Removal of Covered Self-Expandable Metallic Airway Stents in Benign Disorders

Patient-specific models of human trachea to predict mechanical consequences of endoprosthesis implantation

Nowadays, interventions associated with the implantation of tracheal prostheses in patients with airway pathologies are very common. This surgery may promote problems such as migration of the prosthesis, development of granulation tissue at the edges of the stent with overgrowth of the tracheal lumen or accumulation of secretions inside the prosthesis. Among the movements that the trachea carries out, swallowing seems to have harmful consequences for the tracheal tissues surrounding the prosthesis. In this work, a finite-element-based tool is presented to construct patient-specific tracheal models, introducing the endotracheal prosthesis and analysing the mechanical consequences of this surgery during swallowing. A complete description of a patient-specific tracheal model is given, and a fully experimental characterization of the tracheal tissues is presented. To construct patient-specific grids, a mesh adaptation algorithm has been developed and the implantation of a tracheal prosthesis is simulated. The ascending deglutition movement of the trachea is recorded using real data from each specific patient from fluoroscopic images before and after implantation. The overall behaviour of the trachea is modified when a prosthesis is introduced. The presented tool has been particularized for two different patients (patient A and patient B), allowing prediction of the consequences of this kind of surgery. In particular, patient A had a decrease of almost 30 per cent in his ability to swallow, and an increase in stresses that were three times higher after prosthesis implantation. In contrast, patient B, who had a shorter trachea and who seemed to undergo more damaging effects, did not have a significant reduction in his ability to swallow and did not present an increase in stress in the tissues. In both cases, there are clinical studies that validate our results: namely, patient A underwent a further intervention whereas the outcome of patient B's surgery was completely successful. Notwithstanding the fact that there are a lot of uncertainties relating to the implantation of endotracheal prostheses, the present work gives a new insight into these procedures, predicting their mechanical consequences. This tool could be used in the future as pre-operative planning software to help thoracic surgeons in deciding the optimal prosthesis as well as its size and positioning.

Tracheal stricture and fistula: management with a barbed silicone-covered retrievable expandable nitinol stent

OBJECTIVE

The purpose of this study was to evaluate the safety and effectiveness of a barbed silicone-covered retrievable expandable nitinol stent in preventing stent migration in patients with tracheal strictures or fistulas.

SUBJECTS AND METHODS

Under fluoroscopic guidance, barbed silicone-covered retrievable expandable nitinol stents were placed in 15 patients with tracheal strictures, two patients with fistulas, two patients with combined strictures and fistulas, and one patient with variable extrathoracic airway obstruction. The three pairs of barbs were attached to the external stent surface at the middle of the stent at equal intervals. Technical success, improvement in respiratory status, complications, and related interventions were evaluated.

RESULTS

The technical success rate was 100%, and respiratory status improved or the fistula closed in all 20 patients. Complications included sputum retention (three patients), tumor overgrowth (three patients), pain (one patient), and granulation tissue formation (one patient). No stent migration occurred, even in the three patients without fixed strictures. Four stents subsequently were removed because of complications, and one stent was removed because the patient's condition improved. Stent removal was not difficult and was uneventful. The silicone membranes and barbs of the removed stents were intact.

CONCLUSION

Use of a barbed silicone-covered retrievable expandable nitinol stent relieves dyspnea and facilitates fistula closure in patients with benign or malignant tracheal strictures or fistulas. The barbed design of the stent is important in preventing migration.

Detection of stent fractures: a comparison of 64-slice CT, conventional cine-angiography, and intravascular ultrasonography

RATIONAL AND OBJECTIVES

We evaluated the ability of 64-slice computed tomography (CT), conventional cine-angiography, and intravascular ultrasound (IVUS) to detect stent fractures under ideal conditions. Coronary stent fracture has been implicated as one of the mechanisms of stent thrombosis and, perhaps, in-stent restenosis. However, the preferred imaging modality in detecting fractures in coronary stents has not been well established.

MATERIALS AND METHODS

Four different types of commonly used coronary stents (Cypher, Taxus, Vision, Hepacoat) each with three strut fractures (Cypher, 5; Taxus, 5; Vision, 4; Hepacoat, 5) were nominally deployed in polyurethane tubes and imaged with 64-slice CT, conventional cine-angiography, and IVUS. For each stent type, an unfractured control stent was also imaged.

