Dexamethasone treatment does not ameliorate subglottic ischemic injury in rabbits

Following tracheal intubation, a small proportion of patients develop laryngeal inflammation or tissue necrosis severe enough to result in clinical symptoms. Although corticosteroids are frequently advocated to prevent such injury, human studies have been inconclusive because of the low incidence of the problem. This study developed a rabbit model of endotracheal tube-induced laryngeal injury to test the hypothesis that a corticosteroid, dexamethasone, could ameliorate the inflammation and necrosis.

Subglottic injury was induced in 21 anesthetized rabbits by inflating the cuff of an endotracheal tube to 100 mm Hg with the cuff just below the vocal cords. Every 30 min for 2 h, the cuff was deflated, the tube turned 90 degrees, and the cuff then reinflated. After 2 h, the rabbits' tracheas were extubated. Rabbits were divided into two groups: the treatment group received dexamethasone (1 mg/kg) i.v. 1 h prior to extubation with the dose repeated 6 h following extubation; the untreated group received a saline solution placebo. Four additional rabbits were anesthetized for the same period but did not have a tracheal tube inserted. All rabbits were killed 24 h later and the larynxes were harvested. Sections through the larynx at the level of the cricoid cartilage were randomized and submitted blindly to a veterinary pathologist. Larynxes were scored and ranked according to the severity of mucosal inflammation and necrosis, and submucosal hemorrhage, edema, inflammation, and necrosis. Specimens were also evaluated for focal vs diffuse disease.

Injured rabbits demonstrated focal to diffuse mucosal and submucosal inflammation and necrosis. Inflammatory exudates were present in sections from most of the injured rabbits and large sections of the larynxes were denuded of epithelium. There were no differences in injury scores between the treated and untreated rabbits. The four uninjured control rabbits had normal larynxes.

Two hours of endotracheal tube cuff inflation to 100 mm Hg causes an inflammatory laryngeal injury. The histologic features of the injury are unaltered by treatment with 2 mg/kg dexamethasone.