A Guide to Nasotracheal Intubation in Rabbits

Key Points

  • Endotracheal intubation is the gold standard for any anesthetized patient, regardless of species. Intubation provides a patent and protected airway, allows undiluted administration of oxygen and inhalant anesthetic agents to the patient, and reduces environmental pollution with volatile anesthetics. Endotracheal intubation also permits effective positive pressure ventilation.
  • Endotracheal intubation allows accurate end-tidal carbon dioxide monitoring. Capnography can be used for guidance during the intubation process as well as to provide respiratory and cardiovascular feedback during the anesthetic period.
  • Rabbit intubation can be accomplished using either an orotracheal or nasotracheal technique. Both intubation methods can be challenging in rabbit patients and require patience and practice.
  • Nasotracheal intubation may be the preferred approach in situations where maximum access and maneuverability is required in the oral cavity. Nasotracheal intubation is also preferred where an extended recovery is expected.
  • Nasotracheal intubation should be avoided in patients with known or suspected upper respiratory infections or situations in which one or both sides of the nasal passage have preexisting edema or narrowing.

Introduction

Rabbits as pets have been increasing in popularity since the 1960s. The most recent USDA census of rabbit populations in the United States was performed in 2002. This data estimated 5 million pet rabbits and 2 million rabbits raised for the meat industry (USDA 2002). It is safe to assume the numbers have increased in the past 15 years.

As pet rabbit ownership increases, so too does the demand for veterinary care. Numerous rabbit patients will present for services that require anesthesia such as castration, ovariohysterectomy, mass removal, and dental care. Anesthetic care provided to rabbit patients should be on par with the standard of care offered to more traditional canine and feline patients. This includes intubation, analgesia, intravenous catheter placement, and anesthetic monitoring. Historically rabbit intubation was considered “too challenging” to attempt and anesthesia was often maintained with a mask, which does not allow for airway control, adequate positive pressure ventilation, or reliable end-tidal carbon dioxide (ETCO2) monitoring. Administering inhalational anesthesia via an anesthetic mask can dramatically increase waste gas exposure for personnel but may also cause dilution of the administered anesthetic if room air is drawn into the mask.

 

Indications

Ideally, any patient undergoing anesthesia should be intubated. Nasotracheal intubation may be indicated in cases where the maxilla, mandible, or oral cavity is the primary area of interest. Nasotracheal intubation may be preferred in cases with oral infection, oral abscess, or dental overgrowth that prevents passage of an orotracheal tube (Fig 1, Fig 2). Nasotracheal intubation may also be helpful in situations where an animal is required to be repositioned repeatedly as it can be easier to secure the nasotracheal tube.

Endoscopic view of a rabbit with significant abscess and purulent material in the oral cavity

Figure 1. Endoscopic view of a rabbit with significant abscess and purulent material in the oral cavity. Photo credit: Katrina Lafferty.

 

Endoscopic view of a rabbit with dental overgrowth that could hinder orotracheal intubation

Figure 2. Endoscopic view of a rabbit with dental overgrowth that could hinder orotracheal intubation. Photo credit: Katrina Lafferty. Click image to enlarge

Potential complications

Complications are primarily associated with traumatic nasotracheal intubation. Repeated attempts can result in damage to the nasal turbinates and soft tissue, leading to edema and potential blockage of the nasal passage. As rabbits are obligate nasal breathers, obstruction of one or both sides of the nasal canal can lead to respiratory distress. There is some concern when placing an nasotracheal tube in rabbits with an upper respiratory infection or “snuffles.” Placement of the nasotracheal tube may introduce bacterial contaminants further along the respiratory tract. While there is little evidence to confirm infection rates, it may still be prudent to avoid nasotracheal intubation in patients with a known nasal infection.

 

Equipment

Equipment needed for nasotracheal intubation in rabbits is nearly identical to equipment required for intubation in most species.

  • 0.1-0.2ml of 2% lidocaine (keeping under a 2 mg/kg dose range)
  • 1ml needleless syringe
  • Water-soluble lubricant or lubricant containing lidocaine
  • Endotracheal tubes, size 2.0 or 2.5 mm, uncuffed
  • Gauze tie or rubber tie to secure nasotracheal tube after placement
  • Capnograph (optional)

 

Step-by-step instructions

Create an appropriate anesthetic plan for the individual patient that addresses anticipated pain level and duration of the procedure. The use of preanesthetic medication contributes to a smooth anesthetic induction and better conditions for intubation in rabbits. After induction of anesthesia, when sufficient muscle relaxation is achieved, intubation should be attempted. If using an injectable induction protocol provide oxygen via an anesthetic facemask until the patient attains an adequate plane of anesthesia (Lennox 2008).

First, administer 2% lidocaine (0.1-0.2 ml) into the nasal passage with a syringe (Fig 3).  Continue to provide oxygen support for 30-60 seconds after administration to allow the local anesthetic agent to take effect.

