title: [Effects of different mechanical ventilation methods on oxygenation and shunt fraction in patients undergoing valve replacement].
abstract: OBJECTIVE
  To determine the effects of different mechanical ventilation on oxygenation and shunt fraction in patient undergoing valve replacement.
  
  
  METHODS
  Thirty ASA II-III patients (12 males, 18 females), aged 25-56 years, undergoing valve replacement were randomly divided into 3 groups according to the mechanical ventilation method. Anesthesia was induced with midazolam 0.1 mg/kg, fentanl 10 microg/kg,vecuronium 0.1 mg/kg,and etomidate 0.3 mg/kg. Valve replacement was performed with moderate hypothermic cardiopulmonary bypass( CPB). The patients were mechanically ventilated with pure oxygen and I:E ratio 1:2. Group A (TV = 7 ml/kg, f=12 bpm) ,Group B (TV=5 ml/kg, f=15 bpm), and Group C (TV=7 ml/kg, f=15 bpm). ECG, BP, SPO2, and CVP were routinely monitored. Blood samples were taken from the radial artery and pulmonary artery at 30 min after the induction of anesthesia, 10 min before CPB, and the end of operation for blood gas analysis. Respiratory index (P(A-a) DO2/PaO2), and Qs/Qt were calculated.
  
  
  RESULTS
  There was no significant difference in age, weight, duration of operation of CPB time and aortic cross-clamping time among the 3 groups. At the end of operation, PaO2 decreased significantly, P (A-a)DO2, RI, and Qs/Qt increased significantly in group A, while there was no significant change in group B and group C. At the end of the operation, PaCO2 was lower than the baseline value (< 35 mmHg) in Group A, but it was normal in Group B and group C.
  
  
  CONCLUSIONS
  The mechanical ventilation method of lower tidal volume and higher respiratory rate might increase the oxygenation and decrease shunt fraction and might be more suitable in patients undergoing valve replacement.
authors.affiliation: Department of Anesthesiology , Xiangya Hospital, Central South University, Changsha 410008, China. renfei1970@sina.com
authors.forename: Fei
authors.initials: F
authors.lastname: Ren
authors.forename: Hong-wei
authors.initials: HW
authors.lastname: Cai
authors.forename: He-na
authors.initials: HN
authors.lastname: Jiao
mesh_terms: D000328:Adult; D001784:Blood Gas Analysis; D002315:Cardiopulmonary Bypass; D005260:Female; D019918:Heart Valve Prosthesis Implantation; D006801:Humans; D008297:Male; D008875:Middle Aged; D010100:Oxygen / Q000097:blood*; D011652:Pulmonary Circulation / Q000502:physiology*; D012121:Respiration, Artificial / Q000379:methods*
chemical_list: D010100:Oxygen