Surgery

Fernando Soares Vannucci Braz*
Angelo Bustani Loss*
Ricardo Miguel Japiassú*

Nutrition & Surgery - Part I

Introduction

Nutritional support has been available for approximately two decades. It has proved its value as one of the most important therapeutic modalities in this century and perhaps in the history of medicine. The gut has been a major focus on nutritional support over the past decade, and this is likely to continue.

The importance of a satisfactory nutritional status in surgical patients

It is known that nutritional status is a very important factor in the recovery process from all kind of surgical interventions. The concept of nutritional status in surgery evolves all the perioperative nutrition period, including both preoperative and postoperative aspects. Many studies show that preoperative acceptable nutritional conditions help to prevent early and late postoperative complications. Klein et. al. published in 1996 a study that compared 2 groups of patients: a previously malnourished one and another in agreeable nutritional conditions. Both groups undergone in elective lumbar spinal surgery. Of 26 postoperative complications, 24 were in the malnourished group. The authors recommend that close attention be paid to the perioperative nutritional status of patients undergoing in this surgical procedure and also say that individuals with suboptimal nutritional parameters should be supplemented and replenished before elective surgery. Based in many other studies, we can say that these conclusions can be taken as true not only for spinal surgeries but for all kind of operations, always with special and particular considerations. In midline laparotomies, malnutrition is one of the well known risk factors determining wound dehiscences.

As we can see, there is a highly significant correlation between preoperative denutrition and postoperative morbidity. Di Costanzo et. al. say that this correlation also exists for postoperative mortality and it does not depend on whether the operation is performed in gastrointestinal tract or not, whether the primary disease is cancer or not. This study shows that the more important the denutrition, the more frequent the postoperative complications and deaths, with morbidity and mortality rates linearly correlated to denutrition. An important information included in this study is that obesity had the same prognostic value as denutrition. In the same way that preoperative nutritional status is important, postoperative nutrition must be considered. Successful recovering from a surgical intervention depends on many factors and postoperative nutritional support is one of these important factors. Postoperative nutrition should be initiated as soon as possible. The nutrients implemented will help in wound closure, in improving immune responses, in preventing infections or sepsis and in many other processes that play a role in the recovering period. Delaying this support may impair all this period, thus putting in risk patient's life in addition to increase hospital stay time and costs.

Protein and caloric requirements

In a 70 kg man there are about 10 to 11 kg of protein. Daily protein turnover is 250 to 300 g. After digestion, all amino acids are absorbed, save 1 g of nitrogen which is excreted in the stool. Proteolysis accounts for another 50 to 70 g of amino acids. In total, ingested amino acids contribute only 25 g to the free amino acid pool, whereas 250 g is provided by endogenous breakdown. If adequate energy is present, most of these amino acids are resynthesized. Protein turnover decreases with age, but as lean body mass increases, total body turnover remains approximately the same.

Caloric supply is important. Carbohydrate increases muscle protein synthesis under the influence of insulin; fat increases hepatic and other visceral protein synthesis. The average normal requirement of a patient is 0.8 g of protein / kg / day. Any kind of trauma, including surgical one, increases this requirement (see Figure 1).

Figure 1. The increases in resting energy expenditure that have been shown to occur during catabolic phase of trauma situations (injury and infection), when compared with the decreases that develop during partial starvation. (From Sabiston Textbook of Surgery, 15th edition)

Alternative or nonconventional fuels

Glutamine as a fuel for enterocytes has received much attention, with several recent clinical trials. Small insignificant changes in nitrogen balance result from a dipeptide glutamine ester. However, in severe stress, such as bone marrow transplant, a beneficial effect of glutamine in decreasing hospital stay, increasing nitrogen balance and decreasing infection rates has been demonstrated. These effects have been attributed to improved gut barrier function, but improved gut and hepatic protein synthesis are equally possible.

Nutritive solutions enriched with arginine, RNA and omega-3 fatty acids are also important fuels that influence positively the postoperative recovering of many plasma parameters which reflect patient's recovering from surgery. These "enriched solutions" are a better choice than standard diets in improving parameters such as prealbumin concentration, retinol binding protein concentration, delayed hypersensivity responses, phagocytic ability of monocytes and concentration of IL-2 receptors. People who receive the enriched solution has the same risk of developing postoperative infections if compared with people who receive the standard diet, but the infections in the latter group tend to be much more severe and difficult to treat.

It is also important to say that all the other nutrients must be remembered. Vitamins and minerals are necessary and must be administrated within the nutritional support plan.

Causes of inadequate nutrition or increased protein loss

Lack of food is a cause of malnutrition in urban poor populations, especially in alcoholics. However, the most common causes of in-hospital malnutrition are poor food unappetizingly serve, with timing for the benefit of personnel rather than patients. Patients are given nothing by mouth for the most trivial reasons (chest or abdominal films; other radiological exams). Diets are not advanced rapdly after trivial operations.

The hospital administration regards food as an area which to save money.

There is rapid adaptation to resting starvation, and proteolysis is minimal after as little as four days. The metabolic tragedy of sepsis is that this adaptation to starvation does not occur, and breakdown of protein continues, to supply amino acids either for hepatic protein synthesis for host defenses or for gluconeogenesis for the energy needs of the organism.

Methods of assessment of nutritional status

Accumulation of lean body mass is the principal objective of nutritional support; thus determination of lean body mass is the most appropriate means of nutritional assessment. The methods used are: