Management of the anorexic cat (Proceedings)

Why is nutritional support important?

In the fasted healthy state glycogen stores are used as the primary energy source. When glycogen stores become depleted, which can occur quickly in strict carnivores such as the cat, amino acids are mobilized from lean muscle. However, within days, a metabolic shift occurs toward the use of fats for energy allowing lean muscle to be preserved (simple starvation). During illness alterations in hormone concentrations will shift metabolism to the use of proteins for energy (stressed starvation). This results in a negative nitrogen and energy balance which has a negative impact on wound healing, immune function, strength (skeletal and respiratory muscle) and overall prognosis. The goal of providing nutritional support is not to achieve weight gain but to minimize loss of lean body mass and restore nutritional deficiencies. This also provides substrate for possible healing and resolution/repair of an underlying disease process.

Anorexia vs hyporexia

Anorexia in cats may be defined as a complete loss of appetite especially due to disease. Hyporexia means a reduction in appetite rather than a total loss. It is rare that patients that are completely unwilling to eat anything voluntarily can be made to eat enough to meet their energy requirements and need to be provided with feeding tubes or parenteral (intravenous) nutrition while an underlying disease process is managed. Certain practices may be employed to encourage consumption in the hyporexic patient. It is important to assess for and correct dehydration (make sure patient is hemodynamically stable), electrolytes abnormalities, reduce pain, address nausea before, etc implementing the following practices to encourage eating in a hyporexic patient or even before implementing assisted enteral feedings or parenteral nutrition.

     1. Ambiance: minimize stress and find a quiet, peaceful area for the cat to eat. Food should not be placed next to the litter box. Food should be offered by someone that is not poking (doctor) or restraining the cat. Some cats are social eaters and petting or brushing can sooth a cat during eating or before offering food.

     2. Increase palatability: Canned foods may be more enticing to some cats; however there are cats that have eaten dry food their entire lives and will not eat canned foods. Canned foods are typically higher in fat and protein. Warming to a lukewarm temperature or body temperature may increase the aroma of the food. Older patients may have a diminished sense of smell. Offering human foods such as chicken (canned, jarred baby food, or cooked). Canned tuna (especially in oil) salmon, shrimp are aromatic and may entice the appetite of a cat. Make sure the cat is provided with fresh food.

     3. Variety: A variety of foods may be offered to the cat, provided the cat does not have an underlying disease processes that would increase chances of food aversion (uremic crisis). When this is done it is important to make sure that the food is measured to that consumption can be accurately assessed.

     4. Avoid poly-pharmacy: Many drugs can affect appetite causing nausea or decreasing appetite by altering taste.

     5. Eliminating barriers: If a cat is made to wear an E-collar, remove it and watch the animal during eating. It is important to make sure the patient has easy access to the food. Hand feeding can be attempted.

     6. Appetite stimulants: Appetite stimulants may be unpredictable and unreliable. The most commonly used in cats are IV diazepam (very short acting). Oral diazepam can cause idiosyncratic hepatic necrosis in cats and should not be given. Mirtazepine and cyproheptadine are also commonly used in cats. Mirtazepine (Remeron® Merck & Co Inc, Whitehouse Station, NJ) is a human antidepressant medication that was noted to cause increased appetite and weight gain in people. It may have anti-emetic properties in cats and is dosed on an every third day basis (1/8 to 1/4 of a 15 mg tablet every third day).

When to start assisted feeding (tube feeding or parenteral feeding)

As stated previously, it is important to make sure that the cat is cardiovascularlly stable prior to starting assisted feedings. Dehydration, major electrolyte imbalances, severe acid-base abnormalities, hypotension, etc. should be corrected before nutritional intervention is implemented. Shock can decrease blood flow to the intestinal tract decreasing motility and nutrient assimilation. Feeding under these circumstances can cause complications. Assisted feeding should implement in cats at risk of malnutrition or cats that are unable to orally intake resting energy requirements. Malnutrition can be difficult to assess in cats. Things to evaluate include recent weight loss of at least 10% of body weight, poor hair-coat quality, muscle wasting, signs of poor wound healing, hypoalbuminemia and lymphopenia. Situations that lead to malnutrition include sick cats that have not eaten for greater than three days, cats with serious underlying disease (e.g. peritonitis, severe pancreatitis, DKA), cats that cannot tolerate oral feedings from protracted vomiting, facial trauma. Interventional nutrition is essential in cats with hepatic lipidosis.

