In order to provide complete patient care, nutritional support should be part of the therapeutic plan. Providing nutrition may accomplish several goals (Table 1).

Table 1. Goals of nutritional support

1.  Minimize metabolic derangements

a.  Maintain hydration

b.  Attenuate acid-base disorders

c.  Attenuate electrolyte disturbances

d.  Provide disease-specific nutrients

2.  Provide nutrients to facilitate recovery

a.  Suppress hypermetabolic response

b.  Restore or reverse protein catabolism and negative nitrogen balance

c.  Maintain gastrointestinal tract integrity and function

d.  Optimize immune function

3.  Maintain lean body mass and body weight

4.  Avoid complications associated with refeeding

Decisions on how to provide nutrition

There are 2 main "Golden Rules" of nutrition: 1. If the gut works, use it, and 2. Keep it simple.

Enteral nutrition

"If the gut works, use it" is the cardinal rule of nutritional support. Providing nutrition by the enteral route is the safest, simplest, least expensive, and most physiologic means possible. Not only does the enteral route provide nutrients for the whole animal, but also it provides nutrition to enterocytes. Maintenance of enterocyte health is important in order to prevent bacterial translocation from the gastrointestinal tract into the systemic circulation or lymphatics, and to facilitate recovery by the animal. There are some potential disadvantages to providing nutritional enterally: some patients cannot tolerate enteral feeding, some patients cannot assimilate nutrients when provided enterally, and there is a risk of aspiration pneumonia if regurgitation or vomiting occurs.

Enteral nutrition may be accomplished by several means.

1. Nursing care and coaxing: Sometimes good nursing care is all that is necessary to stimulate an animal to eat. This may include hand feeding the animal's food, using a highly palatable energy dense food, warming the food to body temperature (especially cats), adding water to food (especially dogs), providing praise when the animal eats, and/or feeding the animal in a stress free environment that is away from competition. Some animals will not eat while hospitalized, but will eat voluntarily at home.

2. Appetite stimulants: There are some drugs that stimulate appetite. They do not work all of the time. Several pharmacologic agents have been used with variable success (Table 2). Diazepam may cause sedation, and should be used cautiously in animals with liver disease. Glucocorticoids are associated with side effects including catabolism, which limits their usefulness as appetite stimulants. Anabolic steroids are not as effective and may be associated with hepatotoxicity. Megestrol acetate may induce diabetes mellitus, adrenal suppression, and mammary neoplasia in cats. None of these drugs works consistently, and none have been evaluated in a controlled manner.

Table 2. Appetite stimulants that can be used in cats (C) and dogs (D).

3. Forced feeding: Boluses of food in the oropharynx will stimulate swallowing. This may be accomplished by using "meatballs" of canned food or using a syringe. Canned food gruels or convalescent canned veterinary products may be administered via syringe. Forced feeding is easy to perform; however, it may add additional stress to a sick animal. Furthermore, it is difficult to do for more than a couple of days, and it is difficult to meet nutritional needs of large dogs using this technique. 4 Tube feeding: Enteral feeding may be done by placing a tube within the gastrointestinal tract. Such tubes include orogastric, nasoesophageal, pharyngostomy, esophagostomy, gastrostomy, and enterostomy tubes.

Nutrients of concern

The animal should be evaluated as to what type of diet will be provided. It is important to correct fluid, acid-base, and electrolyte abnormalities as part of provision of nutritional support. I usually begin by calculating the energy requirements for the patient. This can be done using various formulas. For most dogs and cats: 1.5 [30(BW_kg) + 70] can be used unless an animal needs more or less caloric intake. This linear formula works well in cats and dogs less than approximately 20 kg. However, in dogs >20kg, use of this formula will overestimate caloric needs. For those dogs, I use the exponential formula: 1.5 [60(BW_kg)^0.75]. Actually, I use the exponential formula for most animals. Protein requirements are approximately 4 gm of protein/BW_kg for dogs and 6 gm/BW_kg for cats. For animals requiring protein restriction (such as those with hepatoencephalopathy or uremia), less protein should be used.

Diets available for tube feeding

Liquid diets are available for use through small bore feeding tubes (usually 3.5 or 5 French tubes). Human enteral products may be used, but they are not complete and balanced for pets, and may not contain enough protein particularly for use in cats. Several pet food companies produce diets designed for use in critically ill animals. These diets tend to be high protein, high fat, low carbohydrate, high moisture, and homogenous so that they can pass through 8 French or larger diameter feeding tubes. These diets have the advantage of being calorically dense and passing through feeding tubes easily especially when they are mixed with water. However, they are also more expensive costing about 3 times more than other therapeutic diets and 5+ times more than maintenance foods. Blended diets may be made from commercially available lifestage or therapeutic diets. Usually an equal amount of water must be blended with an equal volume of food and strained to remove large particles, before they may be administered through feeding tubes.

Initiation of feeding

In animals that are fed enterally, I usually feed the calculated caloric and water requirements on the first day divided into 6 to 8 feedings. If the animal tolerates this schedule, then I divide the total volume of food and water over 4 to 6 feedings on day 2, and over 3 feedings on day 3 (Table 3). It is important that feeding tubes be aspirated prior to administering nutrition to ensure that gastrointestinal motility is adequate. If greater than 15% of the previous meal is present at the time of the next feeding, prokinetic drugs should be administered and the feeding delayed. Prior to placement through the feeding tube, the diet should be warmed to body temperature. The food should be administered over 10 to 20 minutes, and the tube should be flushed with approximately 10 ml of warm tap water to prevent blockage of the tube.

Table 3. Stomach capacity of dogs and cats. Body weight (kg) Stomach volume (ml/kg)

Monitoring nutritional support

Body weight and physical examination should be monitored daily while the animal is hospitalized. The tube site should be cleaned every day or every other day. Blood work should be performed as deemed necessary for optimum care of the patient.

Transition from tube feeding to oral feeding

When the animal begins to eat voluntarily or is able to eat voluntarily, consider making a transition from tube feeding to oral feeding. This should be done over several days. If the tube is not interfering with oral consumption of food, leave it in for a few extra days to use if the animal is not consuming enough diet or if they quit eating again.

Complications of nutritional support

Complications are usually related to mechanical problems with feeding tubes or to diet administration. Peristomal infections may occur if the feeding tube is attached too tightly or if the site is not kept clean. Tubes may clog if they are not flushed adequately. Flushing with warm water, carbonated clear beverages or with a solution of meat tenderizer may unclog the tube. Animals may pull feeding tubes if the tubes are not secured properly or if the animal licks or chews at the ostomy site. Vomiting may occur and is usually due to rapidly administered diet, or to the diet not being warmed to body temperature. Infrequent vomiting may be controlled with antiemetics. Diarrhea may also be a problem. Always check feeding tube placement prior to administering food. If pneumonia occurs, discontinue feeding through the tube, and treat with broad-spectrum antibiotics.