The use of expandable metallic stents for acute tracheal stenosis in the growing lamb

Abstract

Purpose: Expandable metallic stents (Palmaz stents) have been used in the treatment of tracheobronchial obstruction in children and adults. The authors investigated their utility in the management of acute airway stenosis in a growing animal model. Methods: A model for tracheal stenosis was developed in young lambs (mean age, 4 weeks; mean weight, 8.6 kg). Via an anterior tracheotomy, a circumferential mucosal injury to the trachea was produced with electrocautery in 31 lambs. In the control group (n = 10) no further intervention was used. In the treatment groups, either serial balloon dilatation of the stricture was performed (n = 6), or expandable metallic stents were inserted across the stricture (n = 15). All animals were monitored daily for signs of respiratory distress. Body weights, fluoroscopic airway measurements and rigid bronchoscopy were performed at least weekly. Results: The average weekly rate of airway growth was 8.2% ± 5.5% of the tracheal cross-sectional area (CSA). All animals displayed severe stenosis (mean, 90.2% ± 7.5% of CSA) within 13.1 ± 4 days after the injury. All animals in the control group had severe respiratory distress, weight loss and died within 14.6 ± 2.8 days after injury. Serial balloon dilatation of the stricture alone failed to relieve symptoms in all six animals in this group, who died within 20 ± 1 days after the injury, despite two to three dilatations each. With placement of expandable metallic stents, only 3 of 15 lambs died (two of pneumonia, one of iatrogenic perforation). The remaing 12 remained symptom-free and gained weight during a 2-month follow-up period. However, fluoroscopic examination showed partial collapse of the stents in all of these animals (mean, 44.7% ± 21.6% of CSA) requiring an average of 2 ± 0.7 bronchoscopic dilatations. Pathological evaluation showed more pronounced granulation tissue in the stented animals. Conclusions: The authors conclude that expandable metallic stents provide an effective tool in the management of acute tracheal stenosis. However, airway growth, tissue reaction, and the mechanical properties of the stent require close monitoring and stent adjustment.