted to the ICU has remained largely unchanged since the 1990s One in every four children admitted to the PICU shows signs of acute or chronic malnutrition on admission.1,2 Malnutrition is associated with increased physiologic instability and the need for increased quantity of care in the ICU.4 Despite its high prevalence and consequences, awareness of malnutrition is lacking The nutritional status of hospitalized patients is often not routinely assessed, and only a minority of patients are referred for expert nutritional consultation.5 Careful nutritional evaluation upon admission to the PICU 1177 1178 S E C T I O N X Pediatric Critical Care: Gastroenterology and Nutrition will allow identification of children who are at risk for further nutritional deterioration and, hence, candidates for early intervention to optimize intake Efforts by organizations such as the American Society for Parenteral and Enteral Nutrition (ASPEN) have renewed the focus on malnutrition and facilitated a uniform approach to detecting and managing malnutrition in hospitalized adults and children.6,7 Assessment of Nutritional Status The recently revised definition of malnutrition extends beyond anthropometric thresholds to include etiology and pathogenesis of malnutrition and its impact on patient outcomes.7 Uniform use of reference charts and statistics have been proposed to compare individual patient measurements to the reference population and thereby classify malnutrition Furthermore, the new definition of malnutrition accounts for its association with disease states, in particular inflammation Assessment of the nutritional status of the critically ill child is vital but remains challenging Clinicians use a combination of anthropometric and laboratory data to diagnose undernourishment Carefully elicited past history—with details of weight gain/loss, dietary history, recent illness, and medications—helps identify risk factors and early indicators of malnutrition Weight on admission to the hospital is important and may be the only measure of the actual dry weight before capillary leak syndrome results in edema and weight gain Unless regular and accurate weights are obtained, acute changes in nutritional status may be missed or detected late.8 Physical examination should be directed toward specific signs of nutritional and metabolic deficiencies Hair, skin, eyes, mouth, and extremities may reveal stigmata of protein-energy malnutrition or vitamin and mineral deficiencies A variety of other measurements—including arm anthropometry (mid-upper arm circumference and triceps skin fold), body length, and body mass index (BMI)—have been used to monitor growth in children Recommendations for anthropometric variables and thresholds to classify malnutrition in children are shown in eTable 99.1.9 Although bedside anthropometric methods are inexpensive, they may be prone to significant interobserver variability Furthermore, weight changes and other anthropometric measurements in critically ill children should be interpreted in the context of edema, fluid therapy, volume overload, and diuresis In the presence of ascites or edema, ongoing loss of lean body mass may not be evident using weight monitoring alone Body Composition Body composition may be the primary determinant of health and predictor of morbidity and mortality in children The characteristic protein catabolism seen in the metabolic stress response, described in more detail later in this chapter, may cause significant alterations in body composition Preservation and accrual of lean body mass during illness are important predictors of clinical outcomes in patients with sepsis, cystic fibrosis, and malnutrition.10,11 Body composition is assessed in clinical practice by a variety of techniques, including anthropometry, bioelectrical impedance assessment (BIA) and dual-energy x-ray absorptiometry (DEXA) DEXA is a radiographic technique that can determine the composition and density of different body compartments (fat, lean tissue, fat-free mass, and bone mineral content) and their distribution in the body.12 However, DEXA is not practical for application in the PICU BIA, in contrast, is a bedside technique that can be applied to pediatric patients without exposure to radiation and with relative ease.13–15 Electrical current is conducted by body water and is impeded by other body components BIA estimates the volumes of body compartments, including extracellular water and total body water (TBW) TBW measures can be used to estimate lean body mass by applying age-appropriate hydration factors BIA has not been validated in critically ill populations; hence, its application in the PICU outside clinical studies is currently being investigated In