Advances in instrumentation and anesthetic techniques have expanded the boundaries of endoscopic airway surgery. Specialized microinstruments, the dilating balloon, laser, and powered microdebrider are key tools. Primary endoscopic surgery has several advantages over an open approach including potential for improved vocal outcomes and avoidance of the morbidity of an external incision. The need for tracheostomy, intensive care, and hospital stay may also be reduced.
This chapter focuses upon the concepts, considerations, and equipment relating to endoscopic, ‘minimally invasive, and endoluminal airway surgery. Careful patient selection and preoperative planning is essential. Significant disorders of the laryngotracheal framework are more likely to be successfully treated by open surgery while endoluminal concerns may be better suited to an endoscopic approach. The role of endoscopic surgery as an adjunct to open airway surgery is well acknowledged. As with open surgery, the individual surgeon’s experience and the resources of the institution in which care is delivered are crucial considerations along with the personal circumstances of the patient and family.
47 Endoscopic Airway Surgery
47.1.1 History and Evolution
While endoscopic airway surgery is very much a current “hot topic” and exciting area of pediatric ENT, it has a long history. Endoluminal techniques have been used to dilate and treat laryngotracheal stenosis since the 19th century. Inspired and innovative approaches were devised to tackle the effects of infections–namely diphtheria – and trauma. In the 1920s and 1930s the advancement of electrically heated esophageal bougies and the placement of upper airway stents were explored. The concept of scar tissue incision by a “laryngeal dilating knife” followed in the 1950s. The pace of development of airway surgery in the 20th century was driven by two main factors: the intensive care and increased survival of premature infants accompanied by advancements in technique. The survival of premature infants was associated with the need for prolonged endotracheal intubation of a vulnerable airway, which could result in significant acquired laryngotracheal stenosis, principally of the glottis and subglottis.
Endoluminal “minimally invasive” techniques logically evolved alongside open laryngotracheal surgery. From the 1970s onwards, procedures to correct laryngotracheal stenosis developed and progressed rapidly. These open laryngotracheal framework expansion surgeries and the related use of stents were frequently associated with the development of endoluminal granulation tissue and stenosis at anastomotic sites; these pathologies are naturally accessible endoscopically. Outcomes of open surgery can be improved by the use of subsequent endoscopic procedures, which allow for visualization of areas of concern and intervention if necessary.
In order for endoscopic airway surgery to be feasible, the surgeon needs to be able to assess the pathology to be operated upon and then maintain this exposure in order to perform surgery. The operating microscope has been the traditional workhorse for surgery of the supraglottis and glottis and enables both depth perception and two-handed working. The advent of the rigid endoscope, the Hopkins rod, revolutionized the direct visualization of the subglottis and trachea. Harold Hopkins patented his lens system in 1959 however it wasn’t until the later 1960s that the manufacturing and distribution of these revolutionary instruments began. The excellent image and bright illumination, coupled with a wide field of view, proved to be a new and exciting addition to the operating microscope. For the purposes of this chapter, the term “endoscopic” will be used broadly to cover all endoluminal surgery, regardless of whether the microscope or rigid endoscope is used.
In the past 20 to 30 years, both the use and scope of endoscopic airway surgery have increased significantly, facilitated by better anesthetic techniques, tailored instruments and “endoscopic” medications such as steroids and Mitomycin C. The 1980s saw a major interventional advance: endoscopic balloon dilatation. Previous dilatation methods included the advancement of bougies (e.g., esophageal or urethral dilators) or the rigid bronchoscope. Dilatation in this fashion relies upon the conversion of longitudinal to radial force and has the disadvantages of mucosal trauma and shearing forces. Mucosal and submucosal injury can then lead to further fibrosis and increase the likelihood of restenosis. The amount of radial pressure that can be applied is also limited and difficult to gauge.