Instillation of 2% lidocaine into the nasal passage

Figure 3. Instillation of 2% lidocaine into the nasal passage. Photo credit: Katrina Lafferty. Click image to enlarge

Positioning is key for correct nasotracheal intubation. Place the patient in sternal recumbency with the head and neck hyperextended (Fig 4). Hyperextension aligns the nasopharynx with the trachea and makes passage of the endotracheal tube into the trachea possible.

Figure 4. Correct positioning for nasotracheal intubation. Note the rabbit is in sternal recumbency with the head and neck hyperextended. Photo credit: Katrina Lafferty

Figure 4. Correct positioning for nasotracheal intubation. Note the rabbit is in sternal recumbency with the head and neck hyperextended. Photo credit: Katrina Lafferty

The normal rabbit nasal passage is narrow and even in the largest of rabbits, plan to use a 2.0-2.5 mm endotracheal tube (Lichtenberger and Ko 2007). Sterile lubricant should be used on the endotracheal tube to facilitate a smoother and less traumatic placement of the tube. Use caution with the amount of lubricant. Overly enthusiastic application of the lubricant can obstruct the lumen of the endotracheal tube.

Once the patient is properly relaxed and positioned, the lidocaine instilled, and the endotracheal tube lubricated, insert the bevel of the endotracheal tube into the ventral nasal canal (Fig 5). Direct the tube in a ventromedial direction.

Another way to describe the insertion direction is “in and down.” This is “in” through the nostril opening and “down” toward the nasal passage and trachea.

Insertion of the endotracheal tube through the nasal opening

Figure 5. Insertion of the endotracheal tube through the nasal opening. The bevel of the tube is pointed ventromedially. Photo credit: Katrina Lafferty. Click image to enlarge.

As the nasal canal is very narrow, a minor amount of resistance or “drag” is to be expected as the endotracheal tube moves through the nasal passage. However, there should be a very small amount of resistance. If there is a significant amount of resistance or a “crunching” sensation, it means either endotracheal tube diameter is too large or the tube has veered into the nasal turbinates where it can cause tissue damage, bleeding, and edema. If incorrect positioning of the tube is suspected, remove and redirect the endotracheal tube.

Rabbits have a large epiglottis that is often entrapped and can make traditional orotracheal intubation more challenging. Repeated attempts at orotracheal intubation can lead to hemorrhage and edema in the oropharynx (Fig 6). One benefit of nasotracheal intubation is that epiglottal entrapment tends not to hinder passage of the nasotracheal tube (Devalle 2009).

Endoscopic view of soft tissue damage caused by repeated attempts at orotracheal intubation

Figure 6. Endoscopic view of soft tissue damage caused by repeated attempts at orotracheal intubation. Photo credit: Katrina Lafferty. Click image to enlarge

Pass the endotracheal tube through the nasal canal until fogging is visible within the tube (Fig 7). The condensation is visible with an expiratory breath and disappears upon inspiration. The tracheal opening is at its widest on inspiration and the endotracheal tube should be advanced with inspiration or when condensation clears in the tube. In addition to watching for fogging in the tube, a capnograph can be attached to the endotracheal tube and used to monitor correct placement. Detection of end-tidal carbon dioxide and display of a waveform confirms correct endotracheal placement. A word of caution:  if using a side-stream capnograph, there will be a one to two breath delay in the actual readings.

Fogging seen in the endotracheal tube

Figure 7. Fogging seen in the endotracheal tube. Condensation appears in the lumen of the tube with expiration and clears upon inspiration. Photo credit: Katrina Lafferty. Click image to enlarge

Correct placement of the nasotracheal tube can be confirmed by continued fogging in the endotracheal tube, auscultation of bilateral breath sounds during manual ventilation, and continued capnograph readings (Fig 8) (Krüger et al 1994). Secure the endotracheal tube using a rubber tie or gauze tied behind the ears (Fig 9).

Confirmation of nasotracheal placement

Figure 8. Confirmation of nasotracheal placement using a side-stream capnograph. Photo credit: Katrina Lafferty. Click image to enlarge

Nasotracheal tube secured behind the head.

Figure 9. Nasotracheal tube secured behind the head. Photo credit: Katrina Lafferty. Click image to enlarge

As previously mentioned, rabbits are obligate nasal breathers. I recommend only attempting nasotracheal intubation in one side of the nasal passage. If placement of the nasotracheal tube is not successful, consider other intubation techniques such as blind oral intubation or endoscopic intubation (Devalle 2009).

 

Recovery

When clinically indicated, the nasotracheal tube can be left in place until the patient is fully recovered as there is no danger the patient can bite through the endotracheal tube. Supplemental oxygen can be provided for as long as required. Keep in mind, however, that rabbits are also prone to laryngospasm, which can occur with prolonged intubation.

 

Conclusion

Every anesthetic event in the rabbit should include endotracheal intubation as part of the protocol, and nasotracheal intubation may be the preferred technique in select situations. As with any skill, nasotracheal intubation can be mastered with practice and patience, and is ultimately in the best interest of the anesthetized rabbit.

 

References