Care and Use of Feeding Tubes in Dogs and Cats
Feeding tubes are an accepted way of providing nutritional support for animals unable or unwilling to consume adequate calories on their own. This article provides information on the indications for the use of feeding tubes in small animals, the types of tubes available, and ways to initiate nutritional support once the tubes are in place. The pros and cons of the various tubes are discussed, as well as potential complications.
Introduction
Many people question whether feeding tubes have a place in general practice or whether their use should be confined to specialty clinics. Indications for the use of feeding tubes include older animals with no obvious physical problem other than an unwillingness to eat; trauma cases with fractures of the jaw; inappetence associated with advanced renal failure, diabetes mellitus, or inflammatory bowel disease; untreated pain; and fear or anxiety.1 These and many other situations that could benefit from the use of a feeding tube are routinely encountered in general practice.
The most common types of feeding tubes inserted in dogs and cats are nasoesophageal, esophageal, gastrostomy, and jejunostomy tubes. All of these, with the exception of the nasoesophageal tube, require some level of anesthesia for insertion. Jejunostomy tubes usually require surgical placement. Nasoesophageal and jejunostomy tubes are used only in hospitalized animals, while esophageal and gastrostomy tubes can be managed by owners at home after food has been reintroduced during the hospitalization period.
General Principles of Nutritional Support
Many hospitalized and critically ill animals are at risk for becoming severely malnourished, because they lack the appetite or the ability to eat.1,2 When instituting nutritional support, it is important to meet the animal’s nutritional requirements and to prevent further deterioration in its nutritional status, if possible. These nutritional goals can be met by providing protein, carbohydrates, fat, and other nutrients in a formula that is utilized by the body with maximum efficiency, minimal adverse effects, and minimal discomfort.3
When the body uses exogenous rather than endogenous nutrients, the breakdown of lean body mass is slowed, and the response to therapy of the underlying disease is optimized.4 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.5 Tumors and wounds may act as additional burdens by further increasing the animal’s caloric and nutritional requirements.3 When subjected to starvation, all body tissue (except the brain and bone) lose cell mass in varying degrees.3 Protein and energy malnutrition can result from diets that are inappropriate for the physiological status of the animal (e.g., low-protein diet is fed when increased protein levels are required, such as during gestation or lactation).2 Malnutrition from inappropriate diets can also impair immune function and wound healing, decrease organ function, and affect the prognosis for recovery.
It must be clarified as to what constitutes starvation. For a healthy animal, missing one or two meals does not equate to starvation, but anorexia of >3 days’ duration does indicate the need for intervention. In an ideal world, clients contact their primary veterinarian before the anorexia has progressed too long. If nutritional support is withheld until specialty or emergency attention is sought, the outcome may be significantly worse. The magnitude of metabolic aberration with prolonged anorexia is often determined by the severity of the illness or injury and any associated tissue damage.5 Even with initiation of adequate nutritional support, muscle wasting and negative nitrogen balance can occur.5 Unless there is a medical reason to withhold food, all efforts must be made to get the animal eating again.
General indications for the initiation of nutritional support include the loss or anticipated loss of >10% of body weight, anorexia of >3 days’ duration, trauma, surgery, severe systemic infiltrative disease, and increased nutritional loss through diarrhea, vomiting, or draining wounds or burns—especially those associated with decreased serum albumin.5 Other issues that must be taken into account when considering placement of a feeding tube include gastrointestinal tract function, whether the animal can tolerate tube or catheter feedings, the physical or chemical restraint required to place the tube or catheter, whether the animal is at risk for pulmonary aspiration (i.e., megaesophagus present), the availability of nursing care and equipment, and costs to the client.
