title: Remote measurement of the leak around the uncuffed tracheal tube: objective measurement and physical characteristics.
abstract: BACKGROUND
  We have developed a technique for measuring a characteristic of the tracheal tube (TT)-trachea interface: the leak conductance (LC). This study aimed to validate the technique in the laboratory and to compare LC with measurements of fractional volume loss (FVL) in neonates undergoing mechanical ventilation.
  
  
  METHODS
  LC, expressed as leak flow at a lung pressure of 10 cm H(2)O, was derived remotely from ventilator pressure and flow signals. Validation was by simulating breathing circuits for 10 models in which LC was measured directly. LC was compared with FVL for different settings of PEEP, inspired pressure, and time at plateau pressure. Clinically, LC was measured for 135 infants admitted to paediatric intensive care after cardiac surgery and compared with FVL.
  
  
  RESULTS
  No significant differences were found between direct and remote laboratory measurements of LC (P>0.05). FVL varied with PEEP, plateau pressure, and time at plateau (P<0.05) but LC did not (P>0.05). The between-patient standard deviation (sd) of LC (0.4 litre min(-1)) exceeded the within-patient sd of lc (0.05 litre min(-1); P<0.05); the between-patient sd of FVL (22.1%) exceeded the within-patient sd of FVL (1.3%; P<0.05). The median LC was 0.38 (inter-quartile range 0.29-0.46) litre min(-1). LC was correlated with FVL (r=0.82; 95% confidence interval 0.76-0.88) but wide ranges of FVL were observed for patients with similar LC.
  
  
  CONCLUSIONS
  LC can be derived remotely and was correlated with FVL, a conventional proxy for tube fit. It may be a better measure of TT fit than FVL.
authors.affiliation: Department of Medical Physics, Freeman Hospital, Newcastle upon Tyne, UK.
authors.forename: A J
authors.initials: AJ
authors.lastname: Sims
authors.forename: K
authors.initials: K
authors.lastname: Keltie
authors.forename: C A
authors.initials: CA
authors.lastname: Reay
authors.forename: J H
authors.initials: JH
authors.lastname: Smith
mesh_terms: D000388:Air; D000399:Air Pressure; D058109:Airway Management / Q000295:instrumentation / Q000379:methods; D000465:Algorithms; D002138:Calibration; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D007442:Intubation, Intratracheal / Q000295:instrumentation / Q000379:methods* / Q000706:statistics & numerical data*; D008176:Lung Volume Measurements; D008297:Male; D011175:Positive-Pressure Respiration; D012121:Respiration, Artificial; D015656:Respiratory Mechanics / Q000502:physiology; D012122:Ventilators, Mechanical