Nutritional Support and Decision Making for the Post-Operative Trauma Patient

Introduction:
In people, nutritional status is an important determinant of outcome following surgery and there is a clear association between malnutrition and poor clinical outcome. While the evidence is convincing in people, the relationship between nutritional status and outcome in animals remains largely unknown. As malnutrition imparts similar metabolic effects in animals it is assumed that nutritional support is equally essential for the recovery of critically ill dogs and cats. If we accept that nutritional support can be beneficial to clinical outcome, then the aspects that we must carefully consider are how soon to feed patients and how aggressive should the nutritional intervention be.

Metabolic Changes Related to Illness and Disease:
Animals requiring surgical interventions may be afflicted with serious conditions. The metabolic responses to illness or severe injury are complex and place these animals at high risk for malnutrition and its deleterious effects. These effects, which are likely to negatively impact overall survival, include alterations in energy and substrate metabolism, compromised immune function, and impaired wound healing. These effects are of particular interest in surgical patients where proper wound healing is of paramount importance.

While generalizations tend to oversimplify complex systems, the concept of “ebb/flow” offers a basic description of the metabolic response to critical illness or severe injury. According to this model, there is an initial hypometabolic response (“ebb phase”), followed by a period of a more prolonged course of hypermetabolism (“flow phase”). The ebb phase is usually a period of hemodynamic instability associated with decrease energy expenditure, hypothermia, mild protein catabolism, decreased cardiac output, and poor tissue perfusion. Without intervention, this may progress to a state of refractory or irreversible shock characterized by severe lactic acidosis, decreased tissue perfusion, multiple organ failure, and death. Nutritional intervention at this stage carries a greater risk of complications such as electrolyte abnormalities, which may result in further detrimental effects to some critically ill animals. Following successful resuscitation, patients enter the flow phase during which profound metabolic alterations occur. Increases in energy expenditure, glucose production, insulin and glucagon concentrations, cardiac output, and profound protein catabolism are the hallmarks of this response. Provision of nutritional support during this stage of illness can attenuate and sometimes reverse the detrimental effects of malnutrition and this forms the basis for perioperative nutritional support. There is some controversy of the applicability of these models of metabolic responses with clinical patients and the ideal timing for initiation of nutritional support in animals has not been determined.  [...]