title: The pressure drop across the endotracheal tube in mechanically ventilated pediatric patients.
abstract: BACKGROUND
  During mechanical ventilation, the airway pressure (Paw) is usually monitored. However, Paw comprises the endotracheal tube (ETT)-related pressure drop (∆PETT ) and thus does not reflect the pressure in the patients' lungs. Therefore, monitoring of mechanical ventilation should be based on the tracheal pressure (Ptrach ). We systematically investigated potential factors influencing ∆PETT in pediatric ETTs.
  
  
  METHODS
  In this study, the flow-dependent pressure drop across pediatric ETTs from four manufacturers [2.0-4.5 mm inner diameter (ID)] was estimated in a physical model of the upper airways. Additionally, ∆PETT was examined with the ETTs shortened to 75% of their original length and at different curvatures. In nine healthy mechanically ventilated children (aged between 9 days and 29 months), Ptrach was compared to Paw .
  
  
  RESULTS
  ∆PETT was nonlinearly flow dependent. Low IDs corresponded to high ∆PETT . Differences between ETTs from different manufacturers were identified. Shortening of the ETTs' length by 25% reduced ∆PETT on average by 14% of the value at original length. Ventilation frequency and tube curvature did not influence ∆PETT to a relevant extent. In the pediatric patients, the root mean square deviation between Paw and Ptrach was 2.3 cm H2O.
  
  
  CONCLUSIONS
  Paw and Ptrach differ considerably (by ∆PETT ) during mechanical ventilation of pediatric patients. The ETTs' ID, tube length, and manufacturer type are significant factors for ∆PETT and should be taken into account when Paw is valuated. For this purpose, Ptrach can be continuously calculated with good precision by means of the Rohrer approximation.
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.forename: Daniel
authors.initials: D
authors.lastname: Steinmann
authors.forename: Heike
authors.initials: H
authors.lastname: Kaltofen
authors.forename: Josef
authors.initials: J
authors.lastname: Guttmann
authors.forename: Stefan
authors.initials: S
authors.lastname: Schumann
mesh_terms: D000399:Air Pressure; D000465:Algorithms; D000769:Anesthesia, Inhalation; D002675:Child, Preschool; D005260:Female; D005336:Fiber Optic Technology; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D007442:Intubation, Intratracheal / Q000379:methods*; D008297:Male; D017711:Nonlinear Dynamics; D012121:Respiration, Artificial / Q000295:instrumentation*
keywords: airway - resistance; anesthesia - pediatric; equipment - tubes tracheal; respiratory - mechanics; ventilation - airway pressure; ventilation - mechanical