title: Continuous positive airway pressure and ventilation are more effective with a nasal mask than a full face mask in unconscious subjects: a randomized controlled trial.
abstract: BACKGROUND
  Upper airway obstruction (UAO) is a major problem in unconscious subjects, making full face mask ventilation difficult. The mechanism of UAO in unconscious subjects shares many similarities with that of obstructive sleep apnea (OSA), especially the hypotonic upper airway seen during rapid eye movement sleep. Continuous positive airway pressure (CPAP) via nasal mask is more effective at maintaining airway patency than a full face mask in patients with OSA. We hypothesized that CPAP via nasal mask and ventilation (nCPAP) would be more effective than full face mask CPAP and ventilation (FmCPAP) for unconscious subjects, and we tested our hypothesis during induction of general anesthesia for elective surgery.
  
  
  METHODS
  In total, 73 adult subjects requiring general anesthesia were randomly assigned to one of four groups: nCPAP P0, nCPAP P5, FmCPAP P0, and FmCPAP P5, where P0 and P5 represent positive end-expiratory pressure (PEEP) 0 and 5 cm H2O applied prior to induction. After apnea, ventilation was initiated with pressure control ventilation at a peak inspiratory pressure over PEEP (PIP/PEEP) of 20/0, then 20/5, and finally 20/10 cm H2O, each applied for 1 min. At each pressure setting, expired tidal volume (Vte) was calculated by using a plethysmograph device.
  
  
  RESULTS
  The rate of effective tidal volume (Vte > estimated anatomical dead space) was higher (87.9% vs. 21.9%; P<0.01) and the median Vte was larger (6.9 vs. 0 mL/kg; P<0.01) with nCPAP than with FmCPAP. Application of CPAP prior to induction of general anesthesia did not affect Vte in either approach (nCPAP pre- vs. post-; 7.9 vs. 5.8 mL/kg, P = 0.07) (FmCPAP pre- vs. post-; 0 vs. 0 mL/kg, P = 0.11).
  
  
  CONCLUSIONS
  nCPAP produced more effective tidal volume than FmCPAP in unconscious subjects.
  
  
  BACKGROUND
  ClinicalTrials.gov identifier: NCT01524614.
authors.forename: Jun
authors.initials: J
authors.lastname: Oto
authors.forename: Qian
authors.initials: Q
authors.lastname: Li
authors.forename: William R
authors.initials: WR
authors.lastname: Kimball
authors.forename: Jingping
authors.initials: J
authors.lastname: Wang
authors.forename: Abdolnabi S
authors.initials: AS
authors.lastname: Sabouri
authors.forename: Priscilla G
authors.initials: PG
authors.lastname: Harrell
authors.forename: Robert M
authors.initials: RM
authors.lastname: Kacmarek
authors.forename: Yandong
authors.initials: Y
authors.lastname: Jiang
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000402:Airway Obstruction / Q000628:therapy*; D045422:Continuous Positive Airway Pressure / Q000295:instrumentation*; D005260:Female; D006801:Humans; D008297:Male; D008397:Masks; D008875:Middle Aged; D013990:Tidal Volume; D014474:Unconsciousness; D055815:Young Adult