Anand H. Segar, BHB, MBChB, DPhil (Oxon), FRACS and Themistocles S. Protopsaltis, MD
Chemoprophylaxis, in the form of anticoagulation, is commonly used to prevent venous thromboembolism (VTE) which includes deep vein thrombosis (DVT) and pulmonary embolism (PE). Use after posterior surgery at the level of the spinal cord is controversial. A delicate balance exists between the prevention of potentially fatal embolic events and the risk of iatrogenic compressive epidural hematoma (EDH).
EPIDEMIOLOGY OF VTE IN CORD LEVEL SPINE SURGERY
In the current regulatory environment, VTE is a reportable event in national and state databases. Analysis of 237,000 patients in the National Inpatient Sample database showed that patients undergoing posterior cervical fusion had statistically the highest incidences of DVT and PE of all cervical procedures, with a respective incidence of 13.4 and 6.3 per 1000 cases.1 In comparison, those who underwent a posterior cervical decompression had lower rates of DVT, 4.2 per 1000 and PE, 1.4 per 1000. A PE after posterior fusion was associated with a markedly increased length of hospitalization (26.9 vs. 7.3 d), cost ($89,520 vs. $29,169), and mortality (19.7% vs. 1.26%). Predictors of PE were the presence of pulmonary circulatory disease, excessive blood loss, male sex, and electrolyte abnormalities.1
Sebastian et al,2 reviewed the 5405 cervical spine cases at the Mayo Clinic found that VTE was more common in posterior surgery. In their multivariate model, they showed staged surgery, emergent surgery, and paralysis were all associated with increased odds of VTE. The population of spine patients at highest risk of VTE are those spine trauma patients, especially with a cord injury. Myllynen et al3 found a 100% incidence of DVT and 9% rate of PE in paralyzed spine patients. Jacobs and colleagues performed a retrospective case-controlled study of spine trauma patients who underwent surgical stabilization. They showed that without chemoprophylaxis the rate of DVT was 14% and this reduced to 7% with treatment.4 Taken together, these data show that the rate of VTE after cervical or thoracic surgery is considerable. However, prophylaxis must be balanced with the risk of EDH.
CAN CHEMOPROPHYLAXIS BE USED SAFETY AFTER SPINE SURGERY?
From the literature, the rate of EDH is low and unlike VTE is a nonreportable event. A systematic review by Glotzbecker et al,5 found that in patients who received anticoagulation the overall hematoma rate was 0.2% with individual studies ranging from 0% to 0.7%. A separate review by Cheng et al,6 found that a postoperative EDH was only reported in 10 of 2507 patients, yielding a rate of 0.4%. In a randomized controlled trial, Agnelli et al,7 studied the use of prophylactic enoxaparin in 307 neurosurgical patients (spine and brain) and showed no EDHs. In their case-controlled study, Jacobs et al,4 found no EDHs in their study of 277 spine trauma patients.
Gerlach et al,8 studied the use of nadroparin, low–molecular-weight heparin, administered in the immediate 24-hour postoperative period, in 265 cord level posterior procedures. They found no PEs reported and only a 0.05% rate of DVT. Complication wise, they reported 6 cases of EDH; however, these were all in a patient who underwent surgery for an intramedullary tumor. Cox et al,9 published their experience before and after implementation of a universal VTE prophylaxis, that is subcutaneous heparin administered preoperatively or in the immediate 24-hour postoperative period. They found a reduction in DVT rate (2.7% to 1%; P=0.009), without change in the rate of EDH (0.6% to 0.4%; P=0.54).
Despite the low risk of EDH reported in the literature, surgeon opinion would suggest that the rate of hematoma is higher. A survey of 94 spine surgeons found that 47% of surgeons estimated the rate of hematoma as between 1% and 5% with 17% of surgeons estimating the rate of >5%.10 This discrepancy can be explained by the effects of different anticoagulant agents. Cheng and colleagues noted that warfarin was associated with a 5.8% rate of bleeding complications, subcutaneous heparin, 0.9% to 9%, and low–molecular-weight heparin had only a 0.7% rate of EDH. Although EDH is an unwanted complication, vigilant monitoring, and rapid surgical intervention are correlated with the best neurological outcomes.11
LIMITATIONS OF THE LITERATURE
Unfortunately, the literature is formed mostly of heterogenous level IV studies with variability in the dosing regimen, patient populations, and reporting of outcomes. To date, there are no studies directly comparing different prophylactic agents. This is highlighted by the 2010 North American Spine Society guidelines which were unable to make clear recommendations on chemoprophylaxis.12
The balance in the prevention of postoperative of VTE and the risk of EDH is delicate. The prevalence of VTE after spine surgery is not insignificant with increased morbidity and mortality. Furthermore, VTE is reportable to regulatory bodies and this may have institutional implications, whereas EDH is not. The literature supports the role of chemoprophylaxis in reducing the rate of DVT and PE without an increased risk of catastrophic bleeding. However, the current studies are limited, and an element of clinical acumen is required in decision making. Ultimately, the judicious use of chemoprophylaxis is possible without an increased rate of EDH.
