Long-term outcomes of tracheal stents removal under fluoroscopy guidance: comparison of tracheal fistulas with tracheal stenosis

Background: No study compared the techniques and complications of stent removal under Methods: We conducted a retrospective analysis of 152 patients who underwent fluoroscopy-guided stent removal from January 2011 to June 2017. Eighty-five patients underwent stent removal for tracheal fistula (TF group), and 67 patients for tracheal stenosis (TS group). All patients underwent tracheal CT scans before stent removal and during follow up. The technical success rate, complications, survival rate were compared between the two groups. Results: The technical success rate of stent removal was 98.9% and 97.4% for tracheal fistula and tracheal stenosis, respectively. Except for the routine removal for half of patients, excessive granulation tissue was the common indications for stent removal, which was found 142.1±25.9 days later for tracheal fistula, and 89.9±15.0 day for tracheal stenosis. The total incidence of complications was 21.1% and 22.4% for tracheal fistula and tracheal stenosis, respectively. One perioperative death of asphyxia was found in TF group, and 2 deaths in TS group. Recurrence of fistula or stenosis requiring stenting was the most comment complication in both groups. The 0.5-, 3-, 6-year survival rates were 90.3%, 59.6%, and 36.1% for TF group, and 80.4%, 75.7%, 75.7% for TS group. Conclusions: Fluoroscopic removal of tracheal stent is safe and effective for both tracheal fistula and tracheal stenosis, with no significant difference. Recurrence of fistula or stenosis requiring stenting was the most comment complication.


Background
Tracheal fistula and/or tracheal stenosis are severe complications after open thoracic surgery, endotracheal intubation injury, endobronchial tuberculosis, and thoracic trauma [1]. These complications often show high mortality and disability rates; unfortunately, traditional conservative treatment shows a poor curative effect. Besides, some patients may not be willing to undergo open surgery considering that they are too weak or sick under this circumstance [2]. Since first adoption of self-expanding metal stents to treat bronchial obstruction in 1989 [3], the efficacy and safety of tracheal stent has been proven for the treatment of tracheal fistula [4][5][6][7] or tracheal stenosis [8][9][10][11][12][13]. 3 However, tracheal stents placement may bring a series of complications, such as restenosis, migration, fracture, or mucous plugging [14], which make stent removal necessary. Endoscopic removal is the common method for removal of tracheal stents in literatures [15][16][17][18][19][20]. Few studies reported the technique of tracheal stent removal under fluoroscopy guidance [12,21,22]. Is fluoroscopic removal of tracheal stents safe and effective? How long the tracheal stent should be removed? Topics of ongoing investigation include the safety and efficacy of fluoroscopic stent removal as well as the optimal time interval of stent usage. We compared the outcomes of techniques and complications associated with fluoroscopy-guided removal of tracheal stents for tracheal fistula and tracheal stenosis.

Patients
This retrospective study was approved by the Ethics Committee and Medical Records Management Section of our University. All patients gave written informed consents. A total of 152 patients underwent fluoroscopy-guided stent removal from January 2011 to June 2017 in our department. Of which, 85 patients underwent stent removal for tracheal fistula (TF group), and 67 patients for tracheal stenosis (TS group). Following to the doctors' advices, more than 50% of patients underwent routine removal in both groups to avoid long-term complications even if they show no obvious symptoms or signs.

Tracheal stent
Tracheal stents were designed and manufactured according to individual tracheal shape and size measured by CT examination (Nanjing Micro-Tech Medical Company, Nanjing, China), and woven with a temperature-memory nickel-titanium alloy wire. All tracheal stents for fistula were fully covered in TF group, and 70 covered stents and 6 bare stents were used in TS group (Figure 1). Ninety tracheal stents were implanted in TF group, and large Y-shaped single-plugged tracheal stent was the most common type (32.2%). In TS group, 76 stents were implanted and the most common type was straight tracheal stent (73.7%).

Technical preparation before and after tracheal stent removal
Chest CT and bronchoscopy was performed on the day before stent removal. Patients' electrocardiogram, heart rate and blood pressure were routinely monitored during perioperative period. Oxygen was given by nasal catheter and a sputum aspirator was prepared. Ten mg of diazepam and anisodamine (654-2) was intramuscularly injected to calm the patient and to reduce tracheal secretions before stent removal. Ten mg of dexamethasone was injected to relieve dyspnea or to improve the tolerability if necessary. The sputum aspiration tube was then advanced into the tracheal for sputum drainage and to maintain tracheal patency. All patients were monitored by electrocardiogram, heart rate and blood pressure for at least 8 hours after stent removal.

