title: Lung volume in mechanically ventilated patients: measurement by simplified helium dilution compared to quantitative CT scan.
abstract: OBJECTIVE
  We describe a simplified helium dilution technique to measure end-expiratory lung volume (EELV) in mechanically ventilated patients. We assessed both its accuracy in comparison with quantitative computerized tomography (CT) and its precision.
  
  
  METHODS
  Prospective human study.
  
  
  METHODS
  Twenty-one mechanically ventilated ALI/ARDS patients.
  
  
  METHODS
  All patients underwent a spiral CT scan of the thorax during an end-expiratory occlusion. From the CT scan we computed the gas volume of the lungs (EELVCT). Within a few minutes, a rebreathing bag, containing a known amount of helium, was connected to the endotracheal tube, and the gas mixture diluted in the patient's lungs by delivering at least ten large tidal volumes. From the final helium concentration, EELV could be calculated by a standard formula (EELVHe).
  
  
  RESULTS
  The results obtained by the two techniques showed a good correlation (EELVHe=208+0.858xEELV(CT), r=0.941; P<0.001). Bias between the two techniques was 32.5+/-202.8 ml (95% limits of agreement were -373 ml and +438 ml), with a mean absolute difference of 15%. The amount of pathological tissue did not affect the difference between the two techniques, while the amount of hyperinflated tissue did. Bias between two repeated helium EELV measurements was -24+/-83 ml (95% limits of agreement were -191 ml and +141 ml), with a mean absolute difference of 6.3%.
  
  
  CONCLUSIONS
  The proposed helium dilution technique is simple and reproducible. The negligible bias and the acceptable level of agreement support its use as a practical alternative to CT for measuring EELV in mechanically ventilated ARDS patients.
authors.affiliation: Department of Surgical Sciences and Intensive Care, University of Milano-Bicocca, San Gerardo Hospital, Monza, Milano, Italy.
authors.forename: Nicolò
authors.initials: N
authors.lastname: Patroniti
authors.affiliation: Department of Surgical Sciences and Intensive Care, University of Milano-Bicocca, San Gerardo Hospital, Monza, Milano, Italy.
authors.forename: Giacomo
authors.initials: G
authors.lastname: Bellani
authors.affiliation: Department of Anesthesia and Intensive Care, San Gerardo Hospital, Monza, Milano, Italy.
authors.forename: Annamaria
authors.initials: A
authors.lastname: Manfio
authors.affiliation: Department of Surgical Sciences and Intensive Care, University of Milano-Bicocca, San Gerardo Hospital, Monza, Milano, Italy.
authors.forename: Elena
authors.initials: E
authors.lastname: Maggioni
authors.affiliation: Department of Anesthesia and Intensive Care, San Gerardo Hospital, Monza, Milano, Italy.
authors.forename: Angela
authors.initials: A
authors.lastname: Giuffrida
authors.affiliation: Department of Anesthesia and Intensive Care, San Gerardo Hospital, Monza, Milano, Italy.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Foti
authors.affiliation: Department of Surgical Sciences and Intensive Care, University of Milano-Bicocca, San Gerardo Hospital, Via Donizetti 106, 20052, Monza, Milano, Italy. antonio.pesenti@unimib.it.
authors.forename: Antonio
authors.initials: A
authors.lastname: Pesenti
mesh_terms: D000328:Adult; D000368:Aged; D005260:Female; D006371:Helium; D006801:Humans; D007201:Indicator Dilution Techniques; D008176:Lung Volume Measurements / Q000379:methods*; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D015203:Reproducibility of Results; D012121:Respiration, Artificial; D012128:Respiratory Distress Syndrome / Q000503:physiopathology*; D014057:Tomography, X-Ray Computed / Q000379:methods*
chemical_list: D006371:Helium