Barrett S. Boody, MD, Joseph D. Smucker, MD, and Rick C. Sasso, MD
Elective degenerative orthopedic spine and neurosurgical procedures do not have a traditionally high rate of symptomatic VTE events, including DVT or PE, with the use of mechanical prophylaxis.13–15 However, measures pushed by the Agency for Healthcare Research and Quality have made VTE a tracked and highly scrutinized adverse event, and as a result, significant effort has gone into reducing these events. In contrary, complications from chemical anticoagulation in this population have the potential to create significant adverse effects, such as neurological injuries related to EDH, wound complications, etc. The balance of these adverse events is frequently considered at the level of the treating surgical professional and is often a “judgment” based.
The value of chemical anticoagulation beyond mechanical prophylaxis is to reduce the morbidity and mortality from VTE, but VTE is a rare occurrence in cervical spine surgery. Sebastian and colleagues reviewed 5405 patients after spinal surgical procedures, noting 85 VTE events at a rate of 1.57% with 55 DVTs and 51 PEs. Risk factors for VTE after multivariate analysis found staged surgeries, paralysis, and nonelective surgery as independent risk factors.2 Furthermore, Oglesby and colleagues identified 273,396 cervical spine procedures using the National Inpatient Sample database, noting overall low rates of VTE of 5 per 1000 procedures. Anterior cervical fusions (ACF) had the lowest VTE rate of 2.7 per 1000 procedures while posterior cervical fusions had the highest at 13.4 per 1000 procedures. The presence of DVT and PE substantially increased the length of stay as well as mortality in ACF (from 2.8/100 without VTE to 83.6 and 135.1/1000, respectively) and posterior cervical fusions (from 13.0/1000 without VTE to 79.9 and 197.3/1000, respectively). However, the VTE group had significantly higher comorbid risk factors than the non-VTE group and causation cannot be inferred from the NIS data.1 Lastly, Cloney and colleagues reviewed the utility of chemical anticoagulation for VTE prophylaxis in 6869 patients after spinal surgery, of which 2171 underwent cervical or thoracic surgery. Although the chemoprophylaxis patients experienced a higher rate of VTE (3.62% vs. 2.03%; P<0.001), the cumulative incidence of VTE was lower in the chemoprophylaxis group throughout the 30-day postoperative period. However, both chemoprophylaxis and nonchemoprophylaxis experienced similar rates of PE [15 (0.60%) vs. 30 (0.80%) patients, P=0.09].16 From the available data, is it unclear if routine chemical anticoagulation shows value in reducing morbidity or mortality from VTE events, but should be thoughtfully considered in high-risk individuals, such as paralysis, staged procedures, or other significant comorbidities requiring prolonged hospitalization.
The relative paucity of VTE has the potential to confuse the intent of these medical interventions. Despite multiple protocols for prevention over many years, the adult reconstruction specialty has failed to diminish the rate of fatal PE despite modifying the rate of DVT. However, in the absence of strong data to compel the treating surgical team on either side, there is no reason to routinely add chemoprophylaxis to this patient population at this time—why increase the risk of reoperation or postoperative neurological deficit? Although postoperative EDH is also a rare event, and there is no known definitive prevention program that definitively guards against this potentially devastating complication requiring emergent reoperation.
Recently, our practice made an effort to retrospectively assess rare complications in our cervical spine practice as part of a large, multicenter study on rare complications in cervical spine surgery.17 At the time of this investigation, 2216 patients over the age of 18 years were available for analysis. Cervical spine surgery spanning C2–C7 surgeries were included with procedures spanning a 7-year time period assessing for bleeding complications within 30 days of the index surgical procedure. Within our population, the incidence of EDH was low, 0.32%. In this population, there was no history of prior anticoagulation or history of a bleeding diathesis. All anterior patients required reoperation for incision and hematoma evacuation with two third of the patients requiring postoperative intensive care unit observation. In total, 6/7 posterior decompression patients required reoperation, 2/6 with I&D only and 4/6 with I&D and revision laminectomy. In total, 2/7 required a postoperative intensive care unit stay and the average length of stay for these patients was longer at 8 days. The average length-of-stay for this complication was 3 days and all patients recovered neurologically with only transient deficits. On further examination of our population, 1 patient had a history of prior anticoagulation and a second had a history of “easy bruising” without a specific pathologic cause.
Beyond EDH, anticoagulation carries other risks as well such as prolonged wound drainage with potential wound infection, heparin-induced thrombocytopenia, prolonged drain output with potential increased transfusion risks, and many others. Although a paucity of peer-reviewed literature is available on the complications of chemical anticoagulation after spine surgery, these aforementioned risks are based on expert opinion but should be thoughtfully considered. We believe routine anticoagulation in cervical and thoracic spine surgery does not have significant evidence that it reduces clinically meaningful VTE events, carries a low but significant complication profile, and should be thoughtfully applied at the surgeon’s discretion.
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