RESULTS

Overall accuracy (84.1% vs. 73.9%), sensitivity (80.7 vs. 77.2%), and specificity (100% vs. 58.3%) for stent fracture detection was higher with 64 multislice CT compared to conventional cine-angiography. Stent fractures were not accurately detected by IVUS. Fracture detection by multislice CT was best when the stents were imaged at 45 degrees to the z-axis.

CONCLUSIONS

Under ideal in vitro conditions, CT has a high accuracy when used to evaluate coronary stent fractures. The overall accuracy, sensitivity, and specificity of detecting stent fractures are lower by conventional cine-angiography. Stent fractures were not detected using IVUS.

Surgical planning and patient-specific biomechanical simulation for tracheal endoprostheses interventions

We have developed a system for computer-assisted surgical planning of tracheal surgeries. The system allows to plan the intervention based on CT images of the patient, and includes a virtual database of commercially available prostheses. Automatic segmentation of the trachea and apparent pathological structures is obtained using a modified region growing algorithm. A method for automatic adaptation of a finite element mesh allows to build a patient-specific biomechanical model for simulation of the expected performance of the implant under physiological movement (swallowing, sneezing). Laboratory experiments were performed to characterise the tissues present in the trachea, and movement models were obtained from fluoroscopic images of a patient. Results are reported on the planning and biomechanical simulation of two patients that underwent surgery at our hospital.

Recurrent airway obstructions in a patient with benign tracheal stenosis and a silicone airway stent: a case report

Airway stents (silicone and metal stents) are used to treat patients with benign tracheal stenosis, who are symptomatic and in whom tracheal surgical reconstruction has failed or is not appropriate. However airway stents are often associated with complications such as migration, granuloma formation and mucous hypersecretion, which cause significant morbidity, especially in patients with benign tracheal stenosis and relatively normal life expectancy. We report a patient who had frequent critical airway obstructions over 8 years due to granuloma and mucus hypersecretion in a silicone airway stent. The problem was resolved when the silicone stent was removed and replaced with a covered self expanding metal stent.

Anesthetic considerations for airway stenting in adult patients

The attributable morbidity from central airway obstruction is significant. Airway stenting provides a therapeutic option to manage these complex lesions. This article focuses on the relevant anesthetic considerations of airway stenting in adult patients.

Noninvasive correction of a fractured endoluminal nitinol tracheal stent in a dog

An 11-year-old, castrated male Pomeranian was presented for intractable cough and dyspnea secondary to severe tracheal collapse. An endoluminal nitinol tracheal stent was placed with good results. Five months following placement of the prosthesis, clinical signs acutely recurred and failure of the implant was noted. A second stent was superimposed over the fractured stent and resulted in resolution of all clinical signs. The dog died several months later from progression of the tracheal collapse to the carina and mainstem bronchi.

Do airway metallic stents for benign lesions confer too costly a benefit?

Background

The use of self-expanding metallic stents (SEMAS) in the treatment benign airway obstruction is controversial.

Methods

To evaluate the safety and efficacy of SEMAS for this indication, we conducted a 10-year retrospective review at our tertiary medical centre.

Results

Using flexible bronchoscopy, 82 SEMAS (67% Ultraflex, 33% Wallstent) were placed in 35 patients with inoperable lesions, many with significant medical comorbidities (88%). 68% of stents were tracheal, and 83% of patients showed immediate symptomatic improvement. Reversible complications developed in 9% of patients within 24 hrs of stent placement. Late complications (>24 hrs) occurred in 77% of patients, of which 37% were clinically significant or required an interventional procedure. These were mainly due to stent migration (12.2%), fracture (19.5%), or obstructive granulomas (24.4%). The overall granuloma rate of 57% was higher at tracheal sites (59%) than bronchial ones (34%), but not significantly different between Ultraflex and Wallstents. Nevertheless, Wallstents were associated with higher rates of bleeding (5% vs. 30%, p = 0.005) and migration (7% vs. 26%, p = 0.026). Of 10 SEMAS removed using flexible bronchoscopy, only one was associated with incomplete removal of fractured stent wire. Median survival was 3.6 ± 2.7 years.

