Study Protocol Patients were sedated with midazolan and fentanyl (score of -4 to -5 in the Richmond Agitation Sedation Scale)and ventilated in controlled pressure or controlled volume mode (Servo I system v.12 or Servo 900 C, Siemens, Sweden) with VT < 8 ml/kg IBW (51 + 0.9[height in cm- 152.9] for men and 45.5 + 0.91[height in cm- 152.9] for women). Ventilatory and hemodynamic variables were measured before and after FC with the patients in a supine position. Zero pressure was measured at the midaxillary line. The correct position of the pulmonary artery catheter in West's zone 3 was checked as described in the literature.