Body Condition Scoring
The body condition scoring system used for healthy animals often does not apply to sick animals. When an animal is physiologically stressed, lean body mass (i.e., protein) is the body’s preferred energy source. In contrast, healthy animals use stored fat for energy. Stress or illness results in increased body protein catabolism.1 An animal may have increased amounts of body fat but still be at serious risk of malnutrition-associated complications caused by protein catabolism.2 Careful palpation of the skeletal muscles over bony prominences (e.g., scapulae, hips, vertebrae, occipital crest) can identify muscle wasting consistent with increased protein catabolism. Other indicators of poor nutritional status include subcutaneous edema and ascites, which may be associated with low plasma protein levels secondary to malnutrition or disease. Poor hair coat and dermatological disorders can also result from inadequate food intake or nutrient deficiencies (e.g., zinc deficiency).2
Caloric Calculations
Calorie requirements are determined by body weight and function of the animal (e.g., sedentary, hunting, active outdoor animal, etc.) and can be calculated using the resting energy requirement (RER) determined for healthy animals housed in environmentally controlled cages.3 For dogs, RER = 70 + (30 × body weight in kg). For cats, RER = 40 × body weight (kg). The dog formula may be used for both dogs and cats, because the cat formula tends to overestimate the caloric needs, and cats may become sick or gain excessive weight from oversupplementation. The application of illness factors to the RER equation is now thought to be a source of complications, may not improve clinical outcome, and is discouraged.6 Animals that eat more than the calculated RER amount, however, should not be discouraged from doing so while recovering from surgery or trauma. Water requirements are similar to those for energy (i.e., l mL water per l kilocalorie).7
Enteral Nutrition
Enteral (via the gut) feeding is the safest and most natural route for administering nutrients.8 Maintaining the intestinal mucosa may also help to prevent bacterial translocation from the gut to the rest of the body. Voluntary oral intake is the preferred route of enteral nutrition; however, animals must be able to consume at least 85% of their calculated RER for this method to be effective.3,7 If an animal is unable or unwilling to eat voluntarily, tube feeding should be considered. Tube feeding is somewhat limited, because only liquid or gruel diets can be administered through most tubes because of their small diameter. In addition, tubes can become clogged and must be flushed regularly with water.2
Because anesthesia is not required for placing a nasoesophageal tube, this is the easiest tube to insert. Only liquid diets can be administered through nasoesophageal tubes, however, and the tubes can easily become clogged. Flushing the tube frequently with water decreases the incidence of clogging but can also cause fluid overload in the stomach and dilution of the calories administered. If an animal is to be anesthetized for surgery, placement of an esophagostomy or gastrostomy tube should be considered. Both tubes have a larger diameter that can accommodate slurry or gruel diets, but they still may become clogged. Esophagostomy tubes may also stimulate vomiting, and some animals prematurely remove gastrostomy tubes. Gastrostomy tubes are usually placed via endoscopy, but blind insertion procedures have also been developed.2 Jejunostomy tubes require surgical placement, and only liquid diets can be used with these tubes.
Prior to each feeding through enteral tubes, tube location must be checked by gentle application of negative pressure (by aspiration) to the end of the feeding tube. The aspiration of nasogastric and gastrostomy tubes also allows the measurement of residual gastric contents, which indirectly assesses gastric motility. Esophagostomy tubes should contain no residual material if they are correctly located in the esophagus. Because the jejunum has a relatively small holding capacity, aspirating residual contents has little value. Radiography can also be used to verify tube location. Contrast agents are usually not required, as most tubes are radiopaque.
Parenteral Nutrition
Although enteral support is usually preferred over parenteral nutrition, certain exceptions exist, such as gut failure, impaired swallowing, or exacerbation of certain diseases (e.g., necrotic hemorrhagic pancreatitis) by enteral feeding. Partial parenteral nutrition (PPN) solutions are available for use in small animals and can be administered through peripheral catheters, mixed with fluid additives, and given concurrently with enteral feedings. Partial parenteral nutrition solutions contain only small amounts of calories, but they may be useful in preventing further catabolism by supplying readily available glycerol to the body as an energy source. They can be given at the same rate as regular, intravenous rehydration fluids. Partial parenteral nutrition solutions are helpful in animals that are consuming inadequate amounts of food. A PPN solution can be used concurrently with oral feeding to supply additional calories needed to meet the RER for that animal.9 These solutions are commercially available as premade mixtures, or they can be formulated by a compounding pharmacy.
