Enteral Feeding Devices: What�s Old, What�s New?

Stanley Marks South Africa

Most feeding tubes today are made of polyurethane or silicone. These materials have tended to replace the older polyvinylchloride feeding tubes that tend to stiffen when exposed to digestive juices and are more irritating to patients, necessitating frequent tube replacement. Silicone is softer and more flexible than other tube materials with a greater tendency to stretch and collapse. Polyurethane is stronger than silicone, allowing for a tube of this material to have thinner walls and thus a larger internal diameter, despite the same French size. The flexibility and decreased internal diameter of silicone tubes may lead to clogging or kinking of the tube. Both polyurethane and silicone do not rapidly disintegrate or embrittle in situ, providing a longer �wear�. The French (F) unit measures the outer lumen diameter of a tube (each French unit is equal to 0.33 mm). Tubes that are too flexible may be chilled before placement to increase stiffness.

Nasoesophageal

Simple and efficient choice for the short-term (less than 10 days) nutritional support of most anorectic hospitalized patients that have a normal nasal cavity, pharynx, esophagus, and stomach. Nasoesophageal tube feeding is contraindicated in animals that are vomiting, comatose, or lack a gag reflex. Polyvinylchloride (Infant Feeding Tube, Argyle Division of Sherwood Medical, St. Louis, MO) or red rubber tubes (Sovereign Feeding Tube, Monoject Division of Sherwood Medical, St. Louis, MO) are the least expensive tubes, although the polyvinylchloride tubes may harden within two weeks of insertion and cause irritation or ulceration of the pharynx or esophagus. Tubes made of polyurethane (Travasorb Feeding Tube, Travenol Laboratories, Deerfield, IL), or silicone (Cook Nasal Feeding Tube, Cook Veterinary Products, Bloomington, IN) are more expensive; however, they are less irritating and more resistant to gastric acid, allowing prolonged usage. A 5 or 6 French 36 inch tube is recommended for most cats.

The length of tube to be inserted into the distal esophagus is determined by measuring the distance from the tip of the nose to the ninth rib in cats. This will help verify the correct placement of the tube in the distal esophagus rather than the stomach. Nasogastric tubes traverse the distal esophageal high-pressure zone increasing the risk of reflux esophagitis and stricture formation. Chemical restraint is rarely required for passage of a nasoesophageal tube; however, topical installation of a local anesthetic is necessary to desensitize the nasal cavity. Desensitization of the nasal cavity with four or five drops of the topical ophthalmic anesthetic 0.5% proparacaine hydrochloride (Ophthetic, Allergan) is recommended. The tip of the tube should be lubricated with a water-soluble lubricant or 5% lidocaine ointment to facilitate passage. The tube is passed by maintaining the animal�s head in the normal angle of articulation and gently directing the tip of the tube in a ventromedial direction. The tube should move with minimal resistance through the ventral meatus and nasopharynx and into the esophagus. Advancement of the tube into the pharynx usually elicits a swallowing reflex.

If the tube is unable to be passed with minimal resistance into the oropharynx, it should be withdrawn and redirected because it could be positioned in the middle meatus with its tip encountering the ethmoid turbinate. Once the tube has been passed to the level of the attached �butterfly� tape, it should be secured as close to the nostril as possible, with either suture material or superglue. A second tape tab should be secured to the skin on the dorsal midline between the eyes. An Elizabethan collar is usually not required in the cat. Removal of the tube is facilitated by clipping the hair that is attached to the glue.

The tube position is checked by injecting 5 to 10 ml of air while ausculting the cranial abdomen for borborygmus, or by infusing 3 to 5 ml of sterile saline or water through the tube and observing for a cough response. Confirmation of correct tube placement can also be obtained by obtaining a lateral survey thoracic radiograph and observing the position of the radiopaque tube in the esophagus. The most common complications associated with the use of nasoesophageal tubes include epistaxis, dacrocystitis, rhinitis, tracheal intubation and secondary pneumonia, and vomiting. Pneumothorax secondary to nasopleural intubation and esophagitis with stricture formation are less common serious complications. The risk of tracheal intubation can be minimized by verifying the position of the feeding tube before securing it and before each feeding.

