Standing upper airway surgery: what can be done?

Performing many different upper respiratory tract surgeries in the standing sedated horse is advantageous. The accessibility to the head is improved, the anatomy is in the appropriate position and the visibility is superior, not to mention the added benefit of avoiding the risks of general anaesthesia. The ability to flex, extend and move the head and neck to the left and right facilitates improved accessibility. While this may be appealing to the surgeon and the owner, it often requires specialist equipment and always requires attention to detail, with meticulous planning and careful dissection with very little room for error. Table 1 outlines the standing sedation protocol that used by the author, which has been found to be most effective.

This article describes a selection of diseases that can be treated with standing upper airway procedures, focusing on those associated with the larynx, pharynx and soft palate.

Epiglottic entrapment

This occurs when the aryepiglottic membrane envelopes the rostral aspect of the epiglottis (Figure 1). The treatment for this is to transect the membrane to release the entrapped epiglottis; there are a number of ways to do this.

Endoscope-guided, transoral axial deviation of the entrapping membrane

Under sedation, the horse has the entrapping membrane and surrounding mucosal surfaces sprayed with 2% lidocaine hydrochloride (30ml) via a videoendoscope (Perkins et al, 2007). With the head in extension and a gag in place, the mouth is opened and a hand inserted to physically displace the soft palate dorsally. The entire oropharynx is desensitised with 2% lidocaine hydrochloride and the videoendoscope is placed, via an endotracheal tube for protection, into the oral cavity. Under direct visualisation, a curved hook bistoury (Figure 2) is used to divide the entrapping membrane.

Endoscope-guided, transnasal axial deviation of the entrapping membrane

This is exactly the same procedure as the transoral technique, except the endoscope and the hook bistoury are passed up through the nasal cavities (Ducharme, 2012), which have to be desensitised as opposed to the oral cavity, and the soft palate does not need to be displaced. The relatively recent development of the epiglottic scalpel, which is in essence a shielded hook bistoury, has made this procedure very safe and effective (Lacourt et al, 2011).

Videoendoscopy-assisted laser transection of the entrapping membrane

With the horse sedated in the stocks, and with the head and neck extended, the nasal cavities, nasopharynx and entrapping membranes are desensitised with 60ml of local anaesthetic solution. Via the endoscope, a diode or neodymium-doped yttrium aluminium garnet (Nd:YAG) laser fibre is passed and the entrapping membrane is transected from a caudal to rostral direction (Anderson et al, 1995; Rakesh et al, 2008). Owing to the natural tension of the membrane, this can normally be achieved simply with the application of the laser, but a pair of broncho-oesophageal forceps may be passed up the contralateral nostril to elevate and place tension on the membrane. In some cases of thickened or very tight entrapments, a custom-made shield may be required to be placed caudal to the membrane to elevate it away from the epiglottis and therefore protect the epiglottis from the laser as the membrane is transected (Lacourt et al, 2011). The biggest risk associated with this procedure is inadvertent damage to the epiglottis and the formation of granuloma on the transected membranes.

The advantage of the oral technique is that it prevents inadvertent damage to the soft palate, but the development of the epiglottic scalpel mitigates this. Standing transnasal methods are easier and faster to perform. The laser method takes time and is more complicated with little advantage, as well as having the significant disadvantage of possible damage to the epiglottis.

Transnasal transection using the epiglottic scalpel is inexpensive, quick, easy and safe. The overall recurrence rate for epiglottic entrapment is 4% and approximately 10–15% of cases will develop dorsal displacement of the soft palate postoperatively (Ducharme, 2012).

Nasopharyngeal masses

Typically, the diseases here are subepiglottic cysts, granulomas and epiglottic abscesses. The ability to elevate the head facilitates access and the combined use of broncho-oesophageal forceps to grasp and elevate the mass, along with the transendoscopic laser, makes removal of even large cysts relatively simple. An electrocautery loop/snare is a very useful tool to remove large cystic structures via either a transoral (Figure 3) or transnasal approach. The key to successful removal and preventing recurrence is to remove the entire cystic lining which is facilitated using a laser or the electrocautery device.

Intermittent dorsal displacement of the soft palate and palatal instability

This is where the caudal aspect of the soft palate becomes displaced from its normal position ventral to the epiglottis to sit dorsal to it creating an expiratory obstruction (Figure 4) or the soft palate is markedly unstable and ‘flutters’. There cause of intermittent dorsal displacement and palatal instability is unknown, but is likely multifactorial and associated with neuromuscular dysfunction.

There are a range of different methods of treating these conditions, but this article focuses on the commonly performed ones and those that can be done in the standing sedated horse. However, thermopalatoplasty is also now performed routinely in the standing sedated horse.

Laser thermopalatoplasty

Under sedation, a videoendoscope is introduced into either nostril and 20ml of local anaesthetic solution is applied to the surface of the soft palate, with a further 30ml being sprayed into both nasal passages. A pair of broncho-oesophageal forceps is passed up the contralateral nasal passage to elevate the epiglottis. The laser fibre is then used to ‘spot weld’ the nasal surface of the soft palate approximately 5 mm apart. The laser fibre should be placed in contact fashion for only 1–2 seconds, until the mucosa blisters. A total of 30-50 or so applications are typically made for the treatment.