Factors to consider when designing a nutritional plan

     1. Concurrent or underlying disease process: Uremic cats or those with severe hepatic lipidosis leading to hepatic encephalopathy may not be able to tolerate a high protein load. Concurrent or underlying disease processes will help guide diet choice.

     2. Enteral vs parenteral assisted nutrition: Enteral nutrition is always preferred over parenteral. Enteral nutrition is more physiological, less expensive, and, with most methods of enteral nutrition, can be continued after discharge from the hospital. Enteral nutrition helps maintain intestinal mucosal integrity, possibly decreasing bacterial translocation, reducing the risk of complications such as pneumonia and sepsis. Whenever possible the gut should be used. Parenteral nutrition is implemented when enteral feedings are not tolerated such as in protracted vomiting.

          a. If providing enteral nutrition which feeding tube is best?

               i. Is the patient stable enough to undergo anesthesia?

               ii. What is the expected duration of anorexia? Cats with hepatic lipidosis are usually anorexic for 4+ weeks.

     3. How much to feed? Cats should be supplied the resting energy requirements (RER). The most common formula for calculating RER is: RER = (30 x body weight in kg) + 70. In the past the RER was multiplied by an illness factor of 1 – 2 to account for increases in metabolism associated with different lifestyle conditions and injuries. Current recommendations are to just use the RER without the illness factor. Overfeeding can result in metabolic (hyperglycemia) and gastrointestinal complications. Studies have shown in cats supplied with parenteral nutrition that application of an illness factor >1 was increased with higher complication rates.1,2 Depending on the period of time that a cat has been anorexic, the complete daily RER is usually not given of the first day of assisted feeding. The amount supplied is usually gradually increased over 3-7 days to achieve the daily RER.

Parenteral Nutrition

Total parenteral nutrition (TPN) refers to the intravenous administration of all/total nutrient needs of the patient. TPN is composed of carbohydrates, amino acids, lipids, electrolytes, vitamins and minerals. TPN solutions are about 50% dextrose making for a hyperosmolar solution. Partial or peripheral parenteral nutrition (PPN) contain a lesser amount of dextrose (5%) and are less hyperosmolar and able to be given through a peripheral catheter. Total nutritional requirement are not supplied with PPN because of the large volume of fluid that would be required. PPN may be used short tern in non-debilitated patients that are not malnourished. It may provide a supplement to enteral feeding or used in cats in which parenteral nutrition is the only option and central venous access is not possible. Parenteral nutrition (PN) for veterinary patients can be formulated by compounding pharmacies that make human parenteral nutrition or some larger veterinary hospitals/referral centers will compound their own parenteral formulations. Compounding of parenteral solutions should be done aseptically under a laminar flow hood. Commercial human products are available as well. Because of the high osmolarity, a centrally placed catheter (jugular catheter) is required for administration of TPN. Strict aseptic technique should be used when placing the catheter for PN administration. This catheter should be designated only for PN. Sterile gloves should be worn when connecting the PN to the catheter. The connections between the IV catheter, IV lines, and PN bag should be covered with sterile dressing. The lines should not be disconnected unless replacing the PN bag. PN solutions can be stored in the refrigerator for days or weeks. Once warmed to room temperature, bags should be replaced every 24-48 hours. Complications associated with parenteral nutrition include infection secondary to contamination and growth of bacteria and fungi in the PN bag, bacterial translocation particularly from the gastrointestinal tract. Mechanical complications such as IV line breakage, kinking, patient destruction of IV line or catheter, clogging of the IV line, and thrombophlebitis can occur with PN. Electrolyte abnormalities including hypokalemia and hypophosphatemia can be encountered. Hyperglycemia can be seen. For some, PN may be cost prohibitive, upwards of $100/day. Close monitoring of the patient (including daily or twice daily evaluation for electrolyte abnormalities and hyperglycemia) is essential when using PN and adds to the cost.

