title: Detection of optimal PEEP for equal distribution of tidal volume by volumetric capnography and electrical impedance tomography during decreasing levels of PEEP in post cardiac-surgery patients.
abstract: BACKGROUND
  Homogeneous ventilation is important for prevention of ventilator-induced lung injury. Electrical impedance tomography (EIT) has been used to identify optimal PEEP by detection of homogenous ventilation in non-dependent and dependent lung regions. We aimed to compare the ability of volumetric capnography and EIT in detecting homogenous ventilation between these lung regions.
  
  
  METHODS
  Fifteen mechanically-ventilated patients after cardiac surgery were studied. Ventilator settings were adjusted to volume-controlled mode with a fixed tidal volume (Vt) of 6-8 ml kg(-1) predicted body weight. Different PEEP levels were applied (14 to 0 cm H2O, in steps of 2 cm H2O) and blood gases, Vcap and EIT were measured.
  
  
  RESULTS
  Tidal impedance variation of the non-dependent region was highest at 6 cm H2O PEEP, and decreased significantly at 14 cm H2O PEEP indicating decrease in the fraction of Vt in this region. At 12 cm H2O PEEP, homogenous ventilation was seen between both lung regions. Bohr and Enghoff dead space calculations decreased from a PEEP of 10 cm H2O. Alveolar dead space divided by alveolar Vt decreased at PEEP levels ≤6 cm H2O. The normalized slope of phase III significantly changed at PEEP levels ≤4 cm H2O. Airway dead space was higher at higher PEEP levels and decreased at the lower PEEP levels.
  
  
  CONCLUSIONS
  In postoperative cardiac patients, calculated dead space agreed well with EIT to detect the optimal PEEP for an equal distribution of inspired volume, amongst non-dependent and dependent lung regions. Airway dead space reduces at decreasing PEEP levels.
authors.affiliation: Department of Adult Intensive Care, Erasmus MC, Room H623, 's Gravendijkwal 230, Rotterdam 3015 CE, The Netherlands.
authors.forename: P
authors.initials: P
authors.lastname: Blankman
authors.affiliation: Department of Adult Intensive Care, Erasmus MC, Room H623, 's Gravendijkwal 230, Rotterdam 3015 CE, The Netherlands.
authors.forename: A
authors.initials: A
authors.lastname: Shono
authors.affiliation: Institute for Biomedical Technology & Technical Medicine, University of Twente, Enschede, The Netherlands.
authors.forename: B J M
authors.initials: BJ
authors.lastname: Hermans
authors.affiliation: Institute for Biomedical Technology & Technical Medicine, University of Twente, Enschede, The Netherlands.
authors.forename: T
authors.initials: T
authors.lastname: Wesselius
authors.affiliation: Department of Adult Intensive Care, Erasmus MC, Room H623, 's Gravendijkwal 230, Rotterdam 3015 CE, The Netherlands Institute for Immunotherapy, Duderstadt, Germany.
authors.forename: D
authors.initials: D
authors.lastname: Hasan
authors.affiliation: Department of Adult Intensive Care, Erasmus MC, Room H623, 's Gravendijkwal 230, Rotterdam 3015 CE, The Netherlands d.gommers@erasmusmc.nl.
authors.forename: D
authors.initials: D
authors.lastname: Gommers
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000465:Algorithms; D001784:Blood Gas Analysis; D001835:Body Weight; D019296:Capnography / Q000379:methods*; D002245:Carbon Dioxide / Q000097:blood; D006348:Cardiac Surgical Procedures / Q000379:methods*; D001026:Coronary Artery Bypass; D017097:Electric Impedance; D005260:Female; D006801:Humans; D008168:Lung / Q000000981:diagnostic imaging*; D008297:Male; D008875:Middle Aged; D010865:Pilot Projects; D011175:Positive-Pressure Respiration / Q000379:methods* / Q000592:standards; D011182:Postoperative Care / Q000379:methods*; D011650:Pulmonary Alveoli; D012121:Respiration, Artificial / Q000379:methods; D012126:Respiratory Dead Space; D013990:Tidal Volume; D014054:Tomography / Q000379:methods*; D055397:Ventilator-Induced Lung Injury / Q000000981:diagnostic imaging / Q000517:prevention & control
chemical_list: D002245:Carbon Dioxide
keywords: capnography; mechanical ventilation; peep; ventilator induced lung injury