Hot iron thermopalatoplasty (‘firing’)

Under sedation, a gag is placed and the mouth opened wide with the head and neck extended. A splash block of 60ml of local anaes-thetic solution is applied to the oral mucosa and tongue, then the mucosa of the soft palate is injected with 20ml of local anaesthetic solution to form submucosal blebs. Next, a red hot iron is applied to the mucosa under direct visualisation for 3–5 seconds, starting most rostrally and then working caudally (Figure 5). The process is complete once the two parallel mucosal folds have been obliterated and the oral surface of the soft palate is charred.

There is very little evidence to draw on to compare these two procedures. Both require only 10 days out of work and both have very little complications. The aim of these treatments is to generate fibrosis, thereby stiffening the soft palate making it less able to displace.

Permanent displacement of the soft palate

This is a relatively uncommon disease that possibly has a different aetiology to intermittent dorsal displacement and palatal instability, and is sometimes seen as a complication following laryngo-plasty and/or laryngeal tie-forward. It occurs when the soft palate is permanently displaced and the horse cannot replace it, and the treatment for this is a laser staphylectomy. This is performed under standing sedation and local anaesthesia of the nasal passages and soft palate. Under endoscopic guidance a pair of broncho-oesophageal forceps is placed up the nasal passages and is used to grasp the caudal border of the soft palate. Under gentle traction, this is tented and the laser fibre is used to remove a crescent-shaped piece of the soft palate - not exceeding more than 1cm of the free margin of the caudal aspect of the soft palate.

Resection of too much can lead to severe complications such as dysphagia and aspiration pneumonia. Frequently, it is performed in combination with a sternothyroid tenectomy (Anderson et al, 1995), which is also performed under standing sedation and local anaesthesia, as this is designed to reduce the caudal traction applied to the larynx thereby reducing the likelihood of dorsal displacement.

The prognosis is relatively poor with only up to 60% of cases being successfully treated (Anderson et al, 1995).

Medial deviation of the aryepiglottic folds

Medial deviation of the aryepiglottic folds tends to occur bilaterally and may be associated with intermittent dorsal displacement and palatal instability, but can occur independently and unilaterally. Typically, it is right-sided and associated with immobility of the left arytenoid cartilage (Beroza, 1994; Dixon et al, 2004). This is a dynamic diagnosis, in that it can only be diagnosed during exercise. Treatment for this condition is resection of a 2cm wide wedge from affected aryepiglottic folds. This can be readily achieved in the standing horse, either transendoscopically with the laser or using scissors via a laryngotomy (discussed later in this article). Irrespective of the procedure, following topical application of 60ml of local anaesthetic solution to the larynx a pair of broncho-oesophageal forceps are placed up the contralateral nostril to the aryepiglottic folds to be resected. If using scissors via a laryngotomy, the aryepiglottic fold is tented across the rima glottidis and then sharply transected with a pair of scissors. If performing this transendoscopically, the endoscope is passed up the ipsilateral nostril, the aryepiglottic fold is tented in a similar manner and the laser fibre is used in contact fashion to resect the fold running in a straight line from dorsal to ventral. Direct visualisation using the transendoscopic laser is a quick, neat and easy method of aryepiglottic fold resection. The reported success rate is approximately 75% (King et al, 2001).

Recurrent laryngeal neuropathy

This disease is a best classified as a mononeuropathy of the left recurrent laryngeal nerve, with degenerative changes associated with distal axonopathy (Draper and Piercy, 2018). This disease can cause a range of problems ranging from vocal cord collapse (Figure 6a) to complete paralysis of the left cricoarytenoideus dorsalis (CAD) muscle and subsequent collapse of the left arytenoid cartilage (Figure 6b). It is also recognised as a more dynamic problem, with overground endoscopy allowing us to more accurately diagnose the degree of dysfunction that exists and better direct treatment.

Ventriculocordectomy (‘hobday’)

This is the removal of the vocal cord (cordectomy) and the laryngeal ventricle (ventriculectomy) (Figure 7) and tends to be performed for genuine cases of vocal cord collapse or mild cases of recurrent laryngeal neuropathy, in less active horses, or in cases where there is strict budget (Taylor et al, 2006; Henderson et al, 2007; Cramp et al, 2009; Fulton et al, 2012). It is also performed alongside other procedures such as laryngoplasty and laryngeal reinnervation to reduce the abnormal noise associated with recurrent laryngeal neuropathy (Rakestraw et al, 1991; Brown et al, 2005; Fulton et al, 2012; Barakzai et al, 2019). It can be performed in the standing horse in a variety of different ways.

Videoendoscopy-assisted laser ventriculocordectomy

Typically, this procedure consists of a removal of both the left and right laryngeal ventricles and only the left vocal cord. The reason for performing a unilateral left vocal cordectomy is to reduce the risk of laryngeal webbing/cicatrix formation. This presents a significant risk when performing laser surgery as the latent thermal necrosis of the tissue can lead to more tissue being affected than the surgeon planned.