Technical details of tracheal stent removal
A 5F catheter and 0.035inch hydrophilic guide wire (Cook Corporation, Bloomington, IN, USA) were inserted into the main bronchus under topical anesthesia by lidocaine. A 10-12F long sheath was inserted below the tracheal stent via a 0.035inch stiff hydrophilic guide wire. A removal hook was introduced slowly along the sheath with its tip placed next to the end of stent. The tracheal stent was hooked firmly and then withdrawn carefully ( Figure 2). The radiography was performed again to show whether there was a overflow of contrast after stent removal.

Complications of stent removal and follow up
All complications of stent removal were recored and analyzed. Patients were followed up after stent removal, and chest CT scans were performed. Telephone follow-up was used for patients who did not come to the hospital for reexamination.

Statistical analysis
Data were expressed as mean ± standard deviation, and analyzed by student t test and ANOVA.
Qualitative data were expressed in percentage, and analyzed by Fisher's exact test. Patency rate was compared by Log-rank (Mantel-Cox) Test (GraphPad Software, Inc., USA). Statistical significance was considered when p<0.05.

Patient characteristics
Ninety covered tracheal stents were inserted in TF group and 76 tracheal stents were implanted in TS group. 81.2% of patients with tracheal fistulas were caused by malignancy disease in TF group, 82.1% of patients with tracheal stenosis were caused by benign primary disease in TS group. The success rate of stent removal was 98.9% (89/90) in TF group. Only one patient underwent bronchoscopic removal for the retained stent pieces after failure in fluoroscopic removal. In TS group, 74 of 76 tracheal stents were successfully removed, only 2 stents retained, with a technical success rate of 97.4% (74/76). The mean procedure time of stent implantation or removal was similar between two groups. Tumor invasion or tumor operation was the main causes for tracheal fistula, and tracheotomy or trachea cannula was the main causes for tracheal stenosis (p < 0.0001, Table 1).

Indications for stent removal and interval
Following to doctors' advices, 47 stents (52.2%) and 40 stents (52.6%) were routinely removed for tracheal fistula and tracheal stenosis, respectively. Stent migration and stent intolerance were the main indications for early stent removal in both groups. Excessive granulation tissue increased as time interval increased, with a mean interval of 142.1±25.9 days for tracheal fistula and 89.9±15.0 day for tracheal stenosis, which was the most common indications for later stent removal.
Interestingly, tracheal stents were routinely removed after 107.8±9.8 days and 85.4±6.7 days in TF group and TS group, respectively ( Table 2). These two time points are consistent, suggesting that the stent should be removed about 3 months after implantation to reduce the incidence of restenosis. Six bare stents were emergency implanted in TS group for sever tracheal stenosis, of which, 3 stents were removed and replaced by covered stents, with a mean duration of 8.7±3.2 days, and 1 stent was replaced by tracheal T tube.

Complications
The technical success rate of stent removal was 98.9% and 97.4% for tracheal fistula and tracheal stenosis, respectively. In TF group, 75 stents were removed in one piece; stent fracture and retained stent pieces was found in 14 and 1 stent. In TS group, 74 tracheal stents were successfully removed from, 5 stents showed strut fracture. Of which, 2 stents retained, and the 3 retained stent pieces were successfully removed by endoscopy; the remained 71 stents were removed in one piece ( Table 3).
Recurrence of fistula or stenosis requiring stenting was the most comment complications in both 6 groups. Two patients showed severe dyspne in each group and were endotracheal intubation and mechanical ventilation. Symptoms were relieved and the endotracheal tube was removed within 4 hours. Massive hemoptysis occurred in 2 cases during stent removal in TF group. One patient died of asphyxia caused by blood clogging, and bleeding ceased in the other patient after administration of pituitrin. Two patients died perioperatively in TS group, resulting in a clinical success rate of 94.7% (72/76). One patient with tracheal stenosis after resection of esophageal carcinoma died of massive hemoptysis 3 days after stent removal. The other patient died of respiratory failure 2 days after the second stent insertion.

