Transfusion requirements in spinal surgery vary widely based on type and complexity of surgical procedures, variations in technique, and surgical goals. Except in cases of major vessel injury or coagulopathy, diskectomies seldom require transfusion. In contrast, primary and revision fusions of the lumbar, thoracic, or cervical vertebrae frequently require transfusion. The volume of blood loss in these procedures can vary from 0.5 L to 20 L, although the more complex procedures, such as revision fusion, tumor surgery, and multilevel spine surgery, typically result in the highest volumes of blood loss.1
BLOOD LOSS IN SPINAL SURGERY
Direct Causes. Exposure of cancellous bone can result in significant blood loss in spine surgery. Techniques such as cautery and ligation are used to control bleeding in soft tissues. Topical gel foam or bone wax can be used to minimize bleeding from bony surfaces; however, these substances can cause foreign body reaction. Thus, harvesting of bone grafts, from the iliac crest for example, can contribute substantially to blood loss. In spinal fusion, the advantages of exposing cancellous bone are balanced against the risk of increased blood loss. To achieve fusion, exposure of cancellous bony surfaces increases the potential for healing, whereas limited exposure of cancellous bone may contribute to failure of union.
Another direct cause of blood loss in spinal surgery is the stripping of skeletal muscle from ligaments and osseous structures. The wide range of blood loss that can occur in spinal surgery can be attributed to both patient-specific factors and surgeonspecific techniques. The choice of instrumentation for stripping muscle and the skill level of the surgeon are other key factors. The traditional scalpel is effective for stripping muscle, but alternate instruments, designed to strip and cauterize the soft tissues simultaneously, offer better control of bleeding. The hot scalpel and laser scalpel are designed to achieve this; however, there are disadvantages to using these instruments. The hot scalpel has limited availability and can be cumbersome to use, and the laser scalpel requires the use of safety eyewear, tarnished or blackened instruments to avoid deflection of the laser beam and other special precautions to avoid the hazards associated with the laser. The electrocautery knife, another alternative, is perhaps the least cumbersome instrument to use for simultaneous stripping and cauterizing and is readily available in the United States.
Indirect Causes. Coagulopathy, a blood coagulation disorder resulting from several underlying etiologies not directly related to surgery, often results in excessive blood loss requiring the replacement of greater than 1 blood volume.2 Hemostatic failure can be induced by changes in core body temperature3 or clotting factor consumption.4 It may also result from dilution of platelets or clotting factors during spinal anesthesia or when significant blood volume is replaced by packed red blood cells (RBCs) and blood products that lack clotting factors.5 An underlying mechanism for coagulopathy may be the release of tissue plasminogen activator from bone at a graft harvest site or from debridement of a pseudarthrosis, which may activate the fibrinolytic system. Among patients with idiopathic scoliosis or ankylosing spondylitis, there also may be a coexisting congenital defect of coagulation.6
The incidence of surgical coagulopathy has been reported to be as high as 53%.4 However, in a study of spinal surgery patients at our institution between January 1994 and July 1995, only 39 of 244 (16%) spinal surgery patients developed perioperative coagulopathy. For these patients, the initial cause appeared to be perioperative dilution of clotting factors with thrombocytopenia occurring postoperatively. Fresh frozen precipitates were transfused first to replace clotting factors, and were then followed with transfusion of platelets. In a linear multivariate regression model, the use of fresh frozen precipitates, platelets, and cryoprecipitates in this cohort correlated with allogeneic RBC transfusion.
BLOOD MANAGEMENT IN SPINAL SURGERY
One of the primary goals in spinal surgery, as in other surgical specialties, is to minimize blood loss and, therefore, the need for allogeneic blood. The likelihood of achieving this goal is greater if surgical blood requirements can be anticipated with relative accuracy. Knowing the risk factors that correlate with allogeneic blood transfusion can help to determine surgical blood need. In our retrospective analysis, 88 of 244 (36%) patients required allogeneic blood transfusion and 34 (14%) patients required coagulation product transfusion. We found that a low preoperative hemoglobin (Hb) level, a history of pulmonary disease, tumor resection surgery, and the number of posterior levels fused correlated with increased allogeneic blood transfusion, whereas availability of autologous blood for transfusion correlated with reduced allogeneic transfusion.
