Preoperative Evaluation

A key component of the patient evaluation for spinal surgery is the complete medical history, including medications and bleeding tendencies. If indicated, a hematologic profile with coagulation times, platelet counts, and, in some instances, platelet function testing should be obtained.

Anesthetic Techniques for Lessening Intraoperative Blood Loss

Anesthetic techniques may affect operative blood loss. Specific medications, hemodilutional autotransfusion, and induced hypotension have all been used to decrease intraoperative bleeding.

Randomized, controlled trials have shown no difference in the amount of blood loss in patients who received desmopressin compared with those who did not.²⁶ Other studies have shown desmopressin to reduce blood loss in spine surgery by 32.5%.²³ It is administered immediately before surgery at a dose of 10 μg/m² of body surface area, up to a maximum dose of 20 μg. It is prepared by diluting it to a concentration of 0.5 μg/mL in normal saline and infusing over 20 minutes. Desmopressin does lessen bleeding in some subsets of patients, such as those with acquired platelet dysfunction from aspirin administration, von Willebrand disease, and uremia.^5,27 Desmopressin has been found to decrease the partial thromboplastin time, whereas factor VIII coagulant activity and von Willebrand antigen concentrations increased the partial thromboplastin time. A Cochrane review found no convincing evidence that desmopressin minimizes perioperative allogeneic red blood cell transfusion in patients who do not have congenital bleeding disorders.²⁸ Potential postoperative problems include oliguria, which usually responds to furosemide, and hyponatremia due to its potent antidiuretic hormone activity.²⁹

Randomized, controlled trials of aprotinin (Trasylol) in dorsal spinal fusion reveal significant reductions in autologous but not homologous blood transfusion. Aprotinin has been shown to reduce blood transfusion requirements in cardiac surgery, liver resection, and some orthopaedic surgical procedures.³⁰ Aprotinin has been found to increase mortality in cardiac surgery patients and was relabeled by the U.S. Food and Drug Administration (FDA) for use only in high-risk cardiac patients. It was removed from the U.S. market in November 2007.³¹

ε-Aminocaproic acid (Amicar) is an antifibrinolytic agent that has been shown to reduce blood loss in cardiac surgery.³² It has been tested in lumbar spinal fusion and has been shown to reduce autologous blood transfusion in a prospective, nonrandomized study by approximately 50%. No complications were noted, including thromboembolism or DVT. ε-Aminocaproic acid was given in an initial dose of 100 mg/kg, not to exceed 5 g over 15 minutes, followed by a continuous infusion of 10 mg/kg/hr over the remainder of the case, with the infusion terminating at skin closure.³³

Tranexamic acid is a synthetic antifibrinolytic agent that has been studied as a means to reduce blood requirements in scoliosis surgery. In a double-blinded, prospective, placebo-controlled study, tranexamic acid, given in an initial dose of 10 mg/kg at the time of patient positioning and in a maintenance infusion of 1 mg/kg/hr, reduced blood transfusion requirements by 28%.³⁴ A recent study of tranexamic acid using a loading dose of 2 g, followed by a continuous infusion of 100 mg/hr in adults and 1 mg/kg/hr in children, resulted in a 49% reduction of blood loss.³⁵ Because tranexamic acid is an antifibrinolytic agent, it does not change the blood’s intrinsic clotting ability but rather slows the breakdown of preexisting clots. Tranexamic acid has also been studied for use in reducing blood loss in metastatic spine tumor surgery and unfortunately did not significantly reduce blood loss in a retrospective study.³⁶

Recombinant coagulation factor VIIa has shown promise in reducing blood loss in spinal surgery. Factor VIIa has been used in trauma management, craniotomy, and to reverse the effects of warfarin. Factor VIIa is approved by the FDA for use in patients with hemophilia with inhibitors to replacement factor VIII or IX. Use for hemostasis in other conditions is considered off-label at this time. The drug has a short half-life and is given as hourly bolus doses or by continuous infusion. Until more data are available, the drug should be used only as an agent of last resort in the event of bleeding when all other measures have failed. The drug is available in 1200-μg vials, and doses have been given in a wide range, from 16 μg/kg to 212 μg/kg, with no reported incidence of untoward events.^{17,24,25,29,37,38} One multicenter, randomized, controlled trial of factor VIIa used in spine surgery demonstrated no adverse events and significantly reduced blood loss.³⁹

Acute hemodilutional autotransfusion is another technique used to reduce the need for homologous blood transfusion. After the induction of anesthesia, a venesection is performed and 15% to 25% of the patient’s blood volume is withdrawn into a sterile bag containing the anticoagulant citrate. The blood volume withdrawn is then replaced with colloid, on a milliliter-for-milliliter basis, or crystalloid, on a three-to-one basis. At the conclusion of surgery, the autologous blood is returned to the patient. The patient is then diuresed of excess fluid.^35,40 Patients with type O blood have lower concentrations of factor VIII and von Willebrand factor than patients with other blood types. Type O patients are at increased risk for development of disseminated intravascular coagulation (DIC) when blood is replaced with the colloid 6% hydroxyethyl starch.⁴¹

