NMS. Surgery

20

Part I ♦ Foundations 5. As the illness begins to subside, the hormonal milieu changes, which leads to less retention of salt and water and a change from a catabolic protein environment to an anabolic environment . The nitrogen balance is positive, i.e., less nitrogen is lost than is administered to the patient. Nutrition Status Evaluation I. Thin, cachectic patient: Physical exam findings include hollowed cheeks, no body fat, and very little muscle; patients who have acutely lost 10% of their body weight are considered malnourished. II. Obese patient and well-developed patients: May need as much nutritional support as the patient in a poor nutritional state, depending on the underlying disease process. III. Previously well-nourished patient: Generally able to endure a major operation and 5–10 days of starvation without an increase in morbidity or mortality. IV. Patients with severe illness: Consider early nutritional support. Therapy I. Goals: The average hospitalized patient requires ~2,000 cal daily and ~60 g of protein. A. Energy: Determine caloric requirements to provide adequate energy substrates (i.e., carbohydrates, fats) and avoid excess calories in one of four ways. 1. Indirect calorimetry: Measures amount of oxygen inhaled minus amount of oxygen exhaled to determine amount of oxygen consumed, because oxygen consumption (VO 2 ) measured in mL O 2 /min is directly correlated to kcal/day (1 mL O 2 /min = ~7 kcal/day). 2. Fick equation: Amount of oxygen consumed, is determined by multiplying the cardiac output by the arteriovenous oxygen content difference. 3. Harris–Benedict equations: Daily caloric requirements are determined by calculating REE from gender-based equations using gender, height, weight, and age variable and then multiplying by an estimated stress factor. 4. Estimated REE (25 kcal/kg/day): Multiplied by an estimated stress factor. B. Protein: Determine protein requirements in one of four ways: 1. Nitrogen balance: The majority of catabolized protein is lost as urinary urea nitrogen, with ~2–4 g of nitrogen lost in stool. Protein grams divided by 6.25 equals nitrogen grams. Amount of nitrogen intake minus nitrogen output should be positive if adequate protein is given. 2. Visceral protein measurement (e.g., albumin, transferrin, prealbumin) a. Due to the long half-life of albumin (21 days), it should only be used to assess malnutrition in outpatient and elective surgery patients.