Section III: BODY COMPOSITION CHANGES

The body composition changes in the burn patient are involuntary. There is a major difference between involuntary weight loss and voluntary weight loss. The former is dangerous if not well controlled as the problem of weight loss in the surgical patient is that of lean mass loss. Loss of lean mass instead of fat is sure to lead to significant complications. The complications from lost lean mass, caused by the metabolic changes of stress.

Complications correlate with the percent of total lean mass lost assuming normal body composition prior to the loss. Pre-existing losses are added to the loss from a body insult in order to recognize the potential complications expected. The relationship between the loss of lean mass and the degree of morbidity and mortality is shown. A 40% loss of total lean mass is fatal.

Figure 2:

The effect of lost body protein on wound healing relates to the fact that there is competition of protein substrate between the wound and restoration of LBM. The impairment of cutaneous wound healing is also proportional to the amount of lost lean mass. The wound still has priority for protein substrate for healing, with a LBM loss of up to 10% of total. With progressive losses, the lean mass compartment increasingly competes with available protein substrate to restore itself. This self-preservation process is aimed at avoiding further morbidity with lost lean mass, which become a higher risk than the wound itself. As the skin protein decreases throughout the body, new wounds will develop as well as the reopening of old wounds.

Figure 3:

Legend: With a loss of lean mass less than 10%, the wound takes priority over available protein substrate. As lean mass continues to decrease more consumed protein is used to restore LBM with less being available to the wound. Wound healing rate decreases until lean mass is restored. With a loss of lean mass exceeding 20% of total, spontaneous wounds can develop due to the thinning of skin from lost collagen.

Causes of Lean Mass Loss

There are several routes to involuntary weight loss and lean mass loss:

The first route is via the acute injury, surgery, or infection induced process where increased nutrient requirements and wasting of body protein are characteristics. The presence of other stressors, such as pain and anxiety, can lead to the same endpoint. Then PEM occurs rapidly, due to the lack of any adaptive or protective responses. Often the insult or “stress” resolves, but the weight loss and PEM are never corrected in the recovery phase leading to a chronic protein deficit and its resulting complications. With the presence of any catabolic insult the degree of lean mass loss (% of total) exceeds the degree of weight loss, as lean mass is not protected and fat mass is not preferentially used for fuel. Increased nutrient losses due to gastrointestinal disease, can lead to the same endpoint.

The second route is due to inadequate nutrient intake, both quality and quantity. This process is very common in the elderly, those with disability, lack of appetite from chronic illness, mental illness, and poverty. The onset of severe weight loss precedes the PEM as some adaptation will occur and lean mass is initially spared, but eventually protein-energy malnutrition will occur.⁹

The third route is through the disuse atrophy of post-injury bed rest, inactivity and the resulting disability. Whatever the route, the most common cause of weight loss and protein energy malnutrition is the triad of increased nutrient demands, decreased intake, and inactivity.

[Normal Body Composition][Body Composition Changes]