title: Nitrogen washout/washin, helium dilution and computed tomography in the assessment of end expiratory lung volume.
abstract: BACKGROUND
  End expiratory lung volume (EELV) measurement in the clinical setting is routinely performed using the helium dilution technique. A ventilator that implements a simplified version of the nitrogen washout/washin technique is now available. We compared the EELV measured by spiral computed tomography (CT) taken as gold standard with the lung volume measured with the modified nitrogen washout/washin and with the helium dilution technique.
  
  
  METHODS
  Patients admitted to the general intensive care unit of Ospedale Maggiore Policlinico Mangiagalli Regina Elena requiring ventilatory support and, for clinical reasons, thoracic CT scanning were enrolled in this study. We performed two EELV measurements with the modified nitrogen washout/washin technique (increasing and decreasing inspired oxygen fraction (FiO2) by 10%), one EELV measurement with the helium dilution technique and a CT scan. All measurements were taken at 5 cmH2O airway pressure. Each CT scan slice was manually delineated and gas volume was computed with custom-made software.
  
  
  RESULTS
  Thirty patients were enrolled (age = 66 +/- 10 years, body mass index = 26 +/- 18 Kg/m2, male/female ratio = 21/9, partial arterial pressure of carbon dioxide (PaO2)/FiO2 = 190 +/- 71). The EELV measured with the modified nitrogen washout/washin technique showed a very good correlation (r2 = 0.89) with the data computed from the CT with a bias of 94 +/- 143 ml (15 +/- 18%, p = 0.001), within the limits of accuracy declared by the manufacturer (20%). The bias was shown to be highly reproducible, either decreasing or increasing the FiO2 being 117+/-170 and 70+/-160 ml (p = 0.27), respectively. The EELV measured with the helium dilution method showed a good correlation with the CT scan data (r2 = 0.91) with a negative bias of 136 +/- 133 ml, and appeared to be more correct at low lung volumes.
  
  
  CONCLUSIONS
  The EELV measurement with the helium dilution technique (at low volumes) and modified nitrogen washout/washin technique (at all lung volumes) correlates well with CT scanning and may be easily used in clinical practice.
  
  
  BACKGROUND
  Current Controlled Trials NCT00405002.
authors.affiliation: Dipartimento di Anestesia, Rianimazione (Intensiva e Subintensiva) e Terapia del Dolore, Fondazione IRCCS - Ospedale Maggiore Policlinico Mangiagalli Regina Elena, via Francesco Sforza 35, 20122, Milano, Italy. chiumello@libero.it
authors.forename: Davide
authors.initials: D
authors.lastname: Chiumello
authors.forename: Massimo
authors.initials: M
authors.lastname: Cressoni
authors.forename: Monica
authors.initials: M
authors.lastname: Chierichetti
authors.forename: Federica
authors.initials: F
authors.lastname: Tallarini
authors.forename: Marco
authors.initials: M
authors.lastname: Botticelli
authors.forename: Virna
authors.initials: V
authors.lastname: Berto
authors.forename: Cristina
authors.initials: C
authors.lastname: Mietto
authors.forename: Luciano
authors.initials: L
authors.lastname: Gattinoni
mesh_terms: D000368:Aged; D005260:Female; D006371:Helium; D006801:Humans; D008176:Lung Volume Measurements / Q000379:methods*; D008297:Male; D008875:Middle Aged; D009584:Nitrogen; D015656:Respiratory Mechanics / Q000502:physiology; D014057:Tomography, X-Ray Computed
chemical_list: D006371:Helium; D009584:Nitrogen