Food Sources and Feeding Regimen
Animals with stress-related starvation may be glucose intolerant, so glucose is used less efficiently as an energy source.9 In these animals, fat and protein are important sources of energy.9 Before evaluating the need for fat, protein, and carbohydrates, however, a good dietary strategy addresses the animal’s requirements for water and corrects any preexisting fluid and acid-base deficits.9 After these needs have been satisfied, sufficient fat, protein, and carbohydrates are then provided to meet the animal’s energy requirements and minimize the gluconeogenesis (i.e., the breakdown of proteins to glucose for the purpose of providing energy).9
Commercial pet foods are specifically designed to meet dietary needs of dogs and cats, and they contain ingredients (e.g., taurine, carnitine, glutamine) not usually present in liquid or parenteral diets.9 The principle difference between human and animal liquid enteral diets is their protein content and the extent to which the ingredients are subjected to hydrolysis.9 For example, most human enteral diets contain 14% to 17% protein, which is insufficient for dogs and cats. In addition, arginine and methionine levels in human enteral diets tend to be too low, especially for cats.9 Recommended nutrient levels in critical care diets for dogs and cats are summarized in the Table. Pediatric or growth diets are often recommended for tube feeding, because they are highly digestible, have high levels of fat and protein, and are very palatable.8 Meat-based baby foods contain 30% to 70% protein and 20% to 60% fat. Because they are deficient in calcium, vitamin A, and thiamine, baby foods should not be used as the sole dietary source.5
Because providing nutritional support is not an emergency procedure, feedings are started slowly, in small amounts.8,9 In general, 50% of the daily RER is divided into multiple, small meals on the first day. If the feedings are well tolerated, then 100% of the RER is fed the next day. If the feedings are not well tolerated, the amount fed is increased more gradually over the next 2 to 3 days. Smaller meals tend to be tolerated better, because they do not cause distension of the stomach and subsequent delayed gastric emptying, nor do they aggravate nausea by stimulating the vomiting receptors in the stomach.2 If the animal shows discomfort, vomits, or becomes distressed, the diet as well as the route and rate of delivery need to be reassessed.
Multiple recovery diets are available in a gruel form that passes easily through most of the larger bore feeding tubes (=12 Fr). Adding as little as 1 to 2 tablespoons (15 to 30 mL) of water to each can of food can improve passage through the tube. If needed, gruel diets can also be prepared from solid forms of commercial diets. The disadvantage of these mixtures is the inability to know with certainty the caloric amounts in each mL of the final mixture (and the final volume to administer), because these foods tend to fall out of suspension after they’ve been mixed with water.
Typically, tube feedings are started within 12 hours of tube placement. With gastric tubes, a stoma around the tube insertion site must start forming prior to feeding. A complete feeding plan is created for each animal, and written directions are given to the owner.2 While force feeding can be used to provide the necessary nutrients, it is usually too stressful to the animal and is seldom recommended or used.