Enteral Nutrition

Enteral nutrition can be supplied through nasoesophageal or nasogastric tubes, through esophagostomy or gastrostomy (PEG gastrostomy tubes, surgically placed gastrostomy tubes, or non-endoscopically placed gastrostomy tubes) and can be supplied directly into the jejunum (surgically placed jejunostomy tubes, endoscopically or fluouroscopically guided esophagojejunostomy or gastrojejunostomy tubes). Which tube is placed depends on the patients ability to undergo anesthesia or duration of anesthesia, duration of time the tube is expected to stay in place, and the need to circumvent certain segment of the gastrointestinal tract, such as in cats with oropharyngeal or esophageal disorders or pancreatitis.

Nasoesophagel (NE)/nasogastric (NG) feeding tubes: NE/NG tubes are relatively easy to place and do not require anesthesia for placement. These tubes can be placed with no or minimal sedation depending on the status of the patient. These tubes are useful for enteral support that is needed for only a short duration < 10 days. NE tubes are preferred as the presence of the tube traversing the lower esophageal sphincter may cause gastroesophageal reflux, vomiting, and regurgitation in some cats. NG tubes are considered with the cat needs the stomach suctioned of fluid or air. Often times however, the diameter of these tubes are too small to support fluid suctioning. These tubes should only be used in cats that have a functional esophagus, stomach, and intestines. Supplies needed are as follows: topical anesthetic such as lidocaine or ophthalmic drops, a 5 or 8 (only the rare large cat) French tube (red rubber or other designated NE tubes) with length enough to reach the designated area (lower esophagus or stomach), lubricant, suture material (3-0 nonabsorbable) or tissue glue, Elizabethan collar, piece of tape for a marker, plug for the tube terminal (christmas tree adapter with a luer catheter plug). Because of the small diameter of these tubes only liquid diets can be fed through the NE/NG feeding tubes. CliniCare® (Abbot Animal Health, Abbot Park, Illinois), Jevity® 1 cal (Abbot Nutrition, Abbot Park, Illinois) are diets that can be considered for use. These diets contain 1 kcal/mL and have an osmolality in the range of 300-340mOsm/kg. These diets should be diluted approximately 1 part water:1part liquid diet as the osmolality of the undiluted product can cause diarrhea. The osmolality of Ensure® (Abbot Nutrition, Abbot Park Illinois) is about twice that of the previous mentioned diets and contains 1kcal/mL, is high in carbohydrates and sugar and not recommended for cats. Feeding should be done slowly over approximately 10 minutes and the tube should always be flushed prior to feeding, because of the potential for vomiting and aspiration of the tube, and flushed after feeding to prevent clogging. Complication of NE/NG tubes include clogging of the tube due to the small tube diameter, lack of patient tolerance of the tube and patient removal of tube despite E-collar, epistaxis, vomiting of the tube, vomiting and possible aspiration of the tube. Removal is easy; the sutures should be clipped and the tube pulled out.

