Flexible bronchoscopy balloon dilation for nonmalignant airway strictures (bronchoplasty)

INTRODUCTION — Nonmalignant stenosis of the central airways (trachea and main stem bronchi) can result from several conditions (table 1). Flexible bronchoscopic balloon dilation is a simple, minimally-invasive method that may be used alone or in combination with other bronchoscopic therapies to dilate airway stenoses and restore adequate airflow [1-5].

The technique, efficacy, contraindications, and complications of flexible balloon dilation for treating nonmalignant airway strictures (bronchoplasty) will be reviewed here. The diagnosis and management of central airway lesions are discussed separately. (See "Clinical presentation, diagnostic evaluation, and management of malignant central airway obstruction in adults".)

ASSESSING LESION SUITABILITY — Computed tomography (CT) and bronchoscopy are necessary to determine suitability of the lesion for bronchoplasty. Lesions best suited for balloon dilation are symptomatic stenoses that have failed or are not suitable for medical treatment targeted at the underlying cause of the stricture (eg, antimicrobial treatment for tuberculosis, immunosuppressive medications for sarcoidosis). The procedure is most successful in fibrotic lesions [6,7] (eg, those due to prolonged intubation) rather than in those secondary to tracheobronchomalacia, inflammation, calcification, or carcinoma. Lesions that are less suitable are those associated ulceration or mucosal fragility because of risks for rupture. Vascular lesions should probably be avoided because of the risk for rupturing vessels with consequent bleeding. (See "Treatment of drug-susceptible pulmonary tuberculosis in nonpregnant adults without HIV infection" and "Treatment of pulmonary sarcoidosis: Initial approach" and "Clinical presentation, diagnostic evaluation, and management of malignant central airway obstruction in adults", section on 'Management of the underlying cause'.)

Stenotic lesions that do not involve loss of cartilaginous support may be more amenable to balloon dilation (figure 1) [8].    

There is no real limit regarding the length of stricture that can be dilated, as even longer strictures can be dilated gradually and in sections.

In addition, tracheal strictures and strictures down to the first or second order of bronchi (figure 2) can be treated with balloon dilation but lesions beyond that point may be both more difficult to access and provide less symptomatic benefit after dilation.

CONTRAINDICATIONS — Contraindications to bronchoscopic balloon dilation are similar to those for flexible bronchoscopy, including the decision to withhold anticoagulants or antiplatelet agents (table 2). (See "Flexible bronchoscopy in adults: Indications and contraindications", section on 'Contraindications'.)

Balloon dilation is also contraindicated when the airway beyond the stenosis cannot be visualized or when the channel through the stenosis is too narrow to be able to pass the balloon.

Intubation and mechanical ventilation is not a contraindication to the procedure [7,9,10].

EFFICACY — Several case series report variable rates of success with balloon dilation [9,11-21]. However, reports of efficacy are biased, have varying definitions of success, inconsistent lengths of follow-up, and variability in physician expertise and techniques. Nonetheless, in most patients, rates of immediate success (defined as improved airway patency upon direct visualization by bronchoscopy) and short-term success (eg, two to six weeks) are high (>90 percent) with improved airway patency (radiologic and bronchoscopic), symptoms, and lung function (picture 1). However, longer-term success beyond that is unpredictable. In our experience, multiple dilations may need to be subsequently performed in order to maintain a satisfactory result. In general, only fibrous stenoses can be reliably improved with balloon dilation alone, while additional therapies (eg, electrocautery) are often needed in conjunction with balloon dilation for airway stenosis from other causes (table 1).

●In one of the largest series, balloon dilation was used to treat 19 stenoses in 16 patients with varying conditions. Ten patients were lung transplant recipients, four underwent bronchial reimplantation, one received radiation therapy, and one suffered from granulomatosis with polyangiitis [18]. Initial clinical success was achieved in two-thirds of bronchial stenoses; the remaining one-third were unsuccessful because stenoses were caused by focal bronchomalacia. Of the initial successes, half recurred but the majority of those were redilated with success (four of seven cases). Among those with fibrous stenosis, improvement in both respiratory status and appearance by bronchoscopy was seen in 70 percent of patients with a mean follow-up of 22 months.

●Another retrospective study reported that among 59 patients with nonmalignant tracheobronchial stenosis, the initial response rate (bronchoscopically, clinically, radiologically, physiologically) was 83 percent but the recurrence rate was high during a 32-month follow-up (80 percent) [21]. The patency rate was 43 percent in those who subsequently underwent repeat dilation.

