Physiological comparison of spontaneous and positive-pressure ventilation in laryngotracheal stenosis

Abstract

Background: We compared spontaneous and positive-pressure ventilation in patients undergoing general anaesthesia for the treatment of extrathoracic, intralumenal laryngotracheal stenosis to assess the best method of ventilation in this patient group. Methods: Records of 30 patients with laryngotracheal stenosis, but not with a tracheostomy, undergoing lumen-restoring surgery were prospectively reviewed. Awake spirometry and flow-volume loops were recorded before the procedure. Patients received i.v. anaesthesia induction, muscle paralysis, and positive-pressure ventilation through a laryngeal mask airway (LMA). Anaesthetized tidal volume (TV) and flow-volume loop measurements were obtained. Results: We studied 19 males and 11 females [mean age 47 (sd 19) yr], ASA Grade III or IV, with lesions at 31 (10) mm below the vocal cords. Peak inspiratory flow (PIF) and peak expiratory flow (PEF) rates were 2.0 (1.2) litre s-1 and 3.2 (1.7) litre s-1 when awake. Tidal volumes were 657 (193) ml [9.2 (3.6) ml kg-1] and 586 (158) ml [8.3 (3.1) ml kg-1], respectively, when anaesthetized. There was a significant reduction in the PEF/PIF ratio, from a mean of 2.4 (1.3) awake to 1.0 (0.1) when anaesthetized (P<0.0001). A significant correlation was noted between awake PEF and anaesthetized expiratory TV (r=0.57; P<0.001) but not between awake PIF and anaesthetized inspiratory TV. Discussion: Positive-pressure ventilation through an LMA is an effective method of ventilating patients with laryngotracheal stenosis. Spontaneous ventilation creates negative inspiratory intratracheal pressure that exacerbates an extrathoracic lesion, whereas positive-pressure ventilation generates positive intratracheal pressure that improves ventilation. This helps explain the apparent resolution of airway obstruction after positive-pressure ventilation. © The Board of Management and Trustees of the British Journal of Anaesthesia 2008. All rights reserved.