Rebecca L. Remillard,
Diplomate, American College of Veterinary Nutritionists
P.Jane Armstrong, DVM, MS
Diplomate, American College of Veterinary Internal Medicine
Deborah J. Davenport, DVM, MS
Diplomate, American College of Veterinary Internal Medicine
Enteral-assisted feeding is providing nutrients to the patient using some portion of the GI tract. Cats that cannot or will not eat but that can digest and absorb nutrients from the small intestine should receive enteral-assisted feeding. Feeding via the GI tract can be the simplest, fastest, easiest, safest, least expensive and most physiologic method of feeding cats.
Methods of Enteral Delivery
There are several methods of enteral feeding, but the first attempt usually should be oral feeding. Placing a bolus of food in the proximal portion of the mouth may stimulate the swallowing reflex and, if the cat offers no resistance, is a plausible method as long as the cat receives enough food to meet its RER. Syringe feeding a liquid product is also possible. For cats, the syringe tip is placed between the four canine teeth. The cat may choose to swallow the liquid or allow it to flow out of the mouth by gravity. Some cats refuse to swallow boluses of food; therefore, forced feeding may increase the risk of food aspiration. Oral feeding should be discontinued if the cat does not swallow food voluntarily. Appetite stimulants may be used to induce food consumption in some cats; however, voluntary food intake rarely continues and the animals RER is often not met.
Orogastric tubes require placement at each feeding but may provide a useful option for one or two days of feeding. Neonates appear to tolerate multiple daily oral tube feedings better than adults. A red rubber or polyvinyl chloride tube (8 to 24 Fr.), may be used with the tip placed in the caudal esophagus or stomach. An indwelling feeding tube is the method of choice if enteral-assisted feeding is necessary for more than two days.
After an indwelling feeding tube has been placed, feeding is easier and less stressful on the cat than forced feeding or placing an orogastric tube. Nasoesophageal, pharyngostomy, esophagostomy gastrostomy or enterostomy are potential placement sites. Tubes should be placed in the most proximal functioning portion of the GI tract possible via the least invasive method, and whenever possible, the stomach should be used.
Nasoesophageal tubes are generally used for three to seven days, but are occasionally used longer (weeks). Polyurethane tubes (6 to 8 Fr., 90 to 100 cm) with or without a tungsten-weighted tip and silicone feeding tubes (3.5 to 10 Fr., 20 to 105 cm) may be placed in the caudal esophagus or stomach. The preferred placement of all tubes originating cranial to the stomach is in the caudal esophagus to minimize gastric reflux and subsequent esophagitis. An 8-Fr. tube will pass through the nasal cavity of most dogs. A 5-Fr. tube is more comfortable in cats. Either orogastric or nasoesophageal feedings may be used in anorectic patients that do not have nasal, oral or pharyngeal disease or trauma. Anesthesia or tranquilization is not necessary to place an orogastric or nasoesophageal tube. Therefore, these tubes provide enteral access to patients considered anesthetic risks. These tubes are most often used in the hospital, although nasoesophageal tubes can be used at home by conscientious owners.
Pharyngostomy or esophagostomy tubes (8 to 16 Fr.) may be placed in patients with disease or trauma to the nasal or oral cavity. The tip of the tube is placed in the caudal esophagus and the tube can be used for long-term (weeks to months) inhospital or home feedings.
For patients in which the pharynx and esophagus must be bypassed, gastrostomy tubes (mushroom-tipped, 16 to 22 Fr.) can be placed either in tra operatively or percutaneously using an endoscope or a gastrostomy tube introduction device. Gastrostomy tubes are also recommended for long-term feeding (weeks to months) if needed, and have generally replaced pharyngostomy tubes, even when the esophagus is normal. Gastrostomy tubes are convenient and safe for in-hospital and at-home feedings. See Feeding Tube section for descriptions of tube placement.
Any tube that has been placed into the esophagus or stomach allows bolus or meal-type feeding schedules because the stomach acts as a food reservoir. The ex tion to this rule is the patient that cannot tolerate bolus feeding to the stomach without vomiting, Such patients benefit from a slow, continuous drip administration (by pump or gravity) of food to the stomach. Most veterinary patients receive bolus feedings of enteral nutritional support via nasoesophageal or gastrostomy feeding tubes.
Jejunostomy tubes (J-tubes, 5 to 8 Fr.) are placed within the small intestine, ideally at the time of exploratory celiotomy, to bypass the proximal GI tract." Jejunostomy tubes may also be placed by mini-laporatomy. Another method of jejunostomy tube placement is to thread a small feeding tube through a larger esophagostomy, pharyngestomy or gastrostomy feeding tube and place the tip of the smaller tube in the jejunum. A feeding tube with a tungsten-weighted tip may be threaded through the pylorus into the jejunum using an endoscope or during a surgical procedure with the cranial end exiting through a larger tube in the stomach, pharynx or esophagus."' There is risk, however, that even a weighted-tip tube will be returned to the stomach by reverse peristalsis! Ideally, food should be administered through jejunostomy tubes at a slow, continuous drip delivered by a pump. Some patients, however, will tolerate frequent small-bolus feedings. See section for descriptions of tube placement.
