title: 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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Otolaryngology, National Centre for Airway Reconstruction, Charing Cross Hospital, London W6 8RF, UK. rn@cantab.net
authors.forename: S A R
authors.initials: SA
authors.lastname: Nouraei
authors.forename: D A
authors.initials: DA
authors.lastname: Giussani
authors.forename: D J
authors.initials: DJ
authors.lastname: Howard
authors.forename: G S
authors.initials: GS
authors.lastname: Sandhu
authors.forename: C
authors.initials: C
authors.lastname: Ferguson
authors.forename: A
authors.initials: A
authors.lastname: Patel
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000771:Anesthesia, Intravenous / Q000379:methods; D005260:Female; D006801:Humans; D017214:Laryngeal Masks; D007828:Laryngoscopy; D007829:Laryngostenosis / Q000503:physiopathology / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D010366:Peak Expiratory Flow Rate; D011175:Positive-Pressure Respiration; D011446:Prospective Studies; D013147:Spirometry; D013990:Tidal Volume; D014135:Tracheal Stenosis / Q000503:physiopathology / Q000601:surgery*