Airway Management for Pet Rabbits

Rabbits are the third most popular pet in the United States, with an estimated population of 2.2 million pet rabbits.¹ With pet rabbit ownership increasing, veterinary nurses and veterinarians should aim to provide exemplary care. Anecdotally, veterinary professionals fear providing general anesthesia in rabbits, and airway management plans are often neglected. However, the tools and knowledge to provide adequate airway management are readily available. Rabbit anesthetic emergencies are relatively common. Respiratory complications represent one of the main causes of anesthetic-related deaths in rabbits; 1.3% of rabbits die under anesthesia compared to 0.17% of canine patients.² One reason for the higher death percentage in rabbits is attributed to intubation being less commonly performed in rabbits and therefore a patent airway not being maintained during general anesthesia.² To ensure patient safety and allow for effective, reliable inhalation anesthesia, rabbit patients undergoing general anesthesia should be provided with a patent, secure airway following sedation. With this in mind, it is vital that veterinary nurses have a thorough understanding of available airway options.

Endotracheal Intubation

Endotracheal intubation is the standard airway management option for canine and feline patients; however, endotracheal intubation is often neglected in rabbits because it is more technically demanding and the risk of laryngeal collapse is relatively high.^2,3 Without airway management, rabbits are at risk of reflux, regurgitation, inhalation pneumonia, and unreliable inhalation anesthesia.⁴ Additionally, without adequate airway management, rabbits are at a higher risk of upper airway impairment and respiratory complications that can lead to death.^2,5,6

Premedication for sedative effect, multimodal analgesia, and a smoother anesthesia induction should be used. To reduce the risk of laryngeal trauma, polyvinyl chloride (PVC) or silicone tubes without cuffs should be used when intubating rabbits; if cuffless endotracheal tubes (ETTs) are not available, the cuff should not be inflated to reduce the risk of trauma.⁷ As PVC tubes are single use only, the ETT can be included in the anesthetic cost; clients will often accept this extra charge if the risks of not intubating are explained. Silicone tubes are modern veterinary ETTs that can be resterilized for multiple uses and have repairable cuffs. However, silicone tubes have very little curve and can be difficult to place, especially in rabbits. To prevent laryngeal injuries, it is recommended to lubricate ETTs, use an appropriately sized ETT (2 to 4 mm), and use very gentle pressure while following recognized techniques.

For all airway devices, a circuit hold such as the d-grip (Docsinnovent Ltd) should be used to stabilize the device and prevent rotation (FIGURE 1).

FIGURE 1. Docsinnovent Ltd. d-grip holder in use.

Difficulty with intubation is often due to the lagomorph’s relatively large tongue and small oropharyngeal cavity, which limits the ability to directly visualize the glottis. To aid intubation, sedated rabbits should be positioned in sternal recumbency with their head and neck extended.^5,8 Minimal pressure applied to the back of the rabbit’s neck will help reduce tension on the larynx and aid visualization of the glottis. Nontraumatic tissue forceps or a small gauze swab can be employed to pull the tongue to the side. To prevent trauma, care should be taken that the tongue is not depressed on the incisors.

Several intubation techniques for rabbits are recognized; all techniques require practice and time to perfect. Intubation methods can be divided into 2 categories: blind intubation or direct visualization.⁹

Blind intubation is the placement of an ETT without visualization of the glottis, whereby listening to breathing noises guides the veterinary team member to where the tube should be placed. This technique can work well if the veterinary professional  is skilled in this procedure.⁵ However, blind intubation carries significantly higher risks of upper airway trauma, laryngeal spasm, and trauma to the larynx.^5,10 Even if the veterinary professional is skilled in this procedure, direct visualization is recommended to ensure local anesthetic has been applied to the glottis and there are no foreign bodies or trauma present.

Direct visualization of the glottis may require additional equipment such as a rigid or semirigid endoscope; however, intubation is still achievable with a laryngoscope or otoscope.⁸ Compared with blind intubation, direct visualization of the larynx reduces the risk of tracheal trauma and allows food material or foreign bodies to be recognized and cleared.¹¹

All types of intubation require an adequate depth of anesthesia prior to intubation; if the patient is intubated in a light plane of anesthesia, laryngeal spasm is more likely. As with cats and dogs, an adequate depth of anesthesia is needed to be able to intubate as sedation is usually not sufficient and may increase risk of laryngospasm. Local anesthetic can be applied in a spray or trickled down the otoscope onto the glottis for desensitization.

