Enteral Nutrition

5. Enteral Nutrition

Enteral nutrition should be the first choice for nutritional management unless the patient's condition can not support enteral feedings. The mantra "If the gut works, use it" was derived because enteral feeding is considered more physiologically sound than intravenous feeding. Enteral feeding maintains the health of the gastrointestinal tract, and prevents bacterial translocation. A recent randomized controlled clinical trial investigated the effect of early enteral nutrition in dogs with parvo-viral enteritis, compared to nil per os (Mohr et al., 2003).

Enteral nutrition was associated with a shorter time to recovery, increased body weight gain, and improved gut barrier function. This study suggests that early enteral feeding is associated with more rapid clinical improvement. Enteral feeding can be achieved via nasoesophageal, esophagostomy, gastrostomy or jejunostomy devices.

Different Types of Tubes for Enteral Nutrition

The appetite of the hospitalized patient typically waxes and wanes. Hence the meal is offered orally, and if not consumed, is blended and administered via a tube.

Nasoesophageal Tubes

This type of tube is an excellent option for short-term feeding (<7 days) of hospitalized patients. Nasoesophageal tubes do not require specialized equipment and are not expensive. Generally tubes between 3 - 8F are selected. For a dog, the optimal length of the nasoesophageal tube is equal to the distance from the tip of the nose to the seventh rib.

Most critically ill patients will tolerate nasoesophageal tube placement, but some individuals may require sedation. (© SIAMU, École Nationale Vétérinaire de Lyon).

Contraindications include patients that have had severe facial trauma involving the nares, protracted vomiting and/or regurgitation, semiconsciousness, or those patients that have laryngeal, pharyngeal, or esophageal physical or functional abnormalities.

However, the small diameter of the tube can be inconvenient and mandates only liquid feedings. Nasoesophageal tubes may also increase the risk of aspiration pneumonia if the tube is either inadvertently placed in the trachea, or the pet regurgitates the tube and it is inhaled into the trachea. To minimize this complication, the placement of the nasoesophageal tube should always be ascertained prior to feeding.

Esophagostomy Tubes

Esophagostomy tubes are indicated for patients requiring medium term nutritional support. Esophagostomy tubes are generally well tolerated and can easily be placed under a light anesthetic with minimal equipment. The only major associated complication is the potential for infection at the entry site and meticulous care of the surgical wound is essential to maintain the tube. Indications include patients with mandibular, maxillary, nasal and nasopharyngeal disease or an inability to prehend or masticate.

There are three ways of placing an esophagostomy tube:
- Via a percutaneous needle technique
- Via surgical cut-down
- By utilizing the Eld percutaneous feeding tube applicator.

The patient is lightly anesthetized, placed in right lateral recumbency, and an aseptic preparation of the left cervical region is performed. A 5 - 12 Fr red rubber, plastic or silicone feeding tube can be placed.

The tip of the esophagostomy tube should be placed in the mid-esophagus. The exterior portion of the tube is secured to the neck via butterfly or Chinese finger trap suture.

Feeding through the tube can commence once the patient has recovered from anesthesia. The food must be presented in the form of liquid slurry: it may be a dry or canned food mixed with water or a ready to use solution. The wound will heal via granulation tissue within two weeks of tube removal.

Gastrostomy Tubes

Gastrostomy tubes are available in several sizes; 18 - 20 Fr are appropriate for small dogs, and 24 Fr are adequate for larger dogs. Tubes are constructed of latex or silicone. Various designs are available (Figure 3).

An array of feeding adapters can be attached to the feeding tube; a Y-port device is preferred as it has two ports:

- A catheter port for administration of food when the tube has been in place for at least 24 hours

- A Luer tip syringe port used for oral medication.

Figure 3. Different types of gastrostomy tubes. Gastrostomy tubes are available in several sizes and designs and are constructed of latex or silicone. The most common initial placement design is a latex Pezzar-type mushroom catheter. Silicone tubes typically survive 6 - 12 months and are less irritating at the stoma site. (© DA Elliott).

More recently low-profile gastrostomy devices (LPGD's) have been developed and are available in North America for both initial and replacement procedures. These devices are positioned flush with the body wall (Figure 4). LPGD's are constructed of silicone and appear to cause less stoma site inflammation. A feeding adapter is attached to the end of the device during the feeding procedure.

