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September - December 2003: 
Volume 16, Issue 3

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Postintubation tracheal stenosis and endoscopic management
Abstract
ABSTRACT. Postintubation tracheal stenosis is an iatrogenic complication that occurs in critically ill patients receiving mechanical ventilation. It is by far the commonest benign cause of tracheal stenosis with an estimated incidence of 1% among intubated patients. Following simple and concrete preventive measures should avert this severe and potentially fatal complication. High clinical suspicion is vital to promptly diagnosing this condition once it appears. Treatment of post intubation tracheal stenosis may be difficult due to usually poor patient health status at the time of diagnosis. Circumferential sleeve resection of trachea with end-to-end anastomosis remains the treatment of choice, although it is only applied in strictly selected patients by highly experienced surgeons and is related to serious complications and significant relapse rates. Bronchoscopic, non-surgical techniques applied by pneumonologists, including bronchoscopic or balloon dilatation, laser resection and stenting have been proposed as alternatives to open surgery and feature several advantages. Indeed, short, web like stenoses may be definitively cured by laser resection and gentle dilatation, while stents are helpful for splinting lengthy stenoses. In inoperable cases, silicone stents represent the only therapeutic alternative; they are also valuable as initial conservative treatment in view of prospective surgical correction, allowing time for preparing the patient. A multidisciplinary approach engaging pneumonologists, as well as thoracic and ORL surgeons is crucial for the best management of patients with postintubation tracheal stenosis. Pneumon 2003, 16(3):262-270.
Full text

Introduction

Although considered a definite complication of tracheostomy from the outset, tracheal stenosis occurred only rarely before the institution of contemporary methods of mechanical ventilation in the management of respiratory failure. The poliomyelitis outbreak in Europe and the USA in the 1950s spurred major advances in mechanical ventilation systems. Postintubation tracheal stenosis was then found to occur with a quite notable incidence, although the etiology and the sequence of events that led to this complication remained unknown and various hypotheses were formulated to explain it.1

It gradually became evident that mucosal ischemia (necrosis) due to the pressure exerted on tracheal wall by endotracheal tube cuff was the primary cause, with hypotension, infection and prolonged steroid use contributing to mucosal changes. Autopsy studies in patients who died while under mechanical ventilation2 elucidated the nature of these changes and allowed their reproduction in experimental models.3 Attempts to modify endotracheal tubes came as a natural consequence of new knowledge in this field4 and led to the development of the currently used endotracheal tubes with high volume-low pressure cuffs. The contribution of Hermes Grillo et al in this process merits special reference.5

Pathophysiology

In addition to the damage caused by endotracheal tube cuff, a distinct tracheal damage located in the entry site of the tracheostomy tube was also identified. Changes in the cricoid cartilages and expansion of the tracheostomy commonly result in healing with tissue contraction forming the characteristic triangular (A-shaped) stenosis. In contrast, the endotracheal tube cuff causes circumferential erosion of the mucosa, which heals with a concentric (web-like) stenosis. Furthermore, these cicatricial stenoses are often accompanied by various degrees of tracheomalacia, which diminishes tracheal wall support normally provided by cartilagenous parts and contributes to the abnormal overall patency of the airways.

Based on the above-mentioned properties, tracheal stenoses generally fall into three types:6,7

  • Short stenosis (<1 cm), which forms a web as a result of circumferential contraction scarring of the mucosa. Tracheal wall, as well as cricoid cartilages present no or minimal damage and remain functional in general (Figure 1).

Image 1
Figure 1. Short stenosis.
  • "Complex" stenosis. This type tends to be longer (>1 cm), have abnormal borders and it often includes various degrees of tracheomalacia, which cannot be assessed unless the stenotic segment is opened. The whole depth of the tracheal wall is affected, in particular the cartilaginous rings (Figure 2).

 

Image 2
Figure 2. "Complex" stenosis.

 

  • "Pseudoglottic" or A-shaped stenosis. It results from tracheal cricoid cartilage dissection or fracture that is commonly related to tracheostomy; its behavior resembles that of localized tracheomalacia at the scarring site (Figure 3).

 

Image 3

Figure 3. "Pseudoglottic" stenosis.

As regards pulmonary function, tracheal stenosis assimilates to fixed intrathoracic airway obstruction and its diameter does not change with respiratory movements. Airflow limitation is constant, as demonstrated by the classic flattened morphology of both inspiratory and expiratory flow/volume curves (Figure 4). The maximal expiratory to maximal inspiratory flow ratio (MEF50/MEF50) at 50% of the vital volume is equal to 1. As known, the relationship between airflow resistance and the diameter of the airway is not linear. Airflow resistance is proportional to the square of flow velocity and inversely proportional to the fourth power of the airway radius {ΔP=kV2[(R/r)2-1]2.9 In practice, this means that a 50% tracheal stenosis will lead to a 16-fold increase in flow resistance.