47.1.2 Relationship of Endoscopic to Open Airway Surgery
Historically, tracheostomy has been the workhorse of airway surgery providing a means of bypassing obstruction to allow direct access for ventilation of the lungs. Pediatric ENT surgeons have concentrated both their open and endoscopic efforts either to enable decannulation or to avoid such intervention in the first place. Improvements in technology broadened the capabilities of endoscopic approaches. Coupled with the Hopkins rod endoscope and the binocular operating microscope, the tools to treat disease have become more varied. Examples include the carbon dioxide laser, which can now be delivered via a flexible fiber allowing improved access while the thulium laser has the advantage of improved hemostasis. The Coblation wand and microdebrider have delivery systems for endoscopic use and the introduction of the non-compliant airway balloon has been invaluable. Cold steel instruments such as Blitzer and lancet knives have been designed for use in the pediatric airway.
The potential advantages of an endoscopic procedure include a shorter operating time, a decreased length of intensive care, and an overall hospital stay. The morbidity of an external neck incision is also avoided. The significant effect on voice from the disruption to the laryngeal framework that occurs with open surgery, particularly the classic full laryngofissure, is well recognized; endoscopic approaches have the obvious benefit of avoiding this. The need to improve vocal outcomes seen with open surgery is acknowledged as an ongoing goal in pediatric ENT.
Another favorable aspect of the endoscopic approach is that it is possible to assess the effects of surgery on a more frequent basis and then to treat further if required. Current understanding of scar development and wound healing indicates that early and frequent intervention enhances the likelihood of a successful outcome. Direct application of adjuvant therapy (e.g., injectable or topical steroid) is also possible.
The combination of endoscopic and open approaches (combined approach or “hybrid” surgery) is a definite step forward. A more accurate midline division of a congenital laryngeal web is achieved endoscopically, while placement of an anterior cartilage graft to treat the associated subglottic stenosis requires the open approach. A further prime example is the use of the endoscope in the airway while the posterior cricoid is being divided in an open surgery; this again improves the quality of the procedure.
If the main concern to be corrected is intraluminal, this is likely to be amenable to endoscopic surgery. As a rule, if the laryngotracheal framework (“exoskeleton”) is not intact, primary endoscopic surgery alone is unlikely to be successful, and this situation may be best treated by open surgery. Endoscopic cricoid splits and posterior cricoid grafting are however challenging this general principle. Endoscopic surgery as an adjunct to open surgery, for example balloon dilatation or the removal of granulations a few weeks after an open reconstruction, is well recognized as improving long-term outcomes.
This chapter is directed toward the concepts involved in endoscopic airway surgery, but it is important to balance these alongside existing and developing open techniques. Each approach has its merits and the outcome achieved for an individual patient may be best reached by either or from a combination of both. The individual surgeon’s experience and that of the institution in which care is delivered are crucial considerations along with the personal circumstances of the patient and their family.
47.2 Preoperative Evaluation and Anesthesia
47.2.1 History and Examination
Once a diagnosis of upper airway pathology requiring intervention has been made, the aim of a detailed history is twofold; first, the suitability of the pathology to endoscopic surgery must be judged, and second, the patient’s general eligibility for endoscopic surgery needs to be assessed.
Mature and congenital laryngotracheal stenoses, particularly of higher grades, are unlikely to be improved by endoscopic surgery alone. Congenital cartilaginous stenoses such as a congenital subglottic stenosis will not be improved by dilatation alone as it will not impact upon the abnormally thickened cartilage and may risk rupture.
A detailed history of previous endoscopic and open airway surgery is vital. In cases of laryngotracheal stenosis that have been treated by balloon dilatation and no degree of improvement seen, consideration of an alternative technique is suggested. Experience shows that further endoscopic dilatation is not prudent if correction of a stenosis has not been adequate after three serial dilatations, separated by a number of weeks.
It is imperative to check for secondary airway lesions such as malacia or vocal fold immobility. In combination with comorbidities, these may influence both the choice and timing of an approach and the likelihood of treatment success.