Transfusion Guidelines. The application of conservative transfusion triggers can minimize allogeneic blood use. Our institutional transfusion committee has set forth guidelines for transfusion that suggest withholding transfusion until Hb level decreases to 8 g/dL for an otherwise healthy patient, or until Hb level decreases below 11 g/dL for patients with increased risk of ischemia. The guidelines suggest administering transfusion in cases of acute blood loss (i.e., blood loss > 15% of blood volume, diastolic blood pressure < 60 mm Hg, or decrease in systolic blood pressure by > 30 mm Hg) or in symptomatic anemia that results in tachycardia, mental status changes, cardiac ischemia, or dyspnea.
Reducing Intraoperative Blood Loss. In addition to conservative transfusion triggers, a variety of blood management techniques can be employed to reduce perioperative blood loss and to decrease the need for allogeneic blood transfusion. Perioperative blood loss can be reduced by controlled hypotensive anesthesia.7 Currently at our institution, this technique is applied in approximately 60% of the spine surgery patients. In these patients, systolic arterial blood pressure is maintained at 100 mm Hg, which is a relatively conservative level. At systolic arterial blood pressures below 100 mm Hg, the risk of ischemia increases. Patients with an elevated risk of ischemia, however, are not good candidates for hypotensive anesthesia.
Normovolemic hemodilution can also reduce intraoperative blood loss in some settings. In orthopedic surgery, however, its use is more limited.8 Typically, we use normovolemic hemodilution in pediatric idiopathic scoliosis patients. In such cases, a limited blood loss surgery can often be achieved through careful operative hemostasis and normovolemic hemodilution.
Autologous Blood Transfusion and Epoetin alfa. Intraoperative blood salvage, which recovers and transfuses the patient's own blood lost during surgery, is used for most spinal fusions except where tumor or infection is present. It is also avoided in cervical fusion with instrumentation because recovered blood yield in these cases is typically ≤ 1 unit, which falls short of the 2-unit yield for which we find blood salvage to be cost effective.
Because our retrospective analyses demonstrated that availability of autologous blood correlated with fewer allogeneic transfusions, we encourage patients to enter a preoperative autologous blood donation (PAD) program in which they donate between 2 and 4 units of blood at a rate of 1 unit of blood per week. The donation schedule begins 3 to 5 weeks before surgery to allow for an interval of 1 week to occur between the last donation and the day of surgery.
For the entire cohort in the retrospective analysis of 244 patients undergoing multilevel spine surgery, the mean preoperative Hb level was 12.6 ±1.8 g/dL, and the mean postoperative Hb level was 9.7 ±1.4 g/dL. While a separate mean Hb value was not calculated for the 82 (34%) patients who donated autologous blood, previous studies have demonstrated that PAD can lower perioperative Hb levels.9 Furthermore, low baseline Hb is a predictor of risk for allogeneic transfusion.10 In elective orthopedic surgery patients, treatment with recombinant human erythropoietin (Epoetin alfa) can reduce this transfusion risk11 and increase the ability of elective orthopedic surgery patients to donate autologous blood.12 Epoetin alfa may also have a role in multilevel spine surgery patients in facilitating the collection of autologous blood and in increasing preoperative Hb. However, because there have been no well-controlled studies in multilevel spine surgery patients to test this hypothesis, the role of Epoetin alfa in this setting remains to be established.
Spinal fusion surgery frequently requires transfusion with allogeneic blood and blood products. A small percentage of patients in this category develop coagulopathy from a number of etiologies, including perioperative dilution of clotting factors. Integrating multiple blood management strategies may help to reduce patient exposure to transfusion-related risks and improve patient outcomes.
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