A clinical review of nutritional support of the patient

Abstract

Many pathophysiological processes can be expected to respond more favorably to therapy when the patient is well nourished than when he is poorly nourished. Therefore, all members of every health care team, regardless of specialty or area of expertise, should have a working knowledge of how to identify and manage nutritional problems. This is especially important for seriously ill patients for whom provision of adequate enteral or parenteral nutrients may minimize morbidity and maximize survival and quality of life. Until such time as optimal digestion, absorption, and assimilation can be maintained via the alimentary tracts of all patients, knowledge of parenteral and enteral nutrition will be essential for physicians and other members of the health care team. Just as the master practitioners of the past had to gain expertise in anatomy, pathology, physiology, and pharmacology, health care professionals of the present must be proficient in their knowledge of biochemistry. From a practical point of view, parenteral and enteral nutrition represents the clinical application of biochemistry, in that such feeding methods may be the only means by which the substrates that fuel and support all cellular processes may be provided to the patient. The concepts of medicine today must be updated and revised continually. Only a few decades ago the term “shock” implied to many that a patient was anxious and apprehensive, lying prostrate, feeling cool and clammy, appearing pale, and perspiring profusely. Others described shock as a state in which the systolic blood pressure was below 90 mm Hg, the patient’s pulse rate was more than 120 beats per minute, the pulse was faint and thready, and the respiratory rate was rapid, with shallow inspiration. However, these descriptive terms did not explain shock. We know now that the underlying lesion in shock is impairment in perfusion of the body’s tissues, thereby interfering with the exchange of oxygen, carbon dioxide, and metabolites at the cellular level. Understanding of this complex syndrome will undoubtedly improve as investigative efforts continue further into the biochemical basis of shock. In an analogous fashion, our concepts regarding nutrition are changing and must continue to change. Food is defined as anything ingested which has nutrient value. Diet is that food and drink which is consumed or provided on a regular basis. However, nutrition is the sum of the processes by which an organism assimilates and utilizes food substances. Except for the digestion of foods within the bowel, all of the nutrition-related biochemical reactions essential to life take place at the cellular level. Nutrition is basically the provision of biochemical substances in the quantities and ratios which are required for normal intracellular functions. Consequently, whatever is given as nutrient parenterally must be in a form which is suitable for use in the metabolic pathways of the body. Moreover, due consideration must be given to the changes in requirements for nutrients due to pathophysiological conditions that we are called upon to treat or manage. Since the discovery of the circulation, we have been increasingly able to provide nutrition by parenteral means. In fact, today it is possible to provide a truly complete diet by vein. However, as sophisticated as our current parenteral and enteral nutritional regimens may appear to be, they represent only a small step toward our ultimate goal of complete knowledge of the metabolic derangements