Postoperative Medical Complications

Deep Venous Thrombosis

Deep venous thrombosis (DVT) is one of the most common and potentially significant complications following spinal surgery. Rates vary widely, but have been reported to range from 0.3% to 31%, with an overall incidence of 2.2%. This variability is largely owing to different screening methods, with the rate of symptomatic DVTs much lower. Asymptomatic screening is typically not recommended. Rates of DVTs vary based on the complexity and length of surgery, patient comorbidities, type of surveillance, and type of prophylaxis used. Complex approaches such as combined anterior/posterior approaches have been shown to have a higher rate of DVT formation. Other risk factors for DVTs are related to risk factors for thrombosis as described by Virchow’s triad, which includes hypercoagulability, hemodynamic changes, and endothelial injury or dysfunction. Clinical risk factors include patient age, smoking status, trauma, malignancy, prior thromboembolic event, pregnancy, limb weakness/paralysis, and exogenous estrogen replacement.

Most DVTs are silent, meaning the patient is asymptomatic. It is estimated that around 10% to 15% of silent DVTs can lead to pulmonary embolism (PE). Contrast venography is the gold standard for diagnosis of DVT; however, given the cost, limited availability, patient discomfort, and the risk of contrast allergy, this modality is largely limited in favor of less invasive modalities. Venography can still be helpful in the setting of equivocal findings, however. If the patient does present with clinical symptoms concerning for DVT, Doppler ultrasonography and impedance plethysmography are the preferred modalities for diagnosis. Impedance plethysmography involves a pressurized cuff and measurement of the change in electrical impedance of the lower extremity in response to occlusion of the deep veins. This modality has limited sensitivity and specificity for distal DVTs in comparison to Doppler ultrasound. Given Doppler ultrasound’s high rate of sensitivity and specificity, this is largely the modality of choice for diagnosis of DVTs in the clinical setting.

Clinical symptoms of DVT include lower-extremity pain and tenderness, leg edema, and low-grade fevers. Given the fact that most symptoms of DVTs are nonspecific, a high level of suspicion must be maintained to maximize the detection of DVTs in postoperative spine patients. Despite the potential high rate of silent DVTs, most authors do not advocate for routine screening in patients with a lack of clinical symptoms. ^,

Prevention of DVTs following spine surgery remains of utmost importance. Although there are several modalities for DVT prophylaxis, many lack strong clinical evidence. Several studies have documented the utility of sequential pneumatic leg compression devices in preventing DVTs. These devices should be placed before surgery and left in place until the patient is ambulatory. The American College of Chest Physicians released their 9 ^th edition of guidelines for the prevention of thrombosis in 2012. Many of the recommendations for DVT prophylaxis are grade 2C, which are weak recommendation with benefits and risks closely balanced and are typically based on observational studies, clinical experience, or flawed prospective studies. Risks and benefits should be weighed individually for patients, and alternatives should be considered. For patients undergoing routine spinal surgery, the guidelines recommend mechanical prophylaxis (intermittent pneumatic compression [IPC]) over no prophylaxis, low-dose unfractionated heparin (LDUH), or low molecular weight heparin (LMWH) (grade 2C). For patients at high risk for venous thromboembolism (VTE) (including those with malignancy or undergoing a combined anterior/posterior approach) they suggest adding pharmacological prophylaxis once adequate hemostasis is established (grade 2C). For trauma patients at high risk of VTE, including patients with spinal cord injury (SCI) or undergoing spine surgery for trauma, they recommend mechanical prophylaxis and pharmacological prophylaxis when mechanical prophylaxis is not contraindicated by lower extremity injury (grade 2C). In patients with major trauma for whom LDUH and LMWH are contraindicated, they suggest mechanical prophylaxis with that addition of pharmacological prophylaxis with either LMWH or LDUH once the risk of bleeding diminishes (grade 2C). They do not suggest the routine use of inferior vena cava (IVC) filters or routine surveillance with ultrasound in trauma patients. The use of IVC filters may be indicated in high-risk patients or those with contraindications to pharmacological prophylaxis, but data in the literature are lacking. IVC filter use in low-risk patients undergoing elective spinal surgery is typically not recommended.

