The purpose of this study is to evaluate static and dynamic parameters, echocardiographic parameters, and pleth variability index for predicting fluid responsiveness in children. Children who need volume expansion will receive colloid 10 mL/kg. Blood pressure, heart rate, central venous pressure, systolic pressure variation, pulse pressure variation, delta down, aortic blood flow velocity variation, inferior vena cava diameter variation, and pleth variability index will be measure before and after volume expansion. Patients will be classified as responders to volume loading if stoke volume index increase by at least 15%.

Inclusion Criteria:

• neurosurgery under general anesthesia
• < 8 years old

Exclusion Criteria:

• cardiac disease
• pulmonary, renal and hepatic disease
• infectious disease
• hematologic and muscular disease