title: Lung volume assessments in normal and surfactant depleted lungs: agreement between bedside techniques and CT imaging.
abstract: BACKGROUND
  Bedside assessment of lung volume in clinical practice is crucial to adapt ventilation strategy. We compared bedside measures of lung volume by helium multiple-breath washout technique (EELVMBW,He) and effective lung volume based on capnodynamics (ELV) to those assessed from spiral chest CT scans (EELVCT) under different PEEP levels in control and surfactant-depleted lungs.
  
  
  METHODS
  Lung volume was assessed in anaesthetized mechanically ventilated rabbits successively by measuring i) ELV by analyzing CO2 elimination traces during the application of periods of 5 consecutive alterations in inspiratory/expiratory ratio (1:2 to 1.5:1), ii) measuring EELVMBW,He by using helium as a tracer gas, and iii) EELVCT from CT scan images by computing the normalized lung density. All measurements were performed at PEEP of 0, 3 and 9 cmH2O in random order under control condition and following surfactant depletion by whole lung lavage.
  
  
  RESULTS
  Variables obtained with all techniques followed sensitively the lung volume changes with PEEP. Excellent correlation and close agreement was observed between EELVMBW,He and EELVCT (r = 0.93, p < 0.0001). ELV overestimated EELVMBW,He and EELVCT in normal lungs, whereas this difference was not evidenced following surfactant depletion. These findings resulted in somewhat diminished but still significant correlations between ELV and EELVCT (r = 0.58, p < 0.001) or EELVMBW,He (0.76, p < 0.001) and moderate agreements.
  
  
  CONCLUSIONS
  Lung volume assessed with bedside techniques allow the monitoring of the changes in the lung aeration with PEEP both in normal lungs and in a model of acute lung injury. Under stable pulmonary haemodynamic condition, ELV allows continuous lung volume monitoring, whereas EELVMBW,He offers a more accurate estimation, but intermittently.
authors.affiliation: Pathophysiological Experimental Platform, Department of Anaesthesiology, Pharmacology and Intensive Care, University of Geneva, 1 Rue Michel Servet, CH-1205 Geneva, Switzerland.
authors.forename: Gergely
authors.initials: G
authors.lastname: Albu
authors.affiliation: Department of Medical Physics and Informatics, University of Szeged, 9 Koranyi fasor, H-6720 Szeged, Hungary.
authors.forename: Ferenc
authors.initials: F
authors.lastname: Petak
authors.affiliation: Paediatric Radiology Unit, Department of Radiology and Nuclear Medicine, University Hospitals of Geneva, 6 rue Willy Donzé, CH-1205 Geneva, Switzerland.
authors.forename: Tristan
authors.initials: T
authors.lastname: Zand
authors.affiliation: Maquet Critical Care AB, Röntgenvägen 2, 17154 Solna, Sweden.
authors.forename: Magnus
authors.initials: M
authors.lastname: Hallbäck
authors.affiliation: Maquet Critical Care AB, Röntgenvägen 2, 17154 Solna, Sweden.
authors.forename: Mats
authors.initials: M
authors.lastname: Wallin
authors.affiliation: Pathophysiological Experimental Platform, Department of Anaesthesiology, Pharmacology and Intensive Care, University of Geneva, 1 Rue Michel Servet, CH-1205 Geneva, Switzerland ; Paediatric Anaesthesia Unit, Geneva Children's Hospital, University Hospitals of Geneva, 6, Rue Willy Donzé, CH-1205 Geneva, Switzerland.
authors.forename: Walid
authors.initials: W
authors.lastname: Habre
mesh_terms: D000818:Animals; D018893:Bronchoalveolar Lavage; D019296:Capnography; D006371:Helium; D008168:Lung / Q000000981:diagnostic imaging / Q000378:metabolism* / Q000503:physiopathology*; D008176:Lung Volume Measurements / Q000379:methods*; D010366:Peak Expiratory Flow Rate; D019095:Point-of-Care Systems; D011663:Pulmonary Surfactants / Q000378:metabolism*; D011817:Rabbits; D012121:Respiration, Artificial; D036542:Tomography, Spiral Computed / Q000379:methods*
chemical_list: D011663:Pulmonary Surfactants; D006371:Helium
keywords: Capnodynamics; Effective lung volume; Gas exchange; Lung injury; Lung mechanics