Patients with disease have decreased metabolic rates and therefore energy requirements less than those of comparable healthy
individuals. Hospitalized veterinary patients are assumed to be similar to ill people and their daily energy requirements
(DER) are very near their resting energy requirements (RER).
Results of a few preliminary respiration calorimetry measurements in dogs with specific disease conditions support the idea
because most had 24-hour energy requirements near RER. Hospitalized veterinary patients should be fed at their calculated
RER, realizing their actual energy requirement is likely to increase with recovery. Therefore, initially feeding patients
at RER, or at least 50 percent of RER, is a rational, safe recommendation that decreases the probability of metabolic and
There are exceptions when the caloric requirement will be greater than RER. For example, according to indirect respiration
calorimetry, people with severe closed-head and brain injury have energy requirements 40 percent to 60 percent above their
Brain injury apparently increases oxygen consumption and acute-phase protein synthesis, which increase patients' caloric and
protein requirements significantly above RER. Energy requirements of twice RER appear to be the upper limit in the most severe
Energy expenditure may be 30 percent to 50 percent above RER in patients with multisystem trauma.
Severely burned patients also have energy and protein requirements 80 percent to 100 percent above RER, relative to the extent
of skin damage and surface area exposed because the body loses heat, moisture and proteins through wounds that have little
or no epithelial covering.
Hence, severely traumatized patients' actual metabolic rate is related to the degree of trauma and can only be approximated
in a clinical setting. These are rare cases, whereas the majority of hospitalized veterinary patients can be safely fed at
Protein in the body is always in a flux between synthesis and breakdown. Protein synthesis requires that amino acids be present
within cells at the correct time and ratio so that a protein may be constructed successfully. Protein degradation involves
the release of amino acids, and if the amino acid is deaminated, the ketoacid analog is converted to glucose or fat for energy
and the amino group enters the hepatic urea cycle and is ultimately excreted in the urine.
Dietary protein provided to animals in catabolic states spares the breakdown of skeletal muscle protein and supplies essential
amino acids for acute-phase protein synthesis and a robust immune response.
Protein administration should complement the calorie intake because amino acids will be oxidized for energy when and if the
patient's total energy need has not been first met with fat or glucose. Sufficient calories must be available from fat and/or
glucose before amino acids will be used for tissue synthesis and repair.
On the other hand, excessive protein feeding requires energy expenditure to rid the body of the excess nitrogen, which, in
certain patients, may not be handled well by the liver (urea cycle) and kidneys. The result may be hyper-ammonemia with accompanying
clinical signs of encephalopathy.
Commercial products intended for enteral support of critically ill patients provide between 5.5 g and 14.3 g protein/100 kcal.
Due to a lack of evidence to the contrary and because these products appear to work well in canine and feline patients, a
range of 5.5 g to 9.0 g protein/100 kcal is recommended for foods for canine patients and 7.5 g to 9.0 g protein/100 kcal
is recommended for foods for feline patients.
Because of the overlap of these recommendations, several commercial products intended for nutritional support are designated
for use in both dogs and cats (e.g., Canine/Feline CliniCare by Abbott).
Arginine has a marked immuno-preserving effect in the face of immunosuppression induced by protein malnutrition and cancer.
In postsurgical patients, arginine supplementation enhances T-lymphocyte response and augments T-helper cell numbers, with
a rapid return to normal T-cell function postoperatively, compared with controls.
These findings suggest that arginine supplementation may increase or preserve immune function in high-risk surgical patients
and theo-retically enhance their capacity to resist infection. Numerous studies in a variety of animal models demon-strated
the efficacy of arginine-supplemented foods in reducing the catabolic response to major trauma and sepsis and injury. Arginine
is an essential amino acid in dogs and cats. Therefore, most pet foods meeting AAFCO nutrient concentrations will contain
Glutamine is another hot-topic amino acid that plays an important role in many cellular processes but has been considered
a nonessential amino acid in dogs and cats. However, studies suggest that glutamine concentrations in whole blood and skeletal
muscle decrease following injury and other catabolic states, thus making it "conditionally" essential.
Replicating cells such as fibroblasts, lymphocytes and intestinal epithelial cells consume primarily glutamine after injury.
These findings may be important for patients with large wounds or inflammation associated with infection. There is considerable
evidence that glutamine is important in stimulating immune function, possibly through an effect on gut-associated lymphoid
tissue or through stimulation of macrophage function. At least 80 percent of the published data in animals demonstrate a positive
effect with glutamine-enriched feedings because it is the preferred fuel for rapidly dividing tissues such as white blood
cells and intestinal mucosa.
Most diets contain some protein-bound glutamine, and some even have free glutamine added. The glutamine content often is stated
on the label although the optimal concentration of glutamine for different disease states is still uncertain.
Subclinical malnutrition in people is associated with prolonged ventilatory dependence and increased complication rates, with
longer hospital stays and higher associated costs. Similarly in veterinary patients, protein-calorie malnutrition is thought
to increase morbidity and mortality.
In summary, diseased and debilitated patients require nutrients daily to maintain optimal immune function, tissue synthesis
and repair, and drug metabolism.
The patient that has not consumed its minimum daily caloric need (resting energy requirements RER) is subclinically malnourished
and is drawing on skeletal muscle for protein.
On a cellular level, the starved patient's ability to have a competent immune response, repair tissue and metabolize medications
as expected is decreased.
Surely every clinician strives to provide their patients the best possible chance of recovery. Hence, feeding your patient
early (rather than waiting until it goes home) will significantly improve the odds that the pet will go home.