Figure 4. Illustration of a low profile gastrostomy tube after placement. Client and patient acceptance is much higher than with traditional tubes as the patient appears "normal" without a long tube attached to the body or the need for a stockinette cover. In addition, the mushroom tip has an anti-flux valve design to prevent reflux of gastric contents. LPGD's are expensive but have been documented to last at least 12 months. (© DA Elliott).

Silicone tubes typically survive 6 - 12 months and are less irritating at the stoma site (Figure 5).

Figure 5. Illustration of a dog with a traditional gastrostomy tube after placement. Latex tubes are less expensive but generally require replacement within 8 - 12 weeks due to tube wear and tear. (© JY. Deschamps).

Jejunostomy Tubes

Jejunostomy tube feeding is justified only when the stomach or the duodenum must be by-passed. The tube is typically placed via laparotomy and enteropexy. The food used must be liquid and elemental as tubes are typically 5 - 8 Fr in diameter and inserted directly into the jejunum.

Enteral Tube Feeding: Practical Aspects

An endoscope should be used to verify that the gastrostomy tube is in the correct position. (© DA Elliott).

Water is introduced through the feeding tube 12 - 18 hours following initial placement (except for feeding via the esophagus when no delay is necessary), and feeding is scheduled to begin within 24 - 36 hrs. Generally 1/2 to 1/3 of the daily caloric intake (typically RER) is administered on the first day.

*RER = 70 x (body weight in kg)0.75 = kilocalories/day

If no complications occur, the amount fed is gradually increased to reach total caloric requirements by the third or fourth day, or the seventh day in case of prolonged starvation.

The total volume of food is divided into 4 - 6 equal sized meals which should not exceed the gastric capacity of the patient (initially 5 mL/kg to up to 15 mL/kg per feeding). The food should be warmed to room temperature and administered slowly, over 5 - 15 mins (Figure 6). Upon completion, the tube should be flushed with 5 - 10 mL of tepid water.

Figure 6. Enteral feeding. The diet is blended with the least amount of water required to achieve syringability. If the food is administered as a slurry, the tip of the syringe must be sufficiently wide to prevent obstruction. (© JY. Deschamps).

Research shows no beneficial effect from continuous intragastric feeding over intermittent enteral feeding with regard to weight gain and nitrogen balance in healthy dogs (Chandler et al., 1996). However, in animals that are volume intolerant, continuous administration of nutrients is better tolerated.

Frequent small meals are generally better tolerated than larger less frequent meals. If the owner feels able to continue frequent feedings when the dog is discharged from the hospital then such a regimen should be continued. However, if frequency will need to be reduced, it is important that the dog is adapted to the larger less frequent meals that the owner will employ at home prior to discharge. With time and adaptation to the feeding procedure, the meal frequency may be reduced to a convenient BID to TID daily schedule.

Prior to every meal, the gastric residuals should be aspirated with a syringe. If more than 50% of the prior feeding is present, the contents should be returned to the stomach and the feeding skipped until the next scheduled time. Frequent aspiration of the previous meal may suggest delayed gastric emptying and warrant medical management (e.g., metoclopramide 20 - 30 minutes prior to feeding).

Most oral medications should be administered prior to feeding, with the exception of phosphate binders that must be mixed directly with the food.

The position of the tube on the body wall should be examined daily for migration and the stoma site inspected for pain, redness, odor and discharge (Figure 7). The site should be cleaned daily with an antiseptic solution and antimicrobial ointment applied. Food residue should not be left near the stoma.

Figure 7. Migration of the gastrostomy tube in the subcutaneous tissue. This situation is a surgical emergency as it may result in septic peritonitis. (© DA Elliott).

Nutritional Support

Water

Water is one of the four basic macronutrients, and, in a state of deficiency, will cause the most immediate detrimental effects. Therefore, nutritional support in its most minimal form is provided to most hospitalized patients in the form of ad libitum water and/or parenterally administered fluids. Unfortunately, there is a tendency to only administer the minimum and provide no further support. Fluid therapy should be viewed as a component of nutritional support and not as complete nutritional support.

Energy Density of the Diet

Most veterinary clinical nutritionists believe that the energy requirement of most hospitalized patients is close to a patient's resting energy requirement (RER), calculated using the above equation (Remillard et al., 2001).

Although this equation does not always meet the patient's precise needs, it serves as a starting point that should minimize the likelihood of overfeeding or underfeeding the patient. It is the authors' experience that, for most dogs, using RER results in weight stability and maintenance of the patient's BCS during several weeks of hospitalization.

