Enteral Nutrition

5. Enteral Nutrition

A study investigated the percentage of prescribed enteral nutrition delivered to 23 cats and 2 dogs (Michel & Higgins, 2006). This investigation reported a good rate of success for delivery of clearly prescribed enteral nutrition. In addition, consultation with the Nutritional Support Service improved the likelihood that prescribed nutrition would meet the patient’s estimated RER.

"Assisted" Feeding

Cats are known for a tendency to have fixed food preferences and therefore may refuse a new food. When smell or food is associated with positive consequences, the food will be eaten again. Conversely, if the smell or food is associated with distress, such as an unpleasant experience or hospitalization, the food will be avoided in the future. This phenomenon is known as aversion and in cats, aversion sets in very quickly. It is recommended to resist the temptation to coax a cat to eat. Forcing food on a cat who clearly does not want it may risk inducing aspiration pneumonia and a learned food aversion.

The smell alone of a food associated with digestive disorders is enough to elicit aversion. Cats even go so far as to show aversion for their usual food if it is served in the presence of an air current bearing the odor of a food to which they have developed an aversion. Therefore, it is important to be careful when preparing foods for cats at the hospital. Odors may travel and could trigger an aversion reaction even in cats being fed their usual diet. It is best to prepare the cats’ food in a place where food odors cannot reach the cats.

For cats that show some interest in food, several methods can be tried to increase the inclination to eat. One can offer food in a novel setting or have someone different to do the feeding. Stroking and talking to a cat with the food nearby may stimulate interest to eat (Figure 6).

Figure 6. Sometimes a cat will be stimulated to eat if a small amount of food is placed in the mouth or on the lips or paws. (© WALTHAM Centre for Pet Nutrition).

Cats need to feel safe and secure within their environment. To this end veterinarians and owners need to provide facilities for the main behavioral functions of eating, sleeping and playing and also ensure that the cat has the ability to control its own stress through the natural mechanisms of hiding and retreating. One of the problems with hospitalization is that the cat finds itself constantly on display and correspondingly vulnerable. Taking steps to provide the cat with a constant and predictable environment, both in terms of physical structure and scent profiles, will help to increase the cat’s security. Hospitalized cats may be uncomfortable eating because the lack of space causes the spatial requirements of cats to be disrespected (Figure 7).
Figure 7. Moving the cats to larger dog cages which permits the separation of food, lodging and litter may restore the appetite of some cats. (© Hermann Bourgeois).

Early satiety is common in anorectic patients, so it is recommended to divide the day’s food up into as many small fresh meals as possible. This is particularly important in cats as their natural behavior is to eat a large number of small meals each day. They also eat day and night. Therefore, mimicking natural behavior in the hospitalized environment by providing multiple small fresh meals during the day and night may facilitate food intake.

It is important to keep in mind that "mouth feel" is very important to cats. Nutrients that increase palatability for most cats are moisture, fat and protein, and cats prefer foods with an acidic flavor and strong aromas. Adding water to a dry cat food or switching to a canned food may improve food acceptance. Most cats prefer their food at body temperature. Therefore warming the food prior to serving may encourage anorectic cats to eat. For cats showing interest in food but an unwillingness to eat warm food, it is suggested to try offering chilled food (Michel, 2001). For cats that do not achieve adequate caloric intake using the above mention methods, enteral or parenteral feeding is indicated to achieve effective dietary management (Michel, 2001; Elliott, 2008).

Pharmacological Appetite Stimulation

Only a few drugs have been used as appetite stimulants in feline patients (Table 8). There are a number of adverse effects associated with these medications. In numerous authors’ opinion they have no place in the nutritional management of hospitalized critically ill patients. The only means of ensuring adequate caloric intake is through nutritional support (i.e., tube feeding or PN). Appetite stimulants could be used once the patient is recovering from its disease in the home environment (Chan, 2006).

Enteral Feeding Tubes

Enteral feeding can be achieved via nasoesophageal, esophagostomy, gastrostomy or jejunostomy devices (Marks, 1998). Enteral feeding tubes are available in several sizes and designs, and are constructed of latex or silicone. Latex tubes are less expensive but generally require replacement within 8 - 12 weeks due to tube wear and tear. Silicone tubes typically survive 6 - 12 months and are less irritant at the stoma site. An array of feeding adapters can be attached to the enteral tube.

