Comparing aspects of permanent tracheostomy between cats and children – can we learn from pediatric medicine?

Permanent tracheostomy has become a routine clinical intervention in children (> 4000/y in the US) (Watters 2017, Muller et al. 2019, Esianor et al. 2020), but is a rare procedure in small animals (Guenther-Yenke and Rozanski 2007, Stepnik et al. 2009, Occhipinti and Hauptman 2014, Tobias and Johnston 2018, Grimes et al. 2019). Tracheostomy is a surgical procedure during which an opening is created in the ventral trachea in order to bypass an obstructed upper airway (Bluestone and Rosenfeld 2002, Hardie 2014, Aronson 2016, Clarke 2017, Tobias and Johnston 2018, Puri and Höllwarth 2019). Temporary tracheostomies are typically performed to facilitate respiratory ventilation in emergency cases of life-threatening upper airway obstruction or during surgeries where placement of an endotracheal tube is not possible. Permanent tracheostomy is performed in patients with progressive or permanent conditions, which cannot be treated successfully by other methods. The procedure involves the surgical creation of a stoma distal to the obstruction by either removing a segment of the tracheal wall and suturing tracheal mucosa to the skin or, in case of total laryngectomy, suturing the transected end of the trachea to the skin (Hedlund et al. 1982, Bluestone and Rosenfeld 2002, Clarke 2017, Tobias and Johnston 2018, Puri and Höllwarth 2019, Vincenti et al. 2021).

Literature research was performed online with PubMed, ScienceDirect, Researchgate, Sagepub and Google Scholar using the following key search terms: “tracheostomy”, “tracheotomy”, “trachea”, “tracheal histology/anatomy” and a term defining the relevant participants “cats/feline”, “small animals”, “children/pediatric”.

The larynx is composed of three unpaired bilateral cartilages (epiglottis, cricoid and thyroid) and one paired cartilage (arytenoids) (Nickel et al. 2004, König et al. 2007, Hudson and Hamilton 2010). The epiglottis of the feline larynx is spade-shaped (Hudson and Hamilton 2010). The hyoepiglottic muscle is connected to the ceratohyoid bone and is responsible for ventral movement of the epiglottis during breathing (Weissengruber et al. 2002). The arytenoid cartilages are small and the corniculate and cuneiform processes are absent. The arytenoid cartilages are pyramidal in shape and connected by an interarytenoid ligament (Hudson und Hamilton 2010). There are two pairs of tissue folds at the cranial end: the vestibular and the vocal cord folds (Kirby 2014). An absence of laryngeal ventricles has been described in the feline larynx (Fig. 1) (Ettinger and Feldman 2010, Hudson and Hamilton 2010).

The human epiglottis is generally leaf-shaped but 50% of children have an omega-shape appearance (Minnich and Mathisen 2007, Prakash and Johnny 2015). The epiglottis is equipped with a hyoepiglottic ligament rather than the hyoepiglottic muscle described in cats. As this ligament has no contractile function, the thyroepiglottic muscle acts as a depressor of the human epiglottis instead (Amis et al. 1998).

The histologic composition is similar between species despite that variations in the frequency may occur in each cell type/tissue and location (Premanandan and Jennings 2017, Whitsett 2018). The respiratory tract is lined with the same tissue found in the nose, larynx, trachea and bronchi (Premanandan and Jennings 2017, Whitsett 2018). The mucosa comprises a pseudostratified columnar epithelium containing ciliary epithelium, non-ciliary epithelium and secretory cells, which cause an upward stream of mucus and foreign bodies (Jeffery 1978, Wine and Joo 2004, Widdicombe and Wine 2015, Premanandan and Jennings 2017). More distal parts of the airways have smaller and fewer secretory cells than proximal parts. Submucosal glands with included mucous and serous cells, non-ciliated club cells and epithelial goblet cells represent the three most common secretory cell types of the respiratory epithelium (Whitsett 2018). Of these, the mucus-producing goblet cells occur frequently and are filled with mucin, a viscous substance with a high molecular weight. The submucosal glands occupy a significant proportion of the tracheal and bronchial wall and contain seromucous secretions (Jeffery 1978, Ballard and Inglis 2004, Widdicombe and Wine 2015, Premanandan and Jennings 2017, Whitsett 2018). Club cells (previously known as Clara cells) continuously release gel-forming mucin and have stem cell capability. In response to irritation, club cells are able to convert into goblet cells (Widdicombe and Wine 2015).