Conclusion

Ill patients with inoperable lesions may be considered for treatment with SEMAS.

Endotracheal stenting therapy in dogs with tracheal collapse

Tracheal collapse in dogs is a common respiratory disorder, typically presenting with a history of chronic cough, increasing respiratory difficulties, and episodes of dyspnoea. Medical treatment is the therapy of choice and surgical repair is considered when patients do not respond well. Minimally invasive endotracheal stenting is a promising new therapy under investigation, but there remain significant challenges to overcome potential complications. The purpose of this article is to provide a comparative overview of intra-luminal stenting of the trachea in human and veterinary medicine. The currently available stents and their potential clinical application to the veterinary patient will be discussed.

Rare and fatal complication of Gianturco tracheobronchial stent

Tracheobronchial stents are increasingly being used for the management of compromised large airways. Traditionally they have been used to palliate malignant conditions; however, they are now being used more frequently for nonmalignant conditions. The use of Gianturco self-expanding metal stent (William Cook, Bjaeverskov, Denmark) has been challenged for treatment of tracheobroncheomalacia, as fracture of the metal work could prove fatal. In this report we describe a case of fracture in the metal framework of a Gianturco stent resulting in recurrent pneumothoraces; heralding fatal haemoptysis as a result of perforation of the left subclavian artery.

Tracheal Stenting of Iatrogenic Tracheal Injury: A Novel Management Approach

We report the case of a patient who had an intubation-related tracheal injury who we treated by deployment of a covered tracheal stent. This approach may be preferable to other alternatives in patients with a prohibitive risk of mortality with surgical repair or in an injury with sequelae not suitable for conservative management.

Benign tracheobronchial strictures: long-term results and factors affecting airway patency after temporary stent placement

OBJECTIVE

The purpose of our study was to evaluate long-term results and identify factors affecting airway patency after temporary placement of a covered, retrievable nitinol stent for benign tracheobronchial strictures.

MATERIALS AND METHODS

Polyurethane or polytetrafluoroethylene (PTFE)-covered retrievable expandable nitinol stents were placed fluoroscopically in 24 patients with benign tracheobronchial strictures. Improvement in respiratory status and complications were evaluated. Maintained patency of airway after temporary stenting was calculated and compared between the 2- and 6-month stenting groups. Factors for maintained patency after temporary stenting were evaluated.

RESULTS

A total of 30 stents were successfully placed and well tolerated in 24 patients. Tissue hyperplasia, stent migration, and bronchial obstruction of the left upper lobe occurred in 36.7%, 13.3%, and 3.3% of patients, respectively. All stents were successfully removed electively either 2 (n = 12) or 6 (n = 12) months after placement or when complications occurred (n = 6). During the follow-up period (mean, 24 months), dyspnea recurred in 15 of the 24 patients. The 6-month stenting group showed a lower recurrence rate (41.7% vs 83.3%, p = 0.045) and a better mean maintained patency (39.7 +/- 7.8 vs 9.4 +/- 5.4 months, p = 0.001) than the 2-month stenting group. Multivariate analysis showed that duration of stent placement (p = 0.002) and the occurrence of tissue hyperplasia (p = 0.026) were associated with maintained patency after temporary stenting.

CONCLUSION

Temporary placement of a covered, retrievable, expandable nitinol stent may be a safe and effective treatment for benign tracheobronchial strictures during the period the stent is in place. A high symptomatic recurrence rate of 62.5% was found after stent removal. Shortterm placement of the stent and tissue hyperplasia were associated with decreased airway patency.

In vitro study of the safety limits of bronchoscopic argon plasma coagulation in the presence of airway stents

OBJECTIVE AND BACKGROUND

The purpose of this study was to identify the safety limits of bronchoscopic argon plasma coagulation (APC) around indwelling airway stents.