A major disadvantage of nasoesophageal feeding tubes is their small diameter, necessitating the use of liquid enteral formulas. Commercially available canned pet foods that are diluted with water will invariably clog the feeding tube. The caloric density of most human and veterinary liquid enteral formulas varies from 1.0 to 1.5 kcal/ml. Diets are fed full strength on continuous (pump infusion) or bolus feeding schedules.

Pharyngostomy

Although relatively easy to place, the technique has become virtually obsolete with the advent of percutaneous gastrostomy and esophagostomy tube placement. Pharyngostomy requires general anesthesia and meticulous attention to placement to avoid interference of epiglottic movement and partial obstruction of the larynx.

Esophagostomy

The technique for surgical placement of a midcervical tube esophagostomy in dogs and cats was refined in an effort to avoid the complications associated with aspiration or laryngeal obstruction that may occur with pharyngostomy and nasoesophageal tube placement. The tubes are easily inserted, and insertion only requires light general anesthesia or heavy sedation. The only major complication that has been associated with esophagostomy tube placement is wound infection at the ostomy site where the tube exits the skin. Daily meticulous care of the ostomy site has been effective in preventing infection.

Three techniques for tube esophagostomy placement have been described. The patient should be placed in right lateral recumbency, and the left cervical region aseptically prepared for tube placement. The first method is a percutaneous (needle) technique that incorporates the use of an intravenous jugular vein catheter inside a 14-gauge needle. A curved Carmalt forceps is inserted into the esophagus and the tip turned outward as a directional guide for the needle catheter. The needle is inserted through the skin and into the esophagus between the parted blades of the forceps. The pre-measured catheter is fed through the needle and into the thoracic esophagus, whereupon the needle is removed. The second technique involves placing a small-bore feeding tube (5 to 12 French) in the esophagus via a surgical cut-down. One advantage of the surgical placement technique when compared with the percutaneous technique is that tubes larger than 12 French can be used.

An alternative tube esophagostomy technique utilizing an ELD percutaneous feeding tube applicator was recently described by Devitt and Seim. The applicator is inserted into the midcervical esophagus via the oral cavity. The distal tip is palpated and an incision is made through the skin and subcutaneous tissue over the tip of the ELD. The trocar is advanced through the esophageal wall and directed through the incision. The distal end of the feeding tube is secured to the eyelet of the trocar with suture material. The ELD device and attached feeding tube are retracted into the esophagus and exteriorized out of the oral cavity. The feeding tube is redirected into the midcervical esophagus after inserting a wire stylet into the distal tip of the feeding tube. This technique was well tolerated in all animals and was not associated with major complications. The time to healing of the esophagostomy site following tube removal was less than two weeks. In all placement methods, the tube is fixed in place with a friction suture or a tape �butterfly.� The tube is capped and bandaged so that the feeding port exits behind the animal�s head. The ostomy site is allowed to heal by granulation and epithelialization when the esophagostomy tube is removed. Despite the potential for esophageal scarring and stricture formation, esophageal stricture or a persistent esophagocutaneous fistula has not developed.

Gastrostomy

Requires general anesthesia, with placement of the tube via percutaneous placement or during laparotomy. This procedure enables placement of relatively large diameter catheters into the patients stomach, with most cats tolerating placement of 20 Fr tubes.

Percutaneous Endoscopic Gastrostomy (PEG) Technique

Endoscopic and blind placement of gastrostomy tubes necessitates a brief anesthesia. The animal is placed in right lateral recumbency so that the stomach tube may be placed through the greater curvature of the stomach and the left body wall. Patient preparation for both percutaneous procedures is identical and involves surgically preparing the skin caudal to the left costal arch.

The endoscope is introduced into the stomach and the stomach is inflated. The left body wall is transilluminated with the endoscope to ensure that the spleen is not positioned between the stomach and body wall. An appropriate site for tube insertion is determined by endoscopically monitored digital palpation of the gastric wall. A small incision is made in the skin with a scalpel blade and an intravenous catheter is stabbed through the body wall into the lumen of the stomach. The stylet is removed and nylon or polyester suture is threaded through the catheter into the lumen of the stomach. The suture material is grasped with the endoscopic biopsy forceps and the endoscope and forceps are carefully withdrawn through the esophagus and out of the mouth. The suture material is secured to the feeding tube and gentle traction is applied to the suture material at its point of exit from the abdominal wall. The feeding tube is pulled out through the body wall allowing the mushroom end to draw the stomach wall against the body wall. The feeding tube is anchored in this position by the external bumper placed over the catheter at the skin surface. The endoscope is then reinserted into the stomach to verify the correct placement of the mushroom against the gastric mucosa. A plastic clamp is placed over the tube and the tube is capped. A stockinette jacket is fitted to protect the tube.