A refeeding syndrome, which is an electrolyte disturbance that occurs in animals with depleted intracellular cations (e.g., potassium, phosphorus, magnesium), may arise after severe malnutrition or starvation, prolonged anorexia (e.g., hepatic lipidosis), or diuresis (e.g., uncontrolled diabetes mellitus, acute renal failure).2 Animals at the greatest risk for refeeding syndrome are the severely malnourished, with significant loss of lean body mass.2 In this syndrome, resumption of feeding results in a rapid shift of cations from the plasma (where levels were normal before feeding) into the intracellular space.2 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 initiating feeding early in the disease course, monitoring the animal closely, introducing food cautiously (continuous-rate infusion of a commercial gruel diet may be helpful), monitoring electrolytes frequently, and supplementing the diet as needed.3
Choice of Feeding Tubes
The best feeding tubes for prolonged use are made of polyurethane or silicone. For short-term feeding (<10 days), polyvinylchloride or red rubber tubes can be used. These latter tubes are not appropriate for long-term feeding, because they tend to become stiff with prolonged use and may cause the animal discomfort. Silicone is softer and more flexible than other tubing materials and has a greater tendency to stretch and collapse. Polyurethane is stronger than silicone, which allows for thinner tube walls and a greater internal diameter, despite the same overall Fr size. Both silicone and polyurethane tubes do not disintegrate or become brittle in situ. The Fr unit measures the outer lumen diameter of a tube, and each Fr unit is equal to 0.33 mm.2
Nasoesophageal/Nasogastric Tubes
Nasoesophageal tubes can be inserted using minimal equipment and standard techniques. Nasogastric tubes are inserted in a similar fashion as nasoesophageal tubes, but they should be long enough to reach 3 to 4 inches past the last rib. Both types of tubes are useful for providing short-term nutritional support (usually <10 days). They can be used in animals with a functional esophagus, stomach, and intestines. Nasoesophageal tubes are contraindicated in animals that are vomiting, comatose, lack a gag reflex, or have respiratory diseases.10–13 Complications include epistaxis, intolerance of the insertion procedure, and inadvertent removal by the animal. Nasogastric tubes increase the risk of gastroesophageal reflux and thus may increase the incidence of esophageal strictures.2
Because of the small internal diameter of these tubes, only liquid enteral diets can be used with them. Feedings may be delivered via a syringe pump as a continuous-rate infusion or as bolus feedings. If a syringe pump is used, the delivery equipment must be completely changed every 24 hours to help prevent bacterial growth within the system. Clogging of these tubes is a common problem and can be decreased by using a syringe pump or flushing the tube well before and after bolus feedings. If the tube becomes clogged, replacement may be necessary. Diluting the liquid diet with water may also help prevent clogging, but this decreases the caloric concentration of the diet and increases the volume necessary to meet caloric needs. When removing the tubes, they are simply pulled out after the skin adhesive or sutures are removed.2
Esophagostomy Tubes
Esophagostomy tube placement requires general anesthesia, with the animal intubated and in lateral recumbency.12 Complications include tube displacement from vomiting, removal or damage to the tube by the animal, and skin infection around the exit site.2 Depending on the insertion technique used and the size of the animal, an 8 to 20 Fr catheter may be used. The large bore of these catheters allows the feeding of a gruel recovery diet, sometimes without dilution with water. These catheters are also easy for owners to use and maintain, as long as vomiting is not a problem. The tube may simply be pulled out after the sutures are removed. The exit hole is allowed to heal by second intention. A light bandage may be applied over the exit site for the first 12 hours.2
Gastrostomy Tubes
Gastrostomy tubes can be inserted blindly using specialized equipment, placed with the aid of a gastroscope (i.e., percutaneous endoscopic gastrostomy [PEG] tube), or be surgically inserted.12 These tubes can be placed in any animal that can withstand general anesthesia. Anesthesia time is usually 15 to 20 minutes. Animals need not reach a surgical plane of anesthesia but must be anesthetized deeply enough that they lose jaw tone. Esophageal strictures may preclude endoscopic placement of a feeding tube, but surgical placement can often be accomplished. If the animal is not totally anorexic and not metabolically compromised (e.g., electrolyte disturbances, low phosphorus, low hematocrit), the tube can be inserted and the animal can be discharged from the hospital within 1 to 2 days.2,11
A minimum of 12 hours is needed for a temporary stoma to form before feeding can begin, and the feeding tube should be left in place a minimum of 7 to 10 days to allow a permanent stoma to form before removal. These tubes can be left in long term (1 to 6 months), often without replacement. Complications associated with PEG tubes include those that arise acutely during tube placement (e.g., splenic laceration, gastric hemorrhage, pneumoperitoneum) and those that are delayed (e.g., vomiting, aspiration pneumonia, tube removal, tube migration, peritonitis, and infection around the stoma).2,11
Most animals are able to eat normally with gastrostomy tubes in place, and the tubes can easily be used as a source of additional nutritional supplementation until the animal is eating normally. For animals that are difficult to medicate or require long-term medications, many medicines can be given through the feeding tube. The major disadvantages of gastrostomy tubes are the need for general anesthesia during insertion and the risk of peritonitis from inadvertent removal before a permanent stoma develops.13
For animals requiring feeding tubes over a long duration, the initial Pezzer catheter can be replaced with either a low-profile silicone tube or a Foley-type gastrostomy tube. Both of these replacement tubes can be inserted through the external stoma site without an endoscope. Sedation or anesthesia may be necessary based on the individual animal. A rubber catheter has a useful life of 12 to 16 weeks, which is adequate for most cats with hepatic lipidosis and for postoperative feedings in dogs. This duration may not provide enough time, however, for nutritional support of a cat following renal transplantation or an animal with renal failure. Silicone catheters have a useful life of >1 year, depending on maintenance and care.
