Protein status and metabolic expenditure determine the response to intravenous nutrition--a new classification of surgical malnutrition.

To determine whether nutritional and metabolic factors affect the response to intravenous nutrition (IVN) 146 surgical patients were classified according to their protein and metabolic status using direct measurements of body protein and metabolic expenditure. The patients were grouped into four categories: category I, moderate to severe protein depletion without raised metabolic expenditure; category II, moderate to severe protein depletion with raised metabolic expenditure; category III, mild protein depletion without raised metabolic expenditure; and category IV, mild protein depletion with raised metabolic expenditure. After 2 weeks of IVN patients in category I gained a mean(s.e.m.) of 0.43(0.06) kg of body protein (P less than 0.001) and had significant rises in both plasma transferrin and prealbumin (P less than 0.05); patients in category II gained 0.30(0.11) kg of protein (P less than 0.005) and also had significant rises in transferrin and prealbumin (P less than 0.05). Patients in category III lost 0.24(0.11) kg protein (P less than 0.05) and had no changes in either transferrin or prealbumin and patients in category IV lost 0.51(0.13) kg of body protein (P less than 0.001) and although there was a significant rise in plasma prealbumin there was no significant change in plasma transferrin. When postoperative patients were examined separately, they did not differ significantly from preoperative patients except in category I, where their protein gain was only 0.19(0.10) kg, an amount not significantly different from that gained by patients in category II. In each of the four categories described, the changes in total body protein occurring with 2 weeks of IVN were determined by the relative effects of two competing processes; protein depletion and raised metabolic expenditure. With moderate to severe protein depletion (approximately 30 per cent depletion of body protein stores) there was a marked tendency to gain protein with IVN. When the patient had a raised metabolic expenditure or was postoperative this tendency of depleted patients to gain protein was still present but it was less. With only mild protein depletion (approximately 10 per cent depletion) increases in metabolic expenditure made it difficult, if not impossible, to prevent continuing protein loss in spite of aggressive nutritional support. The patient categories we have described determine the response to IVN and form the basis of a new clinical classification of surgical malnutrition.