TECHNIQUE — Although in the past, stenotic lesions were dilated using metal bougies during rigid bronchoscopy, most cases are now performed using flexible bronchoscopy and balloon catheters, the details of which are discussed in the sections below.

The bronchoscopist should be trained and skilled in the procedure as well as in other procedures that might be used in combination with or instead of bronchoscopic balloon dilation. Generally, at least two staff are required, one to operate the bronchoscopic equipment and another to administer medications, and inflate/deflate the balloon.

Sedation, equipment, and balloon dilators — In most patients, balloon dilation is performed via the flexible bronchoscope with topical anesthesia and procedural sedation. However, balloon dilation is a longer procedure than routine diagnostic bronchoscopy, and may therefore require repetitive administration of medications until dilation is completed. For patients undergoing dilation for tracheal lesions (particular critical stenosis) as well as lesions associated with significant airway edema and acute airway obstruction, most experts perform dilation under general anesthesia (with laryngeal mask ventilation or intubation and rigid bronchoscopy) due to the discomfort (from the sense of asphyxiation) associated with complete occlusion of the airway. (See "Flexible bronchoscopy in adults: Overview" and "Procedural sedation in adults in the emergency department: General considerations, preparation, monitoring, and mitigating complications".)

The necessary equipment includes that required for bronchoscopy as well as an appropriately sized balloon catheter. Occasionally a guidewire is required to facilitate passage of the balloon catheter through the stenosis. Preoxygenation is helpful, especially for tracheal lesions since the airway will be temporarily obstructed at the time of balloon inflation. (See "Flexible bronchoscopy in adults: Overview", section on 'Equipment and procedure' and "Flexible bronchoscopy in adults: Preparation, procedural technique, and complications".)

Various sized catheters are available commercially with different types of balloons (picture 2); a selection of balloon catheters of different diameters should be available prior to the procedure since sequential dilation with balloons of increasing diameter is common. Initial balloon catheter size is pre-selected based upon the length and diameter of the stenosis and the desired post-procedure dimensions:  

●Balloons used for dilation are "nonconformal" balloons, meaning they achieve a uniform diameter for a given inflation pressure. These contrast to "conformal" balloons, which are less stiff and would deform around a stenosis as opposed to dilate the stenosis.

●Balloon length – The balloon should protrude enough beyond each end of the stenosis so that dilation of the entire lesion will occur upon balloon inflation. Damage to uninvolved airways may result if the balloon extends too far distally. In contrast, if the balloon does not extend distally enough it tends to slip out of the stenosis upon inflation. The length of the balloon is typically at least 0.5 cm greater than that of the stenotic segment. A 2.5 to 5 cm long balloon is usually adequate. The required length of balloon is estimated by computed tomographic studies (CT) as well as by passing the bronchoscope through the stenosis and measuring the distance between the distal and proximal limits of the obstruction.

●Balloon diameter – The diameter of the inflated balloon needs to be larger than that of the lesion for dilation to occur, but should not be so large that excessive airway injury results. The diameter of the balloon is generally chosen to be the same as that of the lumen measured at the proximal region of the normal airway. The clinician should start with a relatively small diameter balloon and substitute progressively larger balloons as needed. The required width can be estimated from CT images and by comparing the bronchoscope diameter to that of the stenosis.

A syringe with a pressure manometer is most often used to perform controlled dilation with a specific pressure inflating the balloon to a specific diameter. Balloons should be inflated using saline as the liquids are not compressible and will translate to a more "true" volume/diameter of balloon inflation than air. Though nonionic contrast medium (that can be visualized fluoroscopically) can be used, it is usually not necessary because airway strictures are most typically dilated under direct bronchoscopic visualization.

Guidewire placement — Once the patient is adequately anesthetized and sedated, a bronchoscope with an adequate working channel is advanced into the airway. A thorough inspection of the airways is undertaken and the stenosis is identified. If the stenosis appears amenable to balloon dilation, a 0.89 mm diameter guidewire can be passed through the working channel of the bronchoscope and advanced about 1 cm beyond the stenosis, though if there is an adequate lumen, a guidewire is typically not necessary (figure 3). If distal airways cannot be visualized bronchoscopically, the procedure can be monitored fluoroscopically to avoid coiling or sharp bending of, or extension of the wire into the lung periphery, which can penetrate the lung or bronchus. Some experts, prior to the procedure, place markers on the skin above and below the stenosis to help with guidewire placement.  

