The critically ill patient in intensive care may present with serious
metabolic alterations caused directly by the illness or secondarily by
complications (e.g. infections, organ failure or sepsis) developing
within a few hours of hospitaliza- tion or in the following days. Among
the situations which maintain and further trigger rapidly evolving
altered metabolism are complex hormonal reactions, particularly those of
the hypothalamus-hypophysis-adrenal axis, and abnormal stimulation of
the autonomic nervous system. In fact, the sympathetic nervous system is
known to cause significant metabolic alterations. For example, a surgery
patient afflicted by septic complications may become hypercatabolic and
experience significant nitrogen loss; the altered protein metabolism may
in turn heavily influence carbohydrate and lipid metabolism as well.
Thus, it is apparent that for optimal care of patients with altered
metabolic functions, further knowledge is necessary regarding the
physiopathology of metabolism and the physiopathological mechanisms,
which alter the consump- tion of principal energy substrates. Many
experimental and clinical studies have investigated the metabolic
aspects of individual organs or organ systems. However, for a correct
evaluation of such metabolic events, in addition to studying the roles
of metabolic enzymes, active metabolites, and the glutathione system, it
is interesting to consider the use of indirect calorimetry as a valid
and important investigative technique. The critically ill patient with
major alterations in nutritional status may require artificial nutritive
support administered through either parenteral or enteral routes.