Whether primary endoscopic, combined endoscopic and open surgery, or endoscopic surgery as an adjunct to open surgery is being considered, careful patient selection is essential. The patient’s neck movement, mouth opening and dentition are all-important access considerations. In order for endoscopic airway surgery to be possible, a “line-of-sight” access is required from the lips to the operative field (▶ Fig. 47.1). Micrognathia, retrognathia, and a significant overjet (an anterior–posterior overlap of the maxillary central incisors over the mandibular central incisors) are all likely to increase the difficulty of access.
If the child has a tracheostomy this will facilitate administration of oxygen and anesthetic gases. The tracheostoma is also an additional potential port of access to the upper airway for the endoscope and for instruments.
As with open airway surgery, laryngopharyngeal reflux should be identified and treated. This may require medical treatment (e.g., proton pump inhibitor therapy) or in severe cases, surgical management with a gastric fundoplication. Similarly, the presence of infection within the airway should also be preoperatively identified. An infected airway is often apparent on inspection. Microbiological cultures using swabs or aspirates are recommended to enable effective treatment prior to surgery. In patients with long-term tracheostomies, airway colonization and infection is often a concern. Many experienced surgeons advise proactive investigation of infection and prophylactic antibacterial treatment prior to any airway surgery.
Deferral of surgery is advisable in cases where there is an “active larynx”. This may be evidenced by generalized edema and erythema; a cobblestoned appearance of the mucosa of the epiglottic base and eversion of the laryngeal ventricles are also suggestive signs. Work in such an inflamed and reactive airway is likely to be technically more difficult in terms of visualization and surgical intervention. It also risks poorer mucosal healing with its concomitant worries of restenosis and granulation formation. An “active larynx” is known to be a risk factor for surgical failure and warrants investigation and treatment of infection, gastro-esophageal reflux disease (GERD), and eosinophilic esophagitis. In some cases, this “angry state” is idiopathic; deferral of surgical intervention and a waiting period of several months are recommended. Experts have suggested trials of a variety of anti-inflammatory medications such as steroids and antibiotics such as azithromycin.
The pulmonary, nutritive, and cardiac states of the patient should be optimized as far as possible. The age of the child may also be an important consideration, with implications for surgical access, technical feasibility, and postoperative care. Preoperative evaluation and documentation of the patient’s ability to swallow and voice is also crucial. This may not only influence surgical planning but also enable comparison of pre- and postoperative function. The monitoring and recording of these factors is an important consideration in outcome reporting, facilitating the pooling and comparison of research data.
A multi-disciplinary “airway forum” is an ideal discussion opportunity for difficult surgical cases and may aid in planning. Potential complications should be identified and postoperative care preparations made. Intensive care facilities may be required; the patient may require close airway monitoring, tracheostomy care, or remain intubated for a number of days following surgery. The surgical plan including perioperative care must be discussed in detail with the family and child, if applicable. The importance of both effective communication and the management of expectations cannot be emphasized strongly enough. This is often aided by the use of clinical photographs and diagrams.
In addition to pulmonary, cardiac, and nutritive assessments of the patient, several targeted investigations may also be of use when preparing for potential endoscopic airway surgery.
Flexible Endoscopic Evaluation
Flexible laryngoscopy is particularly useful to assess dynamic abnormalities such as vocal cord immobility and laryngomalacia. This may be performed without sedation in the infant or in the older cooperative child, or under anesthesia. Per-oral passage of an endoscope may be performed in the edentulous neonate using a finger between the gums to protect the instrument. It is essential to note the basic but important point that a good laryngeal or tracheal view gained at flexible endoscopic evaluation does not translate to adequate access with the rigid endoscope and/or transoral instrumentation.
Use of CT and MRI of the neck and chest in the preoperative preparation of the child for airway surgery varies widely from center to center. These scans may aid in the evaluation of airway lesions although they are not usually sufficiently sensitive to fully characterize a lesion or stenotic segment. Helical or multidetector CT with multiplanar and 3D reconstruction offers increasingly better definition of fixed tracheal lesions, and can provide “virtual bronchoscopy”. Dynamic changes—primary and secondary tracheobronchomalacia—are not well evaluated by cross-sectional imaging. The degree, maturity, and mucosal quality of a stenosis can be more accurately assessed at endoscopy.
