When it comes to endotracheal intubation, it is important to know the associated anatomy and what to look for when attempting intubation in the species that is being anaesthetised. This article will cover the different ways, the steps to successfully intubate the patient, the appropriate range of endotracheal tubes (ETTs), how to secure the ETT, the ways to confirm the correct placement, cuff inflation techniques and extubation in canine, feline, rabbits, guinea pig and avian patients.
Canine
Endotracheal intubation is commonly performed in sternal recumbency after anaesthesia is induced. Sufficient induction agent(s) should be administered to ensure that the swallow reflex is abolished and to prevent excessive coughing around the ETT. In some cases, intubation may need to be performed in lateral recumbency—for example, in patients with a fractured limb, a head injury (eg following a road traffic accident), or those requiring cardiopulmonary resuscitation (CPR) and who cannot be moved (Auckburally and Flaherty, 2017).
Veterinary nurses who routinely intubate in sternal recumbency should also practise lateral recumbency intubation for these scenarios. The technique remains the same, but patient positioning differs. Proper restraint is essential to facilitate successful intubation, as incorrect restraint can impede laryngeal visualisation, prolonging the procedure (Bryant, 2009).
The use of a laryngoscope is recommended, as it aids intubation and improves visualisation of the trachea, thereby reducing the risk of complications (Faunt et al, 2022). Lubrication may be used based on clinical preference.
Ideally, having three sizes of ETT and visualisation of the trachea opening is one way to identify the correct size ETT to place (Bryant, 2009). Another way is to use the nose area between the nostrils using the end tip of the ETT; the correct size tube would fit between each nostril.
Feline
Cats can be more challenging to intubate than dogs, but with practice, the procedure becomes straightforward. The feline patient should be positioned in either sternal or lateral recumbency, depending on whether they can be moved into a sternal position.
As cats share the same anatomical structures as dogs, intubation is performed using visualisation and a laryngoscope. However, cats are at greater risk of laryngospasm, which is usually self-limiting. If laryngospasm occurs, intubation should be paused, and oxygen should be administered.
Other airway devices can be used in cats, such as the supraglottic airway devices (SGAD) that are common for rabbits (Figure 8).
Lapine: rabbits
Rabbits are difficult to intubate but can be performed in several ways, blind, use of a laryngoscope, SGAD (V-gel), and endoscope. Just like feline patients, rabbits are at high risk of laryngospasm, so lubricant and sometimes 2% lidocaine should be used before attempting to intubate. Lignocaine spray can also be used if it is available (Proença, 2023).
Other airway devices, such as the V-gel, can be used to establish an airway without causing trauma to the larynx (Figure 13). V-gels facilitate the delivery of inhalation gases and oxygen by forming a seal over the laryngeal opening, with the tip positioned in the oesophagus. This device does not enter the trachea.
Placement is performed blindly, and the use of a capnograph is required to confirm correct positioning. Securing the device with a tie is advised, as it is prone to displacement when the patient is moved (Fusco et al, 2021). V-gels do not cause laryngeal irritation or trauma, are easy to insert, have no airway resistance, are available in various sizes, and can be re-used and autoclaved.
However, V-gels do not allow oral access for surgical procedures, and because achieving a tight seal can be challenging, there is an increased risk of aspiration (Hughes, 2016).
Guinea pigs
Guinea pigs have a palatal ostium, which makes intubation challenging. This structure is an opening that connects the oropharynx to the pharynx and is the first anatomical feature visible during intubation (Bament, 2012). Their narrow oral cavity, palatoglossal arches, tongue and soft palate contribute to this difficulty (Larenza-Menzies, 2020). Additionally, guinea pigs exhibit hypersalivation during anaesthesia (Johnson, 2011). The palatal ostium is not the opening to the trachea. Instead, the small vocal folds should be aligned with the palatal ostium (also referred to as the intrapharyngeal ostium), and the ETT should be passed through both to ensure correct tracheal placement. Guinea pigs are unable to vomit and are at increased risk of hypoglycaemia and gut stasis; therefore, fasting is usually not required. Overnight fasting can induce hypoglycaemia, which impairs thermoregulation (Hawkins and Pascoe, 2016). For inducing anaesthesia, they are placed in an induction box or mask to be anaesthetised. During this process, guinea pigs are likely to regurgitate as, despite fasting, they can eat their own faeces and store faeces or food in their cheek pouches. Lacrimation and urination can also occur (Schmitz et al, 2016).
Avian
The avian patient has complete cartilaginous rings around the trachea with no epiglottis, vocal folds, arytenoids, or thyroid cartilage (Lee, 2025). What is seen by visualisation is a glottis (opening to the trachea) (Shelby and McKune, 2023) (Figure 14). Therefore, intubation is considered relatively easy, and the size of ETT needs to be considered, as the trachea is larger than other companions as a result of their highly developed respiratory system.
Cuff inflation
Cuff inflation is important for creating a seal between the ETT and the tracheal wall, preventing environmental contamination when using inhalation gases, reducing the risk of aspiration if a patient regurgitates under anaesthesia and to facilitating assisted ventilation if necessary.
Certain species are at higher risk of regurgitation, including canines, felines, and avian species. Brachycephalic breeds are particularly predisposed to regurgitation because of the high negative thoracic pressure required to overcome upper airway obstruction (Shaver et al, 2017). Feline patients have a significantly lower incidence of gastro-oesophageal reflux compared with canines (Garcia et al, 2017). In avian patients, the risk of regurgitation is increased because the crop serves as a food storage organ and is located close to the mouth (Fryer, 2009).
