Assessment of energy expenditure.

Medical interest in assessing energy expenditure has varied considerably during this century. The increase in recent years has been largely due to the recognition, by surgeons, of the catabolic state present in many of their patients, particularly those recovering from severe injuries and those with septic complications of accidental or surgical trauma. Examples of the last group are patients with subphrenic or pelvic abscesses, peritonitis, leaking bowel anastomoses, fistulae, etc. The interest of the surgeons is generated by the need to feed these patients in order to prevent disastrous weight loss and to keep them alive while the direct treatment of the lesions takes its effect. The object of the surgeon, therefore, is to determine the patient’s energy expenditure and the fuels being used in order to prescribe the level and type of intake. Although direct calorimetry must be considered the absolute method for measuring energy expenditure even the modem form of gradient layer direct calorimeter (Benzinger & Kitzinger, 1949) is not a very practical technique for use with ill patients. The assessment in ill surgical patients must depend on indirect calorimetry. The apparatus for this is simpler to use, gives more immediate results and can be adapted to give additional information about ventilatory equivalents and respiratory patterns which is needed for the care of these patients, Furthermore, if one wishes to know the fuels being used one has to depend on indirect calorimetry. The apparatus for indirect calorimetry is designed to collect, measure and analyse the patient’s expired air. This is most simply done with a mouthpiece and nose-clip, a system of valves and the well-known Douglas Bag (Douglas & Priestley, 1937). However, the crude valves previously used together with the difficulties in handling the collected gas and its analysis by the Haldane technique were all factors in the decline of interest in indirect calorimetry for clinical purposes. The introduction of better mouthpieces and masks with light-weight valves has been a major advance. Using these the Douglas Bag technique has been shown to give the same results as other methods (Wilmore et al. 1977) and should be kept in mind when there is a need to study patients in hospital away from the home institution (Henane et al. 1981). The present tendency is to measure the volume of the expired air and the concentrations of 0, and CO, with on-line apparatus which feeds the data into some form of computer to calculate and print out the results. Examples of commercial instruments of this type are the Beckman Metabolic Measurement Cart, the Siemens-Elema apparatus and the Mijnhardt Oxycon apparatus. These instruments have usually been designed for use in sports physiology, i.e. for exercising subjects with large minute volumes, therefore they may require some adaptation for patients with low tidal volumes. In