By Ashley Self, BS, LVMT, VTS (Nutrition)

Preventing or limiting a nutritionally induced or influenced catabolic state in patients with varying debilitating diseases or metabolic alterations should be an important goal among the veterinary team.

In human medicine, malnutrition is common among hospitalized patients and can be associated with negative health outcomes, such as length of hospitalization, hospital readmission, and higher mortality rates.^1,2 While inadequate or delayed nutritional support and the impact on mortality rate is not as well defined in veterinary patients, early enteral feeding is supported by preservation of gastrointestinal integrity, reduction in bacterial translocation, and improvement in immune function.³

Successful support and management through assisted feeding methods involves identifying those most likely to benefit from nutritional support, making an appropriate nutrition assessment, early intervention, proper tube selection for length of time nutrition support is needed, implementing an effective nutrition plan, and follow-up.

Enteral feeding devices

Assisted enteral feeding occurs through an indwelling tube where the end is placed anywhere from the esophageal lumen to the jejunum. Common tube options include nasoesophageal, nasogastric, esophagostomy, and, finally, gastrostomy.

In efforts to be complete, jejunal feeding tubes provide post-gastric feeding, but are beyond the scope of this article. Selection of the optimal feeding tube type depends upon a variety of factors, including, but not limited to, expected duration of need, gastrointestinal function, anesthesia or surgery plan, and available equipment for tube placement.

Nasoesophageal or nasogastric tubes. Nasal tubes can be placed in one of two locations ending either within the esophagus (nasoesophageal) or the stomach (nasogastric). While two options exist for placement of nasal tubes, and some instances may suggest a benefit in termination point, such as allowing gastric decompression, strong evidence lacks in identifying complication rates differing upon tube termination point. This suggests that nasal tube endpoint does not influence complications such as vomiting/regurgitation, diarrhea, tube displacement, aspiration pneumonia, and clogged tubes.⁴

Nasoesophageal and nasogastric feeding tubes have the advantage of being easy to place and do not require anesthesia. Although, placement should be cautioned in patients with protracted vomiting, dyspnea, increased risk for aspiration of gastric contents, coagulopathy, and injury involving the nose/nasal cavity. Additionally, potential complications may include epistaxis during placement, tracheal intubation, rhinitis, aspiration pneumonia, vomiting, regurgitation, and dislodged or blocked tubes.

Esophagostomy tubes. Also referred to as E-tubes, this type can be useful in patients with conditions affecting the oral cavity, pharynx, or part of the esophagus requiring these locations to be bypassed. E-tubes are also useful in patients requiring assisted enteral feeding over a longer period of time (at least seven days). An advantage to esophagostomy tubes includes the level of tolerance and comfort for the patient compared to nasal tubes.

The larger diameter of these tubes allows for a wide variety of blenderized diets formulated for specific medical conditions (e.g. chronic kidney disease, chronic enteropathy) to be used. They are contraindicated in patients with persistent vomiting, altered consciousness, and animals that have esophageal disorders, or have undergone esophageal surgery. As with nasal tubes, E-tubes pose a risk for aspiration pneumonia. To reduce aspiration risk, the patient should be fully recovered from anesthesia and able to remain in a sternal position.

Gastrostomy tubes. G-tubes can be placed intraoperatively or percutaneously using an endoscope, [percutaneous endoscopic gastrostomy (PEG tube)]. These offer long-term nutritional support via entry into the stomach, and the wider diameter tube allows for a wide variety of blenderized diets to be fed.

Placement of gastrostomy tubes requires general anesthesia and may affect gastric motility for up to three days. While G-tubes provide benefit for patients requiring long-term assisted feeding, contraindications still exist in cases with severe ileus, serious anesthetic risk, and compromised wound healing. Complications can arise, and while most enteral feeding complications are minor, peritonitis, dehiscence of the stoma, cellulitis, and infection can occur with G-tubes.

Nutrition assessment

Regardless of the patient's need for assisted feeding, a nutritional assessment must take place as part of the patient's initial exam—the fifth vital assessment. At absolute minimum, a body weight, body condition score (BCS), muscle condition score (MCS), abbreviated diet history, and resting energy requirement (RER) calculations should be performed/obtained.

