POASAC Study (Preoperative Anemia Severity and Classification Study)

Impact of Preoperative Anemia Severity and Classification on Perioperative Oxygen Supply-Demand Imbalance-Related Complications--A Prospective Observational Multi-center Cohort Study

The goal of this observational study focuses on the effect of different preoperative anemia status on perioperative complications in patients under moderate- to high-risk surgery. Different anemia types conclude iron-deficiency anemia(IDA), anemia of chronic disease/anemia of inflammation(ACD/AI), and combined anemia.The main question it aims to answer is whether there is a difference in the incidence of complication related to oxygen supply and demand imbalance in patients with IDA, ACD/AI or combined anemia.

Patients without preoperative anemia will be recruited as the control group for secondary outcome analysis, which is whether there is a difference in the incidence of complication related to oxygen supply and demand imbalance in patients with or without anemia.

The investigators aim to screen patients according to including and excluding criteria. According to the hemoglobin level, if the patient is anemia, the investigators will offer some lab tests for serum iron, transferrin saturation, C-reactive protein to classify different anemia status. Besides, the investigators will include patients without anemia in a 2:1 ration of anemia to non-anemia. The perioperative assessment and follow-up are the same for all the included patients.

Inclusion Criteria:

• age 18 years or older
• scheduled for elective moderate- to high-risk surgery other than intracranial and cardiac surgery
• predicted surgery time longer than 1 hour and hospital stay longer than 24 hours
• understand and agree to participate

Exclusion Criteria:

• pregnant
• live at areas higher than 2,500 meters above sea level
• with hematological diseases other than anemia
• with severe comorbidities that might interfere outcome assessment, like uremia, dementia, and so on
• can't cooperate or communicate, or reject to sign informed consent form