Background-The risk of preoperative anemia in patients undergoing heart surgery has not been described precisely.Specifically, the impact of low hemoglobin per se or combined with other risk factors on postoperative outcome is unknown. Thus, we determined the effects of low preoperative hemoglobin and comorbidities on postoperative adverse outcomes in patients with coronary artery bypass graft in a large comprehensive multicenter study. Methods and Results-The Multicenter Study of Perioperative Ischemia investigated 5065 patients with coronary artery bypass graft at 70 institutions worldwide, collecting Ϸ7500 data points per patient. In 4804 patients who received no preoperative transfusions, we determined the association between lowest preoperative hemoglobin levels and in-hospital cardiac and noncardiac morbidity and mortality and the impact of concomitant risk factors, assessed by EuroSCORE, on this effect. In patients with EuroSCORE Ͻ4 (nϭ2054), only noncardiac outcomes were increased, whereas patients with EuroSCORE Ն4 (nϭ2750) showed an increased incidence of all postoperative events, starting at hemoglobin Ͻ11 g/dL. Low preoperative hemoglobin was an independent predictor for noncardiac (renalϾcerebral; PϽ0.001) outcomes, whereas the increase in cardiac events was due to other factors associated with preoperative anemia. Conclusions-Anemic patients undergoing cardiac surgery have an increased risk of postoperative adverse events.Importantly, the extent of preexisting comorbidities substantially affects perioperative anemia tolerance. Therefore, preoperative risk assessment and subsequent therapeutic strategies, such as blood transfusion, should take into account both the individual level of preoperative hemoglobin and the extent of concomitant risk factors.

CSF volume is widely variable between individuals. The decreased CSF volume that results from increased abdominal pressure, such as with obesity or pregnancy, may produce more extensive neuraxial blockade through diminished dilution of anesthetic. The mechanism by which increased abdominal pressure decreases CSF volume is probably inward movement of soft tissue in the intervertebral foramen, which displaces CSF.

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