Most commonly, the balloon catheter can be placed directly through the working channel of the bronchoscope (provided the diameter of the deflated catheter is less than that of the working channel) and the bronchoscope is left in place for the dilation component of the procedure to perform the procedure under direct vision.

Balloon dilation — More than one stenosis may be dilated during a single session. Balloon dilation may be used alone or precede or follow other procedures such as mechanical dilation (ie, bougie dilation using rigid bronchoscopy), laser, stenting, cryotherapy, and electrocautery. None of these options or combination approaches have proven superiority. Choosing among them is discussed separately. (See "Clinical presentation, diagnostic evaluation, and management of malignant central airway obstruction in adults", section on 'Choosing among modalities' and "Management of non-life-threatening, nonmalignant subglottic and tracheal stenosis in adults".)

Procedure — The procedure is typically as follows:

●After an adequately-sized balloon catheter has been selected based upon the estimated length and width of the stenosis, it is passed through the working channel of the bronchoscope, or over the guidewire (which is no longer within the bronchoscope) under fluoroscopic guidance. Some balloons have radiopaque markers at the proximal and distal ends so that they can be properly located with respect to the stenosis. (See 'Sedation, equipment, and balloon dilators' above and 'Guidewire placement' above.)

●If performing the procedure with a guidewire, the bronchoscope is then reinserted (preferably through a different route than the guidewire – eg, through the nostril) to allow direct visualization of the balloon during inflation.

●The balloon is inflated with water to pressures between 45 and 131 psi (3 to 9 atm) using a syringe and pressure manometer. The generated pressure is based upon the characteristics of the particular balloon since the diameter of the balloon is proportional to the inflation pressure (picture 3).

•Inflation should be done gradually (over minutes) taking care to not over inflate the balloon and to avoid rupture or over dilation of the airway stricture which might result in mucosal tearing and recurrent stenosis. The initial inflation time is usually short (30 seconds to two minutes).

•A pressure-gauge monitor is used to guide and monitor pressures (and hence diameter) throughout the procedure. Most currently available balloons will dilate to a specific diameter based on a certain pressure measured in the manometer.

•The balloon is kept inflated for up to two minutes, depending upon patient tolerance and effects on oxygenation, and is then deflated. Long inflation times may be less well tolerated for dilation of tracheal lesions (where complete occlusion of the central airway occurs) compared with bronchial lesion; otherwise, there are no real differences in dilating techniques between tracheal and bronchial strictures.

●After deflation, the response to inflation is immediately assessed by direct bronchoscopic visualization. During balloon inflation the typical indent ("waist") made by the stenosis on the balloon is lost but after deflation, the airway diameter should be visibly improved. If the result is inadequate (eg, unsuccessful dilation to the desired diameter or inability to restore improved patency), repeated dilations can be performed with the same balloon or with a longer or wider balloon. Inflation times can usually can be increased as progressive dilation occurs (2 to 3 minutes).

●Once successful dilation has been achieved, the balloon (and guidewire if used) and bronchoscope can be removed, and the patient recovered. Flexible bronchoscopic balloon dilation is typically a day procedure, although some patients may need monitoring overnight (eg, those with complications or severe stenosis).

Radial incisions — For tight, "web-like" circumferential strictures, it can be helpful to first make one or more radial incisions prior to balloon dilation (ie, a linear incision at one point in the lesion- like the spoke of a wheel). There are no clear guidelines on when an incision should be used and it is often-operator dependent (eg, severe stenosis with impending airway closure, repeat dilation for a stenotic lesion that was initially unresponsive to prior dilation).

Radial incisions can be made using neodymium-doped yttrium aluminium garnet (Nd:YAG) laser (using high power density to avoid collateral tissue damage), potassium titanyl phosphate (KTP) laser, carbon dioxide (CO₂) laser, or an electrocautery knife. If an electrocautery knife is used, it is safer to use the blend or coagulation mode, rather than the cut mode, in order to assure hemostasis. (See "Endobronchial electrocautery" and "Bronchoscopic laser in the management of airway disease in adults".)

Where it appears intuitive that radial incisions may increase the risk of complications such as hemorrhage, tearing, or rupture, if used appropriately most experts believe that it may prevent complications such as tearing or rupture due to dilation itself, particularly when the stricture is very tight. (See 'Complications' below.)

