Post Intubation Tracheal Stenosis

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Chapter 8 Post Intubation Tracheal Stenosis

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This chapter emphasizes the following elements of the Four Box Approach: physical examination, complementary tests, and functional status assessment; risk-benefit analysis and therapeutic alternatives; and techniques and instrumentation.

Case Description

This patient is a 55-year-old woman with a long history of gastroesophageal reflux disease (GERD) refractory to proton pump inhibitors, who was admitted emergently to an outside hospital with stridor and respiratory distress requiring noninvasive positive-pressure ventilation (NPPV). Flexible bronchoscopy revealed a severe mid-tracheal stricture with an estimated diameter of 4 mm, based on the fact that a 5.2-mm outside diameter flexible bronchoscope could not be advanced beyond the lesion. Three months earlier, she had undergone surgical repair of a hiatal hernia, during which she was intubated for several hours. Two weeks after surgery, as she became more physically active, the patient developed wheezing and dyspnea, which did not improve with inhaled corticosteroids and bronchodilators. Stridor prompted consultation with an ear, nose, and throat physician, who made the diagnosis of tracheal stenosis and performed rigid bronchoscopy with laser and dilation. Her symptoms recurred, and 2 weeks post intervention she went to a local emergency department with respiratory distress and stridor. An emergent tracheostomy was performed. One month later, the patient was successfully decannulated, but 10 days later, she developed recurrent stridor and respiratory distress requiring hospitalization, NPPV, bronchoscopy, and subsequent transfer to our institution. She had no other medical or surgical history, lived alone, had an active lifestyle, and enjoyed hiking. Her preference was to relieve dyspnea, regain her previous lifestyle, and avoid tracheostomy if possible. Review of symptoms was unremarkable, except that she could not speak in full sentences and had obvious biphasic stridor without hoarseness. Vital signs were normal except for a heart rate of 130 (sinus rhythm). Her chest radiograph was normal. She underwent urgent rigid bronchoscopy with dilation (Figure 8-1). The stricture was circumferential, extending for 1 cm and starting 5 cm below the vocal cords.

Case Resolution

Initial Evaluations

Physical Examination, Complementary Tests, and Functional Status Assessment

This patient was hospitalized for respiratory failure requiring NPPV. This is not an unusual presentation for patients with post intubation tracheal stenosis (PITS). Many patients are diagnosed when stenosis is severe enough to prompt acute respiratory failure necessitating emergency bronchoscopic dilation with or without subsequent curative surgery.1 In one study, 54% of patients presented with acute respiratory failure requiring emergency dilation.2 The noninvasive preoperative evaluation is limited in these emergent circumstances. For instance, the tracheal air column on chest radiograph (CXR) can be overlooked by radiologists and clinicians, and thus deserves careful inspection in any patient with symptoms of central or upper airway obstruction.3 CXR was performed in this patient but was unrevealing (see Figure 8-1). Because CXR does not allow accurate determination of morphology, extent, or degree of narrowing, a computed tomography (CT) scan is warranted. This was not feasible in our patient, who could not lie flat and was unstable from a respiratory perspective. Inspection bronchoscopy would also allow accurate assessment of the stenosis and would provide treatment planning information, including degree of mucosal inflammation, associated cartilaginous collapse, and relative amount and location of hypertrophic fibrotic tissue,4 but could increase respiratory compromise or cause laryngospasm and respiratory arrest. In fact, it is usually our practice to perform flexible bronchoscopy in all patients referred for rigid bronchoscopic interventions; occasionally, this examination is performed on NPPV. It is not known, however, whether such a practice should be generally applied to all cases, especially when results from a previous bronchoscopic examination are known. Indeed, in the setting of respiratory distress and need for NPPV, flexible bronchoscopy can cause airway wall edema and can trigger respiratory failure, potentially resulting in the need for emergent tracheostomy. Although bronchoscopy on NPPV in critically ill patients has been described,5 its safety has not been studied in patients with respiratory distess resulting from tracheal stenosis. We chose to refrain from repeating a flexible bronchoscopy and proceeded directly with rigid bronchoscopic intervention to restore airway patency.

In adult patients, a tracheal diameter of 4 mm usually represents greater than 70% reduction in lumen diameter and is consistent with a severe degree of airway narrowing (Myer-Cotton grade III*) and stridor.6,7 Based on McCaffrey’s system, this stenosis was stage I.8 Although PITS can be localized to the glottis or the subglottis, the most common form is seen at the site of the tube cuff (i.e., cuff stenosis). Bronchoscopically, it is usually circumferential in morphology. This patient had developed PITS 14 days after being intubated for several hours. The exact duration of intubation necessary to cause airway injury and stenosis is not known. In one study, the duration of intubation was less than 2 weeks in more than half of patients, and less than 1 month in 87%, but strictures can develop after only a few days of intubation-related mucosal and submucosal mechanical injury.9,10 As seen in our patient, tracheal stenosis becomes symptomatic within 6 weeks after extubation in more than 50% of patients, and within 2 months after extubation in two thirds of patients.1 Acute inflammation is the initial event that eventually leads to mucosal and submucosal ulcerations, and possibly to exposure and fragmentation of cartilaginous rings.9 The likely pathogenesis of this process is ischemic mucosal damage when cuff-to-tracheal wall tension exceeds mucosal capillary perfusion pressure, usually 20 to 30 mm Hg.6 Compression of the submucosa by the cuff of the tube can cause regional ischemia of the cartilaginous rings because they receive their blood supply from the submucosal plexus.11 Subsequent inflammatory histologic changes can occur within 24 to 48 hours, and healing of the necrotic region by secondary intention occurs within 3 to 6 weeks after removal of the tube.3

