Caloric need – approximately 20–25 calories/kg/day
Calories:
Fat | 9 calories/g |
Protein | 4 calories/g |
Oral carbohydrates | 4 calories/g |
Dextrose | 3.4 calories/g |
Nutritional requirements for average healthy adult male
• 20% protein calories (1 g protein/kg/day; 20% should be essential amino acids)
• 30% fat calories – important for essential fatty acids
• 50% carbohydrate calories
Trauma, surgery, or sepsis stress can increase kcal requirement 20%–40%
Pregnancy increases kcal requirement 300 kcal/day
Lactation increases kcal requirement 500 kcal/day
Protein requirement also increases with above
Burns
• Calories: 25 kcal/kg/day + (30 kcal/day × % burn)
• Protein: 1–1.5 g/kg/day + (3 g × % burn)
Much of energy expenditure is used for heat production
Fever increases basal metabolic rate (10% for each degree above 38.0°C)
If overweight and trying to calculate caloric need, use equation: weight = [(actual weight − ideal body weight) × 0.25] + IBW
Harris–Benedict equation calculates basal energy expenditure based on weight, height, age, and gender
Central line TPN – glucose based; maximum glucose administration – 3 g/kg/h
Peripheral line parenteral nutrition (PPN) – fat based
Short-chain fatty acids (eg butyric acid) – fuel for colonocytes
Glutamine – fuel for small bowel enterocytes
• Most common amino acid in bloodstream and tissue
• Releases NH4 in kidney, thus helping with nitrogen excretion
• Can be used for gluconeogenesis
Primary fuel for most neoplastic cells – glutamine
PREOPERATIVE NUTRITIONAL ASSESSMENT
Approximate half-lives
• Albumin – 18 days
• Transferrin – 10 days
• Prealbumin – 2 days
Normal protein level: 6.0–8.5
Normal albumin level: 3.5–5.5
Acute indicators of nutritional status – retinal binding protein, prealbumin, transferrin
Ideal body weight (IBW)
• Men = 106 lb + 6 lb for each inch over 5 ft
• Women = 100 lb + 5 lb for each inch over 5 ft
Preoperative signs of poor nutritional status
• Acute weight loss > 10% in 6 months
• Weight < 85% of IBW
• Albumin < 3.0
Low albumin (< 3.0) – strong risk factor for morbidity and mortality after surgery
RESPIRATORY QUOTIENT (RQ)
Ratio of CO2 produced to O2 consumed – is a measurement of energy expenditure
RQ > 1 = lipogenesis (overfeeding)
• Tx: ↓ carbohydrates and caloric intake
• High carbohydrate intake can lead to CO2 buildup and ventilator problems
RQ < 0.7 = ketosis and fat oxidation (starving)
• Tx: ↑ carbohydrates and caloric intake
Pure fat utilization – RQ = 0.7
Pure protein utilization – RQ = 0.8
Pure carbohydrate utilization – RQ = 1.0
POSTOPERATIVE PHASES
Diuresis phase – postoperative days 2–5
Catabolic phase – postoperative days 0–3 (negative nitrogen balance)
Anabolic phase – postoperative days 3–6 (positive nitrogen balance)
STARVATION OR MAJOR STRESS (SURGERY, TRAUMA, SYSTEMIC ILLNESS)
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