If the tube has been in place =16 weeks, it may simply be removed manually. This is best accomplished by placing the animal in right lateral recumbency. The tube is grasped with the right hand close to the body wall and the left hand holding the animal. The tube should be pulled firmly and consistently to the right, in an upward motion, with some force.2 It is also helpful to fast the animal prior to tube removal and to place a towel over the stoma site to catch any residual material that leaks out as the tube is removed. If the tube has been in >16 weeks, the incidence of tube breakage is much higher.12 Depending on where the breakage occurs, the remaining portion of the tube may need to be retrieved endoscopically. Larger animals can easily pass retained parts, but smaller animals often need to have them retrieved. The exit hole is allowed to heal by second intention. A light bandage may be applied for the first 12 hours after removal.2,11
Jejunostomy Tubes
Jejunostomy tube feeding is indicated when the upper gastrointestinal tract must be rested or when decreased pancreatic stimulation is desirable. Jejunal tubes can be placed either surgically or threaded through a gastrostomy tube (transpyloric placement).12 Standard gastrojejunal tubes designed for humans are unreliable in dogs because of the frequent reflux of the jejunal portion of the tube back into the stomach. Investigation is ongoing involving endoscopic placement of transpyloric jejunal tubes through PEG tubes.
Common complications of jejunostomy tubes include osmotic diarrhea and vomiting. It is recommended that the jejunal tube be left in place for 7 to 10 days to allow adhesions to form around the tube site, preventing leakage into the abdomen.10,13 Completely changing the delivery equipment every 24 hours helps to prevent bacterial growth within the system. Clogging is a common problem. Use of a syringe or intravenous pump and flushing the tube well every 4 hours may help to decrease the incidence of clogging. When removing the tube, it may simply be pulled out after the sutures are removed. The exit hole is allowed to heal by second intention. A light bandage may be applied for the first 12 hours after removal.2
Home Care
Client Education
Because many owners are unfamiliar with the use of syringes and the procedure for administering food through these tubes, it is often necessary to spend a significant amount of time with them when the animal is being discharged from the hospital. Detailed instructions should be given on tube maintenance, technique of administration, amounts to be fed, etc. It is helpful to supply the owners with well-written, concise instructions and to help them establish reasonable expectations. Owners are usually happy with the results when they are properly instructed on the use of a feeding tube and they see how much better the animal feels. Although feeding tubes require routine daily care (e.g., cleaning around the tube site, flushing with water), not all tubes must be used every day to feed the pet.
Dietary Transition
Although dietary transition may occur while the animal is hospitalized, it typically occurs 2 to 6 weeks after discharge from the hospital. Timing of the transition depends on the diet being fed, the condition of the animal and its response to therapy, as well as the comfort level of the owner. As with initiation of tube feedings, the transition away from tube-assisted feeding should proceed slowly. For example, when converting from a supportive or supplemental diet to a maintenance diet, the amount given orally is increased every 3 to 4 days by a 50% equivalent of the supplemental diet, so the transition phase occurs over 12 to 16 days. If a problem develops at any time during the transition, the owner should revert back to administering the last diet combination (i.e., amount, frequency) that was well tolerated.
Conclusion
The use of feeding tubes can improve the longevity of seriously ill animals and provide them with a better quality of life. Being aware of the nutritional aspects of animal care can also improve the long-term outcome of many disease conditions. Nutritional support and the use of feeding tubes should be recognized as important components of therapy for many critically ill animals.
