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.


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.

Nutritional Questions

  • When was the last time your pet ate or drank? How much was offered? How much was consumed?

  • What type of food is usually fed (canned, dry, table food, scraps)?

  • What brand of food is usually fed? For how long?

  • Have there been any recent changes in your pets eating or drinking habits? If so, what changes over what period of time?

  • Have there been any recent changes in body condition (e.g. muscle loss, swollen abdomen, hair loss or poor grooming)?

  • Has your pet recently taken, or is currently taking any medication? Were there any changes in your pet's condition while taking these medications?

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.


The gut is the safest and most natural route for administering nutrients. This is best accomplished with enteral feeding. Voluntary oral intake is the preferred route for enteral nutrition; however patients must be able to consume at least 85% of their calculated RER for this method of feeding to be effective. If a patient is unable or unwilling to eat voluntarily, tube feeding should be considered. While force feeding can be used to provide the necessary nutrition, this is usually too stressful to the patient, not to mention the stress to the owner. Seldom is this method able to deliver the volume of nutrients necessary to meet the patients' needs.

Tube feeding, however is limited by diet selection. In most instances, only liquid or gruel diets can be fed through the tube because of the small diameter. Acceptable tubes sites would include; nasoesophageal, esophagosotomy, gastrostomy and jejunostomy.

The choice of tube will be dependent on the condition of the patient, the disease being addressed, and expense of administration, availability of intensive care facilities, the preferred food and anticipated length of feeding assistance.

Common complications include osmotic diarrhea and vomiting. It is recommended that the jejunal tube be left in place for 7-10 days to allow adhesions to form around the tube site and prevent leakage back into the abdomen. Completely changing the delivery equipment every 24 hours will help prevent bacterial growth within the system. Clogging is a common problem; a syringe pump may help to decrease the incidence as will flushing well every 4 hours.

Enteral support is preferred over parenteral nutrition. Exceptions would include gut failure, refractory vomiting, and impaired swallowing or if enteral nutrition would exacerbate a disease (e.g. necrotic hemorrhagic pancreatitis).

Total parenteral nutrition (TPN) uses a modified solution with nutrients that can readily be absorbed by cells without passing through the gut. Parenteral solutions can be used alone or as a supplement to enteral nutrition.

TPN has several disadvantages. These solutions tend to be highly osmolar (osmolarity >1200 mOsm) so a dedicated central line is required, and the special nutrient solution must be properly and sterilely prepared. 24 hours monitoring is necessary, and thrombophlebitis and sepsis are serious complications if strict aseptic technique is not followed.

There are commercially available partial parenteral nutrition (PPN) solutions that can be used in veterinary medicine. They lack the lipids provided in TPN solutions. These solutions have a lower osmolality (osmolarity <800 mOsm), and can be administered through peripheral catheters. They can be mixed with most fluid additives and given concurrently with enteral feedings.


Because nutritional support is not an emergency procedure, reinitiating feedings should be started slowly. Generally 50% of the RER divided into multiple small meals is offered the first day. If this is well tolerated, than 100% of the RER can be fed the next day. If feedings are not tolerated, the increases should be more gradual over the next 2-3 days. With some diseases, it may take 7-10 days to get the animal to 100% of its calculated RER. It has been our experience that reintroducing feedings slowly substantially decreases some of the unpleasant side effects that can be associated with nutritional support (i.e. refeeding syndrome, vomiting, diarrhea, constipation, hyperglycemia etc). Smaller meals tend to be tolerated better because they do not cause distension of the stomach and subsequent delayed gastric emptying, or aggravate nausea by stimulating the vomiting receptors in the stomach.

The refeeding syndrome, an electrolyte disturbance that can occur in patients with depleted intracellular ions (e.g. potassium, phosphorus, magnesium), resulting from malnutrition, starvation as seen with hepatic lipidosis or prolonged diuresis as seen with uncontrolled diabetes or acute renal failure. Patients at greatest risk are severely malnourished with significant loss of lean body mass. Feeding results in a rapid shift of these ions from the plasma (where levels are often normal before feeding) to the intracellular space. Profound hypophosphatemia, hypokalemia and/or hypomagnesemia may result, and lead to muscle weakness, intravascular hemolysis (seen with hypophosphatemia), and possible cardiac and respiratory failure. This syndrome can be avoided by monitoring the patient closely, introducing feeding cautiously (continuous rate infusion of a commercial gruel diet may be helpful), monitoring electrolytes frequently, and supplementing the diet as needed.


Nurses responsible for patient treatments should be given instructions listing the type of food to be offered along with how much and how often. The nurse should also note whether any food, amount or technique recorded differs from the orders. Such record keeping provides the veterinarian with an accurate measurement of food intake and the nurses with feeding methods that succeed on a per patient basis.

Although diet transitions may occur while the patient is hospitalized, typically it is done 2-6 weeks after discharge from the hospital. Transition depends on the diet being fed, condition of the patient, their response to therapy, and the comfort level of the owner. As with diet initiation, proceed with the transition slowly, typically this is done over a 5-7 day period. Advising the clients to substitute the food by 1/4 of the total volume every 2 days usually works out well.

Nurses should supply the owners with well-written, concise instructions and reasonable expectations. Owners need to be aware of how prolonged hospitalization can affect their pets and should be advised of reasonable expectations regarding their pet's limitations after discharge.

Nutritional support can not only prolong our patients' lives, but can improve the relationship what we share with both our patients and our clients. Even if we are not able to save our patients every time, the clients understand that we do care and want what is best for their pet.


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