The Reid index is defined as the ratio of the mean thickness of the submucosal mucous secreting glands/ thickness of the bronchial wall of the respiratory tract (Arara 2011). The Reid index value in healthy cats is higher than in healthy humans and ranges between 0.61 and 0.65. The feline bronchial glands are histologically more prominent than in other domestic animals and humans (Arara 2011). The Reid Index in healthy adult humans should be smaller than 0.4. In patients with chronic bronchitis, which causes submucosal gland hypertrophy and hyperplasia, the Reid Index rises to 0.5 or higher. The Reid Index is age-dependent, the physiological ratios in healthy infants with 0.37 and 0.41 are higher than in adults (Ballard and Inglis 2004)

The most common indications for permanent tracheostomy differ between species. The most common reasons for permanent tracheostomy in cats include laryngeal masses, inflammatory laryngeal diseases, laryngeal paralysis and trauma (Stepnik et al. 2009, Tobias and Johnston 2018). Indications for pediatric tracheostomy include upper airway obstruction secondary to infectious disorders as well as respiratory, cardiopulmonary or neurological impairment, resulting in the need for prolonged ventilation support (Gergin et al. 2016).

The literature search revealed only one surgical method for permanent tracheostomy in cats, which is adapted from dogs (Hedlund 1994, Hardie 2014, Aronson 2016, Tobias and Johnston 2018). Tracheostomy is performed under general anesthesia. The cat is positioned in dorsal recumbency, the neck is extended and surgically prepared. The incision is made caudal to the location of the obstruction. The skin incision is made on the ventral midline of the trachea, spanning from the cricoid cartilage to the 6th tracheal ring (Hedlund 1994, Aronson 2016, Tobias and Johnston 2018). Due to a higher incidence of complications, incisions caudal to the 12th tracheal ring are not recommended (Tobias and Johnston 2018). Excessive kinking of the trachea in that region may result in a higher mortality rate secondary to airway obstruction (Tobias and Johnston 2018). Mattress sutures can then be used to appose the previously separated sternohyoid muscles at the dorsal midline of the trachea (Fig. 2a). This moves the trachea in a ventral direction and thus reduces tension on the stoma (Tobias und Johnston 2018). The tracheal stoma is created by removing a rectangular segment (1/3–1/2 of the circumference of the trachea in width) from the ventral aspect of 3 to 5 tracheal rings (Fig. 2b) (Hedlund 1994, Bartoli et al. 2008, Aronson 2016, Tobias and Johnston 2018). A section of the skin, similar to the size of the stoma is resected to form the final opening (Fig. 2b). If excess folds of skin pose a risk of obstruction, a larger section can be resected. In order to prevent tracheal collapse, the tracheal stoma should be kept as small as possible (Hedlund 1994). However, tissue contraction during the healing phase can cause a significant reduction of the stoma and should be taken into consideration (Hedlund et al. 1982, Hedlund 1994, Hardie 2014, Tobias and Johnston 2018). Unfortunately, no species-specific recommendations regarding stoma size currently exist. An H-shaped incision of the tracheal mucosa ensues. The resulting flaps of mucosa are folded over the edges of the tracheal cartilages and anastomosed to the skin (Fig. 2c) (Hedlund 1994, Aronson 2016).

