SIADH is associated with variety of surgical procedures including spinal fusion and deformity correction (6,7,8). The syndrome is characterized by excessive retention of free water, hyponatremia, and hypo-osmolality in the presence of normo- or hypervolemia and of normal renal and adrenal function. This is in contrast to oliguria and retention of free water as a normal response to hypovolemia, where the secretion of ADH is appropriate. SIADH is reported to occur in 5% to 7% of spinal operations with an increased incidence following revision surgery (8,9). The etiology of SIADH following spinal surgery is not fully understood but has been attributed to stress, blood loss, dural manipulation, and traction on neural pathways during the procedure. The increased incidence following revision surgery may be attributed to the increased blood loss and dural manipulation related to the revision procedure.

The diagnosis is made by the clinical and laboratory findings of oliguria, serum hypo-osmolality, and increased urine specific gravity, in the presence of a normovolemic patient. Treatment is fluid restriction along with restoration of electrolyte balance, specifically the hyponatremia. Severe hyponatremia can result in cerebral edema, seizures, coma, and death. Medical consultation is recommended, especially in cases where the duration of SIADH is prolonged and the electrolyte deficit is profound. The most common problem is an inadequate workup in which the oliguria is attributed to hypovolemia. As a result, fluid replacement is given, which further worsens the hyponatremia. Therefore, a high index of suspicion is required to make the prompt diagnosis and provide appropriate treatment.

The risk of thromboembolic phenomena during elective spinal surgery without prophylaxis has ranged from 16% to over 40% among different series (10,11,12). More recent series of adult spinal surgery patients with mechanical prophylaxis have found a 0.8% to 5.0% incidence of deep vein thrombosis (DVT) (13,14,15). The rate of symptomatic pulmonary embolism was found to be up to 6% in one series, with almost all events occurring in patients undergoing combined anterior and posterior procedures (16).

The diagnosis of deep vein thrombosis and pulmonary embolism cannot be made clinically alone. Clinical symptoms and signs are nonspecific and extremely unreliable. However, specific risk factors should be identified and include age, increased operative time, prior history of a thromboembolic episode, malignancy, presence of a heritable hypercoagulable states, and prolonged recumbency. Definitive diagnosis is often made radiologically, in conjunction with the clinical scenario. DVT is often definitively diagnosed by compression Doppler ultrasonography and/or venography. Doppler ultrasound has preferentially replaced venography as the initial diagnostic modality of choice because it is a noninvasive study and voids the risk of exposure to radiation and contrast agents associated with venography. Pulmonary embolism is diagnosed by a contrast CT scan of the chest and/or pulmonary angiography. Pulmonary angiography remains the “gold standard”; however, the use of chest CT scan has become increasingly common.

Routine prophylaxis following elective spinal surgery procedures is performed predominantly through mechanical methods (compression stockings and pneumatic compression devices) and early mobilization. However, routine mechanical prophylaxis alone may not be adequate in some clinical scenarios. Pharmacological agents, namely warfarin, heparin, and low-molecular-weight heparin, are usually reserved for treatment. Their use for prophylaxis in the high-risk patient remains controversial. The safety of low-dose heparin prophylaxis in spinal surgery has been reported in one series (17). Additionally, the efficacy of low-molecular-weight heparin has only been reported following spinal cord injury, not following spinal surgery (18,19). However, other series demonstrate the use of heparin for nonfatal pulmonary embolism (PE) in postoperative spinal surgery patients with an unacceptably high complication rate (20,21). Catastrophic complications of epidural hematoma and resultant paraplegia have been reported and may preclude the use of routine pharmacological prophylaxis in some cases (20,21). The ideal period of time following spinal surgery that anticoagulation can be safely started is controversial and should be determined on an individual basis.

In high-risk patients or patients with a nonfatal pulmonary embolism, inferior vena cava (IVC) filter placement with vascular surgery consultation is recommended. The complication rate of filter placement is relatively low (less than 5%) in comparison to pharmacological treatment (22,23,24,25). Furthermore, newer generations of IVC filters are retractable and can be safely removed weeks following the acute event.

Although the incidence of cardiac complications following spinal surgery has been reported to be less than 5%, both myocardial ischemia and congestive heart failure remain a significant cause of morbidity and mortality in the postoperative period (1,32,33). Preoperative medical and cardiac optimization may help minimize these devastating complications. At our institution, patients undergo an extensive preoperative workup, especially prior to anterior and posterior spinal surgery. This is particularly so for patients who have significant cardiac risk factors, which include age greater than 50 years, male gender, preexisting heart disease, hypercholesterolemia, diabetes mellitus, and smokers. In addition to routine preoperative tests, echocardiography, stress testing, and possible coronary angiography are performed on these at-risk patients. Perioperative betablocker medication is usually initiated by internists and cardiologists and serves a cardioprotective function during the perioperative period.