METHODOLOGY

This is an experimental in vitro study simulating a patient-care environment. Uncovered and covered Nitinol (Ultraflex), uncovered and covered Wallstent and studded silicone stents were deployed in the tracheobronchial tree of a ventilated and oxygenated heart-lung block from an expired pig. APC was performed at power settings of 40 and 80 W using F(I)O(2) of 0.21, 0.40 and 1.00 and an argon gas-flow rate of 0.8 L/min through a flexible fiberoptic bronchoscope. The primary outcome was the time taken for the APC to cause stent damage. Stent damage was defined as discoloration, ignition or rupture.

RESULTS

Airway fires involving all five stents consistently occurred in the presence of 100% oxygen at powers of 40 W and 80 W. At lower F(I)O(2) (0.21 and 0.40) silicone stents were not damaged at 40 W and 80 W. Uncovered Ultraflex stents were undamaged using 40 W at either F(I)O(2) (0.21 and 0.40), but could be damaged using both F(I)O(2) levels when the power was increased to 80 W. Covered Ultraflex and both uncovered and covered Wallstents were damaged at both power settings (40 W and 80 W) and F(I)O(2) (0.21 and 0.40) levels, with a trend towards earlier damage using higher F(I)O(2) and power.

CONCLUSION

Working within the parameters identified in this study (power 40 W, F(I)O(2) 0.21, APC flow-rate 0.8 L/min), APC is a safe method for tissue devitalization and destruction and avoids the risk of airway stent ignition, especially if short bursts of APC are employed. The safety limits identified using an F(i)O(2) of 0.4, however, are also important because some patients undergoing resection may require oxygen therapy.

Stenting allows weaning and extubation in ventilator- or tracheostomy dependency secondary to benign airway disease

Central airway obstruction can cause severe respiratory insufficiency leading to mechanical ventilation (MV) or artificial airway (AA) dependency. Interventional bronchoscopic procedures have been reported to be of help in weaning patients with malignant airway stenoses from mechanical ventilation, whereas their use in benign disease is only anecdotal. The objectives of this study are to evaluate early, intermediate and long-term outcome of interventional bronchoscopy and stent placement in the treatment of MV/AA dependency due to benign airway obstruction. In a retrospective cohort analysis for the period 1999-2004, we evaluated 15 consecutive ICU patients with documented benign central airway obstruction, who were referred for bronchoscopic management of their condition after multiple failed attempts at weaning from MV or decannulation of the AA. Indications for bronchoscopic treatment were surgery refusal, medical or surgical inoperability, or absence of alternative treatment options. Malacia, post-intubation stenosis and goiter were the main causes of airway obstruction and MV/AA dependency. All patients were treated by means of rigid bronchoscopy, dilatation procedures and stent insertion. All but one patient (93.3%) were successfully and permanently extubated/decanulated immediately after the bronchoscopy. Minor complications occurred in 6 patients (40%) leading to a second intervention. All complications could be managed endoscopically and long-term follow up was uneventful. Interventional bronchoscopy with stent insertion can allow successful withdrawal from MV/AA and can offer longstanding airway patency in selected ventilator- or tracheostomy-dependant individuals with benign airway stenoses,when surgery in not feasable or contra-indicated.

Development andin vivo testing of a Nitinol tracheal stent

This article describes the development of a Nitinol tracheal stent (HCPA NiTi-stent) and its application in a feline animal model. Straight-annealed, bright-polished Nitinol wire (55.8%Ni-44.2%Ti) was weaved around a 40-mm-long metal fixture with 8-mm diameter. The prototypes were submitted to different times of shape-setting heat treatment (530 degrees C), which resulted in stents of different colors and caused some variation in length and diameter. The prototypes were then submitted to compression testing, and the most resistant pieces, requiring the greatest force to achieve a 25% reduction in diameter and presenting the least variation in length and diameter (dark blue, 9 min of heat treatment), were submitted to fatigue testing. After that, only dark blue stents were manufactured and implanted in felines. No migration, tracheal stenosis, or any other type of damage were observed after 40 weeks. The integrity of the tracheal wall in contact with the stent was confirmed by macro and microscopic analyses. The development and in vivo testing of the HCPA NiTi-stent were successful.

