Providing nutritional support to patients is critical because adequate caloric and nutrient intake prevents the adverse consequences of malnutrition and optimizes patient outcome. However, in a busy practice, it is easy for patients to receive suboptimal nutrition, whether because of vaguely written or absent feeding orders, anorexia, sedation from pain medications, procedures requiring the animal to be NPO, or other factors that impede adequate calorie intake.1
Inadequate intake of calories and other nutrients can be deleterious to a patient's underlying illness or injury and can negatively impact the outcome. Thus, our goals with this article are to review how to assess the nutritional needs of hospitalized animals, how to use that information to develop an individualized nutrition plan, and how to best incorporate enteral nutrition into practice.
NUTRITION IS IMPORTANT TO OUTCOME
Not only is protein an inefficient source of calories, but this loss of lean body mass also has deleterious effects on the host. While carbohydrates can be stored to a small extent as glycogen in the liver and there is a near unlimited capacity to store fat in adipose tissue, the body cannot effectively store protein. Since all of the body's protein is functional, loss of lean body mass means that the animal may be losing critical functional tissue. This loss of lean body mass during illness or injury has important clinical implications. In people, lean body mass loss has been shown to impair strength, immune function, and wound healing and to reduce overall survival.3-5 And in hospitalized dogs and cats, lower energy intake has been significantly associated with reduced survival.6 Thus, it is critical to provide adequate calories, protein, and other nutrients to ill or injured animals.
New guidelines developed by the American Animal Hospital Association and the World Small Animal Veterinary Association stress the importance of performing a nutritional assessment of every patient at each visit.7,8 (You can find these guidelines at aahanet.org/Library/NutritionalAsmt.aspx and wsava.org/V5.htm, respectively.)
A nutritional screening includes recording a patient's body weight, body condition score (BCS), muscle condition score (MCS), complete diet history, and medical conditions as well as medications the patient is receiving. If any risk factors, such as weight loss, thin body condition, muscle loss, or underlying disease are present, a more thorough diagnostic evaluation is recommended, such as laboratory testing, diagnostic imaging, and any other pertinent diagnostic tests.
BCS primarily assesses fat stores, while MCS assesses muscle. MCS is determined by visual examination and palpation over the temporal bones, scapulae, thoracic and lumbar vertebrae, and pelvic bones. It can be described as normal or can demonstrate varying degrees of atrophy (e.g. mild, moderate, marked). BCS and MCS may not be analogous, as a thin animal may have normal muscle condition and an overweight or even obese animal may have significant muscle loss. Since animals with acute and chronic disease preferentially lose muscle (lean body mass), when caloric intake is inadequate it is critical to assess both fat and muscle stores because this information can help to identify chronic disease and may modify the nutritional plan.7,8
WHEN TO ASSIST FEEDING
Factors that should be considered when determining if a patient requires assisted feeding include the animal's underlying medical condition, the medications it is receiving, and the duration of anorexia (complete absence of appetite) or hyporexia (decreased appetite). Given the loss of critical lean body mass associated with illness or injury, animals that have been—or are anticipated to be—anorectic for longer than three to five days require nutritional support, as this period is when deleterious effects (e.g. enterocyte atrophy, decreased immune function) begin to be observed.2,7,8 It is important to consider a patient's entire duration of anorexia or hyporexia, including time at home before presentation.2 In animals that are already malnourished, the lag time before initiating enteral nutrition should be abbreviated since the adverse effects of anorexia have already begun.
WHICH FEEDING TUBE SHOULD I USE?
See Your feeding tube options and Table 1 for pointers on which feeding tube is best for various presentations.
All nutrition plans should include precise feeding orders, including the amount, route, frequency, and diet to be fed.
The amount of food consumed and the caloric density of the food (calories per can or cup; available from product guides or manufacturers' websites or by calling the manufacturer) must be recorded so you can monitor the patient's caloric intake. If the amount fed and eaten are recorded (e.g. feed diet X orally – ½ can four times a day; ate 50% of food offered [¼ can]), the specific number of calories eaten per day can be calculated and compared with the patient's requirements to ensure adequate voluntary intake.
