A short guide to... Nasal feeding tubes in dogs

Introduction

Nasal feeding tubes are easy to employ in small animal practice and are suitable for various clinical scenarios; they are intended for short-term (1-7 days) use and will allow early enteral feeding to be commenced in a recuperating patient, although only liquid diets can be administered as the diameter of the feeding tube is limited by the diameter of the patient’s ventral meatus.

Inserting a nasal feeding tube is quicker and safer than placement of an esophageal tube, especially where a patient is not stable enough to undergo general anesthesia, or where surgery may result in excessive bleeding – e.g., if a coagulopathy is present. A feeding tube will allow the clinician to determine if the gastrointestinal tract of an anorexic patient will tolerate enteral feeding, and to assess the factors that contribute to optimal feeding (i.e., amount fed, diet composition, and if continuous rate infusion (CRI) or bolus feeding is better).

Materials

There are various factors to consider when selecting a suitable feeding tube (Table 1), and the clinician should select the most appropriate one for the patient. The other items required for tube placement are basic and are shown in Figure 1.

Positioning the feeding tube

There are two options for tube placement:

• A nasoesophageal tube, with the distal tip of the tube sitting in the esophagus at the level of the 9th intercostal space. This method has the advantage of reducing gastric reflux and the potential development of reflux esophagitis or esophageal stricture. However, it does increase the risk that administered food is aspirated into the lungs, especially if the patient is in lateral recumbency.

• A nasogastric tube, with the distal tip of the tube positioned within the stomach at a level caudal to the last rib. This method allows the clinician to check if there is food retained within the stomach prior to administering the next bolus of food, and there is less risk of aspiration if the patient is in lateral recumbency. However, a nasogastric tube does increase the risk of gastric reflux and reflux esophagitis as a result of interference with the cardiac sphincter function.

The advantages and disadvantages of the two methods have not, to the authors’ best knowledge, been properly scrutinized in veterinary medicine, and no recommendation as to the better method is offered. Personal preference, patient characteristics, and disease-related aspects will determine the choice for positioning the feeding tube.

Preparation

• It is essential to measure and mark the feeding tube before placement. The point at which the tube reaches the thoracic inlet is marked with a waterproof pen (Figure 2). If a nasoesophageal method is to be used, the tube should extend to the 9th intercostal space; for the nasogastric option, the tube should extend to a level caudal to the last rib. With either scenario, the point at which the tube will exit the nose when the tip is in the desired position is marked with a small butterfly tape (Figure 3).

• It is important that the tube is of sufficient length; if necessary, extension tubing can be used. The exterior section of the tube or extension should be able to run from the tip of the nose to the dog’s neck without undue tension.
  
  
• The feeding tube can be placed with the animal fully conscious or under light sedation. In either case, local analgesia of the nasal mucosa is necessary; apply one drop of lidocaine into both left and right nares (if tube placement using one side of the nose is difficult, the clinician can try the other side) 2-5 minutes before introduction of the tube. Lidocaine with epinephrine is preferred as this produces local vasoconstriction in the nasal capillary beds.

Introduction of the tube

• The tube should be lubricated with lidocaine or silicone spray. With the dog standing, sitting or in sternal recumbency, its head should be held facing forward, with the nose tilted upwards using a thumb or finger while introducing the tip medially and ventrally to guide it into the ventral meatus of the nose; the tube should slide into the nose without resistance (Figure 4).

• Advance the tube into the pharynx and watch for the dog swallowing; when it does, further advance the tube up to the level of the first mark, indicating that the tip of the tube is at the thoracic inlet (Figure 5). Observe for any coughing or gagging which may suggest inadvertent introduction into the trachea.

• If a guidewire has been used to stiffen the tube, it should be removed at this point (Figure 6). Use a 10-20 mL syringe to check correct positioning in the esophagus (Figure 7a) (Figure 7b). Firstly, apply suction with the syringe; a vacuum should be evident. Secondly, introduce some air to determine if the feeding tube is patent and not accidentally kinked in the trachea (see below).

• If placement of the tube is correct, it can now be advanced to its intended position until the butterfly tape reaches the nares.

Fixation of the tube

• The tube can be sutured to the skin of the muzzle, as close as possible to the side of the nasal planum (Figure 8). The tube can be guided through the lateral groove under the nares. It is important not to bend the tube too tightly; allow some room to prevent kinking.

• Fixation using tissue adhesive is generally not recommended; although the adhesive can be applied easily and will initially hold the tube securely, the glue tends to become brittle, and the tube can become loose shortly after fixation.

• The tube can then be positioned over the top of the nose and between the eyes onto the forehead, where a fixation suture can be used to hold the tube; alternatively, the tube can be positioned along the lateral aspect of the face (above the whiskers and below the zygomatic arch) and sutured in place.

• Finally, the feeding tube can be taped to a bandage lightly wrapped around the neck (Figure 9).

• An Elizabethan collar is often necessary to prevent the patient removing the tube but this can have a negative effect on voluntary food consumption, and the collar should be removed regularly to check if the patient wants to eat unassisted.

Correct tube positioning

Checks should be performed both during placement of the tube and each time before using the tube. The method as described above 1 should result in successful placement, but two other tips are:

• If the dog swallows when the tip of the tube is in the nasopharynx/oropharynx, this gives better assurance that the feeding tube is entering the esophagus.

