Impact of Anemia on Surgical Outcomes
Disclaimer: This article is intended solely for informational and educational purposes only. It does not constitute medical advice.
Anemia is a reduction in the concentration of hemoglobin in the blood that decreases its capacity to transport oxygen to tissues, which can negatively affect surgical outcomes. The World Health Organization defines anemia as a hemoglobin concentration below 13 g/dL in men and 12 g/dL in nonpregnant women. For patients undergoing major surgery, however, a hemoglobin concentration below 13 g/dL has been proposed as the threshold for preoperative anemia in any adult (1). Anemia is particularly important when significant surgical blood loss is expected. A patient who begins surgery with a low hemoglobin concentration has less reserve to tolerate further reductions in oxygen-carrying capacity.
The causes of anemia vary among surgical patients. Iron deficiency is the most common and may result from chronic blood loss or inadequate iron absorption. It is particularly relevant before surgery because it can often be treated prior to an operation (1). Anemia of inflammation is also common in patients with cancer and chronic inflammatory disease. Inflammation limits iron availability and suppresses red blood cell production. Renal disease can cause anemia through reduced erythropoietin production, while vitamin B12 and folate deficiencies impair normal red blood cell formation (2). Identifying the cause is important because treatment must address the underlying mechanism.
Anemia becomes dangerous when oxygen delivery is inadequate to meet tissue demands. The body compensates for a reduced hemoglobin concentration by increasing cardiac output and extracting more oxygen from circulating blood. These mechanisms become increasingly important as anemia worsens and may be insufficient during major surgery, particularly when additional blood loss occurs. Patients with limited cardiovascular or pulmonary reserve may tolerate anemia poorly. Severe reductions in oxygen delivery can ultimately contribute to tissue hypoxia and organ dysfunction.
The effect of preoperative anemia on surgical outcomes has been demonstrated across several surgical populations. In gynecologic surgery, anemia was associated with increased 30-day mortality and an 80% increase in the odds of postoperative morbidity after adjustment for other risk factors (3). Preoperative anemia has also been associated with major morbidity after liver resection. In patients undergoing coronary artery bypass grafting, anemia was associated with greater risks of renal failure and mortality and substantially increased the probability of receiving a red blood cell transfusion (4).
The increased need for transfusion is one of the major consequences of entering surgery with anemia. Red blood cell transfusion can rapidly increase oxygen-carrying capacity and may be lifesaving in severe anemia or major hemorrhage. However, transfusion is avoided when it is not clinically necessary because it exposes the patient to additional risks. These include acute transfusion reactions, circulatory overload, transfusion-related acute lung injury, and alloimmunization. Transfusion has also been associated with postoperative infection and worse surgical outcomes, although the contribution of transfusion itself can be difficult to separate from the severity of illness and blood loss that prompted transfusion (4). For these reasons, transfusion is generally reserved for situations in which its expected benefit outweighs these risks rather than being used routinely to correct preoperative anemia.
Many causes of preoperative anemia can instead be treated before elective surgery. Iron deficiency may be treated with oral or intravenous iron, while vitamin B12 and folate deficiencies require replacement. Other forms of anemia require management directed at their underlying cause (2). Whether surgery should be delayed for treatment depends on the severity of anemia and the urgency of the procedure. Preoperative evaluation therefore provides an opportunity to identify reversible causes, improve hemoglobin when possible, and reduce exposure to transfusion. Appropriate management of anemia may improve a patient’s ability to tolerate surgery and reduce the risk of poor surgical outcomes.
References
- Lin Y. Preoperative anemia-screening clinics. Hematology Am Soc Hematol Educ Program. 2019;2019(1):570-576. doi:10.1182/hematology.2019000061
- Shander A, Corwin HL, Meier J, et al. Recommendations from the International Consensus Conference on Anemia Management in Surgical Patients (ICCAMS). Ann Surg. 2023;277(4):581-590. doi:10.1097/SLA.0000000000005721
- Richards T, Musallam KM, Nassif J, et al. Impact of Preoperative Anaemia and Blood Transfusion on Postoperative Outcomes in Gynaecological Surgery. PLoS One. 2015;10(7):e0130861. Published 2015 Jul 6. doi:10.1371/journal.pone.0130861
- LaPar DJ, Hawkins RB, McMurry TL, et al. Preoperative anemia versus blood transfusion: Which is the culprit for worse outcomes in cardiac surgery?. J Thorac Cardiovasc Surg. 2018;156(1):66-74.e2. doi:10.1016/j.jtcvs.2018.03.109