Hypotensive anesthesia has been evaluated in patients undergoing scoliosis surgery and fusion for degenerative disease.¹⁵ Hypotension was induced with 25 mg of nitroprusside and 125 mg of trimethaphan in 500 mL of 5% dextrose, which was infused to maintain a systolic blood pressure between 60 and 70 mm Hg.^11,15 Enflurane can also be used as a supplement to the general anesthetic agents to induce hypotension. Both methods have been effective in decreasing blood loss in these patients with no adverse sequelae.⁴²

A significant concern associated with patients with spinal cord injuries is whether the hypotension can cause neurologic deterioration. Ullrich et al.⁴³ performed a retrospective study comparing hypotensive and normotensive techniques in patients who underwent fixation of thoracolumbar fractures. There was a significant decrease in blood loss with hypotensive anesthesia, and there was no documented neurologic injury in either group. It is emphasized, however, that hypotensive anesthetic technique, in the presence of a compressive spinal cord lesion, poses at least the potential for further ischemia and adverse neurologic sequelae.

Somatosensory evoked potentials have been used as a monitoring tool in normotensive and hypotensive patients undergoing spinal instrumentation.⁴⁴ In the hypotensive group, the systolic blood pressure was maintained between 80 and 90 mm Hg with nitroprusside alone, or in combination with trimethaphan or propranolol. There was a significant difference in blood loss between the two groups. Intraoperative evoked potentials were altered in 5 of 24 patients, 2 in the normotensive and 3 in the hypotensive group. Wake-up testing revealed satisfactory motor function in all patients, and all 24 patients were neurologically intact postoperatively.

Enderby⁴⁵ reported a series of 9107 anesthesia sessions with an overall death rate of 0.1%. However, of the nine patients who made up the 0.1%, it was believed that only one death was due to the hypotensive technique.

Hypotensive anesthesia has the potential for neurologic or systemic complications. With careful cardiac, renal, and pulmonary monitoring and the maintenance of systolic blood pressure greater than 70 mm Hg, however, many of the complications can be avoided.^25,38 Somatosensory evoked potentials in the normal or incompletely injured patient also offer the ability to monitor physiologic changes during the hypotension and to take corrective measures if indicated.⁴⁴ It is also emphasized that the efficacy of such monitoring techniques is not proven and that the meaningfulness of the information provided is often in question. This can add to the already confusing nature of the decision-making process.

Surgical Techniques for Reducing Blood Loss

Appropriate intraoperative technique can reduce blood loss. Less blood loss is expected if meticulous attention is paid to subperiosteal dissection, hemostasis is applied at each stage of the operation by cautery and packing, decortication is performed at the termination of the operation, and consideration is given to performing fusion with spinous processes instead of iliac crest bone graft. Infiltrating the skin with a dilute solution of epinephrine (1:500,000) and packing with sponges soaked in dilute epinephrine has been reported to diminish bleeding.⁴⁰

Operative time is important, not only for minimizing blood loss but for diminution of the nonhematologic complication rate.⁴⁶ Bostman et al.⁴⁷ evaluated blood loss, operating time, and positioning of the patient. In discectomy patients with a shorter operative time, there was less bleeding. Although the lower blood loss was ascribed to patient positioning, there was a definite correlation between operative speed and blood loss.

Ventral approaches to the lumbar spine have increased in popularity for fusion procedures and disc arthroplasty. The ventral approach to the lumbar spine carries a reported vascular injury rate of 1.9% to 15.6%. The vast majority of these vascular injuries are venous, and hemorrhage may be massive. Teaming with an experienced vascular surgeon for this approach, depending on the experience of the spine surgeon, may be invaluable in lessening this complication and in repairing vascular injuries as they occur.⁴⁸

Keene and McKinley⁴⁹ used spinous processes instead of iliac crest for fusion grafts in patients with thoracolumbar fractures. This eliminated donor site bleeding and decreased operative time, with a resultant decrease in blood loss.

Local Agents for the Reduction of Blood Loss

Bleeding during spine surgery may arise from several sources, including bone, muscle, and epidural veins. The topical agents bone wax, gelatin foam (Gelfoam), oxidized cellulose, and microcrystalline collagen can be very useful in controlling intraoperative bleeding.²⁵

Bone wax consists of beeswax mixed with petroleum jelly. Bone wax is effective for control of bone bleeding. Its mechanism of action is to mechanically seal bleeding bone surfaces. Bone wax should not be used for hemostasis in cases of infection because it decreases the body’s ability of clear the bacteria from bone. Bone wax interferes with bony fusion and bone healing because the agent fills voids in the bone surface, preventing bony bridging across fracture lines.

