Subglottic Stenosis

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Subglottic stenosis has multiple causes, but it is most commonly associated with mechanical trauma secondary to endotracheal intubation. Adequate treatment requires a complete preoperative work-up, which should include a thin slice computed tomography (CT) scan or magnetic resonance imaging (MRI) and a flow volume loop. However, a reliable diagnosis with mapping of the lesion can only be established by direct endoscopy, performed under general anesthesia. Using telescopic optics and palpation, the endoscopist should be able to establish the length of the lesion, the extent of cartilage damage, and the presence of vocal cord fixation or paresis. All these factors combined with the general status of the patient should be taken into account when deciding on the best possible treatment.

Endoscopic management of subglottic stenosis with the CO2 laser was first described by Strong and colleagues in 1979.5 Today, endoscopic techniques employing the CO2 laser continue to be used successfully in properly selected cases. Adequate patient selection is extremely important. A group of factors have been identified which can influence the success or failure of endoscopic laser procedures. Best results are achieved with endoscopic laser treatment when the length of the lesion is less than 1 cm, the stenosis is limited, comprising mainly soft tissue, with minimal cartilage involvement, and good vocal cord function is maintained.13,14 Cases in which a bilateral fixation or a paresis coexists with the subglottic stenosis must be addressed as well. Some factors that may play a deleterious role in the final treatment outcome are the presence of active inflammation of the airway (eg, bacterial, fungal, preexisting tracheostomy, or active Wegener's vasculitis), and the presence of conditions that may impair wound healing such as diabetes, hypothyroidism, and chronic steroid use.15-19

Since 1987, we have employed laser incision and dilation technique to treat selected cases of subglottic and tracheal stenosis (Figure 37-2).19 For this procedure, we prefer the microspot delivered CO2 laser with a 0.25 mm spot size, using a 16x magnification in the microscope. The laser power is set at superpulse, usually at 5 W and 30 pulses/sec.

Under adequate exposure, three to four radial incisions are made through the scar tissue without causing a circumferential defect, since this is likely to induce rescarring. Care is taken to use short pulses of energy exposure of less than 1 sec; usually 0.2 to 0.5 sec to avoid transmission of heat, which could result in further scarring. Islands of mucosa are preserved to assist with reepithelialization. The treated area experiences a race between scar formation and reepithelialization. The incised scar is further stretched or dilated with the use of sequential sizes of ventilating bronchoscopes, used in a "corkscrew" fashion as atraumatically as possible, until reaching an 8.5 mm ventilating bronchoscope. The CO2 microspot delivery system is preferred, due to the precise cutting nature of the focused beam, rather than a waveguide delivery system, which is nonfocused and subsequently less precise. The CO2 laser is preferred to the YAG and other lasers, due to both its superior precision and better control of the depth of penetration.

Recent evidence shows that scar formation is retarded with the topical application of mitomycin-C.20-22 Mitomycin-C modulates the wound healing response by inhibiting proliferation of fibroblasts. Our experience with endoscopic laser surgery, followed by intraoperative application of 0.4 mL of mitomycin-C in 11 patients, has shown improvement both in the size of the airway and in the symptoms.22 However, despite significant decrease in scar formation, some scarring does occur, and patients may require more than one procedure to further improve symptoms.

Previously, employment of intralesional or systemic steroids has had poor results, since these not only modulate the inflammatory response of fibroblasts but also delay the reepithelialization process. Post-operatively, it is important to treat the patient with cool mist inhalation for several days and to use perioperative systemic steroids (48 hours), antireflux medication (30 days), and antibiotics (7 days) to prevent

figure 37-2 A, Treatment of web-like stenosis with laser radial incisions. B, Dilation of the stenotic area with a bronchoscope.

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infection or crusting, which can lead to airway obstruction. We avoid tracheostomy in the acute presentation since this would damage the normal trachea and add a risk of infection. In our 15-year experience, this technique has had a success rate of approximately 70%. However, some patients require up to three times of endoscopic laser treatment before an adequate airway is achieved. In cases in which there is no improvement, or recurrent stenosis, we recommend open resection and tracheothyroid anastomosis rather than rib graft laryngotracheoplasty. The technique is described in Chapter 25, "Laryngotracheal Reconstruction."

Other techniques employing the laser to treat subglottic stenosis have been described. In 1984, Dedo and Sooy introduced the micro-trapdoor flap technique.23 This technique is performed by making a crescent-shaped incision in the mucosa overlying the stenosis. A microelevator is used to elevate a mucosal flap from the superior edge of the stenosis to its inferior aspect. The laser is used to vaporize the scar tissue causing the stenosis. Once the scar tissue has been vaporized, the flap is carefully repositioned. The laser beam is used in a defocused mode to weld the edges of the incision back together or the flap is simply allowed to re-adhere. A success rate of 90% has been reported in lesions of less than 10 mm in length. Our success rate has been poor since it is technically difficult to preserve the elevated mucosal flap.

Other techniques using laser to treat subglottic and posterior stenoses involve the use of the diode laser and exogenous dyes for graft soldering.9 In this technique, a buccal mucosal graft, slightly larger than the size of the surgical wound from the scar resection, is harvested. Submucosal fat is removed and the graft tailored to the size and shape desired. The graft is placed on the wound, which has been covered with indo-cyanine green mixed with autologous fibrin glue, and soldered using the 810 nm diode laser in a noncon-tact mode with a 1 mm spot size at 400 to 800 nW power. Experience with this technique has been limited and a larger series of patients would have to be studied to prove its effectiveness and safety.

The CO2 laser waveguide or bronchoscopic coupler system can be used for lesions located in the mid to distal trachea, where laser energy can not be delivered with precision using a micromanipulator. Alternatively, the KTP laser or contact Nd:YAG laser could also be used to deliver energy through flexible fibers.

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