Nutritional support (Proceedings)
Many hospitalized and critical care pets are at risk for becoming severely malnourished because they lack the appetite or the ability to eat. By instituting nutritional support you want to meet the pets' nutritional requirements, and if possible prevent additional deterioration. These nutritional goals can be met by providing protein, carbohydrate, fat and other nutrients in a formula that can be utilized by the body with maximum efficiency, minimal adverse effects and minimum discomfort.
When the body uses exogenous rather than endogenous nutrients, the break down of lean body mass is slowed and the patient's response to therapy is optimized. Increased protein breakdown in response to illness or injury depletes the body of its protein stores, thereby affecting wound healing, immune and cellular functions, and cardiac and respiratory functions.Protein and energy malnutrition can result from diets that are inappropriate for the physiological status of the patient (i.e. low-protein diet when increased protein is required, such as during gestation or lactation). Malnutrition from inappropriate diets can impair immune function and wound healing, decrease organ function and affect the prognosis for recovery.
What constitutes "starvation"? For a healthy animal, missing one or two meals does not mean starvation, but a 3-day history of anorexia does indicate the need for intervention. Even with initiation of adequate nutritional support, muscle wasting and negative nitrogen balance can occur. Unless there is a medical reason to withhold food, all efforts should be made to get the animal fed. The magnitude of metabolic aberration is determined by the severity of the illness or injury and associated tissue damage. General guide lines for initiation of nutritional support include the loss or anticipated loss of more than 10% of the body weight, anorexia of greater than 3 days duration, trauma, surgery, severe systemic infiltrative disease, increased nutrient loss through diarrhea, vomiting, draining wounds or burns associated with decreased serum albumin. Other issues that must be considered include gastrointestinal tract function, whether the patient can tolerate tube or catheter feedings, the physical or chemical restraint required to place a tube or catheter, venous accessibility, whether the patient is at risk for pulmonary aspiration (i.e. megaesophagus), availability of nursing care and equipment and client cost.
The cornerstones of nutritional assessment are conducting a complete physical examination, obtaining a detailed history, accurate body weight and body condition score, and evaluating complete laboratory profiles including but not limited to a CBC, complete chemistry profile and urinalysis.
The body condition scores used for healthy animals often do not apply to sick animals. When an animal is physiologically stressed, lean body mass is its preferred energy source. This results in increased body protein catabolism. Just because an animal is overweight does not negate the need for nutritional support, in fact these animals often require more aggressive nutritional support than a lean animal would. A 10% change in weight is reflected by a decrease/increase in BCS of 1-2. If using the 5 point scale a 10% change would move the BCS up/down by 1, if using the 9 point scale the BCS would move up/down by 2. These scores are most helpful if they are routinely done with each pet at every visit and used as a frame of reference. Remember that BCS reflects changes in body composition better than does just looking at weight changes.
Calorie requirements are determined by body weight and function (house potato, hunting animal, outdoor animal, etc), and can be calculated using the resting energy requirement (RER) for healthy animals at rest in environmentally controlled cages. The RER for dogs is 70 + (30 × weight in kg), for cats it's 40 × weight in kg. Water requirements equal those for energy (l ml = l kilocalorie). Illness energy requirements may be needed and should be utilized on an individual basis.
Patients with stress starvation can be glucose intolerant and if so, use glucose less efficiently as an energy source. Therefore fat and protein are important sources of energy. Before evaluating the need for fat, protein and carbohydrates, however, a good diet strategy should address the animal's requirements for water and correct any preexisting fluid and acid-base deficits. After these needs have been satisfied, sufficient fat, protein and carbohydrates should be provided to meet the animal's energy requirements and minimize gluconeogenesis of amino acids.
Commercial recovery diets are specifically designed to meet dietary needs of dogs and cats and contain ingredients (i.e. taurine, carnitine, glutamine) not usually present in liquid or parenteral diets. The principle difference between human and animal liquid enteral diets is the extent that the ingredients are subjected to hydrolysis and the protein content. For example, most human enteral diets contain 14-17% protein, which is insufficient for dogs and cats. In addition, arginine, taurine and methionine levels in human enteral diets tend to be too low, especially for cats.
Pediatric or growth diets are often recommended because they are highly digestible, have high fat and protein contents and are very palatable. Meat-based baby foods contain 30-70% protein and 20-60% fat. However, because they are deficient in calcium, vitamin A and thiamine baby foods should not be used as the sole dietary source.