It is recommended to feed a hospitalized, ill animal its resting energy requirement (RER). While the exponential equation for calculating RER (70 x body weight in kg0.75 ) is more accurate, the linear equation (30 x body weight in kg + 70) is a reasonable approximation of caloric needs for animals weighing 3 to 25 kg.2,9
When calculating RER for a patient that is at its ideal weight (4/9 or 5/9 BCS), is underweight (< 4/9 BCS), or is mildly overweight (6/9 BCS), the animal's actual weight should be used.
For an animal that is moderately to severely overweight (BCS > 7/9), using an adjusted body weight to calculate RER may be more appropriate to avoid overfeeding. When calculating RER for animals with a BCS > 7/9, we use the ideal weight plus 25% of the animal's excess weight to account for the proportion of lean body mass that typically accompanies overweight animals. For example, for an 80-lb dog that should weigh 60 lb, the adjusted weight we would use to calculate RER would be 65 lb (60 lb + [25% x 20 lb]).
Once the patient is at home, maintenance energy requirement (MER) can be calculated by multiplying the RER by an activity factor. This activity factor may range from 1 to 1.8, depending on the animal's activity level and metabolism (e.g. neutered adult dog = 1.6; neutered adult cat = 1.2).10 However, it is important to remember that while the calculations for both RER and MER provide a starting point, the amount fed often needs to be adjusted over time to maintain a patient's body weight and optimal body condition.
Appetite stimulants (e.g. mirtazapine) may provide some benefit to animals with decreased appetites11-13; however, the underlying disease must also be addressed. It is still important to give specific feeding instructions and to monitor intake and body weight since many animals receiving appetite stimulants do not consume adequate amounts to achieve RER or maintain weight.
If a patient does not eat sufficient amounts voluntarily, there are many methods by which animals can be encouraged to eat.7,8 Offering the animal its favorite foods or feeding it in a quiet location may be effective. Warming the food or sitting with the animal may also increase food intake. Introducing a new diet to a hospitalized animal (especially a veterinary therapeutic diet indicated for long-term management) should not be prioritized because it may contribute to the development of a food aversion (the animal adversely associates a specific food with a feeling of illness).
For some animals, syringe feeding may be attempted. In these cases, using a liquid enteral diet or a calorie-dense critical care diet may be useful. Careful attention must be paid to the total calories eaten compared with the animal's RER to ensure that underfeeding does not occur. If adequate intake cannot be met or if the animal is exhibiting signs of nausea or stress, syringe feeding should be avoided.
Animals should be offered the option to eat before each feeding. If oral intake is not possible or if an animal will not voluntarily consume enough calories of a complete and balanced diet to meet its energy and nutrient requirements, assisted nutritional support is indicated.
Planning for the feeding route before other procedures are performed is strongly recommended. If an animal with confirmed or anticipated anorexia is to be sedated or anesthetized for a diagnostic or therapeutic procedure, consider placing a feeding tube at that time. Prophylactic placement of a feeding tube can provide a safety net when it is unclear whether an animal will begin eating on its own. In cases in which an animal has intractable vomiting, severe malabsorption, or neurologic disorders in which a gag response is compromised, parenteral nutrition is the preferred route of nutritional support. Information on parenteral nutrition is available from other resources.14,15
Depending on how long the animal was anorectic, feedings should provide 25% to 50% of RER on the first day, divided into four to six feedings (although most animals can tolerate four feedings a day), with each feeding administered over at least 10 to 15 minutes. As long as the animal tolerates the feedings, the amount fed can be gradually increased to achieve 100% RER over two to four days. In our clinical experience, most animals tolerate volumes between 5 to 20 ml/kg per feeding. When sending the animal home, it is best to adjust to three feedings a day, if possible, to aid in owner compliance.
Feeding hospitalized animals by continuous-rate infusion is appropriate for those that do not tolerate bolus feeding (e.g. delayed gastric emptying, ileus).
