Water: Typical requirements are - 2-3 L/day. Increased requirements occur in patients with large-ouput fistulae, nasogastric aspirates and diarrhoea. Reduced requirements occur in patients with oedema, hepatic failure, renal failure (oliguric and not dialysed) and brain oedema.
Energy: Typical requirements are - 7.5-10.0 MJ/day (1800-2400 kcal/day). Disease increases resting energy expenditure but decreases physical activity. Extra energy is given for repletion and reduced energy for obesity.
Protein: Typically 10-15 g N/day (62-95 g protein/day) or 0.15-0.25 g N/kg/day (0.94-1.56 g protein/kg/day). Extra protein may be needed in severely catabolic conditions, such as extensive burns.
Major minerals: Typical requirements for sodium and potassium are 70-100 mmol/day. Increased requirements occur in patients with gastrointestinal effluents. The excretion of these minerals in various effluents can provide an indication of the additional requirements. Low requirements may be necessary in those with fluid overload (or patients with hypernatraemia and hyperkalaemia. The requirements of calcium and magnesium are higher for enteral than for parenteral nutrition because only a proportion of these minerals is absorbed by the gut.
Trace elements: For trace elements such as iodide, fluoride, and selenium that are well absorbed, the requirements for enteral and parenteral nutrition are similar. For other trace elements, such as iron, zinc, manganese and chromium, the requirements for parenteral nutrition are substantially lower than for enteral nutrition.
Vitamins: Many vitamins are given in greater quantities in patients receiving parenteral nutrition than in those receiving enteral nutrition. This is because patients on parenteral nutrition may have increased requirements, partly because of severe disease, partly because they may already have depleted pools of vitamins, and partly because some vitamins degrade during storage. Vitamin K is usually absent from parenteral nutrition regimens and therefore it may need to be administered separately.