Main bronchial reconstruction with sparing of pulmonary parenchyma for benign diseases

Main bronchial reconstruction is anatomically suitable for benign main bronchial stenosis. But, it has been hardly recommended for operative mortality and morbidity. This study was aimed at providing validity and the proper clinical information of bronchoplasty for benign main bronchial stenosis by reviewing the results we obtained over the last ten years for main bronchial reconstruction operations. We retrospectively reviewed admission and office records. Twenty eight consecutive patients who underwent main bronchoplasty were included. Enrolled patients underwent main bronchial reconstruction for benign disease (tuberculosis in 21, trauma in 4, endobronchial mass in 3). Concomitant procedures with main stem bronchoplasty were performed in 19 patients. There were no incidences of postoperative mortality and significant morbidity. There were 2 cases of retained secretions, and these problems were resolved by bronchoscopy or intubation. All of the patients are still alive without obstructive airway problem. Bronchoplasty should be considered as one of the primary treatment modalities, if it is anatomically feasible.

Treatment of Tracheobronchial Obstruction with a Polytetrafluoroethylene-covered Retrievable Expandable Nitinol Stent

PURPOSE

To evaluate the clinical effectiveness of polytetrafluoroethylene (PTFE)-covered retrievable expandable nitinol stents in tracheobronchial strictures.

MATERIALS AND METHODS

With fluoroscopic guidance, PTFE-covered retrievable expandable nitinol stents were placed in 15 symptomatic patients with benign (n = 6) or malignant (n = 9) tracheobronchial strictures. Complications and improvement in respiratory status were evaluated. Stents were removed electively 6 months after placement in benign strictures or if complications occurred. Membrane degradation or separation from the wire mesh was evaluated in removed stents.

RESULTS

A total of 17 stents were successfully placed and were well tolerated in all patients. Sputum retention, stent migration, and tissue hyperplasia occurred in 23.5% (n = 4), 17.6% (n = 3), and 17.6% (n = 3) of stents, respectively. A total of 11 stents were successfully removed electively 6 months after placement (n = 4) or when complications occurred (n = 7). All 11 such stents were removed without difficulty with use of standard techniques, antecedent balloon dilation being necessary in two cases as a result of tissue hyperplasia. No removed stent showed signs of membrane degradation, and two removed stents showed signs of membrane separation from the mesh.

CONCLUSIONS

PTFE-covered retrievable expandable nitinol stents were effective in the treatment of tracheobronchial strictures. Stent removal was easy with use of standard techniques, and no removed stent showed evidence of membrane degradation.

Formation of in vivo tissue engineered human hyaline cartilage in the shape of a trachea with internal support

OBJECTIVE

Treatment and management of congenital as well as post-traumatic trachea stenosis remains a challenge in pediatric surgery. The aim of this study was to reconstruct a trachea with human nasal septum chondrocytes by using the combination of biodegradable hydrogel and non-biodegradable high-density polyethylene (HDP) as the internal predetermined shape scaffold.

METHODS

Human nasal septum cartilage was harvested as excessive tissue after elective septoplasty and digested in 0.6% collagenase II. Chondrocytes were cultured in an equal volume mix of Ham's F12 medium and Dulbecco's modified eagle medium added with 10% fetal bovine serum and basic fibroblast growth factor. After two passages, the cultured chondrocytes were trypsinized and mixed with biodegradable hydrogel Pluronic F127. The chondrocytes-hydrogel admixture was then painted over the HDP as the internal support in a predetermined trachea shape. The composite was then implanted subcutaneously in athymic mice.

RESULTS

After 8 weeks of in vivo implantation, the tissue engineered trachea constructs were harvested. Macroscopic appearance of the tissue engineered trachea constructs demonstrated that the HDP were 80-90% covered with yellowish glistering cartilage like tissue without any sign of inflammation. The tissue engineered trachea cartilage consisted of evenly spaced lacunae embedded in basophilic matrix and stained red with Safranin-O staining denoting abundant proteoglycans production. Type II collagen gene which was expressed in native cartilage was highly expressed in this tissue engineered trachea cartilage.

CONCLUSION

We have successfully reconstructed a trachea in vivo with human nasal septum chondrocytes using HDP as the internal support. This construct has the advantage of bio-inert and strength in which both are important properties in tracheal reconstruction.