Chapter 072. Malnutrition and Nutritional Assessment (Part 3)

Physiologic Characteristics of Hypometabolic and Hypermetabolic States The metabolic characteristics and nutritional needs of hypermetabolic patients who are stressed from injury, infection, or chronic inflammatory illness differ from those of hypometabolic patients who are unstressed but chronically starved. In both cases, nutritional support is important, but misjudgments in selecting the appropriate approach may have disastrous consequences.The hypometabolic patient is typified by the relatively unstressed but mildly catabolic and chronically starved individual who, with time, will develop marasmus. The hypermetabolic patient stressed from injury or infection iscatabolic (experiencing rapid breakdown of body mass) and is at high risk for developing...
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Chapter 072. Malnutrition and Nutritional Assessment (Part 3) Chapter 072. Malnutrition and Nutritional Assessment (Part 3) Physiologic Characteristics of Hypometabolic and HypermetabolicStates The metabolic characteristics and nutritional needs of hypermetabolicpatients who are stressed from injury, infection, or chronic inflammatory illnessdiffer from those of hypometabolic patients who are unstressed but chronicallystarved. In both cases, nutritional support is important, but misjudgments inselecting the appropriate approach may have disastrous consequences. The hypometabolic patient is typified by the relatively unstressed butmildly catabolic and chronically starved individual who, with time, will developmarasmus. The hypermetabolic patient stressed from injury or infection iscatabolic (experiencing rapid breakdown of body mass) and is at high risk fordeveloping kwashiorkor, if nutritional needs are not met and/or the illness does notresolve quickly. As summarized in Table 72-2, the two states are distinguished bydiffering perturbations of metabolic rate, rates of protein breakdown (proteolysis),and rates of gluconeogenesis. These differences are mediated by proinflammatorycytokines and counterregulatory hormones—tumor necrosis factor, interleukins 1and 6, C-reactive protein, catecholamines (epinephrine and norepinephrine),glucagon, and cortisol—that are relatively reduced in hypometabolic patients andincreased in hypermetabolic patients. Although insulin levels are also elevated instressed patients, insulin resistance in the target tissues prevents insulin-mediatedanabolic actions. Table 72-2 Physiologic Characteristics of Hypometabolic andHypermetabolic States Physiologic Hypometabolic, Hypermetabolic,Characteristics Nonstressed Patient Stressed Patient (Cachectic, Marasmic) (Kwashiorkor Riska) Cytokines, Physiologic Hypometabolic, Hypermetabolic,Characteristics Nonstressed Patient Stressed Patient (Cachectic, Marasmic) (Kwashiorkor Riska)catecholamines,glucagon, cortisol,insulin Metabolic rate,O2 consumption Proteolysis,gluconeogenesis Ureagenesis,urea excretion Physiologic Hypometabolic, Hypermetabolic,Characteristics Nonstressed Patient Stressed Patient (Cachectic, Marasmic) (Kwashiorkor Riska) Fat catabolism,fatty acid utilization Adaptation to Normal Abnormalstarvation a These changes characterize the stressed, kwashiorkor-risk patient seen indeveloped countries; they differ in some respects from the characteristics ofprimary kwashiorkor seen in developing countries. Metabolic Rate In starvation and semistarvation, the resting metabolic rate falls between10% and 30% as an adaptive response to energy restriction, slowing the rate ofweight loss. By contrast, resting metabolic rate rises in the presence of physiologicstress in proportion to the degree of the insult. It may increase by about 10% afterelective surgery, 20–30% after bone fractures, 30–60% with severe infections suchas peritonitis or gram-negative septicemia, and as much as 110% after majorburns. If the metabolic rate (energy requirement) is not matched by energy intake,weight loss results—slowly in hypometabolism and quickly in hypermetabolism.Losses of up to 10% of body weight are unlikely to be detrimental; however,losses greater than this in acutely ill hypermetabolic patients may be associatedwith rapid deterioration in body function.