MEASUREMENTS OF ENERGY REQUIREMENTS FOR PARENTERAL NUTRITION

Kinney^[127] pointed out that surgical weight loss can be rapid and can result in massive depletion of up to 20% of normal body weight within 3 weeks of multiple injuries, despite the resumption of some oral intake within the first week. Surgeons have tried to explain this large tissue loss and increased nitrogen excretion on the following basis: a major injury produces a very large increase in the rate of resting energy expenditure (REE) that exceeds the energy availability from fat mobilization; muscle protein is progressively broken down, the resulting amino acids deaminated, and the carbon chains oxidized for energy. The preceding sections outlined the theoretical basis of catabolic response to sepsis as attempts to compensate for decreased peripheral oxidation of glucose and the need for increased hepatic protein synthesis. Partial starvation in the perioperative period aggravates the catabolic loss of lean body mass. It is imperative to consider a nutritional prescription to the septic or stressed patient.

Nutritional Assessment

Four factors have been used to assess the need for nutritional support^[128] : history of unexplained weight loss of 10% of body weight; serum albumin concentration of less than 0.34 g/dL; anergy to a battery of four or five standard skin-test antigens; and abnormally low total lymphocyte count. A patient who manifests all four indexes is severely malnourished. Serum transferrin and prealbumin are better markers than albumin for rapid changes in nutritional status because they have shorter half-lives than albumin. The excretion of 3-methylhistidine (primarily from muscle actin) also has been used as a marker for muscle breakdown.^[129]