When reviewing the nutritional assessment, specific clinical findings may be of value when determining how to initiate nutritional support. They are as follows: the extent of anorexia or hyporexia being mindful when exceeding three days, consumption as it relates to the pet's resting energy requirement (RER) (below RER for less than three days or below RER for more than five days), unintentional weight loss, vomiting or diarrhea and length or time, low BCS (<4/9), muscle wasting, abnormal hematological findings, and expected course of illness (less than two days or more than three days).⁶

When to intervene

Nutrition support should be provided as soon as malnutrition is anticipated or diagnosed. According to the American Society for Parenteral and Enteral Nutrition (ASPEN), malnutrition is "an acute, subacute, or chronic state of nutrition, in which a combination of varying degrees of overnutrition or undernutrition with or without inflammatory activity have led to a change in body composition and diminished function."

Trauma or emergent cases may require medical stabilization prior to initiating nutrition support, but generally anorexia of three to five days or a patient not expected to eat within two to three days (e.g. mandibular fracture) should be provided nutrition support. In healthy cats, impairment of immune function was detected during acute starvation by day four, so in ill cats, with inadequate intake, some form of nutritional support should be instituted after three days.⁷

It is important when quantifying days of inadequate intake to consider days leading up to hospital admission in addition to hospitalization. Hospitalization will likely exaggerate inadequate intake from stress, frequent interruptions of feeding for veterinary nursing care or diagnostic procedures, overlooked NPO status, medication side effects, overall patient unwillingness to eat, and lack of specific feeding instructions.

Prior to the start of nutrition intervention, hydration status and electrolyte disturbances should be addressed, and the patient should be hemodynamically stable.

This effort will minimize risk for the development of refeeding syndrome, whereby intracellular shifts of magnesium, potassium, and phosphorus may result in a decrease in these serum electrolyte values resulting in possible deficits potentially causing fatal pulmonary, cardiovascular, neuromuscular, and neurologic abnormalities.

Developing feeding plans

Feeding plans are often influenced by the extent and time of inadequate intake, ability to tolerate reintroduction of food, and availability of veterinary nursing staff or owners for feeding intervals. The two most common enteral nutrition delivery methods for veterinary patients are continuous rate infusion (CRI) and intermittent bolus feeding.

Adopting CRI feedings in patients that may lack tolerance to high feeding volumes can be advantageous, but one study suggested that outcome and gastric residual volume do not differ between CRI and bolus feeding methods.⁸ When determining calorie goals, calculate the patient's resting energy requirement (RER) by using the following equation:

RER = 70 x (Body weight [in kilograms])^0.75

When determining energy requirements for underweight patients experiencing anorexia or hyporexia, RER calculations should target current body weight. Overweight and obese patients may benefit from modified RER targets limiting excessive calories, as overfeeding may induce additional complications.^9,10

While hospitalized the patient's body weight, BCS and MCS should be monitored daily so the feeding plan and nutrient goals can be adjusted as necessary.

Due to the nature of assisted feeding devices confronting inadequate calorie consumption, reintroduction of diet should be done in a controlled and conservative manner to limit risk of refeeding syndrome. Incremental increases of 25 to 33 percent daily, until full RER is achieved, allows adequate time for physiologic adjustments to respond to reintroduction of food.

Different diets for different tubes

Nasal tubes. Liquid diets are available from both the human and veterinary market. When using a nasal tube, liquid diets are the only option due to the small diameter of the feeding tube. These diets are generally well tolerated, and when targeting appropriate calorie goals, facilitate weight maintenance while hospitalized. While some veterinary liquid diets are formulated for maintenance, most commercially available liquid diets are not complete and balanced, meaning they do not meet every nutrient need of the dog or cat.

Since assisted feeding with a nasal tube generally does not exceed seven days, using these diets will likely not result in clinically significant nutritional deficiencies. However, when using human enteral products in cats, note these products may not have sufficient levels of protein, more specifically, taurine, required to support maintenance feeding.

For many veterinary patients, their disease will limit the dietary choices that can be incorporated into their plan, therefore, there are several veterinary liquid diets targeting specific conditions. Esophageal tubes. A major advantage to E-tubes is the ability to use commercially available canned products, generally, allowing for targeted nutrient profiles supporting a variety of needs. These canned diets can be made into blenderized slurries by use of additional water or enteral liquid products. It is necessary to experiment with different water/liquid ratios to achieve the desired consistency that will easily flow through the selected E-tube size. This will help to avoid tube obstructions and aid in calculating the most calorically dense slurry, limiting overall volume necessary to meet the patient's caloric demands.