Nasoesophageal Tubes

Nasoesophageal tubes are an excellent option for short-term feeding (< 5 days) of hospitalized cats (Figure 8). Placement is described in Table 9. The tip of the nasoesophageal tube should not enter the stomach, but rather, sit in the distal esophagus. If the tube traverses the esophageal-gastric junction, acid reflux is likely, causing esophagitis and contributing to vomiting and irritation.

Figure 8. Nasoesophageal tube placed in a cat. Most critically ill patients will tolerate nasoesophageal tube placement, but some individuals may require sedation. (© DA Elliott).

Contraindications for nasoesophageal tubes include patients that have 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 (Marks, 1998). Nasoesophageal tubes, are small, typically 3 to 5 Fr. Therefore, the selection of diet to feed via a nasoesophageal tube is limited to liquid or reconstituted powder diets. Some critically ill cats may not tolerate the large volumes required of such mixtures (Marks, 1998; Yam & Cave, 2003; Chan, 2006).

Esophagostomy Tubes

Esophagostomy tubes can easily be placed under a light anesthetic with minimal equipment (Table 10). 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. In a study of 67 cats, esophagostomy feeding tubes were placed in 46 cats and percutaneous endoscopic gastrostomy (PEG) feeding tubes were placed in 21 cats. The authors reported that esophagostomy tubes were an excellent and less invasive alternative to the PEG tube (Ireland et al., 2003). Critical care nutritionists believe that mastering the placement of esophagostomy feeding tubes is essential in the management of critically ill cats and this technique should be adopted in almost all practices (Chan, 2006) (Figure 9).

Figure 9. Esophagostomy tube in a cat. Esophagostomy tubes can easily be placed under a light anesthetic with minimal equipment. (© I. Goy-Thollot /SIAMU - ENVL).

Gastrostomy Tubes

Gastrostomy tubes are invaluable for the long-term nutritional support of critically ill patients (Figure 10). Gastrostomy tubes may be placed surgically, or by percutaneous technique assisted with an endoscopic or blind placement apparatus. 16 - 20 Fr tubes are appropriate for cats. They must remain in place for a minimum of 7 - 10 days to allow a seal to form with the abdominal wall. These tubes can be easily maintained for many weeks to months in the chronically ill or anorexic patient (Elliott et al., 2001; Luhn et al., 2004, Mesich & Snow 2004, Thompson et al. 2004) (Figure 11). Peritonitis is a potential complication if the gastrostomy tube leaks or is removed early. The PEG technique is presented in Figure 12.

Figure 10. Gastrotomy tube in an anesthetized cat. A gastrotomy tube must remain in place for a minimum of 7-10 days to allow a seal to form with the abdominal wall. (© DA Elliott).

Figure 11. Gastrotomy tube in a conscious cat. Most patients tolerate the tubes quite well. (© DA Elliott).

Figure 12. Percutaneous endoscopic gastrostomy (PEG).

Jejunostomy Tubes

The jejunostomy tube by-passes the stomach and pancreas and can be used in case of severe pancreatitis, diffuse gastric mucosal disease, protracted vomiting or delayed gastric emptying. The jejunostomy tube requires surgical placement with general anesthesia and laparotomy. New placement techniques have been described whereby the jejunostomy tube is introduced via a gastrostomy tube and directed down through the pylorus with an endoscope (Heuter 2004; Jergens et al. 2007). Due to the narrow diameter of the tube, and placement in the jejunum, feeding must be by a continuous infusion pump with a liquid diet. Therefore jejunostomy tubes are limited to in-hospital use. Peritonitis can occur if the tube is prematurely removed. Contraindications include ascites, peritonitis, immunosuppression and distal small bowel obstructions (Heather et al., 2004).

Feeding Protocols

Nutritional support should be introduced gradually. Generally one-third to one-quarter of the daily caloric intake is administered on the first day. If no complications occur, the amount fed is successively increased to reach total caloric requirements by the third or fourth day (Bartges et al., 2004; Elliott & Biourge, 2006) (Table 11). If necessary, the diet can be modified by blenderizing with water to ensure passage through the feeding tube. The total daily volume is divided into 4 - 6 feedings depending on duration of anorexia and patient tolerance.