Complications related to PEG tubes include those associates with placement of the tube (splenic laceration, gastric hemorrhage, and pneumoperitoneum), and delayed complications such as vomiting, aspiration pneumonia, tube extraction, tube migration, peritonitis, and stoma infection. Laceration of the spleen can be minimized by insufflating and transilluminating the stomach prior to placement of the needle or catheter into the abdominal wall.

Blind Percutaneous Gastrostomy (BPG) Technique

An alternative technique for nonendoscopic and nonsurgical gastrostomy tube placement has been described. The gastrostomy tube placement device can be prepared by purchasing a length of vinyl or stainless steel tubing (diameter 1.2 to 2.5 cm) from a hardware store or utilizing an Eld Gastrostomy Tube Applicator (Jorgensen Laboratories, Loveland, CO) or gastrostomy tube introduction set (Cook Veterinary Products, Bloomington, IN). The reported complication rate for BPG is similar to that of PEG; however the risk of penetrating the spleen, stomach, or omentum is greater when the stomach is not insufflated with air prior to positioning the tube against the lateral abdominal wall. Contraindications to using the �blind� technique include severe obesity precluding accurate palpation of the tube against the abdominal wall and esophageal disease.

Surgical Tube Gastrostomy Technique

Surgical placement of gastrostomy tubes has been superceded by the percutaneous techniques because of the ease and speed of placement, lower cost, and decreased patient morbidity associated with the non-surgical techniques. A surgical approach is indicated in obese patients, patients with esophageal obstruction, or in situations where the patient requires a laparotomy for reasons other than tube placement.

Gastrostomy Tube Removal

For percutaneously placed tubes, it is recommended that the tube be left in place for a minimum of 14-21 days. Patients receiving immunosuppressive therapy or patients that are severely debilitated may require longer than 21 days for a peritoneal seal to form. The tube should only be removed when oral food intake is sufficient to meet the patients caloric requirement. One of two methods of tube removal can be applied. The tube can be cut at the body wall and the mushroom tip pushed into the stomach to be passed in the feces. This method is safe in mid- to large-size dogs because the mushroom and internal bumper should be easily passed in the stool. Alternatively, a stylet can be inserted into the tube to flatten the mushroom tip, while exerting firm traction on the tube. This method is recommended for cats because the mushroom can cause intestinal obstruction. The gastrocutaneous tract should seal with minimal or no leakage within 24 hours.

Gastrostomy Tube Replacement

Premature removal of a gastrostomy tube within 14�21 days of placement (before establishment of the gastrocutaneous tract) necessitates a PEG procedure to evaluate the gastric mucosa and verify correct positioning of the replacement gastrostomy tube. If the tube is inadvertently removed once the gastrocutaneous tract is well healed, one can replace the original catheter with a balloon-type catheter (Flexiflo Gastrostomy tube, Ross Laboratories, Columbus, OH) or a low-profile gastrostomy device (LPGD). Both catheter types do not require an endoscopic procedure for placement.

Surgical (Open) Jejunostomy Technique

The needle catheter jejunostomy is a quick, easy method developed by Delany. A purse-string suture (3�0 polyglactin 910) is placed through the antimesenteric border of the proximal jejunum, through which a 12-gauge hypodermic needle is directed aborally and tunneled subserosally for several centimeters before entering the bowel lumen. A 5 French polyvinylchloride tube (Infant Feeding Tube, Argyle Division of Sherwood Medical, St. Louis, MO) is introduced into the bowel lumen through the hypodermic needle and is advanced for 20 to 30 cm aborally. The needle is removed and the purse-string suture is tightened and tied. The free end of the catheter is exteriorized by advancing it through a second sterile hypodermic needle that is passed from the prepared skin surface on the right ventrolateral abdominal wall into the peritoneal cavity. The enterostomy site is fixed to the abdominal wall with interrupted or continuous sutures passing through the intestinal submucosa and abdominal fascia.

