Anemia is one of the major risk factors that has been shown to compromise surgical outcome in many fields of surgery. Although red blood cell (RBC) transfusions can be used to correct anemia quickly, RBC transfusions are known to be a risk factor that worsens the outcome of surgery. In cerebrovascular disease, anemia can decrease the delivery of oxygen to brain tissue and can cause cerebral ischemia, which can lead to secondary brain damage. On the other hand, RBC transfusion may increase the viscosity of the blood, thereby reducing the cerebral blood flow, or causing side effects such as vasospasm or thromboembolic event. Therefore, there is a growing need for measures to correct anemia and reduce the number of transfusions in the treatment of cerebrovascular diseases.

The effectiveness of ferric carboxymaltose for postoperative anemia correction in orthopedic and general surgery has been reported in several studies. However, researches on the effect of ferric carboxymaltose to correct preoperative anemia is rare, and there has been no study on the efficacy of ferric carboxymaltose, especially in brain surgery. However, as the population of the elderly grows and the technology of inspection develops, the number of diagnosis of cerebrovascular diseases increases. In particular, the incidence of unruptured intracranial aneurysms (UIA) has increased by 29.7% every year since 2008. Accordingly, clipping sugery, known as the treatment of UIA, has increased by 16.0% every year since 2008.21 Therefore, it is necessary to study the efficacy of ferric carboxymaltose to correct the anemia and to decrease the number of transfusion in clipping surgery for UIA.

Seicean et al. analyzed the effects of preoperative anemia and RBC transfusion on the surgical outcomes of 668 patients who underwent surgery for intracranial aneurysms for 7 years. 29.6 % of 668 patients were diagnosed with anemia, preoperatively. 28.3 % of patients with anemia, and 8.1 % of patients without anemia received RBC transfusions, intra-/postoperatively. Patients with preoperative anemia showed significantly higher frequency of RBC transfusions (p\<0.01) in general cohort, and hospital length of stay (LOS) (p\<0.01) and the rate of major complications (p=0.02) was significantly higher in the group receiving RBC transfusions. This study have reported that preoperative anemia was predictive of perioperative transfusion in the general and matched cohorts (data not shown). Other studies also demostrated that lower preoperative hemoglobin was assodiated with perioperative transfusion.

Investigators performed 427 patients who underwent clipping surgery for UIAs in 2017 in single institute (Seoul National University Bundang Hospital), where has the biggest cerebrovascular center in Korea and is one of the world's best hospitals for cerebrovascular surgery. Among 427 patients, Investigators retrospectively analysed the relationship between preoperative anemia and postoperative transfusion for 338 patients treated for UIA sized under 15mm and located in anterior circulation to maintain patient consistency. 15.4% of patients who underwent clipping surgery were diagnosed with anemia before surgery. Though Investigators did not check the level of ferritin or transferrin saturation, most patients were suspected of IDA because all patients had no chronic inflammatory disease or underlying disease causing anemia. The mean amount of intraoperative bleeding was 484.5ml, and 45.7% of the patients were given intra-/postoperative transfusion. In conclusion, the frequency of intra-/postoperative RBC transfusion was significantly higher in patients diagnosed with preoperative anemia. (p\<0.01) Based on these results, investigators hypothesized that correcting anemia before surgery could reduce the need for postoperative RBC transfusion and conducted a pilot study. From November 2018 to April 2019, FERINJECT 500mg was administered to 12 patients who underwent clipping surgery for UIAs. The average haemoglobin (Hb) increased from 11.4g/dl before FERINJECT to 13.1g/dl on the day of surgery. Three patients (25.0%) received a transfusion after surgery. When investigators retrospectively compared the group with patients without correcting the anemia, investigators concluded that the anemia corrected group significantly lowered the probability of postoperative transfusion. (p \<0.01) Accordingly, investigators designed a prospective study to evaluate the effect of preoperative anemia correction using FERINJECT on the need for RBC transfusion and surgical outcome in patients undergoing clipping surgery for UIAs.