Endoscopic airway surgery is a prime example of “shared airway working”, which requires close cooperation and understanding between the surgeon and anesthetist. Safe, efficient, and successful surgery is facilitated by a long-term working relationship with a skilled pediatric anesthetist with a special interest in ENT.
We recommend that the anesthetist is either able to view the screen displaying the endoscopic image, or is able to view a second screen. Depth of anesthesia can be gauged not only by the presence and effort of respiration but also by the degree of vocal cord movement when the larynx is in view. Periods of airway occlusion, for example by balloon dilatation, can also be monitored. This real-time visual feedback complements the close verbal communication between surgeon and anesthetist.
Careful timing of endoscopic airway surgery involves optimization of respiratory fitness and airway irritability. Steady anesthetic conditions with good oxygenation, minimal airway secretions, and lack of mucosal inflammation are the goals. Elective surgery should be deferred in the presence of a current upper or lower respiratory tract infection. Airway irritability, predisposing to coughing, and laryngospasm may persist for a number of weeks following such an illness.
A variety of anesthetic techniques exist for endoscopic airway surgery and vary from center to center. It is probably more important that a theater team work together effectively than that one particular technique is followed. Intubation may be used at the start of the procedure in some centers; however, most units would now use spontaneous respiration throughout rather than neuromuscular blockade and paralysis. Spontaneous respiration has much to recommend itself as a technique; it maintains muscle tone, promotes gas exchange, and is essential to detect dynamic conditions.
Induction of Anesthesia
Some units will use an anticholinergic premedication such as atropine or glycopyrrhonium bromide to facilitate a dry surgical field and improve the efficacy of topical anesthesia; this may impact upon the heart rate. Perioperative steroids are a good precaution, particularly in cases of significant stenosis or when there is likely inflammation and edema. Intravenous induction is preferable for older children though gaseous induction is best in infants, younger children, those with poor venous access, and those with a precarious airway. Topical local anesthetic spray (typically lidocaine) should be applied to the vocal cords when the anesthetic level is sufficiently deep for this to be tolerated. This amount needs to be carefully measured as the preparations used in adults can easily result in overdosage.
Minimum patient monitoring includes temperature, electrocardiogram (ECG), non-invasive blood pressure, and peripheral oxygen saturation (SpO2). Accurate monitoring of end-tidal carbon dioxide is not possible in the absence of endotracheal intubation.
Maintenance of Anesthesia
Two principal anesthetic techniques are used for general anesthesia with spontaneous respiration—maintenance with a volatile agent (e.g., sevofluorane) or total intravenous anesthesia (TIVA) with an infusion such as propofol and remifentanil.
A volatile agent and oxygen mix can maintain a level of anesthesia that allows examination and endoscopic intervention in a child who is breathing spontaneously. Sevoflurane is nonirritant to the airway and has the advantages of rapid onset and no pungency, allowing immediate delivery of high concentrations. This advantage of rapid induction may be offset by a variable effect during periods of relative hypoventilation or airway obstruction.
Airway Tube Technique
An endotracheal tube may be used as a nasopharyngeal airway or “prong’ to provide oxygen and volatile anesthetic agents. This should be carefully positioned above the supraglottis (▶ Fig. 47.2). Should transnasal passage not be possible, an oropharyngeal tube may be used, placed at the corner of the mouth. A significant advantage of this non-intubation technique is that the endoscopist has a view of an airway that has not been altered by the passage of an endotracheal tube. An alternative technique is to intubate the child and withdraw the tube for periods of endoscopic work (apneic anesthesia with intermittent ventilation); this method is not routinely used in our institutions.
Jet ventilation can allow the patient to be paralyzed, preventing coughing. In a pediatric setting it is broadly associated with barotrauma and carbon dioxide retention concerns. This practice is not widespread and use varies significantly from region to region; it is not used in our centers.