Selecting an Enteral Food
Food selection depends on tube size and location within the GI tract, the availability and cost of products and the experience of the clinician. Commercial foods available for enteral use in veterinary patients can be divided into two major types: 1) liquid or modular products and 2) blended pet foods. Nasal and jejunostomy tubes usually have a small diameter (<8 Fr.), which requires use of liquid foods. Orogastric, pharyngostomy esophagostomy and gastrostomy tubes have large diameters (>8 Fr.) and are suitable for blended pet foods. Table lists commercial foods available for enteral use. These foods may be used when patients are able to eat sufficiently on their own; alternatively, the patient may be fed the food it was accustomed to eating before the injury or illness. The latter approach reduces the number of food changes that ultimately will need to be made.
LIQUID FOODS AND MODULES
In general, human liquid foods cost more than veterinary liquid products. Most human liquid foods are adequate for adult dogs but are too low in protein for cats, puppies and adult dogs with increased protein losses (e.g., protein-losing enteropathies, drains). Human liquid enteral products may not contain adequate concentrations of protein, taurine, arginine and arachidomc acid for longterm feeding of cats, but are satisfactory for fewer than seven days.
Liquid foods are of two basic types: 1) elemental or monomeric and 2) polymeric. Foods said to be "elernental" are not truly elemental, but contain nutrients in small hydrolyzed absorbable forms and are best described as monomeric. The proteins are usually present as free amino acids, small dipeptides or tripeptides or larger hydrolyzed protein fractions. The fat source is often an oil of mixed (medium- and long-chain) fatty acids and the carbohydrate sources are mono-, di- and trisaccharides. There are several liquid foods on the human medical market that are positioned as monomeric or hydrolyzed diets and arc suitable when initially refeeding dogs and cats. These monomeric products are homogenized liquids that can be fed through any feeding tube including a J-tube. Monomeric foods are indicated in disease conditions such as inflammatory bowel disease, lymphangiectasia, refeeding parvoviral enteritis and pancreatitis cases and any other condition in which a patient's digestive capabilities are questionable.
Polymeric products contain mixtures of more complex nutrients. Protein is supplied in the form of large peptides (e.g., casein or whey). Carbohydrates are usually supplied as corn starch or syrup, and fats are provided by mediumchain triglycerides (MCT) or vegetable oil. These foods require normal digestive processes and are appropriate for most veterinary clinical situations, especially when a small tube (<8 Fr.) has been placed and particular nutrient profifes are needed (e.g., low sodium, high protein, soluble fiber).
One of the leading liquid veterinary foods is a polymeric form that meets the current AAFCO nutrient allowances for adult dogs and cats. This product is a homogenized liquid containing I kcal/ml (4.2 kj/ml) and is usually accepted better than human liquid products containing MCT oil. This liquid food is the best option currently available in North America when small-diameter nasogastric and jejunostomy feeding tubes have been placed, or when continuous drip feedings are necessary. Historically, these polymeric foods have caused diarrhea in cats after 24 hours of feeding. However, the manufacturer recently reformulated the product to reduce the incidence of diarrhea. The number of osmotically active particles was decreased by replacing a small-chain maltodextrin source with a larger-chain maltodextrin, and the casemate source no longer contains lactose, thereby eliminating a lactase degradation process.
Several liquid milk replacer products are available; however, these products are not appropriate to feed to adult dogs and cats. They typically contain lactose, have high osmolarity, are lower in caloric density and do not meet AAFCO nutrient allowances for adult animals.
Module products are concentrated powdered or liquid forms of nutrients and are primarily supplemental. These products may be added to a liquid product to increase the concentration of a specific nutrient. There are protein, fat and carbohydrate modules (e.g., cascien powder, vegetable oil or corn syrup). For example, a protein modular product may be added to a human liquid product for an animal with high protein requirements. Soluble fiber can be added to these foods using psyllium husk fiber or pectin; however, these fibers may block the small side ports in 8-Fr. and smaller tubes.
BLENDED PET FOODS
Blended pet foods refer to commercial products nutritionally complete and balanced according to AAFCO allowances for dogs and cats. These products can easily be blended with a liquid to make a consistency that flows through a feeding tube. Some products have a blended texture, a high water content and very small particle size, whereas others are products that must be blenderized with water and may have to be strained to remove particulate matter.
The best recommendation when using the blended pet food method is to use a product that has been tested in feeding trials and is proven to be balanced and complete for dogs or cats. These products are more readily available, better tolerated and less expensive than the human liquid foods. These pet food products contain essential amino acids and essential micronutrients properly balanced to the caloric density of the food. Fewer medical complications (e.g., diarrhea) are likely to result. However, blended products are more likely to plug the feeding tube if the tube is not properly flushed after feeding. Patients may later consume the pet food orally, eliminating a diet change when the patient's appetite returns and the tube has been removed. These products are appropriate for patients in catabolic states that are using fat and protein substrates from body stores. When using small-diameter (<8 Fr.) feeding tubes, it will be necessary to dilute the pet food with water, which dilutes the caloric density. Blenderized moist veterinary therapeutic foods may have a place in assisted feeding of patients with specific disease conditions.
