The critical role of nutrition for hospitalized veterinary patients

As we continue to learn the importance of nutrition for a patient's long-term health, veterinary technicians must equip themselves with the knowledge to serve the nutritional needs of their patients. This entails, in part, knowing how to properly assess hospitalized patients for signs of existing malnutrition and being able to intervene before malnutrition develops. Let's explore how to assess the need for nutritional support and create a plan to support and speed the patient's recovery.

Stressed vs. unstressed starvation

Simply put, any fasting animal will adapt by altering its metabolism. These alterations preserve energy reserves and conserve endogenous protein. Carbohydrates, fats, and proteins can all be used as sources of energy. But the metabolism of a healthy fasting animal is very different than the metabolism of an injured or ill fasting animal. A healthy animal will first use carbohydrates and fat stores as fuel. In critically ill or injured animals, protein catabolism is actually accelerated (also known as a hypermetabolic response to injury). When 25 percent to 30 percent of body protein is consumed, cardiac failure, respiratory failure, or infections secondary to immunosuppression can lead to death.

Patients with a history of anorexia or prolonged periods of decreased appetite, nausea, vomiting, regurgitation, or diarrhea are at risk for malnutrition because their nutritional intake is less than optimal. Nutrient digestion and absorption will lead to protein loss if a patient experiences vomiting, regurgitation, or diarrhea. The body has no storage form of protein. All endogenous proteins serve some functional purpose, such as structural proteins, enzymes, and carrier proteins.

A healthy fasting animal will make metabolic adaptations over the course of days or even weeks. These adaptations are aimed at decreasing demands for glucose to fuel tissues that use it either exclusively or preferentially for energy production. Some tissues of the body can only use glucose as fuel. The glucose reserves are used up in the first 24 to 72 hours of a fast. Some tissues can use fat as fuel. Other tissues use glucose but will then switch over to other fuel sources, such as ketone bodies (keto-adapt).

A critically ill animal cannot keto-adapt. Therefore, when the body starts breaking down endogenous protein for energy, it is really the animal's muscle and eventually its organs that are compromised. In a fasting, critically ill patient, it is the lack of amino acids rather than the lack of calories that is likely to be life-threatening.

Conducting a nutritional assessment

There is no gold standard test for diagnosing malnutrition. In most cases, laboratory values alone are insufficient to diagnose the condition. Thus, every animal admitted to the hospital should undergo a nutritional assessment. This includes noting the patient's signalment, reviewing the patient's medical and dietary history, and conducting a physical exam.

Sidebar 1: Metabolic response to fasting

For a young adult that presents adequately nourished with no history of decreased appetite, weight loss, or gastrointestinal problems, a quick nutritional assessment may suffice. This involves determining whether an animal is adequately nourished, borderline malnourished, severely malnourished, or in danger of becoming malnourished. Based on this information, you may determine if a more thorough nutritional assessment is warranted.

Sidebar 2: Hypermetabolic response to injury

For patients that may need nutritional support, it is important to review the medical history, complete a thorough physical exam, and conduct a complete diet history. The type of food and amount fed is important when calculating the animal's intake (for example, ¾ of a 13-ounce can of chicken and rice plus ¼ of an 8-ounce standard measuring cup of adult maintenance twice a day). Always check with the person responsible for feeding the animal to ensure accuracy. Ask the following:

• Has this been the animal's regular diet, or has there been a recent diet change? If the owner has been feeding a home-cooked diet, this should alert you to the possibility of nutritional deficiencies.

• Has the animal had a history of decreased appetite or unintentional weight loss? If so, is the weight loss acute or chronic? A loss of body weight over a three-week period is much more significant than the same loss over a three-month period. This is because in acute loss a greater portion of the weight loss is likely to be lean tissue.

• What is the animal's activity level? Have there been any recent changes in activity level?

• What type of treats or nutritional supplements does the animal receive?

• Has the animal had any problems chewing, swallowing, or prehending food?

• Has the pet shown such gastrointestinal signs as vomiting, regurgitation, or diarrhea?

The physical exam should include weight and evaluation of lean muscle mass. All patients should be assigned a body condition score. A body condition score is a subjective assessment of the patient's fat stores. Various body condition scoring charts are available. Most use a scale from 1 to 9 or from 1 to 5 (1 = emaciated, 9 = grossly obese). The most important thing is to pick one and use it consistently. Then you can compare this information to previous and subsequent visits.

The areas mainly evaluated are over the ribs, down the spinal cord, around the tail base, and along the abdomen. Putting your hands on the animal is important, and it also allows you to assess the degree of muscle wasting present. It's important to note this information in the patient's record. Noting the presence of decreased muscle mass is especially important because body condition scoring charts are designed for evaluating healthy pets. The charts do not take into account critically ill animals that may have visible stores of body fat but are actually in a negative energy balance and have varying degrees of muscle wasting.

During the exam, if you note edema, ascites, skin lesions, or a poor coat, it may be an indication of micronutrient deficiencies. For example, signs of zinc deficiency include anorexia, alopecia, and parakeratosis. Look for any evidence of facial trauma or dental disease that may make eating difficult for the animal.

