Nutritional requirements of surgical and critically-ill patients: do we really know what they need?

Malnutrition remains a problem in surgical and critically-ill patients. In surgical patients the incidence of malnutrition ranges from 9 to 44%. Despite this variability there is a consensus that malnutrition worsens during hospital stay. In the intensive care unit (ICU), 43% of the patients are malnourished. Although poor nutrition during hospitalisation may be attributable to many factors, not least inadequacies in hospital catering services, there must also be the question of whether those patients who receive nutritional support are being fed appropriately. Indirect calorimetry is the 'gold standard' for determining an individual's energy requirements, but limited time and financial resources preclude the use of this method in everyday clinical practice. Studies in surgical and ICU patient populations have been reviewed to determine the 'optimal' energy and protein requirements of these patients. There are only a small number of studies that have attempted to measure energy requirements in the various surgical patient groups. Uncomplicated surgery has been associated with energy requirements of 1.0-1.15 x BMR whilst complicated surgery requires 1.25-1.4 x BMR in order to meet the patient's needs. Identifying the optimal requirements of ICU patients is far more difficult because of the heterogeneous nature of this population. In general, 5.6 kJ (25 kcal)/kg per d is an acceptable and achievable target intake, but patients with sepsis or trauma may require almost twice as much energy during the acute phase of their illness. The implications of failing to meet and exceeding the requirements of critically-ill patients are also reviewed.