General Medical Issues in Spinal Deformity

Paul K. Kim and Joseph T. Alexander

Age represents an independent risk factor for perioperative morbidity at either extreme of the life span. The low tolerance for blood loss, fluid/electrolyte disturbances, and infection in the elderly population present a particular challenge for the surgeon and anesthesiologist. Advanced age is a marker for postoperative morbidity, as the prevalence of coexisting medical issues increases with age.1 Higher rates of postoperative bleeding, wound-healing complications, and urinary tract infections in the elderly undergoing spinal operations have been described.² In addition, patients over 65 years of age are at a higher risk for atherosclerosis with the potential for limitations in myocardial and renal reserve. Therefore, closer monitoring of vital signs, fluid balance, and serum electrolytes is required.

Obese patients have a greater incidence of serious comorbidi-ties and higher rates of postoperative wound breakdown, seroma formation, and thromboembolic complications. The higher rate of wound complications and infections seen in obese patients often results in the use of large, specialized pressure-relieving mattresses and hospital beds designed to minimize wound breakdown and pressure ulcer development in these patients undergoing major spinal surgery. Optimal postoperative care in these patients includes early mobilization, aggressive pulmonary toilet, and appropriate prophylaxis against deep venous thrombosis (DVT). In patients in whom graduated compression stockings or intermittent pneumatic compression (IPC) devices do not fit, consideration should be given to use of anticoagulation for DVT prophylaxis in the perioperative period. Occasionally, it may be advisable to delay elective spinal operation until the patient loses weight by appropriate measures.

♦ Deep Venous Thrombosis Prophylaxis

DVT prophylaxis is a critical part of perioperative management in patients undergoing spinal surgery. A review of the literature estimates the incidence of DVT in spinal surgery patients to range between 2% and 7%.³ Several earlier studies reported no significant increase in the incidence of lower extremity DVT after elective spinal surgery with use of elastic compression stockings alone. However, the current general consensus favors use of IPC, based on more recent studies that more clearly demonstrate a significant reduction in the incidence of acute postoperative DVT after elective spinal surgery with peri-operative use of IPC.⁴ Comparative analysis of several studies has not shown a statistically significant difference in DVT rates when compared by age, sex, blood loss, number of levels fused, length of operation, or duration of bed rest postoperatively.³

Anticoagulation with low-molecular-weight heparin (LMWH) for DVT prophylaxis in elective spinal surgery appears to reduce the incidence of postoperative DVT without a significant increase in hemorrhagic complications. One recent study demonstrated a DVT rate of 0.05% and a hemorrhage rate of 0.4% in a series of 1949 spinal surgery patients who were treated with compression stockings and nadroparin subcutaneously within 24 hours postoperatively.⁵ The majority of these patients with hemorrhagic complications demonstrated a progressive neurologic deficit. However, most studies evaluating postoperative DVT in the spinal surgery population have lacked adequate design, randomization, and control groups, which has led to the difficulty in defining the efficacy of thromboprophylaxis in spinal surgery patients.

Assessment of the risk of postoperative bleeding versus thrombosis can be challenging in patients with preexisting clinical indications for anticoagulation. Those considered to be of high risk for thrombosis who are likely to require anticoagulation perioperatively include patients with older mechanical heart valves, atrial fibrillation with history of cardioembolism, acute DVT (diagnosed within the past 3 months), and hypercoagulable states, such as factor V Leiden, protein C and S deficiency, lupus anticoagulant, and anticardiolipin antibodies. Intermediate risk patients, defined as those in whom anticoagulation frequently may be postponed for a few days, include those with DVT diagnosed within the past 3 to 6 months, atrial fibrillation without cardioembolism, history of cerebrovascular stroke without risk factors for cardioembolism, and newer model prosthetic valves in the mitral location. Low-risk patients in whom no anticoagulation is usually required include those with one remote episode of DVT greater than 6 months age, newer prosthetic valves in the aortic location, and atrial fibrillation without multiple risk factors for cardioembolism.