Tracheostomies are typically performed under general anesthesia with the patient‘s head stabilized and neck extended using a shoulder roll. It is important not to overextend the neck as this can cause a pull of thoracic vessels into the neck (Clarke 2017). To minimize bleeding, a local anesthetic and a vasoconstrictor are used. The transverse skin incision is made halfway between the cricoid cartilage and the suprasternal notch. The subcutaneous fat is removed, and the strap muscles are separated along the midline raphe. If the thyroid isthmus be positioned across the trachea, it can be retracted cranially if possible or severed using ligation or bipolar diathermy (Bluestone and Rosenfeld 2002, Clarke 2017, Puri and Höllwarth 2019). A vertical incision across two tracheal rings is then made in the midline of the tracheal wall between the second and fourth tracheal ring. Since no cartilage is removed in pediatric tracheostomy (Bluestone and Rosenfeld 2002) and the tracheal stoma can close quickly without a tracheostomy tube in place, silicone or silastic tracheostomy tubes are necessary for both temporary and permanent tracheostomy techniques. Tracheostomy tubes come in different sizes and, in children aged under one year, should be chosen according to the following formula: (age in years/4) + 4mm = internal diameter of the tube (Watters 2017). Given the strong foreign body inflammatory reactions seen in children, pediatric tracheostomy tubes have a small diameter without an inner cannula (single lumen cannulas), have no fenestration and are uncuffed. The particularly thin walls of the tube leave room for a larger lumen with minimal friction to the skin of the neck resulting in lower inflammatory response (Bluestone and Rosenfeld 2002, Clarke 2017). After tube placement, maturation sutures can be used to fasten the edges of the tracheal wall to the skin. This facilitates the development of a safe stoma and prevents accidental decannulation and formation of granulation tissue (Craig et al. 2005, Watters 2017).

This technique was developed to reduce the incidence of major complications such as accidental decannulation and pneumothorax. Instead of a transverse incision, an X-shaped skin incision is made between the sternal notch and the cricoid cartilage. The resulting skin flaps are circumferentially undermined, muscles and thyroid isthmus are separated as described above. A cross-shaped incision is used to gain access to the trachea. The triangular skin flaps are circumferentially aligned with the triangular tracheal flaps to create the final stoma (Fig. 3) (Koltai 1998, Solares et al. 2004, Schwarz et al. 2017, Thurnher 2020).

Depending on the underlying indication, an array of other surgical techniques can be utilized to optimize the outcome. One example is the inverted U-shaped “Björk flap”, typically used in adults for long-term tracheostomies, in which a tracheal flap is attached to the skin to create a potentially larger stoma than in other techniques (Fig. 4) (Kennedy et al. 2021). This technique is less common in the pediatric medicine and only used in older children with adequate tracheal width (D’Souza et al. 2016, Watters 2017, Fliss 2021). Another option, known as tracheal window resection involves the excision of a square-shaped of the tracheal rings without tracheal flaps and is also used in veterinary medicine (Scurry and McGinn 2007, Cipriano et al. 2015, Janik et al. 2018). These techniques are not usually used in pediatric medicine primarily due to the limited space and the chances of injury of adjacent structures.

In cats, intensive care and close observation in an intensive care unit (ICU) is necessary in the postoperative period to prevent life-threatening complications (Guenther-Yenke und Rozanski 2007, Stepnik et al. 2009, Tobias and Johnston 2018, Vincenti et al. 2021). Intensive care should be performed for at least two weeks in the ICU with close observation of mucous secretions until the stoma is healed and secretions decrease (Tobias and Johnston 2018, Vincenti et al. 2021). In these 14 days after surgery, the tracheal mucosa undergoes squamous metaplasia with possible excessive mucus production (Hedlund et al. 1982, Tobias and Johnston 2018, Vincenti et al. 2021). In this period, emergency equipment, oxygen supply and material for cleaning and suctioning must be readily available at all times (Aronson 2016, Tobias and Johnston 2018). The stoma must be cleaned, humidified and suctioned at least every four to six hours. Humidification is important to decrease mucus production and should be performed equally regularly (Aronson 2016, Tobias and Johnston 2018). Some authors also recommend applying a thin layer of antibiotic ointment to protect the skin from secretions surrounding the stoma (Aronson 2016, Tobias and Johnston 2018). In dogs, it has been shown that the tracheal epithelium reaches a relatively normal state after 16 weeks (Hedlund et al. 1982). While there is no specific data regarding tracheal re-epithelialization in cats, a similar time frame is to be expected. Before discharging feline tracheostomy patients, owners must receive adequate instructions on cleaning the stoma and suctioning the trachea using a catheter and syringe (Vincenti et al. 2021). Secretions slowly decrease over time but can still cause obstruction in the following weeks. To prevent obstruction, close observation, suctioning, humidification and cleaning of the stoma site should be continued in homecare over 4–8 weeks until secretions decrease dramatically (Hardie 2014, Tobias and Johnston 2018).

