NMS. Surgery

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Chapter 1 ♦ Principles of Surgical Physiology

II. Glucose: Can be stored as glycogen and used as a short-term reservoir of energy. III. Fat: Majority of energy is stored as fat and to a lesser degree as protein (skeletal muscle). Caloric and Protein Requirements I. Caloric requirements A. Basal metabolic rate (BMR): Amount of energy used by an unstressed, fasting individual at rest. B. Resting energy expenditure (REE): Amount of energy used by an unstressed, non-fasting individual at rest. REE is approximately 25 kcal/kg/day. C. Total energy expenditure (TEE): Actual amount of energy an individual uses. 1. TEE can increase significantly above REE by hypermetabolic conditions (e.g., surgery, trauma, sepsis, and burns). 2. TEE can increase by voluntary work (e.g., exercise), whereas during starvation, the BMR decreases as the body adjusts to conserve body mass. Caloric requirements can be determined by indirect calorimetry or the Fick equation . II. Protein Requirements A. Normal 1. Generally, daily protein requirements are low because each protein molecule has a specific purpose and is therefore not available as an energy source. 2. Protein requirements are 0.8–1.0 g/kg/day. B. Starvation 1. The body makes every attempt to conserve protein. Because glycogen 2. In unstressed starvation, protein catabolism can be prevented by administration of glucose. The brain adapts to use ketones , which are produced when fat is metabolized. After all fat is metabolized, protein is degraded until the total body protein stores are ~1/2 of baseline, at which time death occurs. C. Severe illness 1. The body is not able to conserve energy and protein stores. 2. The hormonal milieu increases the BMR, decreases the ability to use fats and ketones, and thereby increases the dependence on glucose as an energy source. 3. As the degree of illness or injury increases, the catabolic rate increases, leading to a breakdown of protein stores and multi-organ dysfunction. 4. Primary treatment: Eliminate the underlying cause of the stress response and provide enough calories and protein to replace metabolic and catabolic losses. stores are metabolized within the first 24 hours of starvation, proteins are broken down and converted to glucose in the liver by gluconeogenesis .