Veterinary nurses improve the standard of care with assisted feeding devices by monitoring for signs of discomfort while administering water flushes or tube feedings, allowing tolerance complications to be caught early.

Signs of discomfort may include, but are not limited to, salivation, coughing, gagging, vomiting, lip licking, and restlessness while feeding. In addition, regular tube checks should be performed every two to four hours to monitor tube placement, stability, and patient comfort. When running a CRI, tubes should be flushed at minimum every four to six hours, and bolus feedings should be flushed pre- and post-feeding with 10 to 15 milliliters of lukewarm water to minimize opportunity for clogs.

Various recommendations have been made for unclogging feeding tubes such as using carbonated beverages or cranberry juice, however, one study reports that water and time were significantly better for clot dissolution.¹¹

Ashley Self, BS, LVMT, VTS (Nutrition) has been the veterinary nurse on the clinical nutrition service at the University of Tennessee for the past nine years. Self received her veterinary nurse nutrition specialty in 2018 and currently serves as the secretary for the American Academy of Veterinary Nutrition (AAVN). She is pursuing her master's degree at the University of Tennessee in Animal Science focusing on equine nutrition. Self hopes to enhance nutrition education and research for veterinary nurses and veterinary students in both small and large animal nutrition and promote the appropriate use of veterinary nurses in nutrition.

References

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2. Finestone HM, Green-Finestone LS, Wilson ES, Teasell RW. Prolonged length of stay and reduced functional improvement rate in malnourished stroke rehabilitation patients. Arch Phys Med Rehabil. 1996;77(4):340–5. https://pubmed.ncbi.nlm.nih.gov/8607756/
3. Campbell JA, Jutkowitz LA, Santoro KA, et al. Continuous versus intermittent delivery of nutrition via nasoenteric feeding tubes in hospitalized canine and feline patients: 91 patients (2002–2007). J Vet16 Emerg Crit Care 2010;20(2):232–236. https://pubmed.ncbi.nlm.nih.gov/20487251/
4. Yu MK, Freeman LM, Heinze CR, Parker VJ, Linder DE. Comparison of complication rates in dogs with nasoesophageal versus nasogastric feeding tubes. J Vet Emerg Crit Care (San Antonio). 2013 May-Jun;23(3):300-4. doi: 10.1111/vec.12048. Epub 2013 Apr 26. PMID: 23621520. https://pubmed.ncbi.nlm.nih.gov/23621520/
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6. Perea, SC. Parenteral Nutrition. In: Fascetti AJ, Delaney SJ, eds. Applied Veterinary Clinical Nutrition. Chichester, UK: John Wiley & Sons, Inc., 2012:355
7. Kimberly A. Freitag, Korinn E. Saker, Elizabeth Thomas, Joan Kalnitsky, Acute Starvation and Subsequent Refeeding Affect Lymphocyte Subsets and Proliferation in Cats, The Journal of Nutrition, Volume 130, Issue 10, October 2000, Pages 2444–2449. https://pubmed.ncbi.nlm.nih.gov/11015470/
8. Holahan M, Abood S, Hauptman J, Koenigsknecht C, Brown A. Intermittent and continuous enteral nutrition in critically ill dogs: a prospective randomized trial. J Vet Intern Med. 2010 May-Jun;24(3):520-6. doi: 10.1111/j.1939-1676.2010.0487.x. Epub 2010 Mar 15. PMID: 20337910. https://pubmed.ncbi.nlm.nih.gov/20337910/
9. Lippert AC. The metabolic response to injury: enteral and parenteral nutritional support. In: Murtaugh RJ, Kaplan PM, editors. Veterinary emergency and critical care medicine. St Louis (MO): Mosby Yearbook; 1992. p. 593–617. 1239 NUTRITION IN CRITICAL ILLNESS
10. Freeman LM, Chan DL. Total parenteral nutrition. In: DiBartola SP, editor. Fluid, Electrolyte, and acid-base disorders in small animal practice. 3rd edition. St. Louis (MO): Saunders Elsevier; 2006. p. 584–601
11. Parker, Valerie & Freeman, Lisa. (2013). Comparison of various solutions to dissolve critical care diet clots. Journal of veterinary emergency and critical care (San Antonio, Tex.:2001). 23. 10.1111/vec.12047. https://pubmed.ncbi.nlm.nih.gov/23621492/