In patients with an acute DVT who are deemed unsafe for anticoagulation postoperatively, placement of an inferior vena cava (IVC) filter remains an alternative treatment option. The value of IVC filters is not well-defined for patients with hypercoagulable states or cardioembolic risk factors. Routine ultrasonographic DVT surveillance ranging from every 72 hours to weekly should be considered in patients with risk factors for venous thromboembolism. If a calf DVT is detected, many recommend continuing surveillance every 3 to 4 days over a 2-week period without medical therapy, unless there is further development/propagation of the clot. However, detection of a proximal DVT should be treated with LMWH and Coumadin (warfarin Sodium) at the time of diagnosis postoperatively or an IVC filter if the surgeon deems anticoagulation to be contraindicated.

♦ Nutrition

Nutrition remains an important issue for patients undergoing major spinal surgery. There is increasing evidence that insufficient caloric intake may not meet the increased metabolic demands brought on by the hypercatabolic state induced by surgery or trauma.6 This results in significant skeletal and visceral protein depletion. These malnourished patients have increased rates of mortality and morbidity from sepsis, wound complications, and prolonged recuperation. If nutritional inadequacies or malnutrition are identified, a regimen of nutritional supplementation should be started and monitored throughout the postoperative period. In patients who cannot tolerate or meet their caloric needs solely with oral intake, enteral nutrition may be achieved alternatively via feeding tubes. If adequate enteral nutrition is not possible, peripheral or total parenteral nutrition should be considered. In fact, an increasing body of literature is pointing to the use of preoperative enteral and parenteral hyperalimentation in malnourished patients undergoing major surgery as a means of reducing postoperative infection and wound-healing complications, which constitute some of the most common postoperative problems seen in compromised patients undergoing spinal surgery.⁶ Also contributing to wound-healing complications is the long-term use of medications such as corticosteroids, immunosuppressive agents, or cytotoxic agents. In addition, renal failure, diabetes mellitus, malnutrition, and other immunocompromising diseases significantly increase susceptibility to infection, which may be caused by common or opportunistic organisms.

♦ Cardiovascular Disease

According to the American College of Cardiology standards, major spine surgery is considered an intermediate- to high-risk surgery due to the length of the procedure and potential fluid shifts involved.⁷ Preoperative evaluation should be focused on ensuring that the patient’s cardiovascular system is capable of handling anticipated blood loss, fluid loads, and blood pressure swings that are possible during surgery for spinal deformities. Four major factors involved in assessment of cardiac function are the presence of coronary artery disease (CAD), left ventricular dysfunction, symptomatic arrhythmias, and valvular disease. Preoperative evaluation should be focused on these four factors to determine if more extensive evaluation and treatment are indicated.

Evidence of CAD can be manifested as a past myocardial infarction (MI) or angina. However, subtle complaints, such as shortness of breath, chest tightness, radiating arm/neck pain with exertion, or nocturnal dyspnea are highly suggestive of CAD. High-risk groups, such as patients with diabetes mellitus, hypertension, hypercholesterolemia, and those with a strong family history of CAD, should also be treated with a degree of suspicion for CAD. A perioperative MI has a significantly higher mortality rate, up to 37 to 50%, than the mortality from a MI occurring outside the operating room.⁸ The risk of perioperative MI is ~1 to 2% in patients undergoing major noncardiac surgery; this risk is nearly doubled in patients with known CAD. In the first 6 months after an MI, the risk of another perioperative MI is dramatically increased, ranging from 4 to 37%. However, after that, the risk of perioperative infarction falls to 4 to 6%, assuming the patient does not suffer an MI later in life.⁹ Thus, elective surgery for spinal deformities should ideally be postponed until at least 6 months after a MI to allow for healing of myocardium and optimal medical management.

In the absence of an infarction, the severity and stability of angina is a guide for further workup. The American College of Cardiology guidelines indicate that if a patient’s angina has been stable in severity, frequency, and precipitating causes and the patient has had a cardiac evaluation within the past 2 years, further evaluation is not indicated.⁷ However, if there has been an increase in the severity or frequency of the patient’s angina or if the patient has developed congestive heart failure at any point, further noninvasive testing is warranted to stratify overall cardiac risks. Included in these tests are echocardiography, dobutamine stress echocardiography, dipyridamole thallium imaging, and treadmill stress testing. Based on evaluation of these studies, the cardiologist can determine if the patient should undergo coronary angiography as the definitive test as to whether the severity of the patient’s CAD is sufficient to require operative or nonoperative (i.e., coronary stenting or percutaneous transluminal coronary angioplasty) revascularization prior to elective surgery.¹⁰

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