Procedural Strategies

Indications

PITS resulted in stridor and respiratory distress at rest. The bronchoscopic procedure was expected to restore airway lumen patency and improve symptoms.1,12 During our initial encounter with the patient in the intensive care unit, we did not know the exact extent of the stricture, although we knew that its morphology was circumferential. This type of stricture would respond transiently to dilation, but the contractile scar usually recurs within several weeks, as had already happened in our patient. Published literature suggests that total loss of normal airway wall structure with replacement by fibrotic tissue permits no alternative to a concentric cicatrix, which tends to contract over time.9 This process might explain the general failure of dilation as a method of treatment, unless lesions are not circumferential (i.e., when well-demarcated eccentric fibrotic bands are identified).9 Surgical data support this concept, suggesting that tension at the site of anastomosis and incompletely excised fibrotic tissue are independent risk factors for stricture recurrence after open resection of tracheal strictures.13,14 To prevent recurrence in complex nonsurgical lesions, some experts promptly insert a silicone prosthesis at the first rigid bronchoscopic intervention rather than performing laser-assisted dilation.1 This is not a universally accepted practice because stents themselves can cause granulation and potentially extend the degree of stenosis, making additional surgical interventions difficult or impossible. We elected, therefore, to perform dilation alone, unless significant malacia were present, which would require stent insertion.

Expected Results

Tracheal vascular anatomy* and mechanisms of tracheal wall injury in PITS highlight the transmural nature of lesions. These explain in part the limited success of purely endoluminal therapies such as laser treatment resection or dilation.15,16 Stenotic lesions are prone to radial compressive forces and might respond favorably, albeit temporarily, to dilation. Factors negatively impacting the success rates of rigid bronchoscopic interventions include an extent longer than 1 cm and the presence of chondritis, resulting in cartilaginous collapse (malacia); in one study of patients with such complex stenoses, during a follow-up period of 28 to 72 months, only 22% of patients were treated successfully using laser-assisted mechanical dilation, whereas 78% required stent placement.17 In another study, all patients with complex stenoses had undergone tracheal stent placement during initial rigid bronchoscopy. After 6 months of follow-up, a majority (n = 9/10) of those patients who continued to be considered inoperable eventually required permanent bronchoscopic airway stent insertion.1

Risk-Benefit Analysis

Mechanical dilation (with or without laser assistance) provides only temporary benefit in patients with extensive (>1 cm) circumferential lesions. Repeated interventions, especially if laser is used, might increase the extent of injury in some cases, possibly resulting in damage to the cricoid posterior plate. Similarly, stent insertion could increase the length of stenosis. Some experts recommend avoiding this treatment in all patients who are candidates for surgical intervention, stating that laser or stent insertion should be performed only in patients with absolute contraindications to surgery.18 Some believe that when one or more cartilaginous rings are involved, endoscopic treatment is contraindicated unless surgery is not a consideration.19 However, the general applicability of such an approach has not been demonstrated. In our patient, who had an unstable respiratory status, the risks of rigid bronchoscopy were outweighed by the benefits of immediately improving airway patency, resolving respiratory distress, and avoiding respiratory failure.

Therapeutic Alternatives for Restoring Airway Patency

To optimize a patient’s functional status for potentially curative open surgery, mechanical dilation with or without laser resection is often necessary. In one large reported surgical series, most patients underwent one or two preoperative rigid bronchoscopies.1 If surgical repair is deferred for a prolonged period, or is not technically feasible, repeat dilation can be performed, but management with airway stents, laser, silicone T-tube, or tracheostomy has also been described.

1. Self-expandable metal stents (SEMSs) should never be used in patients who are potential candidates for resection because these are likely to cause additional airway injury and may make a potentially resectable patient unresectable.20 Results from a surgical study suggest that all patients with tracheal and subglottic stenosis who had undergone covered or uncovered metallic stent placement developed new strictures or granulation tissue; this occurred after a short duration of stent insertion, either precluding definitive surgical treatment or requiring more extensive tracheal resection.20 In fact, metal stents ideally should be avoided in any benign airway disorder, unless surgery and silicone stents are not a consideration.21

2. Silicone stents are helpful for splinting extensive post intubation stenoses and are appropriate for palliating airway narrowing in nonsurgical candidates.*1,19,22 Stent-related complications, however, are not uncommon and include migration (17.5%), obstruction from secretions (6.3%), and significant granulation tissue formation at the proximal or distal extremities of the stent (6.3%).23 Silicone stent insertion performed using rigid bronchoscopy under general anesthesia is an acceptable alternative to surgery for inoperable patients with complex stenosis.* These stents are reported to provide long-term airway patency with minimal complications.1 In a study of 42 patients with complex stenoses, only 9 were surgical candidates and 33 were treated with silicone stent insertion, with a success rate of 69%.10

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