HUMAN BABY FOODS
Veterinarians have fed human baby foods packed in jars because some canine and feline patients voluntarily cat these products. in general, the meat and/or egg baby foods are high in protein (30 to 70% DM) and fat (20 to 60% DM), which compares favorably with blended pet food products. However, baby foods are more costly, contain only one or two food types (protein, protein/grain) and do not contain a balanced mixture of other essential nutrients (amino acids, vitamins and minerals). For example, these products contain only 10% of the calcium required by dogs and cats, and therefore have a large inverse calcium-phosphorus ratio. Some products contain onion powder, which has resulted in Heinz body formation in cats."' These products will flow through 8Fr. or larger feeding tubes and may be used on a very limited, short-term basis when an appropriate pet food is unavailable. The human and veterinary liquid products have a better nutritional profile than do the human baby food products.
Enteral Feeding Schedule
The feeding schedule is often determined by the patient's ability to tolerate food and the logistics of feeding. Feeding an amount equal to the patients RER during the first 24 hours of food re-introduction, if physically tolerated, is recommended. initially feeding one-third of the RER and then increasing the amount by one-third every 24 hours is a more cautious approach to initial feeding but isn't always necessary. Foods should be warmed to room temperature, but not higher than body temperature e before feeding.
Food boluses must be infused slowly (over approximately one minute per bolus) to allow gastric expansion. Daily food dosage should be divided into several meals according to the expected stomach capacity. Capacities for cats and dogs are 5 to 10 ml/kg body weight during initial food reintroduction. Maximum capacities as high as 45 to 90 ml/kg body weight have been measured in cats and dogs when fully re-alimented. Most often, meeting the patient's RER can be done in volumes far less than these maximums. Salivating, gulping, retching and even vomiting may occur when too much food has been infused or when the infusion rate is too fast.
Research in people has demonstrated that the stomach does not "shrink" during a prolonged fast, but rather the stretch receptors are more sensitive and stimulated by a smaller volume when refeeding occurs."' Feeding should be stopped at the first sign of retching or salivating, the meal size reduced by 50% for 24 hours and then increased by 25% gradually. Foods provided via J-tubes must be infused slowly and often in either very small quantities or by a slow gravity drip or enteral pump with an hourly rate equal to RER/24 hours because the jejunum is volume sensitive.
Each meal must be followed by a water flush to clear the feeding tube of food residue. When the patient is volume sensitive, it is important to know the minimum volume required to flush the tube. The patient's daily fluid requirement must also be met and additional tap water may be administered through the feeding tube to meet that requirement. Liquid oral medications may also be administered easily through feeding tubes. Plugged feeding tubes can be cleared by filling the tube with water or a nonalcoholic carbonated beverage and allowing time for the food plug to dissolve. In general, endport tubes are easier to maintain than sideport tubes because food tends to become trapped in the blind end of sideport tubes. All tubes except orogastric and nasoesophageal tubes require standard every-other-day bandage care.
Commercial products used for enteral feeding of veterinary patients.*
|Commercial Veterinary Products||Form||
Abbott CliniCare Canine
Abbott CliniCare Feline
|Abbott CliniCare Feline RF||L||1||5.6||57||21||6.41||350||
|Hill's Prescription Diet Canine/Feline a/d||MH||1.3||8.8||53||12||2.2:1||372||
|Iams Eukanuba Maximum Calorie
Canine & Feline
Purina CNM CV-Formula
|Select Care Canine Development Formula||M||0.9||8||30||42||10.3:1||na||
|Select Care Feline Development Formula||M||1||10.4||54||10||5.3:1||na||na|
|Waltham/Pedigree Concentration Diet/Canine||M||1.4||11.4||48||23||na||na||na|
|Waltharn/Whiskas Concentration Diet/Feline||M||1.2||11||64||3||na||na||na|
|Waltham/Pedigree Concentration Instant Diet/Canine||L||1.5||14.3||37||25||na||na||5/8**|
|Waltham/Whiskas Concentration Instant Diet/Feline||L||1.3||11||48||15||na||na||5/8**|
|Key: L = liquid, M = moist, MH = moist homogenized, FA =
fatty acid, CHO = soluble carbohydrate, na = information not available or not applicable.
*These products meet or exceed AAFCO nutrient profiles for intended species.
**5/8 French is the smallest tube size using a feeding pump/catheter-tip syringe and comfortable pressure.
***18 French is the smallest tube size using a catheter-tip syringe and comfortable pressure.
|Adapted from Assisted Feeding in Hospitalized Patients: Enterial and Parenteral Nutrition. Remmilard RL, Armstrong PJ, Davenport DJ|
PEG Tube Placement
Feeding Tube Maintenance
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