Nutrition and the metabolic response to injury

Cuthbertson described the metabolic response to injury as consisting of an "ebb" phase and a "flow" phase.2526 The "ebb" phase is the period of traumatic shock or hypometabolism during the first few hours or days after injury. This phase is soon replaced by the "flow" phase that is a period of hypermetabolism that may last for weeks or months depending on the nature of the injury and obstacles to recovery. In the case of minor injury, such as elective surgery, both of these phases may be relatively brief and of minor magnitude. In the case of multiple trauma or large percent body surface area burns, both ebb and flow may be of maximum magnitude and duration. In this latter group of patients, nutritional support becomes critical, because the potential to deplete the body's nutrient reserves is high. On the contrary, in a patient of good preoperative nutritional status undergoing routine elective surgery, it is unlikely that perioperative nutritional support will have a measurable effect on outcome of the healing wound.26-28

The wound is an effective parasite on the substrate available in the rest of the body. Much like the human fetus, the wound demands high priority of circulating nutrients. In a teleological sense, this would be expected, because healing of the wound is crucial to the survival of the organism. During periods of metabolic stress, the body is able to effectively catabolize the carcass (muscle, skin, bone) to support visceral protein synthesis of acute phase proteins, immunoglobulins, inflammatory cells, and collagen, needed to fight infection and heal the wound.25 26 29-31 In the case of proteins, intricate shuttling mechanisms have developed to allow redistribution of the substrate from the periphery to the viscera (Figure 1.3 and Figure 1.4). Although this has been well studied in the case of protein, it is likely that similar mechanisms apply to other nutrients.2629 32 As seen in Figure 1.4, glucose and protein metabolism are intricately linked in the glucose-alanine cycle so that energy needs and amino acid needs are met simultaneously. This could also apply to micronutri-ents. Because a large percentage of body zinc stores are found in the skin, it would not be surprising that if the skin proteins are catabolized, this might also allow mobilization of skin zinc to provide cofactors for enzymatic activity in other parts of the body.

Clearly, though, in patients with chronic malnutrition the situation is entirely different. These individuals may have inadequate reserves with which to respond appropriately to the metabolic demands of even a minor trauma. This is similar to the described conversion of individuals with marasmus (protein-calorie malnutrition) to kwashiorkor (a more severe form of protein-calorie malnutrition characterized by protein deficiency greater than the caloric deficiency) with the onset of infection.33 These marginally compensated individuals lack the reserve to respond to infection and may ultimately succumb to the infection that might otherwise not be life threatening. Deficiency of even a single micronutrient such as vitamin C may lead to disastrous results in the healing process. This is discussed in Chapter 8 in greater detail.

Nutrients may be arbitrarily divided into "macronutrients" and "micronutrients." However, the difference between these categories is not well defined. Macronutrients

Ebb Phase Medical Definition

FIGURE 1.3 The metabolic process of injury results in a peripheral to visceral redistribution of nutrients. The carcass is effectively catabolized to contribute to a systemic amino acid pool to support wound healing and the manufacture of acute phase reactants. (From Molnar, J.A., Wolfe, R.R., and Burke, J.F., in Nutritional Support of Medical Practice, 2nd ed., Harper & Row, Philadelphia, 1983, adapted from Benotti et al., Crit. Care Med., 7, 520, 1979. With permission.)

FIGURE 1.3 The metabolic process of injury results in a peripheral to visceral redistribution of nutrients. The carcass is effectively catabolized to contribute to a systemic amino acid pool to support wound healing and the manufacture of acute phase reactants. (From Molnar, J.A., Wolfe, R.R., and Burke, J.F., in Nutritional Support of Medical Practice, 2nd ed., Harper & Row, Philadelphia, 1983, adapted from Benotti et al., Crit. Care Med., 7, 520, 1979. With permission.)

FIGURE 1.4 The glucose-alanine cycle effectively supports the metabolic needs of the healing wound by shuttling amino acids from the carcass to the liver to support gluconeo-genesis. This mechanism is an example of the complex interrelationships between nutrients. (From Molnar, J.A., Wolfe, R.R., and Burke, J.F., in Nutritional Support of Medical Practice, 2nd ed., Harper & Row, Philadelphia, 1983. With permission.)

FIGURE 1.4 The glucose-alanine cycle effectively supports the metabolic needs of the healing wound by shuttling amino acids from the carcass to the liver to support gluconeo-genesis. This mechanism is an example of the complex interrelationships between nutrients. (From Molnar, J.A., Wolfe, R.R., and Burke, J.F., in Nutritional Support of Medical Practice, 2nd ed., Harper & Row, Philadelphia, 1983. With permission.)

include carbohydrates, protein, and fat. Micronutrients include all the vitamins and trace elements and have also been described as those nutrients consumed in quantities less than some arbitrary level per day.34 As will be discussed below, when some micronutrients are consumed in what might be considered pharmacologic quantities, these quantitative distinctions become blurred. For the purposes of this text, micronutrients will be defined as all nutrients other than carbohydrates, fats, and proteins.

Your Metabolism - What You Need To Know

Your Metabolism - What You Need To Know

If you have heard about metabolism, chances are it is in relation to weight loss. Metabolism is bigger than weight loss, though, as you will learn later on. It is about a healthier, better you. If you want to fire up your metabolism and do not have any idea how to do it, you have come to the right place. If you have tried to speed up your metabolism before but do not see visible results, you have also come to the right place.

Get My Free Ebook


Post a comment