Considerations for proper nutrition of surgical patients

Nutrition of surgical patients is one of the key points, if not the most important, in the evolution of their clinical picture.
Nutritional disorders, in fact, can further increase the risk linked to the underlying disease and to the surgery.
The malnourished patient can be defined as "critically ill". The body response to the additional insult of the surgery involves quantitative and qualitative changes in metabolism that are defined as "reaction to trauma."
The above is understandable, if we consider what happens after surgery.
Indeed, the immediate post-operative period is the most delicate moment in which latent, unrecognized, or previously underestimated nutritional deficiencies become manifest.
• In a first phase metabolism is catabolic oriented, and, simultaneously, there is a general depression of vital activities (metabolism, temperature, cardiac output).
• In a second stage these activities are enhanced, thus further increasing catabolism (proteolysis glycogenolysis, lipolysis), which results in a kind of autocannibalism.

Therefore, malnutrition prior to surgery significantly influences the metabolic response because:
1. the body's resistance threshold decreases, so that even a modest trauma can trigger serious reactions affecting both, the outcome of surgery, and the probability of survival;
2. the body's defense reaction to infection is altered, due to a significant impairment of the immune system, which increases the risk of postoperative complications;
3. nitrogen balance becomes negative, with rapid and progressive decreases in proteins, leading to serious imbalances and healing delays, due to a reduced capacity to repair the tissues.
Consequently, we must emphasize that malnutrition of surgical patients must be corrected in a timely manner, pre-and post-operatively.
However, there is no agreement in defining the precise magnitude of the caloric requirements of surgical patients.
Usually the requirements amount to around 3500-4000 Kcal/ day, but according to some authors, frequent complications, such as fever and infection, hyperventilation, convulsions in head injuries cases, etc, may raise them to between 4500 -8000 kcal/day.
The administration of large quantities of protein foods by mouth, which would seem to be the more comfortable and safe procedure, does not always meet the particular needs of the patient that requires a more rapid reconstruction of the sharply reduced protein tissue reserves.
If we add the possible impracticality of the oral route (obstruction of the upper digestive tract, intestinal malabsorption, stress ulcers, etc.), one can understand the need for effective artificial nutrition, or intravenous total parenteral nutrition (TPN).
It is therefore necessary to fully evaluate the nutritional status of surgical patients, bearing in mind that the calories and protein requirements depend on the degree of catabolism, which, in turn, increases on a percentage relative to the energy consumption at baseline (BEE : Basal-Energy-Expenditure).
The basal caloric needs can be calculated using the Harris-Benedict formula, which takes into account:
1. weight (w)
2. height, (h)
3. age (a)
4. sex (m-f).

B.E.E.m: 66 x 13.7 (w) x 5 (h) - 6.8 x (a)
B.E.E.f: 65.5 x 9.6 (w) x 1.7 (h) - 4.7 x (a).

The percentage increase can be calculated by determining the Nitrogen (N) losses, since there is a constant relationship between these losses and increasing caloric intake. To calculate the total daily losses of N in the absence of protein intake, just add a constant proportion of 3.5 g to urinary urea nitrogen, which represents almost all the losses via feces, sweat and non-urea urinary nitrogen.
On this basis of these elements we can distinguish various degrees of catabolism: normal, mild, moderate and severe.
As for the biochemical data, it is important to note that among the serum proteins, albumin and transferrin are reduced mainly in those malnourished or stressed patients.
Creatinuria is the index of muscle catabolism and, therefore, its variations from the norm reflect the degree of this phenomenon.
The impaired immune response is highlighted by the lymphocyte count and by a delayed skin sensitivity test.
Control of blood glucose plays an important role. Indeed, studies in this regard have shown that stressful conditions, such as surgery, suppress insulin secretion mediated by circulating catecholamines, in turn associated to glucose intolerance, and high plasma lipids levels. Subsequently Insulin resistance with high insulin levels and glucose intolerance set in.
As a general rule, the ineffectiveness of nutritional therapy occurs when an incomplete diet, although able to direct the metabolic disorder of the patient in an anabolic direction, but missing some essential nutrients, is administered.
The ideal preparations, regardless of their route of administration, must contain all the components of a balanced diet.
The omission of some nutrients should be undertaken only when such an omission has offered some specific advantages, or, in the presence of contraindications for that particular component.
In this regard it is important to state that, aside from real needs, certain habits in prescribing fasting result from superficial knowledge of the actual need to suspend the feeding, or from the absurd idea that fasting can have a cathartic effect.