Because rabbits are obligate nasal breathers, the soft palate is disengaged from the epiglottis before intubation. Cyanosis of the soft palate is common following intubation; therefore, speed is important, as is oxygenation between attempts and confirmation of ETT placement.^11,12 ETT placement can be confirmed by auscultating both lung fields to ensure that the ETT lies within the trachea. Bronchial intubation can occur if the ETT has passed the bifurcation and lies within one of the main bronchi, causing uneven ventilation and atelectasis in the contralateral lung. Thoracic movements should result in positive-pressure ventilation of the anesthetic breathing circuit if the ETT is placed correctly. If a PVC or silicone tube is used, condensation of respiration should appear, and capnography can be used to confirm gaseous exchange.

Failed endotracheal intubation can result in trauma to the upper airway and inadequate ventilation; to avoid laryngeal collapse, intubation should not be attempted more than 3 times.² However, it is worth noting that significant swelling may occur with only 1 attempt. If this is the case, alternative airway management, such as nasal intubation, a supraglottic airway device (SGAD), or a face mask, should be considered.¹³ Trauma during intubation is usually associated with poor technique, rough intubation, or repeated attempts. All of these factors are very common in rabbits and can cause hematoma formation, lacerations, cartilage damage, and tracheal avulsion or rupture.

Nasal Intubation

Nasal intubation is an easy, less traumatic method of intubation when compared to orotracheal intubation. Because rabbits are obligate nasal breathers, passing a soft nasogastric tube through the nasal passages into the nasopharynx theoretically leads to direct access to the trachea. The patient can be positioned into sternal or dorsal recumbency with the neck extended upward. A lubricated 1- to 2.5-mm nasogastric tube is inserted into the external naris and gently directed ventromedially; rabbits will often cough once the tube enters the trachea.⁵ A local anesthetic agent can be applied to the tube or nares to reduce the risk of laryngospasm.⁵ Confirmation of placement is similar to endotracheal intubation, with the use of capnography, condensation within the tube, and visualization of the reservoir bag. Potential complications include the possibility of introducing pathogens. Nasal intubation maintenance will require higher oxygen flow rates.

Supraglottic Airway Devices

SGADs are becoming favorable among veterinary professionals; these devices are soft, anatomically shaped cuffs that provide an airway seal around the pharyngeal, laryngeal, and upper esophageal structures. SGADs have been found to have increased airway patency when compared to face masks and allow for intermittent positive-pressure ventilation (IPPV).¹² Studies have shown that SGADs provide a gas-tight seal, which prevents wastage of anesthetic gases, and have significantly less leakage during IPPV compared with the standard ETT and face masks.¹² Therefore, SGADs provide a more superficial and stable level of anesthesia while reducing environmental pollution risks.

SGADs such as the v-gel (Docsinnovent Ltd.) do not enter the trachea or larynx (FIGURES 2 AND 3), avoiding cilia damage, tracheal necrosis, and tracheal perforation; these factors reduce the risk of laryngospasm.¹⁴ The use of topical anesthetic to desensitize the larynx is recommended when placing SGADs. Before placing an SGAD, an appropriate size should be selected for the patient; the correct size can be confirmed prior to insertion by measuring against the patient. Previously, SGADs were expensive to stock a variety of sizes for cats and rabbits; however, the v-gel Advanced (Docsinnovent Ltd.) is priced as a single-use device, and stocking costs are reasonable. Clinics should stock a minimum of 3 consecutive sizes to provide a range of choices for patients.

FIGURE 2. Anatomical positioning of the v-gel. Courtesy Docsinnovent Ltd.

FIGURE 3. Positioning of the v-gel in a rabbit patient. Courtesy Docsinnovent Ltd.

When placing the v-gel, the patient should be held in the same manner as during endotracheal intubation. At a suitable plane of anesthesia, the tongue can be moved aside, and a lubricated v-gel can be advanced gently along the hard palate. The v-gel will often be felt dropping into position, which can be confirmed with capnography. Free training materials, including videos, are available at docsinnovent.com, and clear instructions for use are provided with the v-gel; however, veterinary professionals may gain further confidence by undertaking continuing education on SGADs.

