title: Tidal ventilation distribution during pressure-controlled ventilation and pressure support ventilation in post-cardiac surgery patients.
abstract: BACKGROUND
  Inhomogeneous ventilation is an important contributor to ventilator-induced lung injury. Therefore, this study examines homogeneity of lung ventilation by means of electrical impedance tomography (EIT) measurements during pressure-controlled ventilation (PCV) and pressure support ventilation (PSV) using the same ventilation pressures.
  
  
  METHODS
  Twenty mechanically ventilated patients were studied after cardiac surgery. On arrival at the intensive care unit, ventilation distribution was measured with EIT just above the diaphragm for 15 min. After awakening, PCV was switched to PSV and EIT measurements were again recorded.
  
  
  RESULTS
  Tidal impedance variation, a measure of tidal volume, increased during PSV compared with PCV, despite using the same ventilation pressures (P = 0.045). The distribution of tidal ventilation to the dependent lung region was more pronounced during PSV compared with PCV, especially during the first half of the inspiration. An even distribution of tidal ventilation between the dependent and non-dependent lung regions was seen during PCV at lower tidal volumes (< 8 ml/kg) and PSV at higher tidal volumes (≥ 8 ml/kg). In addition, the distribution of tidal ventilation was predominantly distributed to the dependent lung during PSV at low tidal volumes.
  
  
  CONCLUSIONS
  In post-cardiac surgery patients, PSV showed improved ventilation of the dependent lung region due to the contribution of the diaphragm activity, which is even more pronounced during lower assist levels.
authors.affiliation: Department of Adult Intensive Care, Erasmus MC, Rotterdam, The Netherlands.
authors.forename: P
authors.initials: P
authors.lastname: Blankman
authors.forename: S M
authors.initials: SM
authors.lastname: VAN DER Kreeft
authors.forename: D
authors.initials: D
authors.lastname: Gommers
mesh_terms: D000328:Adult; D000368:Aged; D006348:Cardiac Surgical Procedures; D018592:Cross-Over Studies; D003964:Diaphragm / Q000503:physiopathology; D017097:Electric Impedance; D005260:Female; D006801:Humans; D008168:Lung / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D019095:Point-of-Care Systems; D011175:Positive-Pressure Respiration; D011312:Pressure; D011446:Prospective Studies; D012123:Pulmonary Ventilation; D012121:Respiration, Artificial / Q000379:methods*; D013990:Tidal Volume; D055397:Ventilator-Induced Lung Injury / Q000517:prevention & control