Gastric dysmotility is a common abnormality in critically ill patients. Prokinetic agents appear to have a beneficial effect on gastrointestinal motility and feeding tolerance in critically ill patients (Corke, 1999; Booth et al., 2002). The use of anti-emetic drugs should be considered in cats where vomiting and nausea are a problem (Table 12). Metoclopramide, in addition to having some antiemetic effects, may be beneficial in patients where delayed gastric emptying is a problem (Michel, 2001; Mohr et al., 2003). Chan & Freeman (2006) recommend continuous infusions of metoclopramide at 1 - 2 mg/kg/day. More recently, potent anti-emetics belonging to the HT3-antagonist family of drugs (ondasetron, dolansteron) have been recommended, however efficacy trials are lacking. A new type of anti-emetic (maropitant, an NK-1 antagonist), has been introduced. However, clinical experience in cats is not yet available.

A common misconception is that animals fed via enteral tubes will not eat voluntarily, and therefore ad-libitum feedings are withheld. Anorexia typically resolves once the primary disease is addressed. Therefore, food can be offered to cats to assess their appetite, and to help to determine when to wean them from enteral tube feeding.

Complications

Aspiration Pneumonia

The most serious complication of enteral feeding is aspiration pneumonia. This can be a fatal complication in critically ill cats. Patients at risk of pulmonary aspiration include patients who have had a prior episode of aspiration pneumonia, patients with impaired mental status including those receiving sedatives and certain analgesics, patients with neurological injuries, patients with reduced or absent cough or gag reflexes, and patients receiving mechanical ventilation (Michel, 2004; 2006). Nasoesophageal tube displacement from the esophagus into the trachea will cause aspiration pneumonia. The risk of aspiration pneumonia can be minimized by ensuring correct positioning of the feeding tube prior to each and every feeding.

Mechanical Complications

Mechanical complications such as tube obstruction, premature removal or dislodgement are the common complications seen with enteral nutrition. Tube obstruction can be minimized by adequate dilution and blending of the diet prior to administration. The enteral formula should never be allowed to sit in the feeding tube and the tube should be flushed with warm water after every feeding or whenever GI contents are aspirated via the tube. Obstruction of esophagostomy tubes can be dramatically reduced, by enlarging the distal exit hole prior to placement. Techniques to facilitate removal of the obstruction include massaging the outside of the tube while simultaneously flushing and aspirating with water; instilling carbonated drinks, 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.

While it is tempting to employ a feeding tube for medicating a patient, this practice should be used with caution. If possible, only liquid medications should be given through feeding tubes. Viscous medications should be diluted with water and tablets crushed to a fine powder before mixing with water. Only one medication should be administered at a time and with the exception of phosphate binders for renal disease, separately from enteral feedings to avoid drug-drug and drug-nutrients interactions.

Premature tube removal or dislodgement is best prevented by choosing a tube that the patient will be comfortable with and by using Elizabethan collars or body wraps as appropriate. Marking the tube where it exits the body at the time of tube placement with indelible ink will aid in monitoring whether a tube has migrated from its original position. Whenever the location of a tube is in doubt it should be verified radiographically. Iodinated contrast media can be infused through a gastrostomy or enterostomy tube to check for leaks into the peritoneal cavity (Michel, 2004).

Feeding Intolerance

Feeding intolerance is a common complication, especially in critically ill animals. Animals that vomit persistently and frequently (more than 3 times a day) probably should not be fed via the enteral route. Altering the feeding strategy is recommended for cats that vomit small amounts and infrequently (less than 2 times a day). For example, smaller volumes administered over a longer duration, more frequently can improve feeding tolerance. If bolus feeding is still not tolerated, feeding via continuous infusion could improve feeding tolerance. It is recommended to start at a very low rate, e.g. 2 mL/hour and slowly increase the rate based on patient response, until the daily caloric intake is achieved. In such cases, reaching caloric target may be delayed by a few days (Marks, 1998; Michel, 2004; Chan, 2006; Chan & Freeman, 2006).

