Chapter 072. Malnutrition and Nutritional Assessment (Part 3)

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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 is catabolic (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) 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 is
catabolic (experiencing rapid breakdown of body mass) and is at high risk for developing kwashiorkor, if nutritional needs are not met and/or the illness does not resolve quickly. As summarized in Table 72-2, the two states are distinguished by differing perturbations of metabolic rate, rates of protein breakdown (proteolysis), and rates of gluconeogenesis. These differences are mediated by proinflammatory cytokines and counterregulatory hormones—tumor necrosis factor, interleukins 1 and 6, C-reactive protein, catecholamines (epinephrine and norepinephrine), glucagon, and cortisol—that are relatively reduced in hypometabolic patients and increased in hypermetabolic patients. Although insulin levels are also elevated in stressed patients, insulin resistance in the target tissues prevents insulin-mediated anabolic actions. Table 72-2 Physiologic Characteristics of Hypometabolic and Hypermetabolic 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 Abnormal starvation a These changes characterize the stressed, kwashiorkor-risk patient seen in developed countries; they differ in some respects from the characteristics of primary kwashiorkor seen in developing countries. Metabolic Rate In starvation and semistarvation, the resting metabolic rate falls between 10% and 30% as an adaptive response to energy restriction, slowing the rate of weight loss. By contrast, resting metabolic rate rises in the presence of physiologic stress in proportion to the degree of the insult. It may increase by about 10% after elective surgery, 20–30% after bone fractures, 30–60% with severe infections such
as peritonitis or gram-negative septicemia, and as much as 110% after major burns. 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 associated with rapid deterioration in body function.