specific populations, such as children with sepsis, BIA has been studied, along with other anthropometric measurements to estimate outcomes.16 Body impedance spectroscopy (BIS) uses the principle of frequency-dependent conduction of electric current through different tissues and employs a larger spectrum of currents to determine the composition of body tissues Biochemical Assessment The nutritional status can also be assessed by measuring the visceral (or constitutive) protein pool, the acute-phase protein pool, nitrogen balance, and resting energy expenditure Visceral proteins are rapid turnover proteins produced in the liver Low circulating levels of visceral protein are seen in the setting of malnutrition, inflammatory states, and impaired hepatic synthetic function The reliability of serum albumin as a marker of visceral protein status is questionable Albumin has a large pool and a half-life of 14 to 20 days, and it is not an indicator of the concurrent nutritional status Serum albumin may be affected by changes in fluid status, albumin infusion, sepsis, trauma, and liver disease; these changes are independent of nutritional status Prealbumin (also known as transthyretin or thyroxine-binding prealbumin) is a stable circulating glycoprotein synthesized in the liver It binds with retinol-binding protein and is involved in the transport of thyroxine and retinol Prealbumin, so named because of its proximity to albumin on an electrophoretic strip, is readily measured in most hospitals and is a good marker for the visceral protein pool.17,18 It has a half-life of 24 to 48 hours and reflects more acute nutritional changes Prealbumin concentration is diminished in liver disease Acute-phase reactant proteins are elevated proportional to the severity of injury in response to cytokines released during stress response and have been used to longitudinally monitor the inflammatory response Serum levels of acute-phase protein are elevated in children within 12 to 24 hours after burn injury due to hepatic reprioritization of protein synthesis.19 When measured serially, serum prealbumin and C-reactive protein (CRP) are inversely related (i.e., serum prealbumin levels decrease and CRP levels increase with the magnitude proportional to injury severity and then return to normal as the acute injury response resolves) In infants after surgery, decreases in serum CRP values to less than mg/dL have been associated with the return of anabolic metabolism and are followed by increases in serum prealbumin levels.20 The relationship between inflammation and malnutrition is intriguing; the use of acutephase inflammatory markers as well as cytokines and nutrition requires further exploration Chemistry profiles should be monitored on admission and repeated periodically Serum electrolytes, blood urea nitrogen, glucose, coagulation profile, iron, magnesium, calcium, and phosphate levels are routinely monitored Adequacy of cellular immunity can be estimated through the measurement of total lymphocyte count and by delayed-type hypersensitivity testing with a series of common antigens (e.g., Candida, Trichophyton, tuberculin) 1178.e1 eTABLE Indicators of Pediatric Malnutrition Based on Single Anthropometric Measurements 99.1 Primary Indicators (z -Score) Mild Malnutrition Moderate Malnutrition Severe Malnutrition Weight for height 21 to 21.9 22 to 22.9 23 or lower Body mass index (BMI) for age 21 to 21.9 22 to 22.9 23 or lower Length/height No data No data 23 Mid-upper arm circumference 21 to 21.9 22 to 22.9 23 CHAPTER 99 Nutrition of the Critically Ill Child the rapid synthesis of proteins that act as inflammatory response mediators and are used for tissue repair Protein breakdown may continue for an extended period in an attempt to channel the amino acids through the liver, wherein their carbon skeletons are used for gluconeogenesis to produce glucose as the preferred energy substrate for the brain, erythrocytes, and renal medulla Reprioritization of protein during metabolic stress increases the synthesis of acute-phase reactant proteins such as CRP, a1-acid glycoprotein, haptoglobin, a1-antitrypsin, a2-macroglobulin, ceruloplasmin, and fibrinogen Plasma concentrations of other proteins, including transferrin and albumin, decrease with injury or sepsis Overall, the intense protein catabolism during critical illness outstrips anabolism with net negative protein balance.23 Prolonged stress response may result in significant loss of lean body mass The intense catabolism seen in metabolic stress cannot be suppressed by supplying calories, and negative protein balance continues relentlessly This is one of the principal differences between stress response and starvation Starvation, or protein-calorie