Metabolic Complications

Different types of metabolic disturbances can occur with nutritional support.

Patient’s Inability to Assimilate Nutrients

For example, a cat with impaired renal function might become azotemic on a high protein diet. This disturbance can be anticipated by a thorough nutritional assessment of the patient before formulating the nutritional regiment.

Refeeding Syndrome

The refeeding syndrome can develop in patients who have experienced severe muscle wasting as a result of prolonged starvation or catabolic disease (Michel, 2004; Armitage-Chan et al., 2006). This is perhaps the more severe complication associated with nutritional support of critically ill patients and may develop after oral, enteral or parenteral nutrition although this remains a rare occurrence. In people, this syndrome results in widespread systemic effects including depression of myocardial function, cardiac arrhythmias, hypoventilation, seizures and mental dysfunction, poor neutrophil function, muscle weakness, and hemolytic anemia.

While it is tempting to employ a feeding tube for medicating a patient, this practice should be used with caution. (© Isabelle Coy-Thollot).

Most of these effects occur secondary to hypophosphatemia however deficiencies of magnesium and potassium may also contribute. Hypophosphatemia develops due to the rapid increase in insulin release upon reintroduction of nutrition. Increased insulin activity stimulates anabolic processes, which require incorporation of phosphate into high-energy substrates such as adenosine triphosphate (ATP) and 2,3-diphosphoglycerate (2,3-DPG). There is a transcellular shift of phosphate, which in the face of whole-body phosphate depletion results in hypophosphatemia. The reduction in ATP synthesis and consequent energy deficit, contributes to many of the clinical signs associated with the refeeding syndrome (Solomon & Kirby, 1990; Miller, 2000; Armitage-Chan et al., 2006). Hemolytic anemia secondary to hypophosphatemia associated with the refeeding syndrome has been reported in cats (Justin & Hohenhaus, 1995). Patients identified with severe hypophosphatemia usually respond to phosphate supplementation at a rate of 0.01 - 0.06 mmol/kg/hour (Justin & Hohenhaus, 1995).

Prevention of the refeeding syndrome requires stabilization of the fluid, electrolyte and acid-base status of the patient before starting nutritional support (Armitage-Chan et al., 2006). (© Fabio Viganò).

Hyperglycemia

Hyperglycemia is another common metabolic complication that has only recently received attention in veterinary medicine. Possible consequences of hyperglycemia in critically ill animals include higher infection rates and increased mortality, however, it is not yet clear if insulin administration is indicated or influences outcome (see § 2,b,1) (Chan et al., 2006; Crabb et al., 2006). The risk of hyperglycemia associated with nutritional support is more common with parenteral nutrition (Crabb et al., 2006).

Fluid Overload

Diets used for enteral tube feeding are > 80% water, and water is used to flush the enteral tube upon conclusion of feeding. Therefore, fluid overload can occur in cats receiving nutritional support. Patients with pre-existing cardiac disease on high volumes of enteral tube feeding and receiving intravenous fluids are most at risk of fluid overload. Clinical signs consistent with fluid overloaded include dyspnea, pulmonary edema, and pleural effusion. Prevention requires thorough clinical evaluation to identify those patients most at risk, and to formulate an appropriate nutrition and fluid therapy plan to maintain hydration and yet avoid fluid overload (Chan & Freeman, 2006).

Monitoring and Reassessment

Monitoring parameters for patients receiving enteral nutrition include body weight, serum electrolytes, the patency of the enteral feeding tube, the appearance of the stoma site, and clinical signs consistent with gastrointestinal intolerance, volume overload or pulmonary aspiration (Chan & Freeman, 2006). The number of calories, and indeed the macronutrient composition of the diet selected may need to be adjusted according to the patient’s changing needs and tolerance. In patients unable to tolerate the prescribed amounts, the clinician should consider reducing the amounts of enteral feedings and supplementing the enteral feeding with parenteral nutrition. With continual reassessment, the clinician can determine when to transition the patient from assisted feeding to voluntary consumption of food. The discontinuation of nutritional support should only begin when the patient can consume at least 75% RER, without coaxing (Chan, 2006).