COMPLICATIONS — Flexible bronchoscopic balloon dilation is generally well tolerated. Most of the complications are those associated with flexible bronchoscopy, which are detailed elsewhere (table 3). (See "Flexible bronchoscopy in adults: Preparation, procedural technique, and complications", section on 'Complications'.)

Complications due to balloon dilation itself are unusual. Chest pain during balloon inflation and periprocedural bronchospasm or atelectasis have been reported [7,10,22]. Excessive balloon inflation may lacerate or rupture the airway, theoretically producing hemorrhage, pneumothorax, pneumomediastinum, or mediastinitis, but these complications are quite rare and often do not require intervention. Similarly, no reported deaths have been attributed to balloon dilation [23,24].

Rare cases of balloon rupture have been reported without major clinical effect [11].

Although lacerations are a risk during dilation, especially when the stenosis is tight and circumferential, they often heal spontaneously after conservative treatment [23,24]. Radial incisions prior to dilation may offset this potential complication. (See 'Radial incisions' above.)

FOLLOW-UP — We and other experts typically assess patients clinically (signs and symptoms) approximately two weeks after balloon dilation. Some experts also perform pulmonary function tests (PFTs) to determine whether there is improvement in ventilatory function but it is not routine. Follow-up flexible bronchoscopy and computed tomography (CT) of the airway are not generally routinely performed unless the patient has signs and symptoms suggestive of significant residual or recurrent stenosis; however, this practice is operator-dependent.

For some patients who fail dilation, the procedure can be repeated or performed in combination with other local endobronchial therapies such as stenting and, occasionally, surgery. Choosing among these therapies is operator-dependent with no clear guidelines on the optimal second procedure. (See "Clinical presentation, diagnostic evaluation, and management of malignant central airway obstruction in adults" and "Airway stents".)

SUMMARY AND RECOMMENDATIONS

●Nonmalignant stenosis of the central airways (trachea and main stem bronchi) can result from several conditions (table 1). Flexible bronchoscopic balloon dilation (bronchoplasty) is a simple, minimally-invasive method that dilates stenotic airway lesions and restores adequate airflow. It may be used alone or in combination with other endobronchial bronchoscopic therapies to dilate airway stenoses and restore adequate airflow. (See 'Introduction' above.)

●Lesions best suited for balloon dilation are symptomatic lesions that have failed or are not suitable for first-line therapies (eg, therapy targeted at the underlying cause). In particular, the procedure is more successful in fibrotic lesions rather than those associated with tracheobronchomalacia, inflammation, calcification, or cancer. Vascular lesions should be avoided. (See 'Assessing lesion suitability' above.)

●Contraindications to bronchoscopic balloon dilation are similar to those for flexible bronchoscopy. Balloon dilation is also contraindicated when there is nonvisualization beyond the lesion. (See 'Contraindications' above.)

●In most patients, rates of immediate success (defined as improved airway patency upon direct visualization by bronchoscopy) and short-term success (eg, two to six weeks) are high (>90 percent) with improved airway patency (radiologic and bronchoscopic), symptoms, and lung function (picture 1). However, longer-term success beyond that is unpredictable.

●Balloon dilation is performed via the flexible bronchoscope with topical anesthesia and procedural sedation. An adequately-sized balloon catheter is passed either directly through the stenosis or over a guidewire through stenotic lesion (figure 3 and picture 2). Under direct bronchoscopic visualization, the balloon is inflated for one to two minutes, sometimes longer if tolerated. Multiple dilations with the same or a larger balloon may need to be performed to obtain a satisfactory result. For tight, circumferential strictures, it can be helpful to first make one or more radial incisions prior to balloon dilation to prevent epithelial tearing. (See 'Technique' above.)

●The complications of bronchoscopic balloon dilation are similar to those for flexible bronchoscopy. In addition, chest pain during balloon inflation, periprocedural bronchospasm, and periprocedural atelectasis may occur. Excessive balloon inflation may lacerate or rupture the airway. No deaths have been attributed to balloon dilation. (See 'Complications' above.)

●Patients should be assessed clinically at two weeks after the procedure for the signs and symptoms of recurrence. Some experts also perform pulmonary function testing. If recurrence is suspected, computed tomography (CT) and bronchoscopy should be performed with a view to repeating the dilation procedure or combining it with another endobronchial modality. (See 'Follow-up' above.)