Esophagostomy (E) tubes: E tubes are probably the most commonly placed enteral feeding tubes in cats. These tubes are easy and quick to place, requiring only a short duration of anesthesia, and do not require special equipment. Medications (liquids, crushed pills) may be given through these tubes, and owners typically find these tubes very user friendly. Gas anesthesia is preferable for placement; however injectable anesthesia (propofol) can be used for placement. Regardless, endotracheal intubation is a must to protect the airway and assure that the tube is not being placed in the trachea. E tubes are usually very well tolerated by cats, can be used for expected long duration need of assisted feeding (1+ months), and will support blenderized canned foods and the tube diameter is greater than with NE/NG tubes. A cat needs to have a functional esophagus, stomach, and intestines. Supplies that are needed include as follows: clippers, surgical scrub, sterile gloves (although this is not a completely sterile procedure) a Carmalt forceps, blade +/- blade handle, suture (2-0 non-absorbable suture), 12-14 French tube with appropriate length to reach the lower esophageal sphincter (red rubber or other commercially available feline esophagostomy tubes), a permanent marker for marking the tube after it is measures, small surgical pack that includes thumb forceps, needle drivers, and sterile gauze sponges, bandage material, catheter adapter and luer plug if needed. With the anesthetized cat placed in right lateral recumbency the fur on the left cervical neck is clipped cranially from the ramous of the mandible caudally to the area of the thoracic inlet and surgically prepped. Diet choice should be tailored to the cats needs, taking into account concurrent or underlying disease conditions. Canned foods can be mixed with water, preferably blenderized, to achieve a smooth, semi-liquid consistency. Food should be warmed to room temperature or a lukewarm temperature. If a microwave is used food should be tested to make sure it is not too hot. Feeding should take place over about 10-15 minutes. If the cat appears nauseous, uncomfortable or vomits during feeding, feeding should be stopped, the cat allowed a break and feeding resumed at a slower rate with possible less volume. Every attempt should be made to create a calm, stress free environment for feeding. Most cats will tolerate a maximum of 10-15 mls of food/kg cat at each feeding. My maximum is typically 70-80 mls (including volume of water used for flushing) for an average sized cat. A cat that has been anorexic for > 2-3 days will likely not tolerate this volume on first feeding. Volume/feeding should be gradually increased over 3-10 days depending on duration of anorexia, and degree of nausea the cat seems to be experiencing. Initially cats should be fed multiple small volume meals per day (4-6 times, 20-40 ml/feeding). After the tube is used for feeding or medication administration it should always be flushed with water (7-15 mls) to prevent clogging. The tube stoma site should be checked and re-bandaged daily or every other day for evidence of infection: pain, redness and swelling, and presence of purulent material. A small amount of redness, discharge and crusting is expected. The stoma site should be cleaned daily or every other day. Very diluted surgical scrub and water can be used or simply a soft paper towel or 4x4 sponge wetted with warm water to remove debris and crusting. Complications of E tubes can include inadvertent placement into the airway (avoided with endotracheal intubation at time of placement), inadvertent placement into the mediastinum, tube site abscessation, dislodgement from vomiting, or dislodgement by the patient. It is uncommon but possible for a cat to vomit the tube and bite it causing a foreign body. Removal is simple. Cut the sutures and pull the tube. The stoma should not be closed but allowed to close with granulation tissue. A neck wrap can be applied for 24-48 hours.

Troubleshooting the E tube:

Vomiting: Esophageal tube feeding can contribute to vomiting. If vomiting or nausea occurs feeding more slowly, feeding in a quiet, serene room, feeding less volume should be done. It is also important to make sure that the tip of the tube is not traversing the lower esophageal sphincter as this can lead to gastro-esophageal reflux, esophagitis, regurgitation, and vomiting. Anti-emetics can be given as well.

Tube clogging: Clogging of the E tube is not an uncommon occurrence. Prevention with making sure that the diet is of smooth and semi-liquid consistency in addition to flushing the tube after every use is best to avoid clogging. If the tube clogs, sometimes vigorous flushing of the tube may dislodge a clog. This may also cause the cat to vomit/regurgitate. Some advocate flushing the tube with Coke or Diet Coke, Coca-Cola trade name recommended as they are the most corrosive. Alternatively flushing with pancreatic enzymes may help to break down a clog. These products should be allowed to sit in the tube for 5-10 minutes, followed by vigorous flushing with water. The author has never had success using Coke or pancreatic enzymes to unclog an E tube. If the previous techniques do not result in alleviation of the clog a flexible guide wire or long small diameter polypropelene catheter can be carefully (don't poke through the tube) fed down the tube to try to relieve a clog.

Inadvertent removal of the tube: If the tube is removed completely before the cat has resumed eating, it is very difficult almost replace finding the same stoma into the esophagus and there is risk of feeding it into the mediastinum. The stoma also closes fairly quickly. Often times, again under anesthesia another E tube needs to be replaced or a gastrostomy tube can be considered. If the tube becomes dislodged and not completely removed, a new tube can be replaced with the cat under anesthesia using the old tube as a guide for placement.