As with ETTs, capnography is a valuable tool that allows for the monitoring of the adequacy of ventilation and circulation.⁵ Changes in end-tidal carbon dioxide can signify airway obstruction and disconnection from the anesthetic circuit. Capnography can also be a highly beneficial tool to measure the success rate of intubation.¹⁵ Several studies have shown that SGADs are quick and easy to place compared to ETTs,^10,16,17 often showing that SGADs reduce the time for the first clinically viable capnography to be taken. SGADs can also be beneficial in an emergency because they may be easier and faster to apply than ETTs.¹⁰ Alongside capnography, placement can be confirmed by feeling breath at the end of the SGAD, and the use of a pulse oximeter can confirm adequate cardiovascular function.⁵ Other methods such as auscultating the lung fields, positive-pressure ventilation of the anesthetic breathing circuit, and cotton wool movement at the end of the connector can be used to confirm placement.

The v-gel is often rapid to place and causes minimal trauma to the upper airway compared to blind endotracheal intubation.¹³ Although both techniques effectively maintain general anesthesia in rabbits, blind intubation techniques may require multiple attempts, potentially contributing to laryngeal trauma and increased postoperative mortality. Previous studies have found that the v-gel becomes dislodged easily if the patient is moved during the anesthetic procedure, and cyanosis may occur if the v-gel compresses the tongue.^5,15,18 However, these studies relate to the original v-gel, which has since been discontinued; the v-gel Advanced is less likely to dislodge or cause lingual congestion.

Face Masks and Induction Chambers

Face masks and induction chambers are often used as the sole induction and airway management for many exotic patients (FIGURE 4). However, due to rabbits’ rising popularity and concurrent advances in evidence-based veterinary medicine, veterinary professionals now have the scope to improve rabbit anesthesia and safety protocols.

FIGURE 4. Use of an induction chamber for inhalation anesthesia in a rabbit patient.

Rabbits induced by inhalation anesthesia via face masks and induction chambers will often exhibit signs of stress such as bucking, struggling, and elevating their heads to avoid inhalation anesthesia.^3,11 Exacerbated by the relatively long time required for inhalation anesthetics to induce unconsciousness, rabbits will breath-hold if induced with inhalation anesthesia alone, causing hypoxia.¹⁹ Dogs and cats show similar results; therefore, veterinary professionals should try to standardize care, including anesthetic protocols, across species. Induction anesthesia with both face masks and induction chambers has been shown to cause periods of apnea and bradycardia, which often result in hypercapnia and respiratory acidosis.³ Furthermore, face masks and induction chambers have increased dead space and create high levels of atmospheric pollution, which can compromise staff safety.^20-22 To reduce the risk to staff, the level of contamination at the workplace should be kept at a minimum pollution level by avoiding inhalation anesthesia, active scavenging, and air circulation systems.^23,24

It is worth noting that face masks and induction chambers can be useful for preoxygenation prior to induction. Face masks are preferred because a tight seal can be created by gently placing the mask over the mouth and nose. Some rabbits will exhibit signs of stress when face masks are used for preoxygenation. In these cases, an induction chamber may be preferred for preoxygenation. Induction chambers can be filled with blankets to reduce dead space and so that the rabbit feels comfortable; if a rabbit is very stressed when handled, an induction chamber can be a safe way to provide preoxygenation.

Summary

ETTs, SGADs, face masks, and induction chambers all have their purpose in small animal practice. Any patient undergoing general anesthesia should have a form of airway management to provide a patent and safe airway. Several studies have shown staff safety concerns with induction chambers and face masks; therefore, ETTs, nasogastric tubes, and SGADs can be safer and more reliable options. Face masks and inductions chambers can be used for preoxygenation; however, inhalation anesthesia should be avoided to prevent stress and injuries. Although ETTs are notoriously known for being technically demanding to place in rabbits, with practice and time, they can provide a reliable and safe airway option. On the other hand, with the introduction of SGADs, veterinary professionals can now easily and reliably manage rabbit airways while minimizing laryngeal problems. SGADs may not replace ETTs but can provide a superior alternative to face masks and induction chambers. It is essential that veterinary nurses and veterinarians research and review airway management options for each patient and select an appropriate device each time. This individualized approach to airway management is the gold standard for today’s rabbit patients.