To keep the volume of any single bolus at a minimum, the energy density of the diet must be maximized. To achieve this, the volume and type of liquid used to lower the viscosity of a canned food must be carefully selected. The importance of finding a balance between slurry energy density and viscosity cannot be overemphasized. Even small increases in the kilocalories per unit volume can often have a large impact on the frequency and the volume of enteral feedings. This, in turn, can significantly affect the success of the feeding program and the ability to meet the animal's energy requirements.

Oil provides the maximum amount of energy, but also the greatest dilutional effect on nutrients. Thus, essential nutrients can be significantly decreased inadvertently. Using water does not change the ratio of nutrients to kilocalories, but does decrease the amount of kilocalories per unit volume. Alternatively corn or maple syrup can be used in dogs to increase the energy density of a slurry while still decreasing the diet's viscosity. In most cases, water can effectively be used to create slurries that can then be fed through a 12 Fr or larger feeding tube. As a general guide, increasing the canned diet to a moisture level of 80% typically creates a slurry once blenderized that is both relatively energy dense (diet dependent) and easily administered (Figure 8).

Figure 8. Algorithm to assist the selection of the enteral tube feeding diet.

Balance of Energy Sources

The basic macronutrients that provide energy are protein, fat and carbohydrate. When the patient's resting energy requirement is not met with the administration of a single energy-providing macronutrient, there is debate as to how the macronutrient is utilized. Some believe that all macronutrients are used solely for energy until the patient's energy requirements are met. Others advocate that some substrates may have a limited, protein-sparing effect even when the patient's caloric requirements are not being achieved.

Fats

High fat diets, as a rule, are usually well accepted and tolerated. Fat provides at least twice as many calories per unit of volume, thereby enabling an increased caloric consumption in patients with limited food intake. Although fat can increase the palatability and the initial acceptance of a diet, it is the authors' experience that sudden increases in dietary fat appear to be one of the most consistent and least recognized causes of gastrointestinal distress, especially pancreatitis.

Many highly digestible commercial foods are not fat-restricted and often provide up to 30% of the calories from fat. The use of these diets should be limited to patients in which there is no concern of fat intolerance.

When initially refeeding a hospitalized patient, such foods as cottage cheese or skinless chicken combined with rice are often recommended. These foods are palatable, highly digestible and are excellent alternatives to high-fat commercial foods.

Amino Acids

Enterally administered amino acids such as glutamine have been suggested to have a protein-sparing effect. There is one study that supports the potential benefit of enterally administered glutamine based on whole-body leucine kinetics (Humbert et al., 2002).

Unfortunately, there is no clinical evidence that a patient will tolerate an enterally administered amino acid solution in amounts to meet their energy needs, when they will not tolerate a complete diet. However, a constant rate infusion of an enteral product below the patient's RER, with the concurrent administration of the remaining caloric requirement parenterally may be of value in reducing the occurrence of villous atrophy and bacterial translocation (Qin et al., 2002; Kotani et al., 1999).

Complications Linked to Enteral Feeding

For critically ill dogs, the majority of the monitoring is focused on avoiding complications associated with nutritional support.

Surgical Complications

Splenic laceration, gastric hemorrhage, pneumoperitoneum, displacement into the peritoneal cavity and peritonitis have been reported as infrequent placement complications.

Patient tolerance of the feeding tube should be closely observed. This can manifest as sneezing, cellulitus at the stoma, gagging, and/or vomiting, depending upon the type of tube. The major associated complication is the potential for infection at the entry site.

Meticulous care of the surgical wound is essential to maintain the tube. Abnormalities at the stoma site including discharge, pain, swelling, erythema, abscess formation and ulceration which can be minimized by strict attention to cleaning and prohibiting the patient from licking the site. Warm packs containing antiseptic solution placed on the stoma site will minimize problems or hasten recovery.

Inappropriate patient removal of the tube is undoubtedly the most problematic complication. In one review approximately 20% of dogs removed their gastrostomy tubes which emphasizes the importance of restraining the gastrostomy tube in a stockinette and utilizing e-collars (Figure 9) (Elliott et al., 2000).

Figure 9. Fixation of the tube. A traditional gastrostomy tube must be protected from the risk of displacement by the dog. This can be achieved by securing the gastrostomy tube to the body wall, placing a stockinette over the abdomen, and using an Elizabethan collar. (© DA Elliott).

