Intraoperative hypothermia may affect tissue microcirculation and can induce myocardial injury, wound infection, and coagulopathy. During off-pump coronary artery bypass surgery without cardiopulmonary bypass or induced hypothermia, maintenance of normothermia is important for clinical outcome. The investigators hypothesized that prewarming during induction of general anesthesia would reduce drop of body temperature and change of peripheral microcirculation.

Microcirculatory parameters can be obtained from vascular occlusion test. Among those parameters, recovery slope during vascular occlusion test is known to reflect recruitment of microvasculature in response to hypoxic or ischemic insult. In this study, we will compare the recovery slope during vascular occlusion test between prewarming treatment group and control group.

Inclusion Criteria:

• off-pump coronary artery bypass surgery

Exclusion Criteria:

• refuse to enroll
• cannot undergo vascular occlusion test: anatomical abnormality of both arms, severe peripheral vascular disease, presence of A-V fistula
• preoperative left ventricular ejection fraction < 35%
• preoperative continuous infusion of vasopressor or inotropes
• pregnancy

3 months