title: Continuous monitoring of the bronchial epithelial lining fluid by microdialysis.
abstract: BACKGROUND
  Contents of the epithelial lining fluid (ELF) of the bronchi are of central interest in lung diseases, acute lung injury and pharmacology. The most commonly used technique broncheoalveolar lavage is invasive and may cause lung injury. Microdialysis (MD) is a method for continuous sampling of extracellular molecules in the immediate surroundings of the catheter. Urea is used as an endogenous marker of dilution in samples collected from the ELF. The aim of this study was to evaluate bronchial MD as a continuous monitor of the ELF.
  
  
  METHODS
  Microdialysis catheters were introduced into the right main stem bronchus and into the right subclavian artery of five anesthetized and normoventilated pigs. The flowrate was 2 mul/min and the sampling interval was 60 minutes. Lactate and fluorescein-isothiocyanate-dextran 4 kDa (FD-4) infusions were performed to obtain two levels of steady-state concentrations in blood. Accuracy was defined as [bronchial-MD] divided by [arterial-MD] in percent. Data presented as mean +/- 95 percent confidence interval.
  
  
  RESULTS
  The accuracy of bronchial MD was calculated with and without correction by the arteriobronchial urea gradient. The arteriobronchial lactate gradient was 1.2 +/- 0.1 and FD-4 gradient was 4.0 +/- 1.2. Accuracy of bronchial MD with a continuous lactate infusion was mean 25.5% (range 5.7-59.6%) with a coefficient of variation (CV) of 62.6%. With correction by the arteriobronchial urea gradient accuracy was mean 79.0% (57.3-108.1%) with a CV of 17.0%.
  
  
  CONCLUSIONS
  Urea as a marker of catheter functioning enhances bronchial MD and makes it useful for monitoring substantial changes in the composition of the ELF.
authors.affiliation: Department of Anesthesia and Intensive Care, St, Olavs Hospital, Trondheim, Norway. stig.s.tyvold@ntnu.no
authors.forename: Stig S
authors.initials: SS
authors.lastname: Tyvold
authors.forename: Erik
authors.initials: E
authors.lastname: Solligård
authors.forename: Oddveig
authors.initials: O
authors.lastname: Lyng
authors.forename: Sigurd L
authors.initials: SL
authors.lastname: Steinshamn
authors.forename: Sigurd
authors.initials: S
authors.lastname: Gunnes
authors.forename: Petter
authors.initials: P
authors.lastname: Aadahl
mesh_terms: D000818:Animals; D001826:Body Fluids / Q000737:chemistry*; D001980:Bronchi / Q000378:metabolism*; D001992:Bronchoalveolar Lavage Fluid / Q000737:chemistry*; D017551:Microdialysis / Q000379:methods*; D008991:Monitoring, Physiologic / Q000379:methods*; D015203:Reproducibility of Results; D020545:Respiratory Mucosa / Q000378:metabolism*; D012680:Sensitivity and Specificity; D013552:Swine; D014508:Urea / Q000032:analysis*
chemical_list: D014508:Urea