 

Image 4
Figure 4. Flow-volume curve in intrathoracic (left) and extrathoracic (right) tracheal stenosis. These two morphologies may variably coexist on the same curve, depending on stenosis level.

 

When tracheal stenosis becomes symptomatic, it is most likely to have exceeded 75% of the airway diameter leaving a patent part of the lumen not wider than 5 mm. However, manifestation of clinical signs and symptoms depends not only on the degree of the stenosis, but on airflow velocity in the airway as well. A moderate stenosis, for example, may be completely asymptomatic at rest, but it becomes clinically evident during exercise as inspiratory airflow increases.8

Thirty years after acquiring and communicating this knowledge, (iatrogenic) tracheal stenoses still occur, even though at lower rates, and cause severe disability in patients who required mechanical ventilation. Postintubation tracheal stenosis currently remains the main indication for tracheal resection or restoration.9 As discussed later on, this procedure is neither easy nor without risks, whereas it becomes extremely difficult when the stenotic area includes more than 2 or 3 cartilage half-rings.

"Low pressure" endotracheal tube cuffs are made of plastic with limited distensibility and not of latex, as originally proposed. This implies that such a cuff may be changed to a "high pressure" one, if it happens to inflate it more than instructed. Subsequently, great care is needed as to the cuff volume during inflation and deflation if mucosal injury due to high cuff pressure is to be avoided. In the same context, effective support of tracheostomy tube and additional component parts so as not to press and cause tracheal wall to inflame would prevent erosion of tracheostomy edges, which would result in tracheostomy expansion. Several reports point out the importance and usefulness of such simple preventive measures that are often not taken.9

Incidence

The few available prospective studies report incidence rates of postintubation and/or posttracheotomy tracheal stenosis ranging from 10 to 19%.10,11 However, stenoses actually impairing pulmonary function and causing clinical symptoms and respiratory failure are much more fewer and most probably do not exceed 1% of the cases. A recent study conducted in North France has estimated that tracheal stenosis occurs in about 1 in 1000 ICU patients.12 Nevertheless, it seems that the incidence of tracheal stenoses was much higher in the past and that the use of endotracheal tubes with low-pressure/high-volume cuffs did in fact reduce the occurrence of this complication, although it still depends largely on the quality of the provided medical and nursing care.13 Apart from cuff pressure and operative tracheal trauma, duration of intubation has also been proposed as an important pathogenetic factor. Literature data, however, do not support this assumption, but on the contrary present cases with stenotic tracheal scars after intubation that lasted only a few days. This has been confirmed by the research activity of Bishop et al using experimental animal models who showed that the risk of laryngeotracheal stenoses does not increase significantly when the intubation lasts more than seven days. Further studies have demonstrated that cases that develop a tracheal stenosis present clinical symptoms immediately after removal of the endotracheal tube or certainly within the first three months.6,12,14 Lastly, the incidence of tracheal stenosis does not seem to be related to repeated intubations, the route of intubation (orotracheal vs nasotracheal) or the emergency character of the procedure of intubation.7

Since this complication does not present specific signs and symptoms that would directly lead to its diagnosis and therefore it is often confused with other clinical entities, the above described epidemiologic characteristics are of high clinical value: onset or deterioration of shortness of breath in a patient who a few days or weeks earlier had been mechanically ventilated, should lead to including tracheal stenosis in the differential diagnosis process, even if the patient was intubated only for a few days.

Clinical presentation - Diagnosis

Typically, postintubation tracheal stenosis (PITS) is diagnosed based on a combination of presenting airway obstruction signs and symptoms with a recent history of tracheal intubation. Airway obstruction presents with inspiratory and expiratory wheezing and shortness of breath at first during exercise and later at rest; rarely, it leads to uni- or bilateral pneumonitis due to bronchial obstruction. Peak expiratory flow (PEF) is surely significantly reduced and flow/volume curves would be the expected, although spirometry is difficult to perform due to the severity of respiratory failure or cannot be interpreted meaningfully due to concomitant chronic obstructive pulmonary disease (COPD). Furthermore, this complication occurs during the recovery phase in patients who were managed in an ICU, which means that physical activity in such cases is usually reduced and, hence, symptoms of tracheal stenosis may not be clinically evident until much later when the patient will assume his/hers normal activities. Chest radiographic examination is usually normal; as a result, a significant proportion of these patients are diagnosed with "late onset" asthma. Grillo and Donahue report that as a result of PITS being often misdiagnosed many patients with tracheal stenosis had been receiving 50-60 mg prednisone for months.9 In the 32-patient-series of Brichet et al, only 56% of the patient were diagnosed correctly at hospital admission.6,14 The rest of the patients were diagnosed as cases of asthma-bronchospasm (25%), exacerbation of chronic respiratory failure (9%), pulmonary embolism (6%) etc. It is worthy of note that a patient with respiratory muscles fatigue may not be able to produce significant flows and, as a consequence, the characteristic inspiratory wheezing may be absent. In cases of lower intrathoracic tracheal stenoses, the predominant auscultatory findings relate to the expiratory phase of breathing, which may enhance diagnostic confusion. It is therefore important that patients with a recent or even a remoter past history of tracheal intubation and mechanical ventilation presenting signs and symptoms of upper airway obstruction are treated as cases of organic (anatomical) tracheal stenosis until proved otherwise.9

