Effects of Short- and Long-Term Tracheal Intubation on the Ventilation with Clma™ for PDT

Background: The classic laryngeal mask airway (cLMA™) reduces traumatic complications from percutaneous dilatational tracheostomy (PDT) such bleeding, pneumothorax, pneumomediastinum and lesions of the trachea. In some patients, however, cLMA™ is ineffective because of displacement, need of high ventilation pressures or because of laryngeal lesions that develop during prolonged ventilation with endotracheal tube (ETT). This study was aimed to investigate the impact of different lengths of tracheal intubation on laryngeal integrity and on efficacy of cLMA™ ventilation. Methods: The study was carried at a 18 bed ICU of Padova University Hospital on two groups of thirty consecutive patients each who underwent PDT (Ciaglia percutaneous tracheostomy kit, Cook Critical Care, Bjaeverskov, Denmark) after either short (< 2 days, STI) or long ( > 16 days, LTI) ETT ventilation. Patients were switched from ETT to cLMA ventilation, PDT was then performed under cLMA™ guided bronchoscopy and patient were switched to tracheal tube (TT) ventilation. Laryngeal lesions were scored on a five-grade scale (i.e. none, erythema, edema, marked edema, ulceration) just before switching patients from ETT to cLMA™ ventilation. Ventilatory efficacy of cLMA™ was evaluated by assessing changes in peak airway pressures and in arterial blood gases from prior to after both changeovers and the inspiratory gas leakage fraction (FL = inspiratory volume – expiratory volume/inspiratory volume x 100)) during cLMA ventilation. Statistical group differences were assessed with Student t test (P < 0.05). Results: cLMA ventilation allowed to carry out PDT in all patients but group differences were observed in laryngeal lesions and cLMA™ efficacy. The STI group presented mild lesions of larynx (erythema 13/30 patients, edema 5/30 patients) and, after switching from ETT to cLMA™, mild decreases of arterial pH (table 1). In comparison to the STI group, the LTI group presented significantly (P < 0.05) more frequent and more severe laryngeal lesions (edema 12/30 patients, marked edema 18/30 patients, ulceration 6/30 patients) that were associated with larger air leaks (ie 18 vs 11 % mean FL values) and transitory abnormalities in blood gases (table 1). Degrees of FL and scores laryngeal lesion correlated significantly (ie correlation coefficient 0.169).[table1] Discussion: In our patient populations cLMA™ proved to be effective. However, because of laryngeal pathological changes that develop over time during ETT ventilation, efficacy may decline to the point that cLMA™ is not advisable in some LTI patients. Given the potential advantages of cLMA™ for PDT, the safety issue in LTI should be addressed in a larger study.