Inclusion Criteria:  Adult patients Patients scheduled for a high-risk abdominal surgery Patients equipped with an arterial line connected to an cardiac output hemodynamic monitoring device ( Flotrac, EV1000, Edwards Lifesciences, Irvine, USA) Patients in whom a recrutment maneuver is planned as per standard of care  Exclusion Criteria:  Arythmia ( atrial fibrillation) Right ventricular dysfunction