Gelfoam holds clotting factors in place so that clotting is promoted. This process may be facilitated by soaking the Gelfoam in thrombin. Gelfoam does not function optimally when insufficient clotting factors are present. Excess Gelfoam should be removed once hemostasis is achieved because Gelfoam swells and may cause neural compression, leading to adverse outcomes. Gelfoam does not appear to inhibit bony fusion or healing.

Oxidized cellulose promotes clot formation and has the additional advantage of possessing antibacterial properties. The mechanism of action appears to be the development of a caustic artificial clot caused by the low pH of the material. This activates the intrinsic and extrinsic clotting cascades. The antibacterial activity of oxidized cellulose is also due to the low pH of the material. Unfortunately, the acidic environment caused by oxidized cellulose inhibits bone healing and bony fusion.

Microcrystalline collagen provides a surface for platelet aggregation and allows the platelets to undergo their release reaction, resulting in hemostasis. Because functioning platelets are required for hemostasis, microcrystalline collagen is not effective in cases of thrombocytopenia. Microcrystalline collagen works best when applied dry, and any excess should be removed because the material can absorb fluid and swell, which may cause neural compression. Some evidence suggests that the microcrystalline collagen causes less epidural scarring than some of the other topical agents.⁵⁰ Microcrystalline collagen does not appear to inhibit bone healing or fusion.^37,51

Positioning

Positioning for spine surgery, especially for lumbar surgery, ideally decreases intra-abdominal pressure, and subsequently venous pressure. A lower pressure in the inferior vena cava decreases the volume of blood in the Batson plexus. This in turn decreases blood loss from epidural veins. Multiple operative frames have been designed to decrease the pressure on the abdomen while the patient is in the prone position.^7,11,47,54 Although the kneeling position has been strongly advocated by some authors to decrease abdominal pressure and blood loss, others have shown no relationship between blood loss and vena caval pressure.⁵⁵ More recent studies have demonstrated a correlation of the use of the Jackson table with decreased blood loss during spine surgery.^5,7

Intraoperative and Postoperative Blood Salvage

Intraoperative autologous transfusion (IAT) has been shown to be a safe and effective method to reduce the need for homologous blood use.^11,25,56,57 IAT blood may even have the potential to deliver more oxygen to the tissues than previously stored blood, and may contain more platelets and clotting factors than bank blood.^11,45 IAT requires a system that suctions the wound, separates the red blood cells from other blood products and debris, washes the red blood cells, and returns them to the patient.^11,45,57 Flynn et al.^9,58 estimated that approximately 54% of red blood cells were returned to the patient with this technique. To improve efficiency, they recommended an open-tip suction wand with suction pressures below 100 mm Hg, the avoidance of blood pooling and clotting, the use of fewer sponges, and rinsing of the sponges to collect the red blood cells.^9,59,60

Certain precautions, however, should be observed with IAT. If antibiotic irrigation is used, the cells must be washed with large volumes and slow cycle times to remove the antibiotic from the solution. Red blood cell contact with water, povidone-iodine, or any solution with a temperature greater than 42°C should be avoided because excessive hemolysis results. Collagen powder, collagen sponges, and collagen pads (Avitene, Helistat, and Hemopad, respectively) should not be used with autotransfusion systems. If these collagen products are introduced into the operative field, use of the autotransfusion system should be discontinued, the wound irrigated copiously with saline, and, finally, the use of the autotransfusion system reinstituted.

Gelfoam, oxidized cellulose, and thrombin are safe when IAT is used. However, they should not be directly aspirated into the system.

There are some limitations to IAT. Approximately half of the red blood cells are salvaged by standard autotransfusion techniques. IAT may be contraindicated in patients with systemic infections, gross wound infections, or malignancy because of the potential for hematogenous spread of the disease.⁶⁰ It also potentially depletes the coagulation factors if they are not appropriately replaced. For every 1000 mL of autologous red blood cells returned to the patient, one unit of fresh-frozen plasma should be administered. The platelet count should be maintained at greater than 85,000 µL.^9,40

Pulmonary complications due to tissue debris accumulation and reinfusion are rare.⁹ Hemoglobinuria may occur in as many as 5% of patients. With adequate hydration and urine output (>100 mL/hr), these complications should be transient, with minimal or no clinical sequelae.^9,54

Just as intraoperative blood can be retransfused, so can postoperative blood.⁹ It is collected, filtered, anticoagulated, washed, and returned to the patient. Unwashed blood, however, appears to be associated with few complications. This technique has been reported to be safe and may decrease blood bank requirements significantly.⁶¹ Newer postoperative drainage systems have been used in orthopaedic surgery and are used to reinfuse blood without filtration directly from the drain into the patient. These systems only return blood lost during the first 8 hours after surgery. These, however, are safe and effective.

