The aim of the study is to evaluate whether changes in Perfusion Index (PI) and Pleth Variability Index (PVI) during passive leg raising test can predict fluid responsiveness in spontaneously breathing patients.

Fluid responsive patients are defined as showing an increase in cardiac output >10% during a passive leg raising test, measured semi-invaseively with FloTrac® (Edwards LifeSciences. Irvine, United States).

Inclusion Criteria:

• Adult patients admitted to the intensive or intermediate care unit after abdominal surgery (including urological and gynecological surgery performed in laparotomy)
• Spontaneous breathing
• Arterial line already in place
• Oral and written informed consent obtained

Exclusion Criteria:

• Age <18 years
• Abdominal trauma as the reason for surgery
• Missing informed consent