Methods

A team approach to nutrition has been recommended. A dietitian helps to provide a high-quality service sensitive to the needs of individual critically ill patients. The roles of team members must be clearly defined.

Nutritional requirements can be estimated from indirect calorimetry and nitrogen balance studies, approximated from formulas (e.g. the Harris-Benedict equation), or based on simple calculations (e.g. protein, 1.5-2.0 g/kg/day; non-protein energy, 25-35 kcal/kg/ day (105-145 kJ/kg/day)). There is no evidence that more sophisticated methods for estimating needs lead to better patient outcomes. Most commercially available enteral feeds provide 100 to 180 kcal/g (420-765 kJ/g) of protein nitrogen, although feeds providing as little as 90 kcal/g (380 kJ/g) of nitrogen are promoted for critically ill patients (e.g. after major trauma). Excessive energy, particularly as carbohydrate, increases fat synthesis and carbon dioxide production. The increased carbon dioxide production may delay weaning from ventilation of patients with limited ventilatory reserve. Neither hypercaloric nor isocaloric nutritional support prevent protein catabolism in medical patients with multiple organ failure, but supplying this much energy increases energy expenditure, urea production, and glucose and lactate concentrations. Hypocaloric nutrition in terms of usual energy estimates may be better in patients with early multiple organ failure. Enteral nutrition can also be constrained by restrictions on fluid intake, glucose intolerance, renal impairment, large gastric aspirates, and fasting for procedures. Intensive care patients commonly receive only about 75 per cent of estimated needs.

Enteral nutrition is frequently increased in steps to the estimated daily need by increasing feed volume and concentration, but this process is usually unnecessary unless enteral feeding starts after prolonged starvation.

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