Ultimately the decision on DVT prophylaxis must be taken on a case-by-case basis, weighing the risks of prophylactic agents with the risks of thromboembolic events. Many surgeons routinely employ mechanical prophylaxis in all spine patients, given the extremely low risk profile. The addition of pharmacological prophylaxis has been shown to decrease thromboembolic events; however, the risks of postoperative hemorrhage must be weighed. However, there are several studies showing benefit in spine surgery patients. ^, The North American Spine Surgery work group has recommended that, in the setting of posterior, low-risk surgeries, pharmacological prophylaxis may not be warranted, but for higher risk patients, such as those undergoing an anterior/posterior approach, those undergoing long and complex surgeries, those with known thromboembolic risk factors, those with SCI, those with malignancy, and those with a hypercoagulable state, postoperative chemoprophylaxis should be considered.

In the setting of a confirmed acute DVT, management is employed to reduce the risk of further complications such as propagation of the clot and PE. Anticoagulation is the treatment of choice for acute DVT; however, the hemorrhagic risk of employing anticoagulation agents must be weighed.

Pulmonary Embolism

Many clinicians and authors discuss PE and DVTs as different presentations of the same disease process, as DVTs can lead to PE. The incidence of PE has been reported to range from 0% to 13%. This varies based on several factors, including the type and length of procedure performed.

PE typically presents with clinical symptoms, such as tachypnea, dyspnea, tachycardia, and pleuritic chest pain. Suspicion of PE must remain high in the postoperative setting, as these symptoms are nonspecific. Initial workup consists of chest x-ray (CXR), electrocardiogram (EKG), and arterial blood gas (ABG). The CXR and EKG largely serve to rule out other potential causes of the patient’s symptoms, including myocardial infarction (MI), pneumonia, and pneumothorax. EKG findings in the setting of PE may include a right axis deviation, ST-T abnormalities, or a right bundle branch block that may suggest PE, but these are nonspecific findings, and oftentimes EKG findings are normal except in massive PEs. CXR findings also vary and are nonspecific. ABG findings can include respiratory alkalosis, reduction in partial arterial oxygen pressure, and widening of the alveolar-arterial oxygen pressure gradient. ABG findings can also be normal or nonspecific in the setting of acute PE. Measurement of brain natriuretic peptide has high sensitivity but low specificity for PE, and usefulness in diagnosing PE is limited. ^, Likewise, measurement of serum D -dimer has high sensitivity but low specificity for PE. D -dimer testing’s main role is to rule out a PE if there is low suspicion (<500 ng/mL); however, D -dimer is often elevated in the postoperative setting, further limiting its use.

In the setting of a suspected PE, the imaging modality of choice is typically the computed tomography pulmonary angiography (CTPA, also known as the CTPE). This is the first-choice imaging modality given its high sensitivity and specificity for the diagnosis of PE, especially in the setting of high clinical suspicion. ^, CT angiography is widely available and can typically be obtained in an emergent fashion. Ventilation perfusion scan (V/Q scan) is largely used when the CTPA is contraindicated, or when findings are inconclusive and additional testing is needed. Likewise, formal pulmonary angiography, whereas the historic gold standard, has largely been replaced by CTPA because of its invasive nature and operator variability. Pulmonary angiography is typically reserved for patients with a high suspicion of PE in whom CTPA and/or V/Q scans are inconclusive.

Treatment of a diagnosed PE is similar to DVT, with the addition of supporting therapy, such as oxygenation and cardiopulmonary stabilization, in the setting of symptoms. Risks and benefits of anticoagulation must be weighed in the postoperative setting. Anticoagulation agents such as LMWH, Fondaparinux, unfractionated heparin (UFH), oral factor Xa inhibitors/direct thrombin inhibitors, or warfarin may be considered. There are limited data that support LMWH or Fondaparinux as being superior to UFH, as well as the oral factor Xa inhibitors rivaroxaban or apixaban being similar in efficacy to LMWH/warfarin. ^, However, in the postoperative setting, when bleeding risk may be high, and short-acting agents with readily available reversal agents are needed, UFH, with a half-life of 3 to 5 hours and a known reversal agent (protamine sulfate) remains a mainstay in DVT/PE treatment. In the setting of a “massive” or life-threatening PE, additional treatment, such as thrombolysis, percutaneous embolectomy, or open embolectomy, may be required.