title: Characterization of airway device cuff volumes at simulated altitude.
abstract: BACKGROUND
  Cuff volume of an air-filled airway device varies inversely with ambient pressure at altitude. This may result in problems with ventilation, aspiration, and tissue ischemia in intubated patients transported by aircraft. We aimed to characterize cuff volume changes in airway devices as a function of altitude.
  
  
  METHODS
  Four inflatable airway devices lendotracheal tube (ETT), Combitube, King tube, and laryngeal mask airway (LMA)I, each inflated with air or water, were evaluated for cuff volume changes in an altitude chamber simulating ascent and descent from ground level to 15,000 ft (4572 m). A novel cuff-less supraglottic device called i-gel was also tested. Multivariate linear regression was used to assess the effect of altitude and cuff content on cuff volume.
  
  
  RESULTS
  We found a linear relationship between air-filled cuff volume and altitude in all the inflatable airway devices. The Combitube (correlation coefficient R = 0.94) and King tube (R = 0.98) showed the clearest linear relationship; the ETT (R = 0.70) and LMA (0.86) showed modest correlations. With water-filled cuffs, the rate of increase was relatively smaller in all the inflatable devices except the ETT, which remained constant. The difference between air- and water-filled cuffs was statistically significant in each inflatable device (P < 0.001). The i-gel showed no volume change at any of the tested altitudes.
  
  
  CONCLUSIONS
  Cuff volume of inflatable airway devices increased linearly with altitude. The dual-cuffed supraglottic devices showed greater volume changes, likely due to the combined effect of their two cuffs. Of the inflatable devices, the water-filled ETT was the least sensitive to altitude changes.
authors: University of California Davis Medical Center, Sacramento, CA, USA. jelaw@utmb.edu
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