Tracheal linear tomograms, as well as the more sophisticated method of "virtual" bronchoscopy using reconstructed digital signals from computerized tomography images will depict the level and morphology of the stenotic area, provided that the clinical practitioner has suspected the diagnosis of tracheal stenoses in the first place. However, the diagnostic test of choice that both provides a definitive diagnosis and determines the type, location and severity of stenosis is flexible bronchoscoy, which is relatively easy to perform in these patients. Furthermore, bronchoscopy directs the clinician as to the appropriate type and time of treatment.

Treatment of tracheal stenoses

A. Surgical treatment

Surgical resection of the stenotic area of the airway with end-to-end anastomosis (sleeve resection) remains as yet the treatment of choice that leads to cure. In order to perform this anastomosis, larynx is mobilized downwards, but in cases of lengthy stenoses preparation and upwards mobilization of the tracheobronchial split is more appropriate (Figure 5). The operation is performed on strictly selected patients following meticulous preoperative assessment and dilatation or laser treatment sessions for widening the stenotic segment.9 For example, in some of the largest reported series, 71%, 53% and 26% of the patients had to undergo 1, 2 or 3 preoperative sessions of rigid bronchoscopy, respectively.7,16 It is hence clear that this procedure is not indicated in the acute setting. Long-term failure (recurrence) rates in large series of surgically treated patients is about 15%, whereas reported postoperative mortality ranges from 1.8 to 5%.7,16-18 Reference centers unanimously pinpoint the necessity of great experience to perform the procedure, as well as the difficulty of re-operating on an unsuccessfully operated patient. Surgical treatment of cases with recurrent stenosis or inoperable cases due to extensive stenoses or severe concomitant diseases (e.g. cardiopulmonary failure etc) involves permanent tracheostomy and placement of Montgomery T endotracheal tube.

 

Image 5
Figure 5. PITS surgical treatment.

 

B. Endoscopic treatment

Taking into account that 50% of PITS cases are diagnosed in the acute setting presenting severe dyspnea or poor general status, namely under conditions that contraindicate surgery, at least temporarily, conservative endoscopic treatment offers significant advantages.

Non-surgical procedures, such as dilatation using a rigid bronchoscope or special balloons (similar to those used in angioplasty procedures), laser dilatation and placement of special stents, have been suggested and are already used in clinical practice. However incomplete as a therapeutic treatment, dilating the stenotic segment using a rigid bronchoscope has always immediate and spectacular results, which are also confirmed by pulmonary function tests.7,19

In a series of 16 patients with simple web-like tracheal stenoses, Mehta et al showed that radial incisions of the membranous web using Nd-YAG laser followed by airway dilatation with the rigid bronchoscope led to sustained cure in 60% of the patients after 1 to 3 sessions (Figure 6).

 

Image 6
Figure 6. Radial incision of tracheal stenosis web using Nd YAG laser. Following this stage, dilatation and probably endotracheal stent placement will be performed. Further resection is not justified as it may result in granulomatous tissue hyperplasia.

 

The same results were subsequently confirmed in larger series of patients.12 In those patients with recurrent stenosis after laser photodissection (LPD) and airway dilatation that are inoperable due to some contraindication, the only therapeutic alternative is bypassing the stenotic area with the placement of a Montgomery T tube, or, preferably, a specially designed endotracheal stent, such as a Dumon stent. These stents are made of silicone and are available in a variety of sizes and diameters (Figure 7).21 Their effectiveness and good tolerance (Figure 6) has been extensively confirmed.22 Inserted through a rigid bronchoscope by a pneumonologist specialized in endoscopic procedures, the stent is placed in the stenotic area after tracheal dilatation. The patient is under general anesthesia and gas exchange is ensured using jet ventilation via the bronchoscope (Figure 8). Interestingly, the stenotic tracheal wall that is splinted with the stent, quite often "matures" and becomes hard with time, thus allowing the removal of the stent. Stent removal after some time (usually 12-18 months) does not present special difficulties and renders an eventual surgical intervention in later time possible, if indicated. A relatively recent prospective study demonstrated the remarkable effectiveness of these stents in a series of 52 patients with PITS who were successfully treated applying this endoscopic procedure. Furthermore, in 80% of the patients who were considered cured, the stent was removed 18 months later without recurrence of the stenotic lesions. Complications associated with the use of stents, all of which are immediately manageable, include: stent migration (17.5%), obstruction (6.3%) and formation of granulomas at either end of the stent (6.3%). Similar findings are reported in relevant references, which are in agreement with the overall European experience with more than 260 cases of tracheal stent placement.12 One of the main drawbacks of this type of silicone stents is hampering of normal expectoration and elimination of tracheobronchial secretion that may lead to acute stent obstruction. A fatal case of acute stent obstruction has been reported, but it occurred in a center lacking adequate experience in these procedures.23