Diet Selection

The type of formula to feed the patient will depend on the selected route of feeding, the functional status of the gastrointestinal tract, and the patient�s nutrient requirements. Other factors, such as cost, availability, and ease of use may also be important. Patients that are fed via nasoesophageal or jejunostomy feeding tubes are limited to receive liquid enteral formulas. Most commercially available liquid diets have a caloric density of approximately 1 kcal per ml. The protein content of an enteral nutrition product is probably the most important component. When selecting a liquid formula for feeding, one should pay particular attention to the amount of protein in the formula, the type of protein (intact proteins, peptides, and amino acids), and the quality of the protein. Protein quality is dependent on protein digestibility, absorption, and its amino acid composition. Whole egg has the highest biologic value, followed by cow milk, lactalbumin, beef, soy, and casein. Most human liquid formulas contain less than 20% protein calories, precluding their use for the long-term (longer than three weeks) feeding of cats. The lower protein formulas should be supplemented with protein modules such as Promod (Ross Laboratories, Columbus OH), Casec (Mead-Johnson, Evansville, IN) or Promagic (Animal Nutrition Laboratories, Burlington, NJ) at 15-30 g casein or whey powder per 8 fl oz. can. Almost all human liquid enteral formulas lack taurine, an essential amino acid in cats, necessitating its supplementation (250 mg taurine per 8 fl oz. can) in this species. High-protein commercial human liquid formulations contain between 21% to 30% protein calories and include Impact (Sandoz Nutrition, Minneapolis, MN), Immun-Aid (McGaw, Inc., Irvine, CA), Alitraq (Ross Laboratories, Columbus, OH), Promote (Ross Laboratories, Columbus, OH), and Traumacal (Mead-Johnson, Evansville, IN).

Commercial blenderized pet food diets should be used for feeding into the stomach via pharyngostomy, esophagostomy, or gastrostomy tubes. In select cases, the feeding of a liquid enteral formulation may be indicated (nasoesophageal or jejunostomy tube feeding). There are a number of complete and balanced veterinary enteral formulations, which contain adequate amounts of protein, taurine, and micronutrients, precluding the need for supplementation in most situations. Feeding should be delayed for 24 hours after placing a gastrostomy tube, to allow gastric motility to return, and to allow formation of a fibrin seal. Jejunal feeding can be started within six hours of tube placement if peristalsis is present. Continuous feeding must be used with jejunostomy feeding to avoid abdominal cramping and diarrhea associated with bolus feeding via this route. Continuous infusion is recommended at an initial flow rate of 1 ml/kg/hour and increased gradually over 48 hours until the total daily volume can be given over a 12- to 18-hour period. Diet can be administered as bolus feedings or continuous infusion when feeding via gastrostomy tube. Improved weight gain and decreased gastroesophageal reflux have been reported in human patients given continuous feedings, although similar studies are lacking in the veterinary literature. A recent study completed in 10 healthy dogs revealed no significant differences in resulting body weights, serum chemistries, glucose tolerance test findings, hydrogen breath test findings, digestibility trials, or nitrogen balance between dogs fed continuously or intermittently for 10 days. Although no advantage was found with continuous enteral feeding in this study, caution should be exercised in extrapolating these results to sick patients that have been ill for a prolonged period and may be more susceptible to gastric atrophy and earlier satiety. If continuous feeding is employed, it should be interrupted every eight hours to determine the residual volume by applying suction to the feeding tube. If the residual volume is more than twice the volume infused in one hour, feeding should be discontinued for two hours, and the rate of infusion decreased by 25% to prevent vomiting. Treatment with metoclopramide (1 to 2 mg/kg/24 hour as a continuous infusion) may be used to enhance gastric emptying and prevent vomiting.

With bolus feeding, the required daily volume of food should be divided into four to six feeds. Patients are usually fed approximately 25% of their caloric requirement on the first day of feeding, with a gradual increase of 25% of the caloric requirement per day. Most patients are able to reach their energy requirement by the fourth or fifth day of feeding. The food should be warmed to room temperature and fed slowly through the tube to prevent vomiting. Flushing of the tube with 15 to 20 ml of lukewarm water will help prevent clogging. Before each feeding, aspirate the tube with an empty syringe to check for residual food left in the stomach from the previous feeding. If more than half of the last feeding is removed from the stomach, skip the feeding and recheck residual volume at the next feeding.

Suggested Reading available on request