The American Animal Hospital Association (2020) recommends fasting healthy canine and feline patients for 4–6 hours before anaesthesia, with free access to water until premedication. Avian patients require different fasting protocols, typically involving crop palpation or emptying before anaesthesia, as food should not be withheld for more than 2–3 hours (Fryer, 2008). However, in cases where a Cole ETT is used, a non-cuffed tube designed to prevent tracheal mucosal injury can still help reduce the risk of aspiration.
The appropriate inflation pressure of an ETT cuff varies depending on species, brand, model and material (Klonner et al, 2023). In canines and felines, which are prone to regurgitation, using a cuffed ETT is highly recommended to form a seal. However, excessive pressure must be avoided to prevent tracheal mucosal injury, stricture formation, tension pneumothorax or reduced capillary perfusion of the trachea (Veen and de Grauw, 2022).
Several techniques exist to ensure correct cuff inflation pressure, although there is limited data on the prevalence of each method in clinical practice (White et al, 2020). One method involves the use of a Tru-Cuff syringe, which allows visual observation of a green and red line to indicate appropriate inflation (Figure 15). Another option is the AG CUFFILL, a digital manometer that measures the exact pressure applied during cuff inflation (Figure 16). A specifically designed manual manometer can also be used, which attaches to the pilot balloon of the ETT and is squeezed until a pressure of 20–30 cmH2O is achieved (Figure 17). The PressureEasy device functions differently, as it has three connectors: one placed between the ETT and the circuit, one attached to the pilot balloon and a third for the syringe. Air is injected until a green bar appears, indicating appropriate pressure (Stein, 2018) (Figure 18). Literature suggests that the PressureEasy device is the most effective method for achieving the recommended cuff pressure (White et al, 2020) (Figure 11).
For high-volume, low-pressure cuffs, the recommended inflation pressure is 20–30 cmH2O (Klonner et al, 2023). Cuffed ETTs should be used in canines and felines, whereas other species typically require uncuffed tubes. Most species require a cuff pressure of 20–30 cmH2O (Klonner et al, 2023).
There are currently no evidence-based guidelines for achieving an optimal tracheal seal following endotracheal intubation (Veen and de Grauw, 2022). The recommended methods include pilot balloon palpation, where the firmness of the pilot balloon is assessed subjectively to estimate cuff inflation. The minimal occlusion volume technique involves two people, with one administering intermittent positive pressure ventilation (IPPV) while the other inflates the cuff in small increments using a syringe until an audible leak at the mouth ceases (Scales, 2020) (Figure 19). This is called the ‘listening for a leak’ test, which determines whether the cuff is adequately inflated to provide a proper seal. In larger animals, capnograph waveform observation can be useful, as a well-shaped waveform indicates effective tracheal sealing (Veen and de Grauw, 2022). These methods help ensure the cuff is sufficiently inflated to prevent inhalation leakages while allowing effective IPPV.
Extubation
If using a cuffed ETT, the cuff should be deflated before extubation. If there is concern about fluid or foreign material around the tube, this should be removed or visually checked using a laryngoscope. Alternatively, the cuff can be partially deflated so that, when the ETT is removed, any excess material is pulled out with it, reducing the risk of aspiration (Bednarski et al, 2011). Close monitoring during the recovery period is advised to prevent complications. All patients should be spontaneously ventilating before extubation and provided with 100% oxygen via a mask or breathing circuit through the ETT (Nutt et al, 2014).
Dogs can be extubated when a strong palpebral or swallowing reflex is present, or when there is obvious limb or head movement. In brachycephalic breeds, prolonged extubation is advised, as they generally tolerate it well and are often fully conscious with the tube still in place. The ETT should be removed when the patient begins chewing on it. Oxygen supplementation and monitoring of respiratory patterns are essential to prevent obstruction during recovery. Additional ETTs, a laryngoscope, a pulse oximeter and an inducing agent should be readily available in case re-intubation is required (Grubb, 2022).
In cats, because of the risk of laryngospasm, extubation should be performed when a strong palpebral reflex, ear flick, cough, increased respiratory rate, or tongue movement is observed (Nutt et al, 2014). Small mammals, such as rabbits, should be closely observed and extubated at the first signs of coughing, tongue movement or signs of light anaesthesia. They should then be placed in sternal recumbency with oxygen provided via a mask (Lee et al, 2019).
Avian patients recover rapidly, and extubation should be performed when head movement is observed (Kubiak et al, 2016). They should be wrapped in a towel during extubation to prevent excessive wing flapping, which can cause self-injury. This is particularly important for birds of prey to ensure the safety of both the patient and the handler (Hollwarth, 2023).
Conclusions
Each patient requiring anaesthesia will be different, and when working with different species, each presents a unique approach to completing the task. Whether it is intubation, as in this case, or procedures such as blood withdrawal, intravenous catheter placement or assessing planes of anaesthesia, some species require specific techniques to perform these tasks successfully.
Although each species presents challenges—such as intubation—they share similar anatomical structures, including the trachea and lungs, and the same physiological process of respiration. These similarities remain despite variations in size, equipment and the methods used to locate and intubate them. The fundamental principles of intubation still apply, including identifying the tracheal opening, ensuring correct placement and using end-tidal CO2 monitoring for confirmation. However, species-specific differences can make intubation more challenging.
Veterinary nurses and technicians must rely on their training and knowledge to adapt and perform these tasks successfully.