Second stenting after removal
Eight stents were replaced immediately and 5 stents were replaced 5 to 9 days after removal in TF group. Replacements included Y-type tracheal stents (n=5), L-type tracheal stents (n=3), Y-shaped single-plugged stents (n=2), straight tracheal stents (n=2) and 1 combination of a large and a small Y-type tracheal stent. One patient required stenting due to proximal re-obstruction of the stent after removal of a straight tracheal stent, and the same size of straight tracheal stent was implanted immediately. In TS group, 20 tracheal stents (15 straight tracheal stents and 5 Y type tracheal stents) were implanted again after removal for replacement of bare stents (n=3), or due to restenosis (n=9), migration (n=3), inadequate expansion (n=3), and intolerance (n=2).

Follow up
All patients were followed up except for perioperative deaths. Five patients (6.0%) lost in TF group and 4 lost (6.2%) in TS group during follow up. Thirty-three patients were cured and 20 patients were improved in TF group. In TS group, 29 patients were cured and 20 patients were improved; six patients underwent tracheotomy and tracheal T tube implantation after stent removal. Twenty-four patients died in TF group, tumor progression was the most common cause of death. Besides, one died of respiratory failure due to asphyxia, and 2 patients died of massive hemoptysis and hematemesis (Table 4). The 0.5-, 3-, 6-year survival rates were 90.3%, 59.6%, and 36.1% for TF group, and 80.4%, 75.7%, 75.7% for TS group (Figure 3). 7 Tracheal stent has been widely used clinically for the treatment of tracheal fistula [4][5][6][7] or tracheal stenosis [8][9][10][11][12][13]. However, tracheal stents placement may bring a series of complications, and stent removal sometimes is necessary [23]. Currently, tracheal stent is commonly removed under bronchoscopic guidance and general anesthesia [17,[24][25][26][27] or local anesthesia [28,29]. Few studies reported fluoroscopic removal of tracheal stent [12,21,22], and no study compared the long-term outcomes of techniques and complications associated with fluoroscopic removal of tracheal stents between tracheal fistula and tracheal stenosis.

Discussion
In the present study, 97.4% of stents for tracheal stenosis were successfully removed under fluoroscopy guidance, which is higher than that of silicon stent removal in patients with tracheobronchial stenosis [30]. Additionally, 83.3% of stents were removed in one piece and only one stent showed retained stent pieces in this study. However, 73% of stents were removed piecemeal with rigid alligator forceps [24]. Our data indicate that fluoroscopic removal of tracheal stents is a feasible procedure for tracheal fistula and tracheal stenosis.
Although the process of fluoroscopic removal of tracheal stent is rapid, serious complications may occur during stent removal, such as massive bleeding, acute tracheal obstruction, and even death [24,31,32]. In our study, one patient died of asphyxia caused by blood clogging in TF group; one patient died of massive hemoptysis 3 days after stent removal, and the other patient died of respiratory failure in TS group. In addition, the total incidence of complications was 21.1% and 22.4% for tracheal fistula and tracheal stenosis, respectively. Compared with previous reports in rigid bronchoscopy [24,25,29,31], we showed a lower rate of complication.
How long of indwelling interval suitable for stent removal in the treatment of tracheal disease is a problem worthy of investigation [25]. The incidence of stent restenosis induced by granulation tissue hyperplasia and stent fracture may increase as indwelling time increases [33][34][35], and may bring difficulty or failure of stent removal [28]. According to our findings, excessive granulation tissue was found 142.1±25.9 days later for tracheal fistula, and 89.9±15.0 day for tracheal stenosis.
Interestingly, tracheal stents were routinely removed about 3 months after implantation in this study.
A indwelling interval of 1 to 3 months should be recommended for stent removal to avoid long-term 8 complications.
There are weaknesses in our study. This is a retrospective study conducted in a single center. We solely performed stent removal under fluoroscopy guidance, stents should be removed by variety of technologies including bronchoscopy.

Conclusions
Fluoroscopic removal of tracheal stent is safe and effective for both tracheal fistula and tracheal stenosis, with no significant difference. Recurrence of fistula or stenosis requiring stenting was the most comment complication.

Ethics approval and consent to participate
This study obtained approval from the institutional review board of Zhengzhou University First Affiliated Hospital to review and publish information obtained from patient records. Written informed consent was obtained from all patients.

Consent to publish
We informed each patient of the publication, which includes the individuals personal data in any form (including individual details, images, or videos), and obtained written informed consent.

Availability of data and materials
The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Competing interests
The authors declare that they have no competing interests.     Technique of tracheal stent removal. A retrieval hook was inserted through a sheath and the tip of hook was placed next to the proximal end of the stent. The stent then was carefully dissected from the tracheal wall.