title: Compensating Artificial Airway Resistance via Active Expiration Assistance.
abstract: BACKGROUND
  Artificial airway resistance as provided by small-lumen tracheal tubes or catheters increases the risk of intrinsic PEEP (PEEPi). We hypothesized that by active expiration assistance, larger minute volumes could be generated without causing PEEPi compared with conventional mechanical ventilation when using small-lumen tracheal tubes or a cricothyrotomy catheter.
  
  
  METHODS
  We investigated the active expiration assistance in a physical model of the respiratory system and estimated its hypothetical performance in terms of maximal flow generated with endotracheal tubes ranging from 3.0 to 8.0 mm inner diameter (ID); with microlaryngeal tubes of 4.0, 5.0, and 6.0 mm ID; and with a cricothyrotomy catheter. Furthermore, we determined the minute volumes that could be achieved without generating PEEPi by ventilating a physical lung model using conventional mechanical ventilation or using active expiration assistance.
  
  
  RESULTS
  The inspiratory and expiratory flow during active expiration assistance increased with increasing supply flow and decreased with decreasing ID of the connected endotracheal tubes (both P < .001). With small-lumen tracheal tubes, the active expiration assistance generated similar or higher minute volumes than conventional ventilation. Conventional mechanical ventilation with PEEPi <1 cm H2O was not achievable via a microlaryngeal tube of 4.0 mm ID and smaller lumen tubes.
  
  
  CONCLUSIONS
  For mechanical ventilation via small-lumen tubes or thin catheters, active compensation of airway resistance might be a necessary means to generate adequate minute ventilation without causing PEEPi. Active expiration assistance can generate reasonable respiratory minute volumes via small-lumen tubes or thin catheters.
authors.affiliation: Department of Anesthesiology and Intensive Care Medicine, University Medical Center Freiburg, Freiburg, Germany. steffen.wirth@uniklinik-freiburg.de.
authors.forename: Steffen
authors.initials: S
authors.lastname: Wirth
authors.affiliation: Department of Anesthesiology and Intensive Care Medicine, University Medical Center Freiburg, Freiburg, Germany.
authors.forename: Luc
authors.initials: L
authors.lastname: Seywert
authors.affiliation: Department of Anesthesiology and Intensive Care Medicine, University Medical Center Freiburg, Freiburg, Germany.
authors.forename: Johannes
authors.initials: J
authors.lastname: Spaeth
authors.affiliation: Department of Anesthesiology and Intensive Care Medicine, University Medical Center Freiburg, Freiburg, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Schumann
mesh_terms: D000403:Airway Resistance / Q000502:physiology*; D045853:Exhalation / Q000502:physiology*; D005240:Feasibility Studies; D006801:Humans; D007442:Intubation, Intratracheal; D008168:Lung / Q000503:physiopathology*; D008176:Lung Volume Measurements; D008953:Models, Anatomic; D018467:Positive-Pressure Respiration, Intrinsic / Q000209:etiology / Q000517:prevention & control*; D012121:Respiration, Artificial / Q000009:adverse effects / Q000295:instrumentation / Q000379:methods*; D014132:Trachea
keywords: active expiration; airway resistance; difficult airway; intrinsic peep; mechanical ventilation; respiratory system mechanics