Self-expanding metallic stents that allow the development of normal mucosa ensuring mucociliary clearance on the stent surface represent an alternative stenting option that needs to be prudently evaluated. Removal of these stents is particularly difficult, if at all possible; therefore, they are generally not preferred, especially in stenoses caused by benign conditions. Complications associated with endotracheobronchial stents occur usually acutely and require emergency treatment. At present, all centers that perform these procedures provide their patients with a special ID card. This card contains information related to the type, size and location of the stent (in case emergency intubation is required), as well as the clinical signs and symptoms that should make the patient and the physician suspect the respective complications.

 

Image 7
Figure 7. Silicone endotracheal stent, Dumon type external struts promote stent stabilization on broncial mucosa.
Image 8
Figure 8. Endotracheal stents at the site of tracheal stenosis and airway patency establishment.

 

Management algorithm

Optimal treatment of benign postintubation tracheal stenoses has not been clearly defined. The management of this iatrogenic complication has a bearing on differences in how the problem is perceived by different medical specialties that may or may not treat such cases. Studies conducted by investigators with a surgical background tend to ignore the great number of patients that are considered inoperable, whereas series from pulmonary medicine-endoscopy units do not take into account those patients that end up in an operating theater.

A recent prospective study on 34 PITS patients (15 with web-like stenoses and 17 with complex stenoses) attempted to determine the optimal treatment modality by formulating a therapeutic algorithm with the assistance of a panel of pulmonary medicine specialists, thoracic and ENT surgeons and ICU practicioners.12 Simple, web-like, stenoses were initially dilated using a rigid bronchoscope and laser therapy for a total of three sessions. Recurrence after the third bronchoscopy session led to the patient being evaluated as to his/hers suitability to undergo surgery. If judged inoperable, a Dumon stent was placed. Patients with complex stenoses had a Dumon stent placed from the beginning and were re-evaluated 6 months later as to their operability. If they were judged operable, the stent was removed and, if stenosis should recur, they underwent surgery. If they were judged inoperable, the stent remained in place.

Of the 15 patients with simple stenoses, 10 were cured with endoscopic treatment alone, 2 were operated on and 2 required permanent tracheostomy. The recurrence rate in the 17 patients with complex stenoses after stent removal at 6 months was significant. Nevertheless, endoscopic treatment was successful in 12 of these patients, whereas only 4 patients eventually required surgery. There was no pre-, peri- or postoperative mortality. Although a control group was not included for comparisons, the results of this study were far better than those of previous studies by the same authors, in which a therapeutic algorithm had not been used.14 The number of rigid bronchoscopy procedures per patient was lower (1±1 vs 3.8±1.7) and in patients who required surgical treatment conditions of stability and good general status were met since the operation was performed at least 6 months following bronchoscopy.

It is by all means evident that a multifactorial and structured therapeutic management is required ensuring the collaboration of medical specialties bordering this clinical problem in the best interest and safety of the patient.

Future perspectives

The significant advantages of endoscopic (non-surgical) management of benign tracheal stenoses, as well as an array of other airway disorders have led to a remarkable sophistication and increase in the use of these methods around the world. The fact that endoscopic procedures provide an alternative treatment option and good quality of life in inoperable cases is extremely important. Research is directed towards the development of simple endoscopic procedures that would be easy to implement by pneumonologist/endoscopists: jet ventilation to ensure a comfortable and safe rigid bronchoscopy, simple stent placement techniques without the use of complicated equipment, better and more stable stents associated with lower complication rates,24,25 improved bronchoscopy equipment, fiberoptic technology and video monitoring that would allow better imaging and recording of the whole procedure.

Postintubation tracheal stenosis is an iatrogenic complication that should be averted with the use of simple and concrete preventive measures. Should it occur, timely diagnosis and effective management taking into account the severity of the stenosis and patient status are vital. Endoscopic treatment offers significant advantages over classic surgical treatment and may be employed either alone or in the initial management of patients that will later undergo corrective surgery, or even as palliative treatment in serious inoperable cases. The new discipline of interventional pulmonary medicine sets the stage for specialists in this field to assume a central role in the decision making process regarding the management of tracheal stenosis cases.

 

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References