All enteral diets should be refrigerated after opening and should be discarded after 48 hours since contamination can occur. Enteral diets should then be warmed to room temperature before administration to the patient. Choosing the most appropriate diet depends on several factors, including the animal's medical condition and nonpatient factors such as the tube type, diet availability, and cost.
For patients with small-bore tubes (NE, NG, J tubes), a liquid enteral diet must be given. One liquid enteral diet that meets nutritional requirements for dogs and cats is CliniCare Canine/Feline Liquid Diet (Abbott Laboratories). For cats with underlying renal disease that require decreased protein and phosphorus or for dogs requiring phosphorus restriction but minimal protein restriction, CliniCare RF Feline Liquid Diet (Abbott Laboratories) is a better choice; however, this product provides too much protein for a dog that requires significant protein restriction.
Not all enteral diets marketed for dogs and cats are nutritionally complete and balanced, so they should be evaluated carefully to ensure that they meet the Association of American Feed Control Officials minimums for all nutrients before use.
Some liquid enteral diets for people (e.g. Ensure—Abbott Nutrition, Peptamen—Nestlé HealthCare Nutrition) can be used short term in dogs, but these diets do not provide complete and balanced nutrition and modifications are necessary if they are to be given for more than a week. When human enteral products are given to dogs and cats in the short term, additional protein, B vitamins, arginine, and taurine is almost always required, and calcium, zinc, iron, and choline supplementation is almost always required for long-term administration of these products. However, the specific nutrients and amounts that need to be supplemented vary with each product. A board-certified veterinary nutritionist can assist you in selecting (and modifying, if necessary) the most appropriate enteral product for your practice.
When these critical care diets are contraindicated for an individual animal (e.g. a dog with advanced kidney disease or a cat requiring a novel ingredient diet), commercial canned veterinary diets may be given for enteral feeding if liquified by adding water and using a high-speed blender for two or three minutes. The amount of water added to each diet varies based on the individual diet, but the resulting caloric density is typically well below that of critical care diets (e.g. 0.5 to 1.2 kcal/ml). Additionally, these diets require careful flushing to avoid tube clogging.
MANAGEMENT OF FEEDING TUBES
The care of enteral feeding tubes is critical for their success. The first step is keeping tubes securely in place with sutures. A light bandage should be used to cover all E, G, and J tubes. The tube site should be checked daily for redness, swelling, and discharge as well as for tube displacement. Drawing a line with a permanent marker at the insertion site on an E or a G tube allows owners to monitor for tube displacement at home. NE and E tubes may become malpositioned if the animal vomits. Displacement or early removal of a G or J tube constitutes a surgical emergency if it occurs before a strong stoma forms because food or gastrointestinal contents will leak into the peritoneum.
Exercise caution when administering medications through feeding tubes as they may not be compatible with enteral formulas or may clog the tube.16,17 Some medications should not be crushed (e.g. chemotherapeutic agents, extended-release tablets) or removed from capsule form (e.g. enteric coated). Some medications have better bioavailability when administered with food while others should be administered on an empty stomach.
Feeding tubes are typically well-tolerated, but complications can arise and are characterized as mechanical, metabolic, or gastrointestinal.16,18,19 They are minimized by providing good instructions and careful monitoring.
Mechanical complications include tube clogging, inadvertent removal of tubes, and tube migration. To reduce the risk of tube clogging, a few precautions should be taken. Only liquid enteral diets should be administered through small-bore (< 10-Fr) tubes. Canned diets should be blenderized thoroughly (at least two or three minutes in a blender) before administering them through E or G tubes. Crushed tablets should not be administered through small-bore tubes.
Tubes should be flushed well with room temperature water before and after food and medication administration. Depending on the size, tubes generally require between 3 and 10 ml of water to adequately flush them. If a tube does clog, inject a solution of ¼ teaspoon pancrelipase plus 325 mg of sodium bicarbonate in 5 ml of warm water, let it sit for five minutes, and then flush the tube with water.20 Keeping the tube capped between feedings will also help prevent clog formation.
To prevent the inadvertent removal of tubes, E-collars and bandages or stockinets should be used.