Tracheostomy tubes are used for temporary tracheostomy in small animals (Mann and Flanders 2012, Aronson 2016, Tobias and Johnston 2018). There are several types of tubes, with single or double cannulas, cuffed and uncuffed. The double cannula has an inner cannula that can be removed, leaving the outer cannula in the trachea. For cleaning, the inner cannula can easily be removed and cleaned separately. The single cannula is more difficult to clean; the entire tracheostomy tube must be replaced if it cannot be cleaned effectively (Mann and Flanders 2012, Aronson 2016, Tobias and Johnston 2018).

After the surgery, the patient is monitored in an ICU for a minimum of five to seven days (Puri und Höllwarth 2019). Emergency equipment, including different sizes of tracheostomy tubes should be readily available. Regular cleaning of the tube and stoma is essential to prevent infection and obstruction. Suctioning of the tube is important to clear airway secretions. To avoid damage of the trachea, suctioning of the tube is only performed when necessary to remove excessive secretions and prevent obstruction (Nawrocki et al. 2021). Instillation of sterile saline before suctioning is no longer recommended due to a possible adverse effect on oxygen saturation (Nawrocki et al. 2021). In the immediate postoperative period, it is recommended to use an active heated humidity system. Active humidification devices use a heated humidifier with or without ventilator support (Volsko et al. 2021). Passive humidification should be continued using a heat and moisture exchanger (HME) that sits permanently on top of the tube (Birk et al. 2017, Puri and Höllwarth 2019). A HME should not be used when secretions are thick (risk of airway obstruction), a large leak around the tube is present or the patient cannot tolerate the additional dead space (Volsko et al. 2021). Recommendations about active warming and humidification of air exist for the care of a tracheostomized child with an inspired air temperature of 32–34 °C and humidity of 36–40 mg H₂O/L. In a study, a reduction in lower respiratory tract infection, tube obstruction and emergency tube change was achieved with long-term use (ten weeks) of active humidification at night and a HME during the day (McNamara et al. 2014). Inadequate humidification (< 25mg H₂O/L for 1 h or < 30mg H₂O/L for 24 h) has been reported to cause mucosal malfunction (Volsko et al. 2021). To keep the airway hydrated and humidified, an adequate water intake and infusions are necessary considering the greater fluid loss due to the tracheostomy (Avelino et al. 2017).

The complication and mortality rates in cats with permanent tracheostomy are high. Two retrospective studies found that the mean survival time of cats with permanent tracheostomies ranges from 20.5 to 42 days with 46% of cats dying shortly after the procedure due to post-operative complications (Guenther-Yenke and Rozanski 2007, Stepnik et al. 2009). In one report of a cat undergoing a permanent tracheostomy following a total laryngectomy, the cat was still alive 13 months after surgery (Vincenti et al. 2021). The most common complications include mucous plug formation with subsequent stoma or airway obstruction and dyspnea (14 out of 21 cats [Stepnik et al. 2009]) or death by asphyxiation (11 out of 21 cats (Stepnik et al. 2009) and two out of five cats (Guenther-Yenke and Rozanski 2007). Local tracheal collapse, stoma stricture, pulmonary edema and pneumonia, surgery site swelling, vomiting and anorexia/dysphagia have also been described (Guenther-Yenke and Rozanski 2007, Stepnik et al. 2009, Vincenti et al. 2021). Cats with a history of airway inflammation tend to show a significantly increased mucus production and epithelial irritation, according to one study (Stepnik et al. 2009). The mortality rate in these cats was 6.61 times as likely as in cats without any history of inflammatory laryngeal disease (Stepnik et al. 2009).