However, there is a recognition that the remaining right vocal cord can result in continued abnormal noise production (Barakzai et al, 2019). To reduce this, it is possible to perform a cordotomy, which is simply transecting the right vocal cord at its mid-point and allowing the remaining tissue to contract, thus removing the leading edge of the cord and preventing collapse into the airway without risking the complication of cicatrix/webbing formation. In the author's experience, this is easy to do but there remains significant abnormal noise and does not result in such a smooth scar as complete vocal cordectomy. Alternatively, the right vocal cord can be removed in a separate procedure 2 weeks later.

A videoendoscopy is passed up the ipsilateral nostril to the vocal cord to be removed and a pair of broncho-oesophageal forceps is passed up the contralateral nostril. Initially, the base of the vocal cord can be transected under its own tension in a rostral to caudal direction, avoiding the blood vessel in the distal aspect (Figure 9). Next, the forceps are applied to apply tension to the remaining cord which can be resected in a straight line from dorsal to ventral. The ventricles are removed by inserting the forceps into the ventricle, grasping the mucosa and everting it, the laser is then fired to transect it from dorsal to ventral.

Bilateral ventriculocordectomy via a laryngotomy

This is performed in the standing sedated horse with head and neck extended and an incision made on the ventral aspect of the throatlatch, between the paired sternothyroideus muscles, to enter the larynx via the cricothyroid membrane (Figure 8). The laryngeal ventricles are everted using a roaring burr and transected with scissors. The vocal cords are grasped with a pair of Lahey Gall forceps to tent the leading edge of the cord and a curved cut is made with a pair of Metzenbaum scissors, removing a crescent-shaped piece of vocal cord. The same is repeated on the opposite vocal cord. It is important to leave approximately 1 cm of ventral cord intact to ensure that the vocal cord fornix is preserved and prevent cicatrix/webbing formation. This method allows for full and complete removal of the laryngeal ventricles and for a bilateral vocal cordectomy, without the risk of complications. The only real disadvantage is the presence of the laryngotomy, which can be closed but is more often than not left open to heal by second intention, which it generally does without complication over the next 2–3 weeks.

Laryngoplasty (‘tie-back’)

Rossignol et al (2015) published the technique for laryngoplasty under standing sedation and local anaesthesia. They reported that the technique was advantageous because it removed the risk of general anaesthesia, reduced costs and allowed for more accurate intraoperative adjustment of the degree of arytenoid abduction. Since then, this technique has been well adopted and is now routine. In addition to the advantages mentioned, once familiar, the dissection is straight forward and the accessibility of the larynx for accurate suture placement is enhanced as a result of the increased exposure. With no endotracheal tube in place the larynx can be manipulated which is an advantage of the procedure. It would appear that the results of the procedure are the same compared as if the same procedure is performed under general anaesthesia.

Laryngeal reinnervation

This is not a new procedure but has been the focus of a lot of recent research and interest. Up until recently it has been performed using neuromuscular pedicle grafts (Fulton et al, 1991) but the advent of direct transposition of the first and second cervical nerves has made this procedure more simple and possible to do under standing sedation and local anaesthesia. The advantages of laryngeal reinnervation remain the same, as do the disadvantages which surround incomplete abduction in cases of chronic paralysis, such as the duration of time it takes for the reinnervation process and function to be restored. A new process of using the spinal accessory nerve shows promise, although there is no published data as of yet. The idea behind this is that the nerve will stimulate the CAD muscle with every breath, as opposed to only at more intense levels of exercise, as is the case with the first and second cervical nerves. The proposed benefit of this is that it will speed up the reinnervation process. Currently, it remains a difficult recommendation for horses in training, but it is being increasingly used for sports horses and for younger horses with less severe grades of recurrent laryngeal neuropathy.

However, more longitudinal studies are required before this can be established as the mainstay of treatment.

Partial arytenoidectomy

Partial arytenoidectomy is the treatment of choice for horses with advanced arytenoid chondritis or a failed laryngoplasty and has been the preserve of general anaesthesia until a publication by Gray et al (2019) described the results of partial arytenoidectomy in 14 horses under standing sedation. They reported that the process of partial arytenoidectomy without mucosal closure under standing sedation was performed easily and successfully. They reported that 9/14 horses returned to athletic use without respiratory noise, two had residual noise and one horse was retired to breeding.

Conclusions

Confidence and familiarity with standing upper airway surgery is growing and more and more procedures are being performed this way. There are clear advantages of standing surgery and specifically, standing upper airway surgery. Cost is often listed as one and this can be viewed in two ways. First, the cost to the client, as these procedures can be performed with less expense and the bill generated to the client can therefore reduced. Second, the required skill and equipment can be viewed as cost to the practice and a greater margin can be charged for these procedures. In the author's opinion, performing standing surgery of any type requires specialist equipment, facilities and a higher level of skill and confidence of the surgeon, especially in the face of a greater risk of being injured. Most of the advantages are conferred to the horse and to the owner and this should be charged for. Furthermore, it is the author's opinion that a standing surgical procedure should command a higher fee, not a lower one.