Inadvertent food aspiration can occur because of underlying disease (e.g. megaesophagus), inappropriate tube placement, or the migration of tubes. Tube placement should be confirmed radiographically before the first feeding. Some clinicians recommend techniques to help ensure proper tube placement before feeding, such as aspirating the tube before each feeding to test for negative pressure or injecting a small amount of saline solution into the tube. However, further studies are needed to determine whether these measures provide additional safety benefits. Animals at risk for aspiration should be fed in an upright position.
Potential metabolic complications include overhydration, electrolyte disturbances, and refeeding syndrome. Concurrent intravenous fluids must be adjusted when initiating enteral feeding to account for the water volume provided by the food and for multiple flushes, which can greatly contribute to daily water intake.
Refeeding syndrome, which results in hypophosphatemia, hypokalemia, and hypomagnesemia, is most likely to occur in animals that have not eaten for marked periods. In patients that have been anorectic for more than a week, feeding should be initiated slowly (25% to 33% on day 1 and progress over three or four days) and electrolytes should be closely monitored during the first 12 to 72 hours after initiating feedings.21
Refeeding syndrome can have serious consequences, but incidence rates for this complication are not well-documented. One study reported that 2.5% of cats receiving parenteral nutrition developed refeeding syndrome,22 and another study of 46 dogs fed by nasoenteral tube reported that none developed refeeding syndrome.23 However, it is important to note that most studies of enteral and parenteral nutrition do not specifically assess the rates of refeeding syndrome but more commonly report individual electrolyte abnormalities. For example, a retrospective study of cats receiving enteral nutrition reported that 2% of cats developed hypophosphatemia,24 while retrospective studies of parenteral nutrition in dogs and cats report rates of hypophosphatemia between 0% to 28%.25-29
Gastrointestinal complications may include vomiting, diarrhea, or abdominal discomfort. Antiemetic therapy may have some benefit and was recently reviewed,30 but feedings may need to be adjusted (e.g. decrease volume, increase frequency, change of diet). Changing to a lower-fat diet may benefit some animals but will often result in feeding an increased volume of food.
Once an animal is discharged, body weight, BCS, and MCS should be evaluated every one or two weeks initially to ensure adequate caloric intake. The amount fed may need to be adjusted to achieve and maintain ideal body weight, BCS, and MCS. Tube monitoring should be continued at home, and bandages should be changed once a week or sooner if needed. Owners should be instructed to bring the animal in for evaluation if they have any concerns about the placement of the tube or have difficulty feeding the animal. Superficial skin infections at tube sites are not uncommon and can be treated with either topical or systemic antibiotics.
DISCONTINUING ENTERAL FEEDING
When the animal is voluntarily consuming at least 60% of its RER orally, enteral feedings can be gradually decreased. It is imperative to not remove enteral feeding tubes too early. Animals should be eating their full RER voluntarily and maintaining their body weight for at least a week before tubes are removed. If an animal is eating without assistance, the tube should be flushed with 3 to 10 ml water four times daily to maintain patency. Once tubes are removed, E and G tube sites typically heal within 24 to 48 hours by second intention.
Nutritional support can be provided to ill or injured animals in many ways. The key is to perform a thorough nutritional assessment of every animal and to initiate nutrition early. Once it is determined that a patient requires a feeding tube, its nutritional needs can be determined and the appropriate tube can be placed. Early institution of an individualized nutritional plan allows enhanced nutritional management, reduced risk of malnutrition, and ultimately, improved patient outcome.
Editors' note: Dr. Parker's nutrition communication residency is funded by P&G Pet Care.
Also read about the perks of proactive feeding in your patients and how to get clients to comply here.
Valerie J. Parker, DVM, DACVIM*
Lisa M. Freeman, DVM, PhD, DACVN
Department of Clinical Sciences
Cummings School of Veterinary Medicine
North Grafton, MA 01536
*Current address: Department of Veterinary Clinical Sciences
College of Veterinary Medicine
The Ohio State University
Columbus, OH 43210
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