• Check visually and manually on the left side of the neck to verify correct placement whilst advancing the tube down the esophagus.

Once the tube is in position, it is prudent to check the placement before each feed. This can be done in several ways.

• Check with a syringe as described above. However, note that dyspnea or nausea can make a patient swallow air; this may result in an initial aspiration of gas with the syringe, giving the impression that the tube has entered the trachea. However, if aerophagia is present, the amount of air retrieved should be limited. In addition, if air can be easily flushed through the tube with a syringe, it offers reassurance that the tube is not kinked.

• Flush the feeding tube with 2-20 mL (depending on the size of the dog) of isotonic electrolyte solution; if the tube is in the airway, it should elicit coughing (but note that very sick patients with reduced consciousness or animals under sedation may not cough).

• With a nasogastric tube, 5-15 mL of air can be injected in the tube; borborygmi may be heard by auscultating the cranial abdomen.

• Unless the tube can be seen/felt within the cervical esophagus, none of the above techniques are foolproof. If in doubt, lateral thoracic radiography can be performed (Figure 10).

Contraindications and complications

There are various situations where using a feeding tube is contraindicated or should be used with caution. These include vomiting, dyspnea, or where there is an increased risk for aspiration of gastric contents (e.g., if the swallowing reflex is absent, if the patient has reduced consciousness, or is in lateral recumbency). In addition, a tube may not be suitable if the patient has a head injury involving nose/nasal cavity or pharynx, or if there is a coagulopathy, where tube placement can cause epistaxis.

Various complications can also arise with a feeding tube. These include:

• Epistaxis

• Rhinitis/sinusitis

• Dacryocystitis

• Aspiration pneumonia (if the tube is accidentally placed in the airway or there is food reflux)

• Kinking of the tube (usually where the tube exits the nose; this in turn is dependent on the material used for the tube and how the tube is positioned)

• Clogging of the tube (more common if the tube has a small diameter and/or side holes rather than open ended; inadequate maintenance can also lead to clogging). It is important to flush the tube frequently (see below); a blocked tube may be cleared by installation of water, a carbonated beverage or pancreatic enzyme solutions

• Esophageal irritation or gastric reflux esophagitis

• Tube dislodgement by vomiting or sneezing

The tube may also be removed by the patient, either accidentally or deliberately. Deliberate removal can occur if the patient feels discomfort, e.g., due to irritation from the holding sutures, painful rhinitis, or if the tube interferes with the animal’s field of view or facial whiskers (more commonly in cats).

If the cause cannot be determined, or the problem resolved, it may be necessary to use an Elizabethan collar (Figure 11) or to consider another method of assisted feeding (e.g., an esophageal feeding tube).

Continuous or intermittent feeding?

In a retrospective study looking at both feline and canine patients fed via naso-enteral tube for 24 hours, no significant differences in gastrointestinal complications (vomiting, regurgitation and diarrhea) were demonstrated for continuous rate infusion (CRI) versus bolus feeding 2. However, each case should be treated on its own merits and the clinician should be aware of possible problems; for example, it has been reported that cats with feline hepatic lipidosis may have a reduced stomach volume, which could initially increase the risk of emesis, nausea and discomfort if bolus feeding is employed 3.

• Continuous rate infusion is recommended for debilitated patients that have been anorexic for a long period of time, as they may have limited gastrointestinal capacity. In such situations, trickle feeding is often combined with the administration of prokinetic drugs (e.g., metoclopramide or cisapride). This method is less labor intensive and is less likely to cause gastric distension and discomfort during feeding. However, CRI does not resemble normal physiologic food intake, and accumulation of food in the stomach may go unnoticed, leading to regurgitation or vomiting. The liquid diet should be kept at room temperature (i.e., not chilled) and it is important to ensure the food does not precipitate in the syringe or bag; this can be prevented by regular agitation of the mixture.

• Intermittent (bolus) feeding can be used in less debilitated patients, e.g., if the animal is discharged with the tube in place for the owner to feed at home. This method is more physiologically normal and allows monitoring of the feeding process, and also permits the clinician to ensure that the stomach does not become overfull. It is, however, more labor intensive and can cause discomfort and nausea in some patients. Always make sure the food is lukewarm and administer it slowly (< 3 mL/kg/min): rapid distension of the stomach in an anorexic patient may cause nausea, discomfort and emesis. A syringe pump can be used to administer small volumes of food at a set pressure; if feeding manually, excess force can cause the tip of the feeding tube to vibrate and induce vomiting; this is more likely with a nasoesophageal tube. After feeding, the tube should be re-flushed and the end closed to prevent food or water escaping.

Tube maintenance

The feeding tube should be checked regularly, at least every 2-4 hours for CRI and before each use for bolus feeding. This involves:

• A visual check to ensure the tube is positioned correctly and that the sutures are holding. If the tube is missing, check to see if the dog has vomited the tube or bitten off the exterior section of the tube.

• Aspirating the tube to determine if food can be retrieved: if a large amount is aspirated with a nasogastric tube it can be an indication of residual stomach contents due to decreased gastrointestinal motility and prolonged stomach emptying. CRI tubes should be flushed regularly – at least every 4-6 hours, or more frequently if required – with 5-10 mL of lukewarm water (depending on the size of the tube) whilst observing the dog for discomfort (e.g., salivation, coughing, gagging, or vomiting); the same technique should be employed for bolus feeding before each meal.