hypermetabolism

Hypermetabolism is a state of sustained elevation in metabolic rate beyond the body's normal baseline, often measured as increased resting energy expenditure. It is commonly associated with catabolic activity, loss of lean body mass, and altered nutrient utilization. Hypermetabolic responses can occur in a variety of clinical contexts and may persist for weeks to months after the inciting event.

Causes include major trauma, extensive burns, major surgery, severe infection or sepsis, cancer cachexia, hyperthyroidism, and other endocrine or inflammatory disorders. Prolonged immobilization and certain medications can contribute. In critical illness, the response is part of a systemic inflammatory and neuroendocrine reaction.

Pathophysiology involves activation of the sympathetic nervous system and elevated levels of cytokines, glucocorticoids, and thyroid hormones, which raise energy expenditure and drive proteolysis and lipolysis. Mitochondrial uncoupling and insulin resistance further alter substrate use, with increased glucose production and muscle protein breakdown to supply energy and substrates for healing and immune function.

Clinically, patients may show tachycardia, weight loss, muscle wasting, fever, and hyperglycemia. Resting energy expenditure can be markedly higher than predicted by standard equations. Indirect calorimetry is the preferred method to quantify REE, though clinical assessment and markers of catabolism are commonly used.

Management focuses on treating the underlying cause and providing adequate nutritional support, typically with early enteral feeding and higher protein intake to preserve lean mass. Pharmacologic interventions such as anabolic agents or anti-catabolic strategies may be used in specific settings. The prognosis depends on the underlying illness and the ability to control catabolic processes; prolonged hypermetabolism is associated with worse outcomes if not managed.