title: Airway ventilation pressures during bronchoscopy, bronchial blocker, and double-lumen endotracheal tube use: an in vitro study.
abstract: OBJECTIVE
  To quantify inspiratory flow resistance of instrumented single-lumen and double-lumen endotracheal tubes.
  
  
  METHODS
  Bench-top in vitro experiments.
  
  
  METHODS
  Laboratory of a university hospital.
  
  
  METHODS
  In vitro lung simulator.
  
  
  METHODS
  A lung simulator was ventilated mechanically via several single- and double-lumen endotracheal tubes (ETT) that were instrumented with adult and pediatric bronchoscopes as well as bronchial blockers. While ventilating with a square-flow wave and increasing peak inspiratory flow from 10-100 L/min, the pressures proximal and distal to the instrumented ETT were measured. Flow (Q) and the pressure loss (∆P) were related with regression of the quadratic equation: ∆P=k1Q+k2Q2.
  
  
  RESULTS
  With all combinations of single-lumen endotracheal tubes, double-lumen endotracheal tubes, bronchial blockers, and adult and pediatric bronchoscopes, ∆P was accurately related to Q using the quadratic equation with excellent fit, R2>0.99 for all combinations. The regression parameters k1 and k2 were statistically significant for all combinations except k1 with a bronchoscope through 37-Fr double-lumen endotracheal tube. Parameter k2 was dominant at flows above 10 L/min for uninstrumented airways and 20 L/min for instrumented airways. ∆P increased dramatically with flow, and increased with decreasing endotracheal tube size or addition of instrumentation in a quantitatively predictable manner.
  
  
  CONCLUSIONS
  Pressure loss across instrumented endotracheal tubes follows a predictable flow-dependant quadratic pattern. Using the quantitative in vitro results of this study, a clinician can maximize inspiratory ventilation pressures during these situations without delivering excessive airway pressures to the patient.
authors.affiliation: Department of Anesthesiology, Perioperative and Pain Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, MA.
authors.forename: Alexander S
authors.initials: AS
authors.lastname: Kuo
authors.affiliation: Department of Anesthesiology, Perioperative and Pain Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, MA.
authors.forename: James H
authors.initials: JH
authors.lastname: Philip
authors.affiliation: Department of Anesthesiology, Perioperative and Pain Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, MA. Electronic address: tedrich@partners.org.
authors.forename: Thomas
authors.initials: T
authors.lastname: Edrich
mesh_terms: D000402:Airway Obstruction / Q000628:therapy*; D020680:Bronchoscopes; D001999:Bronchoscopy / Q000379:methods*; D004867:Equipment Design; D006801:Humans; D007442:Intubation, Intratracheal / Q000295:instrumentation*; D011312:Pressure; D012121:Respiration, Artificial / Q000379:methods*
keywords: airway pressures; bronchial blocker; bronchoscopy; double-lumon tubes; endotracheal tubes; model; tracheal pressure