After obtaining approval from the Institutional Review Board of our institution, written informed consent is obtained from patients undergoing interventional cerebral aneurysm coiling procedure are enrolled in this prospective study and randomly allocated into one of two groups: Group-C (n=15) and Group-HES (n=15).

All recruited patients will be given patient identification number (PIN) for the present study of 01-30 according to their order of interview and recruitment. Investigators will prepare 15 yellow and 15 green cards, which will be inserted in 20 thick-paper envelopes. Then, all envelopes will be sealed, mixed and randomly allocated to get numbers of 01 to 30 (Envelop number). After printing the envelope number outside envelope, all sealed envelopes with cards will be conveyed to and kept in pharmacy department.

According to the color of the card, attending anesthesiologists will give crystalloid for yellow card or HES for green cards, respectively, to maintain stroke volume variation lesser than 15 during volume controlled ventilation (8 ml/kg tidal volume) of O2/air mixture.

Patient data and statistical analyses:

Patients demographic data, whole blood viscosity, PaO2, FiO2, Hemoglobin, urine amount, s-glucose will be obtained

Inclusion Criteria:

• Patients undergoing coiling embolization procedure due to cerebral aneurysm
• Patients provided a written informed consent.
• Patients with preoperative serum hemoglobin concentration >13 g/dL (male) and >12 g/dL (female)
• Patients with PaO2/FiO2 ratio >150

Exclusion Criteria:

• Patients with history of anemia, dyspnea, active infection.
• Patients with endocrine disease
• Patients received or receiving intraoperative and preoperative blood salvaged, allogenic blood transfusion, anti-platelet drug, anti-fibrinolytic agents or recombinant human erythropoietin, or undergoing acute normovolemic hemodilution.