EPO and Iron deficiency anemia: Furthermore, preoperative Hb*SpO2 < aaHb can also be an alterable factor during the perioperative period, clinicians can make efforts to optimize preoperative Hb levels before surgery, like limiting blood sampling and correcting coagulopathy to reduce blood loss, providing oral or intravenous iron to treat preoperative iron deficiency anemia, and even giving short-acting erythropoietin to further correct preoperative Hb levels if necessary.