Hemoglobin is the protein within red blood cells responsible for transporting oxygen from the lungs to every tissue in the body. This function is particularly important during the physiological stress of surgery, which often involves anesthesia and blood loss. When a patient has low hemoglobin, known as anemia, the body’s capacity to deliver oxygen is compromised. Anemia complicates surgery because it reduces the reserve capacity needed to cope with the increased oxygen demands and potential blood loss during and immediately after an operation.
Hemoglobin Thresholds and Surgical Postponement
The decision to proceed with surgery when a patient’s hemoglobin (Hb) level is low depends on the severity of the anemia, the type of surgery planned, and its urgency. Anemia is generally defined by the World Health Organization as an Hb level below 12 grams per deciliter (g/dL) for women and below 13 g/dL for men. These thresholds often flag a patient for further pre-operative evaluation.
For elective surgery, a low hemoglobin level is a major reason for postponement. Delaying the procedure allows time for interventions to raise the Hb level, reducing the need for a blood transfusion and lowering the risk of post-operative complications. If the surgery is urgent, such as for a life-threatening injury, the procedure must proceed despite the low Hb, with concurrent and immediate treatment for the anemia.
The concept of Patient Blood Management (PBM) provides a framework for these decisions, aiming to optimize a patient’s blood volume and minimize unnecessary transfusions. PBM guidelines emphasize that the acceptable hemoglobin range for safe surgery is individualized, considering factors like existing heart disease or ongoing blood loss. While transfusions are rarely needed when the hemoglobin is above 10 g/dL, a restrictive strategy—such as transfusing only when levels fall below 7 g/dL in a stable patient—is often recommended to avoid the risks associated with donor blood.
Physiological Risks of Anemia During Operation
Undergoing surgery with pre-existing anemia subjects the body to significant physiological strain due to reduced oxygen delivery capacity. Surgical trauma, combined with anesthesia and blood loss, compounds this deficit, leading to an oxygen supply-demand mismatch in vital organs. The heart is forced to work harder, pumping faster to circulate the limited oxygen available.
This increased cardiac workload can result in myocardial ischemia, increasing the risk of a post-operative heart attack. Low oxygen availability also impairs the body’s ability to heal and fight infection, as these processes require substantial oxygen and nutrient delivery. Consequently, patients with anemia have a greater chance of experiencing delayed wound healing and a higher rate of surgical site infections.
Anemia also affects other major organ systems, contributing to a higher incidence of post-operative kidney injury and cognitive dysfunction. These adverse outcomes translate into a longer hospital stay, a more complex recovery, and an increased rate of re-admission or death. Even mild anemia is independently associated with increased perioperative morbidity and mortality.
Strategies for Pre-Surgical Hemoglobin Optimization
For elective procedures, the goal is to safely increase the hemoglobin level above the established risk threshold prior to the operation. Treatment depends on the underlying cause of the anemia, which is identified through diagnostic testing. Iron deficiency is the most frequent cause of pre-operative anemia and is treated with iron supplementation.
Oral iron is a common first-line approach, being inexpensive and accessible. However, it requires several weeks or months to be effective and is often associated with gastrointestinal side effects that affect patient compliance.
If the time until surgery is short, the iron deficiency is severe, or the patient cannot tolerate oral iron, intravenous (IV) iron infusions are preferred. IV iron delivers a high dose of iron directly into the bloodstream over a shorter period, providing a faster increase in iron stores needed for red blood cell production.
In cases where the anemia is related to chronic inflammation or disease, such as kidney failure, erythropoietin-stimulating agents (ESAs) may be considered in addition to iron. Erythropoietin is a hormone that prompts the bone marrow to produce more red blood cells, and its synthetic form is effective in raising hemoglobin levels when used in conjunction with iron. Packed red blood cell (PRBC) transfusions are typically reserved for the most urgent situations or for patients with severe, symptomatic anemia, as transfusion carries risks, including adverse reactions and immune complications.