The mortality rate in tracheostomized children and infants (under two years of age) is reported at 8% and 23.5% respectively (Watters 2017, Esianor et al. 2020). However, major complications of the procedure are rare and the majority of deaths is linked to the initial cause of hospitalization (Watters 2017, Esianor et al. 2020). According to recent studies, better knowledge of the anatomy of the infant’s neck as well as better surgical routines have rendered perioperative complications such as accidental damage to the surrounding structures (esophagus, recurrent laryngeal nerve, brachiocephalic vein), major bleeding and pneumothorax/pneumomediastinum a rarity (Puri und Höllwarth 2019). Due to improved surgical techniques, intensive care and the creation of new medications, complication and mortality rates associated with the tracheostomy in the last three decades have decreased significantly (Dal’Astra et al. 2017, Lubianca Neto et al. 2020). In the immediate postoperative period, late hemorrhage of the trachea or surrounding structures, tracheal obstruction by secretions, tube dislodgement, accidental decannulation and surgical emphysema are the most common life threatening complications (Thompson et al. 2012). Obstruction of the trachea and accidental decannulation are among the most common late postoperative and homecare complications. As a long-term complication, persistent granulation tissue induced by chronic irritation and repeated suctioning has been reported. Granulation tissue growing into the tip of the cannula can induce airway obstruction and bleeding. Local infection is uncommon and antimicrobial treatment is successful in most cases. After decannulation, tracheal fistulas occur in 20–40% of cases and require revision surgery. Overall tracheostomy-related complications are experienced by 15%–20% of patients in recent studies (Berry et al. 2009, Watters et al. 2016, Watters 2017).

On an anatomical level, the feline larynx and trachea are very similar to those of children. The adult feline trachea has a diameter of 7–10 mm (Hardie 2014) which is comparable to the tracheal diameter seen in children aged 2–10 years (7.4 mm–10.5 mm) (Griscom und Wohl 1986). Pediatric tracheostomy protocols thus appear to provide a good basis for the development of recommendations for performing the procedure in cats. However, exact data regarding the length and in situ positioning of the feline trachea are still lacking. In addition, data about the healing and adaptation process of the tracheal epithelium in cats were not reported and further anatomical and clinical studies are needed.

Pediatric tracheostomy management appear to provide a promising basis for the development of protocols in the cat. Interestingly, data regarding precise anatomical dimensions of the feline trachea turned out to be extremely scarce. Furthermore, exact reports of the response to chronic irritation were not found. To reduce the high rate of complications and mortality in feline permanent tracheostomy patients, further anatomical and clinical studies are necessary. A modified surgical technique such as the Björk flap could be an option to extend the tracheal stoma and therefore reduce the onset of life-threatening complications. Postoperative guidelines for medical staff and owners may then be adapted to the feline patient to achieve a significantly better outcome.

The authors would like to thank Moritz Zimmermann for his friendly support and the design of all the graphics in the manuscript.

There are no protected, financial, professional or other personal interests in a product, service and/or company that could influence the content or opinions expressed in the manuscript. In case of possible conflict of interest it has to be indicated clearly.

The authors declare that they had no financial support for this publication.

Authors assure to have met common international ethical guidelines during the genesis of the work, the underlying research and its publication. Informed consent: This work did not involve the use of animals and therefore informed consent was not required. No animals or humans are identifiable within this publication, and therefore additional informed consent for publication was not required.

Conception/design of the work: SV.

Data collection: JZ.

Data analysis and interpretation: JZ.

Drafting the article: JZ.

Critical revision of the article: SV, JZ.

Final approval: SV, JZ. 

Dr. Simona Vincenti, simona.vincenti@vetsuisse.unibe.ch