Gastrostomy (G) tubes: Gastrostomy tubes always require gas anesthesia for placement and are placed on the left side of the body. Percutaneous endoscopic guided (PEG) gastrostomy tubes are the most commonly placed G tube. This requires special equipment for placement. Techniques have been described for percutaneously placed non-endoscopic guided gastrostomy tubes. This technique still requires special equipment, a gastrostomy tube introducer, which is essentially a long hollow metal rod with an angular end that is placed into the stomach via the oral cavity and pushed against the stomach wall so that it can be located on the outside of the animal. An introduction catheter is placed through the skin and stomach wall into the rod and a wire thread through the catheter and G tube introducer to the other side. Gastrostomy tubes can be placed surgically as well. G-tubes are indicated for cats requiring long term feeding (> 4-8 weeks) or in situations where the esophagus needs to be bypassed. G tubes can be of wider diameter than E tubes (16-18 French). Mushroom tip catheters are commonly used. There are also commercially available G tube kits (PEG tubes). G-tubes should not be used for a period of time after placement. At least 12 hours should be allowed before water is placed down the tube and about 16-24 hours before the tube is used for food to allow for an adhesion to be made between stomach wall and abdominal wall. Since these tubes can be of bigger diameter than E tubes food consistency can be a little thicker. Canned diets mixed with water and blenderized can be fed through a G tube. Feeding through G tubes is very similar to that described with E tubes except most will aspirate through the G tube prior to feeding. This is to account for residual volume in the stomach. If there is > than 30 mls remaining in the stomach, delaying the meal may be recommended to avoid overfilling. This residual volume should be given back to the patient to avoid causing electrolyte abnormalities. Again it is very important to flush the tube after use to prevent clogging of the tube. If clogging occurs, the techniques described above for unclogging an E tube can be applied to the G tube. As with E tubes the G tube stoma site should be inspected daily for evidence of infection. It should be cleaned daily as well. Some cats will be painful after PEG tube placement for the first 3-5 days. Pain medications should be given. Complications associated with G tubes can include vomiting during feeding, hitting the spleen during placement, clogging of the tube, pulling of the tube out of the stomach but not out of the body (tube end is sitting in the abdominal cavity), premature pulling of the G tube. It takes about 2 weeks for a complete adhesion to form between the body wall and stomach. If the tube is pulled prior to this time there is risk of leakage of stomach contents into the abdominal cavity requiring surgery to address this problem. Pulling of the tube usually required sedation or pain medications. If the tube has been in the stomach for an extended period there is risk of breaking the mushroom or expanded tip off of the tube leaving a foreign body in the stomach. Endoscopic retrieval can be considered if this happens. Some large cats will pass the mushroom tip.

Jejunostomy (J) tubes: J tubes can be placed surgically, through an esophageal stoma (EJ tubes) or through a gastric tube (J through G) using endoscopy or fluoroscopy to feed the tip of the tube into the jejunum. J tubes are most commonly indicated for severe pancreatitis in dogs with protracted vomiting to bypass the duodenum. Since vomiting is not a common sign of feline pancreatitis, most anorexic cats can be managed with other forms of assisted feeding. Other indications include gastric outflow obstruction or recurrent severe aspiration secondary to protracted vomiting. J tubes are rarely placed in cats. J tubes are typically used for a shorter duration than E or G tubes. Bolus feeding cannot be performed through a J tube due to the small storage capacity of the jejunum and feedings necessitate use of a continuous infusion pump. Only liquid diets can be used (CliniCare®, Jevity® as above). Elemental diets contain nutrition that requires very little or no digestion for absorption from the intestine. These diets are ideal for J tubes but are very costly. J tubes are not practical for at home use.

References

1. Pyle SC, et.al. J Am Vet Med Assoc 2004; 255: 242–50.

2. Crabb SE, et.al. J Vet Emerg Crit Care 2006;16:S21-S26.

3. Delaney SJ, Vet Clin Small Anim 2006;36:1243-1249.