malnutrition, may be caused by socioeconomic, psychosocial, disease-related, or iatrogenic factors The metabolic response to starvation involves decreased secretion of insulin and thyroid hormones, normal secretion of glucocorticoids and catecholamines, and decreased oxygen consumption In starvation states, the body tries to preserve itself by using less energy for basic metabolic functions; thus, overall metabolic rate decreases Metabolism shifts to use fat as a primary energy source, and the corresponding ketones help provide fuel for the brain and spare glucose and protein utilization However, body tissues still must be broken down to supply amino acids for other critical functions, eventually leading to a loss of lean body mass, vital organ wasting, and possibly death Unlike the stress response, muscle catabolism from starvation is reversed by supply of macronutrients Table 99.2 summarizes the basic differences between starvation and metabolic stress Carbohydrate turnover is simultaneously increased during the metabolic stress response, with a significant increase in glucose oxidation and gluconeogenesis The administration of exogenous glucose does not blunt the elevated rates of gluconeogenesis, Metabolic Consequences of Critical Illness The energy burden imposed by the metabolic response to injury, surgery, or inflammation cannot always be accurately estimated, as it varies in intensity and duration between individuals Importantly, nutritional support itself cannot reverse or prevent the metabolic stress response but may help offset the catabolic losses, particularly protein losses, during this state Failure to provide optimal calories and protein during the acute stage of illness may exaggerate existing nutritional deficiencies and further exacerbate underlying nutritional status Respiratory compromise involving loss of respiratory muscle mass, cardiac dysfunction and arrhythmias involving loss of myocardial muscle tissue, and intestinal dysfunction involving loss of the gut barrier contribute to the morbidity and mortality of critical illness On the other hand, overestimation of this energy cost of metabolic stress may result in provision of energy in excess of requirement and is associated with poor outcomes Hence, large energy imbalances attributable to underfeeding and overfeeding in critically ill children must be avoided.3 This can be prevented by individualized nutritional regimens that are tailored for each patient and reviewed regularly during the course of illness In a trial of a 12-week individualized nutritional intervention in home-ventilated children, significant improvements were observed in respiratory and body composition variables.21 A basic understanding of the metabolic events that accompany critical illness and surgery is essential for planning appropriate nutritional support in critically ill children The unique hormonal and cytokine profile manifested during critical illness is characterized by an elevation in serum levels of insulin, glucagon, cortisol, catecholamines, and proinflammatory cytokines.22 Increased serum counterregulatory hormone concentrations induce insulin and growth hormone resistance, resulting in the catabolism of endogenous stores of protein, carbohydrate, and fat Fig 99.1 illustrates the basic pathways involved in the metabolic stress response In general, the net increase in muscle protein degradation, characteristic of the metabolic stress response, results in a high concentration of free amino acids in the circulation Free amino acids are used as the building blocks for Lipolysis ↑ fatty acids Ketones fuel for brain Loss of lean body mass Trauma Sepsis Critical illness Muscle breakdown Tissue repair wound healing Acute inflammatory proteins Protein synthesis Amino acids Gluconeogenesis Burn Surgery Glycolysis ↓ utilization 1179 ↑↑ Glucose Hyperglycemia Urea Fuel for brain, RBC, and kidneys • Fig 99.1 Metabolic response to stress RBCs, Red blood cells (From Mehta N, Jaksic T The critically ill child In: Duggan C, Watkins JB, Walker WA, eds Nutrition in Pediatrics 4th ed Hamilton, Ontario, Canada: BC Decker; 2008:663–673.) ... with nutrient provision, many perceived barriers to bedside nutrient delivery may be avoidable This chapter will review some of the evidence-based and consensus statements around procedures for... of a critically ill child in the PICU and the approach to optimal and safe nutrient delivery in this group Malnutrition in the Pediatric Critically Ill Patient Critical illness increases metabolic... risk of deteriorating nutritional status and anthropometric changes with increased morbidity.1 This effect is more pronounced in a subgroup of patients who are already malnourished or at risk