Blood Management and Complex Spine Surgery

Medication History

Patients with a history of transient ischemic attack, stroke, deep venous thrombosis (DVT), vascular stents, heavy bleeding after minor trauma, alcoholism, hepatic dysfunction, neuromuscular scoliosis, cerebral palsy, and cardiac disease have an increased risk of bleeding, either from the disease state or from pharmacological therapies for their condition.

Patients who take warfarin (Coumadin) may require cessation or acute reversal of anticoagulation. Occasionally, under the guidance of their internist, cardiologist, or hematologist, bridge therapy may be recommended. Patients will be placed on a shorter-acting anticoagulant or antiplatelet agent (commonly subcutaneous injection of low molecular weight heparin) to provide protection during the period of time in which their usual anticoagulant drug therapy is suspended. Bridge therapy substitutes a shorter-acting anticoagulant for one with a longer half-life and thereby lessens risk of vascular misadventure. The shorter-acting agent is suspended shortly before surgery to allow for safe spine surgical intervention, while also minimizing the risk of a thrombotic event. Those rare patients with congenital coagulation deficits typically require consultation with a hematologist and often perioperative selective clotting factor replacement.

Multiple oral anticoagulants called direct-acting oral anticoagulants and antiplatelet drugs are emerging on the marketplace or are now commonly in use. Knowledge of these medications is critical to preoperative planning. Many of these drugs have no known antidote or reversal agent or, where they exist, they can be prohibitively expensive. Platelet function can be impaired by drugs including aspirin (acetylsalicylic acid [ASA]), nonsteroidal antiinflammatory drugs, and specific platelet inhibitors. ASA can be held preoperatively in most patients without deleterious effects. However, patients with known coronary or cerebral vascular disease or significant risk factors for coronary artery disease should remain on ASA at a dose of 75 to 81 mg to lessen the risk of infarction in the perioperative period. Abrupt ASA cessation may cause a rebound effect on platelet aggregation, increasing risk of arterial thrombosis. In cases where ASA should be continued, surgical bleeding can be expected to be 1.5 times greater than normal, but the overall risk to the patient is lessened.

Nutritional supplements and herbs that inhibit platelet function include alfalfa, anise, bilberry, bladderwrack, bromelin, cat’s claw, celery, soleus, Cordyceps, dong quai, evening primrose oil, fenugreek, feverfew, garlic, ginger, ginkgo biloba, ginseng, grape seed, green tea, guggul, horse chestnut seed, horseradish, licorice, prickly ash, red clover, reishi, same, sweet clover, turmeric, and white willow. In general, all supplements should be held for 2 weeks before surgery because their exact ingredients and their physiological effects are highly variable and not well studied.

Table 84.1 contains a listing of medications that interfere with coagulation, and Table 84.2 lists the protein complex concentrates available today as reversal agents for some anticoagulant drugs. The table lists antidotes where known and gives reported guidelines, estimating the amount of time that must pass before the anticoagulant effects of these medications abate. These estimates are based on the time equivalent to three to four drug half-lives and are more restrictive than those published for needle-based procedures. The primary path for drug metabolism is annotated in the table to alert surgeons treating patients with renal failure/insufficiency or liver dysfunction to agents in which the time needed for coagulation to normalize will be increased. The estimated wait times after drug cessation reported in this table are longer than those noted in other surgical literature because spine surgeries are associated with greater blood loss than most other types of surgeries, and this greater blood loss stresses the coagulation system more than small, less invasive procedures. These timelines are recommendations based on experience and synthesis of the limited literature on the topic, as higher-level evidence guiding the optimal perioperative management of anticoagulation medications is lacking.

Preoperative Estimation of Blood Loss

Factors increasing blood loss during spine surgery include tumor, preoperative anemia, increased numbers of levels fused, pulmonary disease, patient habitus and positioning, anticoagulants, and antiplatelet drugs. ^{, ,} When surgery is contemplated for reconstruction in cases of spinal metastasis from renal cell carcinoma, preoperative embolization has been shown to significantly reduce intraoperative blood loss. Further, embolization should be considered as a preoperative adjunct in all vascular spinal tumors to minimize blood loss.

Blood loss for any operation should be estimated and plans generated to ensure that blood can be replaced if needed. An estimate of 200 mL of blood lost per fused segment can be made preoperatively to plan if and how much blood will be required for replacement. Patients can usually tolerate a loss of 15% of the blood volume before transfusion. In a 70-kg patient, estimating 70 mL blood/kg body weight, a volume of 735 mL would reflect a 15% blood loss. Table 84.3 outlines the calculations used to determine percentage blood loss and amount of blood loss required to reach a specified Hgb level. Where blood loss is greater, transfusion thresholds have shifted to be more restrictive over time. The volume of blood lost or preplanned Hgb transfusion trigger should be calculated before the start of the procedure and communicated to the anesthesia provider. Although higher (“liberal”) trigger points (Hgb 9–10 g/dL) have been used historically, more recent study demonstrates that lower thresholds provide better outcomes, especially in healthy patients. Recent guidelines published in 2016 by the AABB (formerly the American Association of Blood Banks) and the Journal of the American Medical Association recommend a restrictive red blood cell (RBC) transfusion policy, with transfusion recommended for patients undergoing orthopedic procedures who have a Hgb of 8 g/dL in the postoperative period. A Hgb as low as 7 g/dL can be used as a transfusion trigger for healthy patients undergoing surgical procedures who are no longer bleeding acutely, whereas unhealthy patients with known coronary artery disease or cancer may require a higher threshold (Hgb >9 g/dL) ( Box 84.2 ).

Autologous Blood Use

Autologous blood donation, although previously a more common strategy, has lost favor in recent years, especially preoperative donation, as it does not appear to significantly reduce the need for allogenic transfusion. A review of the National Inpatient Sample database (2004‒2009) demonstrated that preoperative autologous donation was actually a significant predictor of allogenic transfusion after spine surgery, especially following fusion of the thoracolumbar spine. That said, in certain patients where the estimated blood loss exceeds 15% to 30% of the blood volume, autologous blood donation remains an option in the perioperative blood management program.

Autologous blood can be obtained in three ways: preoperative donation, intraoperative salvage, and postoperative salvage. The benefits (in terms of decreased allogenic transfusion rates) of salvage techniques are greater, and the costs and risks are lower than preoperative donation, thus they are still commonly used, especially in cases in which higher blood loss is predicted, like posterior deformity surgery. Although preoperative donation is expensive, a reduction in the potential for allogenic transfusion-related morbidities, like transfusion reaction and infection transmission, may offset the cost. Nevertheless, there are risks to autologous blood transfusions, which include septicemia from bacterial contamination of the unit, nonimmune hemolytic transfusion reactions (HTRs), febrile reactions, and volume overload, with the most common still being clerical error.

One unit of blood can be predonated per week if the hematocrit (Hct) remains above 34%. Other guidelines for autologous donation include a patient age range of 12 to 70 years and a Hgb of at least 11 mg/dL. Full units can be taken from patients weighing more than 50 kg, and half units from those between 25 and 50 kg. Supplemental iron is recommended. In some instances, recombinant erythropoietin can be administered to facilitate increased blood volume for autologous donation. ^, This has been shown to increase blood production significantly in both animal and clinical studies.