title: Manual in-line stabilization increases pressures applied by the laryngoscope blade during direct laryngoscopy and orotracheal intubation.
abstract: BACKGROUND
  Manual in-line stabilization (MILS) is recommended during direct laryngoscopy and intubation in patients with known or suspected cervical spine instability. Because MILS impairs glottic visualization, the authors hypothesized that anesthesiologists would apply greater pressure during intubations with MILS than without.
  
  
  METHODS
  Nine anesthetized and pharmacologically paralyzed patients underwent two sequential laryngoscopies and intubations, one with MILS and one without, in random order. A transducer array along a Macintosh 3 laryngoscope blade continuously measured applied pressures, and glottic view was characterized.
  
  
  RESULTS
  With MILS, glottic visualization was worse in six patients, and intubation failure occurred in two of these six patients. Maximum laryngoscope pressure at best glottic view was greater with MILS than without (717 +/- 339 mmHg vs. 363 +/- 121 mmHg, respectively; n = 8; P = 0.023). Other measures of pressure application also indicated comparable increases with MILS.
  
  
  CONCLUSIONS
  Pressures applied to airway tissues by the laryngoscope blade are secondarily transmitted to the cervical spine and result in cranio-cervical motion. In the presence of cervical instability, impaired glottic visualization and secondary increases in pressure application with MILS have the potential to increase pathologic cranio-cervical motion.
authors.affiliation: Department of Mechanical Engineering, Orthopaedic Bioengineering Research Laboratory, Colorado State University, USA.
authors.forename: Brandon G
authors.initials: BG
authors.lastname: Santoni
authors.forename: Bradley J
authors.initials: BJ
authors.lastname: Hindman
authors.forename: Christian M
authors.initials: CM
authors.lastname: Puttlitz
authors.forename: Julie B
authors.initials: JB
authors.lastname: Weeks
authors.forename: Nathaniel
authors.initials: N
authors.lastname: Johnson
authors.forename: Mazen A
authors.initials: MA
authors.lastname: Maktabi
authors.forename: Michael M
authors.initials: MM
authors.lastname: Todd
mesh_terms: D000328:Adult; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007442:Intubation, Intratracheal / Q000295:instrumentation* / Q000379:methods*; D020704:Laryngoscopes; D007828:Laryngoscopy / Q000379:methods*; D008297:Male; D008875:Middle Aged; D011312:Pressure; D014160:Transducers, Pressure