**2. Clinical effects of anemia in cardiac surgery**

Anemia is frequently found in patients undergoing cardiac surgery and is associated with postoperative adverse outcome. Cohort studies in patients with cardiovascular diseases, documented that anemia was associated with an increase in mortality. In a large cohort of 78,974 patients older than 65 years with acute myocardial infarction, patients with lower hematocrit (Ht) levels had a higher 30-day mortality rate and red blood cell (RBC) transfusions significantly reduced the mortality rate in patients with a Ht level of less than 30% at admission (Wu et al., 2001). In contrast, a post hoc analysis derived from three large cardiovascular studies showed that patients with an acute coronary syndrome who had received RBCs during the acute phase had (after adjustment for other predictive factors) significant higher 30-day mortality than non-transfused patients (Rao et al, 2004).

In cardiac surgery preoperative as well as postoperative anemia are important prognostic factors for outcome. One study showed that preoperative hemoglobin (Hb) level below 6.2 mmol/l (10.0 g/dl) is associated with higher mortality rate compared to patients with higher Hb values (Kulier et al., 2007). Furthermore, it has been observed that preoperative anemia is associated with increased risk of stroke or kidney failure (Karkouti et al., 2009). The preoperative anemia was also an independent predictor for renal and cerebral complications in patients with a low EuroSCORE; whereas in patients with high EuroSCORE all cardiac and non-cardiac postoperative adverse events were significantly higher in anemic patients. This proves that anemia is less tolerated in patients with higher comorbidities and preoperative anemia should be taken into account in the preoperative preparations (Murphy et al., 2007). Anemic patients had a higher early and late mortality than non-anemic patients undergoing cardiac surgery and not only preoperative anemia also the nadir of the Hb concentration during cardiac surgery is related with worse adverse outcome (van Straten et al., 2009). Furthermore blood loss is a common problem in cardiac surgery, which requires some re-interventions, while massive blood loss (the replacement by transfusion of more than 50 percent of a patient's blood volume) is associated with an 8 fold increase in mortality (Karkouti et al., 2004). These studies in homogenous patient population with high number of blood transfusions show that pre-and postoperative anemia in cardiac surgery are both predictive in early and late mortality.
