Biochemistry, Nutrition and the Metabolic Response to Injury
The metabolic response
Cuthbertson described an early ebb phase (hypovolaemia, reduced metabolic rate, lasting hours) followed by a flow phase driven by catecholamines, cortisol, glucagon, growth hormone, antidiuretic hormone and aldosterone, with cytokines interleukin-1, interleukin-6 and TNF. The result is hyperglycaemia and insulin resistance, sodium and water retention, potassium and phosphate loss, negative nitrogen balance (up to 15–20 g daily after major burns) and a raised resting energy expenditure. The flow phase is catabolic, then anabolic during recovery.
Nutritional assessment and support
Body water is about 60% of weight; two-thirds is intracellular and one-third extracellular, with plasma only about 5% of body weight. Albumin and prealbumin fall with inflammation and are negative acute-phase reactants, not nutritional markers. Use weight trend, BMI, handgrip strength and intake history. Energy needs are approximately 25–30 kcal/kg/day with protein 1.2–1.5 g/kg/day, higher in burns. Enteral feeding is preferred whenever the gut works; it maintains mucosal integrity and reduces septic complications.
Refeeding syndrome
Reintroducing carbohydrate drives insulin release, pushing phosphate, potassium and magnesium intracellularly. Hypophosphataemia is the hallmark and can cause arrhythmia, weakness and heart failure. Start at low caloric rates, monitor electrolytes daily and give thiamine before feeding in the malnourished.
Worked example: a 70 kg man three days after laparotomy needs roughly 25–30 kcal/kg, i.e. 1750–2100 kcal/day, and 1.2 g/kg protein, about 84 g/day. Tight glycaemic control below 6 mmol/L is harmful; target approximately 7.8–10 mmol/L.