Develop a nutritional plan

Next, consider whether a lack of nutritional intervention will negatively affect the patient's outcome. If the answer is yes, it's time to develop a plan and set nutritional goals. Further investigation into the animal's medical history will determine how aggressively you need to initiate nutritional support.

Sidebar 3: Equations for estimating pets’ energy requirements

Patients that present malnourished, have a serious illness, and cannot meet minimum caloric goals should automatically be considered candidates for nutritional support. If an animal presents with a prolonged history (greater than three to five days) of partial or complete anorexia or is expected to not receive anything orally for an extended period, it is best to initiate nutritional support sooner rather than later.

Evidence shows that patients' prognosis is better when you initiate nutritional support early on in their illness. Keep in mind that even an animal that presents in good body condition can quickly lose ground if facing severe illness and a prolonged hospital stay.

Methods of nutritional support

Many options are available for patients needing nutritional support. An animal's current status will determine which method is most appropriate. Is the patient receptive to coax feeding? If so, is it possible, without causing stress, to meet the animal's caloric needs? Establish an animal's estimated feeding goals, and write specific feeding instructions. This is an easy way to determine if the patient is able to meet minimum requirements on its own. Animals showing overt signs of nausea should not be coax fed. It is always best to feed enterally (by mouth) if possible.

Enteral nutrition. This form of nutrition is easier and less expensive to provide. It is also considered safer and requires less monitoring than parenteral (intravenous) nutrition. Research also suggests that the enteral route of nutrition may be important in maintaining the immune system and decreasing the possibility of bacteria from the gastrointestinal tract entering the portal blood, causing systemic bacterial sepsis.1 It may also play a role in blunting the hypermetabolic response to illness.2

However, there are many reasons why this is not possible for all patients. Patient evaluation for enteral feeding should include an assessment of gastrointestinal tract function. An animal that is actively vomiting or regurgitating is an aspiration risk. Enteral feedings are contraindicated until the vomiting or regurgitation is brought under control. An animal that is not able to protect its airway (i.e., no gag reflex) is also not a good candidate for enteral feedings. Aspiration pneumonia can be a fatal complication.

In addition, patients should not be fed enterally if they are not mentally appropriate (bright, alert, and responsive) or do not possess a normal gag reflex. For these patients, consider parenteral nutrition.

Parenteral nutrition. This form of nutrition is delivered intravenously. It has numerous associated risks, including a higher risk of infection, and should only be used for patients unable to tolerate enteral feedings and whose outcome would be negatively affected if nutritional support is not initiated. Another consideration is the anesthetic risk involved in tube placement. Esophagostomy, gastrostomy, and jejunostomy tubes all require general anesthesia. For patients not stable enough to undergo general anesthesia, a nasoesophageal tube, which generally requires at most light sedation, may be a safer option.

Determining how much to feed

There is much debate surrounding the caloric requirements of a critically ill patient compared with that of a healthy individual. A good starting point is to estimate the patient's resting energy requirement (RER). (See formulas.) An animal's RER is the estimated amount of energy needed to maintain basic life processes. These basic life processes would include energy used for digestive processes, body temperature regulation, and physical activity.

A daily assessment helps ensure that the goals you establish for each patient are correct. Part of the assessment includes weighing and recording the patient's body. You will quickly notice if you have underestimated the RER, and you can make appropriate adjustments to the feeding orders.

Selecting a diet for tube feeding

Ideally, a diet should be balanced to meet all of a patient's nutritional needs. The type of diet you select should be based on the patient's illness and renal and hepatic function; the size, type, and location of the feeding tube; the patient's nutrient requirements; and diet accessibility.

Sidebar 4: The next step

Smaller bore tubes, such as nasoesophageal or jejunostomy tubes, can only accommodate a liquid diet. Commercially complete and balanced liquid diets are available for veterinary patients. Human liquid diets may be used but will usually require supplements. This is especially true for cats, whose requirements for taurine and arginine cannot be met with a human formulation.

For larger bore tubes, such as gastrostomy and esophagostomy tubes, an appropriate canned diet blended with water works well. Some veterinary diets are specifically made for tube feeding. Remember that these high-fat, high-protein diets may not be suitable for all patients.

Conclusion

Nutrition is an important part of your patient's recovery process. It's critical to perform a nutritional assessment on every hospitalized patient and establish realistic feeding goals. This will allow you to see that your patient's nutritional needs are being met and whether nutritional support is needed. Following through with these goals while continuing daily patient assessment can positively affect your patient's outcome.

Charlotte Higgins, AS, CVT, is a nurse practitioner in nutrition at the MJ Ryan Veterinary Hospital of the University of Pennsylvania in Philadelphia. She's also a charter member of the Academy of Veterinary Nutrition Technicians.

REFERENCES

1. King KG, Boag A. BSAVA manual of canine and feline emergency and critical care. 2nd ed. Gloucester, UK: British Small Animal Veterinary Association, 2007.

2. Michel K. Department of Clinical Studies, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, Pa. Personal communication, 2012.