Patient removal of the gastrostomy tube is an emergency. In most situations a new tube can be placed through the existing stoma site using a guide catheter. Appropriate replacement should be verified radiographically following injection of an iodinated contrast agent. If the tube has been in place for less than seven days, or there is evidence of peritonitis or radiographic contrast agent leakage, an exploratory laparotomy is required to correct the situation. The use of LPGD's may reduce the incidence of inadvertent gastrostomy tube removal.

Obstruction of the Tube

Periodically tubes will become blocked with food. Techniques to facilitate removal of the obstruction include massaging the outside of the tube while simultaneously flushing and aspirating with water; instilling carbonated drinks (e.g., cola soda), meat tenderizers or pancreatic enzyme solutions for 15 to 20 minutes; or gently using a polyurethane catheter to dislodge the obstruction. The final resort is tube removal and replacement.

Aspiration Pneumonia

The perception of enteral feeding increasing the risk of aspiration pneumonia in the critically ill patient is most likely justified if the enteral feeding increases the risk of the patient vomiting, or aspirating or if the patient is laterally recumbent, sedated or anesthetized. Incorrectly positioned nasoesophageal tubes will cause aspiration pneumonia when the food is inadvertently placed into the trachea, and not the esophagus.

Gastric contents following enteral feedings serve as an excellent reservoir of pneumonia-genic compounds given their acidity and high microbial load. However, it should be noted that a human produces up to 63 mL per hour of bacteria-laden saliva (McClave & Snider, 2002). Thus, it is most likely inappropriate to assume that all aspirated material comes from the stomach. The role of enteral feeding in the development of aspiration pneumonia is controversial in the human arena (McClave & Snider, 2002). However due to the more horizontal, rather than vertical posture of dogs, it appears likely to play a significant role in the canine patient.

Overfeeding

Volume intolerance is a frequent complication of enteral feeding in humans (Davies et al., 2002) It can lead to simple nausea or to vomiting.

Intolerance to enteral feeding is usually related to an excessive meal volume which exceeds gastric capacity. The frequency with which clients can administer feedings is generally limited.

Patient discomfort, the risk of diarrhea and vomiting can be minimized by:
- Reducing the total volume (increase the meal frequency and/or the meal energy density)
- Slowing down the rate of administration
- Serving the food at ambient temperature
- Reducing the food’s osmolarit
- Simultaneously managing fluid, electrolyte and acid base disturbances.

The total number of daily kilocalories to be delivered has a large impact on individual bolus volume. Overestimating the energy requirement of a patient increases the risk of volume intolerance. In human medicine, initial energy requirement recommendations for enteral feeding that are too aggressive often result in the patient receiving fewer kilocalories per day due to skipped feedings based on residuals and/or volume intolerance (McClave & Snider, 2002).

There is debate regarding the predictive ability of gastric residuals (leftover stomach contents measured by aspiration before the next feeding) in avoiding aspiration pneumonia in humans (McClave & Snider, 2002). The volume of each feeding may not be solely responsible for residual volume as gastric emptying rate also plays a role. However, intuitively, it seems like a good indicator of feeding volume tolerance.

Finally, diarrhea can occur with any form of enteral feeding, especially when undigested nutrients or non-elemental diets are fed too rapidly into the jejunum (due to osmotic effects), or when the food is too cold.

Refeeding Syndrome

This syndrome may occur after enteral feeding, as studies on cats and humans have shown (Solomon & Kirby, 1990; Justin & Hohenhaus, 1995).

In order to prevent Refeeding Syndrome, the following three steps should be taken:

1. Slow re-introduction of food to animals that have been unfed for extended periods (greater than 5 days);
2. Provide adequate supplementation of potassium, phosphorus and potentially magnesium; and
3. Closely monitor electrolytes during the first 24 hours of refeeding.

In a state of starvation, the body maintains extracellular concentrations of many electrolytes at the expense of intracellular concentrations. This shift can result in inward rectification when glucose and, subsequently, insulin are reintroduced to the patient with refeeding. This inward rush results in acute decreases in vital serum electrolyte concentrations that can potentially be life threatening. For example, serum potassium concentration is maintained as intracellular potassium is depleted. When blood glucose rises in response to feeding, the body releases insulin that pumps glucose and potassium intracellularly. The result is a rapid and profound hypokalemia (Figure 10). Hypomagnesemia and hypophosphatemia have also been reported (Justin & Hohenhaus, 1995; Macintire, 1997). Hypophosphatemia has been associated with hemolysis and could lead to additional cardiac and neurological complications (Justin & Hohenhaus, 1995).

Figure 10. Physiological mechanisms that may result in hypophosphatemia associated with the Refeeding Syndrome.