Postoperative Drugs and Blood Loss

Deep venous thrombosis occurs after spinal surgery in about 2.2% of cases. However, in the case of spinal cord injury, DVT may occur in up to 80% of cases. DVT prophylaxis with heparin, enoxaparin (Lovenox), or warfarin increases postoperative bleeding. The risk of prophylaxis should be balanced between the risk of DVT and other risks, such as neurologic deterioration from epidural hematoma. Patients with the following risk factors are at increased risk for development of DVT: age greater than 60 years, body mass index of 30 or more, genetic thrombophilia, history of prior DVT, and those undergoing a ventral and ventral/dorsal combined procedure.⁵⁰ Of note, ketorolac (Toradol) has been used after microlumbar discectomy with good control of pain and no reported increase in bleeding-related complications.⁴⁵

Treatment and Diagnosis of Diffuse Intraoperative and Postoperative Bleeding

Significant intraoperative hemorrhage rarely occurs. When it does, the causative factors include platelet washout, acute thrombocytopenia, platelet dysfunction, heparin administration, DIC, impaired hepatic function, an undiagnosed hereditary coagulation disorder, or laboratory error failing to detect a coagulopathy. The source(s) of bleeding should be carefully ascertained (e.g., solely from the wound site, from intravenous cannula wounds and other puncture sites, and from occult or distant sites). Isolated bleeding from the surgical site may indicate a coagulation disorder or simply poor surgical hemostasis. Bleeding from multiple sites strongly suggests dysfunctional clotting mechanisms, in which case prothrombin time, partial thromboplastin time, fibrinogen, d-dimer, complete blood count, platelet count, fibrin split products, and bleeding time should be assessed.

While awaiting these laboratory results, the anesthesia record should be examined to determine if heparin, hypothermia, platelet washout, or dilution of clotting factors is a likely cause. Heparin may be reversed with protamine. If hypothermic, the patient should be warmed. Thrombocytopenia may be treated by platelet transfusion, and elevated prothrombin times and partial thromboplastin times may be treated with fresh-frozen plasma. Low fibrinogen levels may require cryoprecipitate transfusion.

DIC is a syndrome characterized by the generation of thrombin in the peripheral blood. The principal target protein of thrombin is fibrinogen. A delicate balance exists between the synthesis and catabolism of fibrinogen. In DIC, this balance is upset and greatly shifted toward catabolism. DIC can be caused by tissue damaged in spine surgery. The diagnosis can be confirmed by the observation of an elevated prothrombin time, an elevated partial thromboplastin time, a low fibrinogen, and a positive d-dimer test. Treatment is directed toward clotting factor replacement.^62,63

The surgeon should be aware during the operation as to whether clot exists in the operative site. If there is no clotted blood in the operative site, a coagulopathy probably exists. At this point, coagulopathy screens should be performed. The greater the time the problem is left uncorrected, the worse it gets, and a vicious cycle begins.

Summary

The management of blood loss during spine surgery begins well before the patient enters the operating suite. A thorough medical history is obtained, with attention given to medications and those items indicating hemorrhagic tendencies. For elective surgery, an estimate of potential blood loss is made, and plans for collecting autologous blood are established. The procedure itself should be performed with controlled alacrity and with the use of appropriate hemostatic agents, pharmacologic agents, and surgical and anesthetic techniques.

The transfusion of homologous blood is performed only in patients who have no autologous blood available and who have symptoms of hypovolemia or a hemoglobin of less than 7 mg/dL. IAT can be used in those patients whose preoperatively estimated blood loss is 2 to 3 U or greater.

The use of hypotensive anesthesia may be considered relative to the individual patient’s symptoms and neurologic condition. Patients with a history of hypertension, ischemic cerebral or cardiovascular disease, or other major medical problems should be evaluated carefully before using hypotensive anesthesia. Without the ability to monitor spinal cord function during surgery, hypotensive anesthesia should be very cautiously considered.

Thought is given to patient positioning, to avoiding abdominal compression, and to controlling blood loss at each stage of the operation. The surgical procedure is planned so that any available potential bone fusion material, such as laminectomy remnants or spinous process, can be used instead of or in addition to iliac crest. Intraoperative cell salvage and autotransfusion is extremely useful to avoid the use of homologous blood.

Diffuse postoperative and intraoperative bleeding should be aggressively investigated for its cause, and treated accordingly. With the use of the aforementioned surgical techniques and technical tools, the use of homologous blood can be significantly decreased.