The diagnosis of a myocardial infarction (MI) is made through clinical presentation, laboratory findings, and abnormalities in the electrocardiogram (ECG) and/or echocardiogram. Skeletal muscle injury during the surgical dissection can lead to elevated levels of CK-MB, which makes the diagnosis of cardiac ischemia difficult to interpret during the perioperative period (34). Troponin I is the only molecular marker of myocardial injury not expressed in regenerating muscle. As a result, troponin I has been found to be as sensitive as and more specific than CK-MB in the diagnosis of a perioperative MI (35).

Prevention is key. Hypotensive anesthesia can be challenging in these at-risk patients and requires a delicate balance between minimizing intraoperative blood loss and reducing coronary blood flow, which may induce a myocardial ischemic event. Avoiding episodes of sustained hypovolemia and hypoxia with adequate fluid resuscitation and blood replacement are effective treatment strategies to prevent a perioperative myocardial ischemic event. In contrast, prevention of congestive heart failure may require fluid restriction and diuretics. Also, episodes of prolonged tachycardia are not well-tolerated in elderly patients with preexisting heart disease. These states of prolonged tachycardia
should be avoided, as they place excessive demands on cardiac function and may induce an ischemic event. When a cardiac complication does occur, prompt medical consultation and treatment will provide the best opportunity to have a good outcome.

In contrast to cardiac complications, perioperative pulmonary complications (atelectasis, pneumonia, and respiratory failure) are common, especially following combined anterior and posterior procedures and procedures requiring entrance into the thoracic cavity. Jules-Elysee et al. assessed 59 patients with spinal deformities who underwent combined anterior-posterior procedures and found that 42% and 34% of their patients had radiographic evidence of pleural effusion and atelectasis, respectively (36). Of the remaining 59 patients, 38 (64%) developed roentgenographic abnormalities. The most common radiographic finding was an effusion found in 66% of these patients, followed by atelectasis in 53%.

In a review of the senior author’s case series of anterior-posterior deformity correction in 56 patients older than 60 years, it was found that nearly 27% of the patients had pneumonia complicating their perioperative course (1). Also, 11% of these patients sustained respiratory failure requiring reintubation and continued ventilatory support. Poor preoperative pulmonary function and presence of medical comorbidities were the two most important risk factors for early and late complications.

It is important to identify high-risk procedures (i.e., thoracic surgery, large thoracic deformities) and high-risk patients (smokers, underlying pulmonary disorders). A multidisciplinary approach with pulmonology and anesthesiology consultation is recommended to optimize the patient’s preoperative respiratory status. Preoperative pulmonary function testing is recommended in these patients to evaluate the baseline level of dysfunction and to assess pulmonary reserve. Of all the patients with a preoperative predictive forced expiratory volume in one second (FEV1), <66% sustained a respiratory complication in the senior author’s series (1).

Despite thorough preoperative assessment, medical optimization, and preventive treatment (incentive spirometry, chest physiotherapy, and early mobilization), pulmonary complications remain frequent. Treatment is largely supportive and includes incentive spirometry, aggressive chest physiotherapy, supplemental oxygenation, and ventilatory support in the setting of respiratory compromise. Empirical antibiotic treatment is initiated when there is a clinical suspicion of pneumonia. Respiratory complications should be managed using a team approach with pulmonologists, critical care specialists, and respiratory therapists.

Mental status change, specifically postoperative delirium, is defined as an acute deterioration in global cognitive function. It is not an uncommon event, especially during an elderly patient’s postoperative hospital course, and has a reported incidence of 15% to 40% (37,38). Postoperative delirium is associated with increasing age, preexisting cognitive deficits, and a history of alcohol abuse (37,38,39). A change in mental status is a symptom, and not a diagnosis. The diagnosis of “sundowning” or “ICU psychosis,” often seen in the elderly patient, is one of exclusion. An aggressive medical workup is indicated to rule out any organic pathology. The differential diagnosis for mental status changes during the postoperative period is extensive and includes cerebrovascular accident, pulmonary embolism, infection, meningitis, narcosis from opiate medications, and drug interactions.

Medical workup includes laboratory studies, arterial blood gas analysis, electrocardiogram, and chest radiograph. Other diagnostic modalities such as Doppler ultrasonography of the lower extremities, chest CT, or head CT are ordered when clinically indicated. The underlying disorder should be remedied. Once any organic pathology has been ruled out, treatment is generally supportive and includes antipsychotic medication such as haloperidol and physical restraints to protect the patient from self-injury.