Evaluation of the Palmaz Stent in the Trachea and Mainstem Bronchi of Normal Dogs

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Abstract
This study evaluates the efficacy of the Palmaz balloon expandable intraluminal stent in the trachea and mainstem bronchi of normal dogs. Effects of the stent were evaluated by physical examination, thoracic radiography, respiratory tract fluoroscopy and endoscopy, tracheal diameter measurement, postmortem examination, and airway histomorphometry. Ten normal beagle dogs. Stent size was estimated from thoracic radiographs in awake dogs. Group I dogs (n = 4) had two stents placed: one in the thoracic trachea (TT) plus a randomly chosen mainstem bronchus (MB). Group II dogs (n = 3) had stents placed in the MB (one stent), TT (one stent), and mid- or proximal cervical trachea (CT) (one or two stents). Three dogs were used as sham-operated controls (group III). Temperature, pulse, respiration, and cough were measured twice daily. Dogs were evaluated at 21 and 49 to 56 days after stent placement, euthanatized, and tissues were collected for histomorphometric analysis of stent integration and epithelial pathology. Mean tracheal diameters of awake (10.5 +/- 1.7 mm) and anesthetized dogs before stent implantation (13.9 +/- 2.0 mm) were significantly different (P < .01). Complications associated with stent placement included acute pulmonary edema (n = 2), stent migration (n = 7), stent collapse (n = 4 CT, 2 TT, and 1 MB), and positive tracheal culture (n = 10). Group II dogs coughed more at rest, exercise, and with tracheal palpation than dogs in other groups (P < .01). Group I dogs coughed more at rest than group III dogs (P < .01). Stent integration ranged from 0 to 91.3%. Squamous metaplasia and epithelial ulceration associated with stents ranged from 0 to 57.5% and 0 to 32.7%, respectively. Determination of stent size should be based on measurements taken on anesthetized dogs because use of inappropriately sized stents may promote stent migration, squamous metaplasia, and/or ulceration. Epithelialization over stent struts may occur if the stent is closely associated with tracheal epithelium. Palmaz stents do not appear to be appropriate for placement in the CT of dogs; however, with technical modifications, application in the TT and MB may be feasible.