Heart rate, mean arterial pressure, stroke volume, pulse pressure variations, pleth variability index, and photoplethysmographic waveform were recorded before lung recruitment maneuver (application of continuous positive airway pressure of 25 cm H2O for 20 s), during lung recruitment maneuver when stroke volume reached its minimal value.

Cardiac index measured before and after volume expansion (10ml/kg saline, 0.9%, infused during 10 min). Patients were considered as responders to fluid administration if cardiac index increased greater than or equal to 15%.

Lung recruitment maneuver (application of continuous positive airway pressure of 25 cm H2O for 20 s)