title: Incidence and predictors of difficult and impossible mask ventilation.
abstract: BACKGROUND
  Mask ventilation is an essential element of airway management that has rarely been studied as the primary outcome. The authors sought to determine the incidence and predictors of difficult and impossible mask ventilation.
  
  
  METHODS
  A four-point scale to grade difficulty in performing mask ventilation (MV) is used at the authors' institution. They used a prospective, observational study to identify cases of grade 3 MV (inadequate, unstable, or requiring two providers), grade 4 MV (impossible to ventilate), and difficult intubation. Univariate and multivariate analyses of a variety of patient history and physical examination characteristics were used to establish risk factors for grade 3 and 4 MV.
  
  
  RESULTS
  During a 24-month period, 22,660 attempts at MV were recorded. 313 cases (1.4%) of grade 3 MV, 37 cases (0.16%) of grade 4 MV, and 84 cases (0.37%) of grade 3 or 4 MV and difficult intubation were observed. Body mass index of 30 kg/m or greater, a beard, Mallampati classification III or IV, age of 57 yr or older, severely limited jaw protrusion, and snoring were identified as independent predictors for grade 3 MV. Snoring and thyromental distance of less than 6 cm were independent predictors for grade 4 MV. Limited or severely limited mandibular protrusion, abnormal neck anatomy, sleep apnea, snoring, and body mass index of 30 kg/m or greater were independent predictors of grade 3 or 4 MV and difficult intubation.
  
  
  CONCLUSIONS
  The authors observed the incidence of grade 3 MV to be 1.4%, similar to studies with the same definition of difficult MV. Presence of a beard is the only easily modifiable independent risk factor for difficult MV. The mandibular protrusion test may be an essential element of the airway examination.
authors.affiliation: Department of Anesthesiology, University of Michigan Medical School, Ann Arbor, Michigan 48103, USA. sachinkh@med.umich.edu
authors.forename: Sachin
authors.initials: S
authors.lastname: Kheterpal
authors.forename: Richard
authors.initials: R
authors.lastname: Han
authors.forename: Kevin K
authors.initials: KK
authors.lastname: Tremper
authors.forename: Amy
authors.initials: A
authors.lastname: Shanks
authors.forename: Alan R
authors.initials: AR
authors.lastname: Tait
authors.forename: Michael
authors.initials: M
authors.lastname: O'Reilly
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Ludwig
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D000758:Anesthesia / Q000009:adverse effects; D006801:Humans; D007442:Intubation, Intratracheal / Q000009:adverse effects; D017214:Laryngeal Masks / Q000009:adverse effects*; D008875:Middle Aged; D011237:Predictive Value of Tests; D011446:Prospective Studies; D012307:Risk Factors; D012308:Risk Management