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Orthopedic and Spine Surgery
ANESTHESIA FOR ORTHOPEDIC AND SPINAL SURGERY provides a multitude of challenges. Children often present with concomitant diseases that affect cardiovascular and respiratory function. The ability to maintain a clear airway during anesthesia is not straightforward for some children, such as those with arthrogryposis multiplex congenita. Operating times can be protracted. Significant blood loss can occur that requires strategies for blood product management and transfusion reduction (see Chapter 12 ). Major trauma causing orthopedic injuries invariably involves other organ systems that may adversely interact with or compromise anesthesia management (see Chapter 39 ). The risks of pulmonary aspiration of gastric contents and the requisite fasting times, after even minor trauma involving an isolated forearm fracture, continue to be debated. Fat embolus is uncommon in children with long-bone fractures but should be considered in any child with hypoxia and altered consciousness in the perioperative period. Tumor surgery may be complicated by chemotherapy, altered drug disposition, or bone grafting considerations akin to those for plastic and reconstructive surgery (see Chapter 35 ), and complex postoperative pain management may be required (e.g., phantom pain, reflex sympathetic dystrophy) (see Chapter 45 ).
Children with chronic illnesses present repeatedly for surgical or diagnostic procedures. A single bad experience can blight attitudes about anesthesia for a long time. Positioning children on the operating table involves care, especially for those with limb deformities and contractures ( ). Padding, pillows, and special frames are required to protect against damage from inadvertent pressure ischemia while achieving the best posture for surgery. Plaster application, particularly around the hip, should allow for bowel and bladder function, avoid skin breakdown caused by pressure or friction, and allow access to epidural catheters. Postoperative management of casts on peripheral limbs must account for the possibility of compartment syndromes attributable to restrictive casts or compartment pathology. Major plexus blocks may mask pressure effects under plaster casts or compartment syndrome, but epidural blocks using low-dose amide anesthetics do not mask the discomfort of pressure. Intraoperative temperature regulation may be affected by tourniquet application or disease (e.g., osteogenesis imperfecta, arthrogryposis multiplex congenita). The use of radiology is common during orthopedic surgery; anesthesiologists should take precautions against excessive radiation exposure.
Regional anesthesia (see Chapter 42 ) reduces anesthesia requirements intraoperatively and provides analgesia postoperatively. The use of ultrasound techniques to locate neural tissue improves the rate of successful blocks and reduces local anesthetic doses (see Chapter 43 ). This has heralded increasing use of peripheral nerve blockade rather than central blockade for unilateral lower limb surgery. Acetaminophen (paracetamol) and nonsteroidal antiinflammatory drugs (NSAIDs) are the most common analgesics prescribed for moderate pain. Regular administration of acetaminophen and NSAIDs decreases the amount of systemic opioids administered, but NSAIDs decrease osteogenic activity and may increase the incidence of nonunion after spinal fusion. Intravenous acetaminophen improves the early effectiveness of this drug before the child is able to tolerate oral intake, but this formulation is not available in all countries. Long-term pain associated with limb-lengthening techniques (e.g., Ilizarov frame) may require oral opioids after hospital discharge.
Scoliosis Surgery
Children presenting for scoliosis surgery represent a spectrum, ranging from uncomplicated adolescents to severely compromised patients with neuromuscular disease, respiratory failure, and cardiac problems. The age range at presentation varies from infancy to young adulthood. Anesthesia techniques for scoliosis surgery vary with individual patient requirements. Approaches aimed at minimizing blood loss and transfusion requirements have progressed from extremes of hypotension and hemodilution to a more balanced approach involving moderate degrees of both, use of antifibrinolytic agents, predonation programs, and intraoperative cell salvage. The impact of anesthetic agents on complex physiologic signals has become increasingly important as more sophisticated measurements of neural transmission using somatosensory evoked potentials (SSEPs) and motor evoked potentials (MEPs) have become the standard of care.
Terminology, History, and Surgical Development
Early Hindu literature (3500 to 1800 bc ) describes Lord Krishna curing a woman whose back was “deformed in three places.” The terms scoliosis (i.e., crooked), kyphosis (i.e., humpbacked), and lordosis (i.e., bent backward) originated with the Greek physician Galen. Scoliosis is a lateral deviation of the normal vertical line of the spine, which is greater than 10 degrees when measured by radiographs. Scoliosis consists of a lateral curvature of the spine with rotation of the vertebrae within the curve. Lordosis refers to an anterior angulation of the spine in the sagittal plane, and kyphosis refers to a posterior angulation of the spine as evaluated on a side view of the spine. Curves may be simple or complex, flexible or rigid, and structural or nonstructural. Primary curves are the earliest to appear and occur most frequently in the thoracic and lumbar regions. Secondary (or compensatory) curves can develop above or below the primary curve and evolve to maintain normal body alignment. Various combinations of curve types have different pathophysiologic consequences.
The magnitude of the scoliosis curve is most commonly measured using the Cobb method. Measurement is made from an anteroposterior radiograph and requires accurate identification of the upper and lower end vertebrae involved with the curve. These vertebrae tilt most severely toward the concavity of the curve. The Cobb method of angle measurement is shown in Fig. 32.1 .
Hippocrates (circa 400 bc ) developed treatments that relied primarily on manipulation and traction, using an elaborate traction table called a scamnum . Nonsurgical treatments for spinal deformities persisted until 1839, when a surgical treatment in the form of a subcutaneous tenotomy and myotomy was described by a French surgeon, Jules Guerin.
Posterior spinal fusion was first described by Russell Hibbs for tuberculous spinal deformity in 1911. The original spinal instrumentation system was the Harrington rod system. Modification of this technique that allowed segmental fixation of the rods and early mobilization followed. These systems treated the lateral curve but did not allow for correction of the axial rotation. Subsequent developments allowed both corrections by cantilever maneuvers using Cotrel-Dubousset instrumentation.
Pedicle screws rather than hooks were the next advance. They were initially used as a distal anchor for lumber curves and were found to enhance correction and stabilization, even when used with hooks for the more proximal curves (i.e., hybrid constructs). Pedicle screw instrumentation techniques for total curve correction offer better curve correction than hook techniques and the hybrid pedicle screw and hook technique. Sublaminar polyester bands are often used as part of the hybrid technique in children with dysmorphic or osteoporotic spines because of concerns about pedicle screw placement, although bands may be associated with more neurologic complications.
Classification
Classification of scoliosis deformities is imperfect because the systems used are clinically rather than etiologically based. Most classifications are surgically based and used for surgical decision making. Curves can be described on the basis of age at onset, associated pathology, and anatomic configurations of the curve, such as single, double, or triple curves; amount of pelvic tilt; curve flexibility; and three-dimensional (3D) analysis of the curve. A classification that could indicate the risk of an adverse outcome of anesthesia, particularly respiratory failure, would be of clinical benefit. Children younger than 5 years of age with early-onset scoliosis or with independent cardiac or pulmonary disease appear to be at increased risk for respiratory failure, whereas those with idiopathic scoliosis in whom the curve develops at adolescence appear to have minimal risk. A classification adapted from that proposed by the Scoliosis Research Society in 1973 remains relevant for anesthesiologists ( Table 32.1 ).
TABLE 32.1
Classification of Scoliosis With Associated Key Anesthetic Risk Factors
Modified from Goldstein LA, Waugh TR. Classification and terminology of scoliosis. Clin Orthop Relat Res. 1973;93:10–22.
| Classification | Issues Associated With Scoliosis Surgery | Increased K + With Succinylcholine | Expected High Blood Loss | Respiratory Complications and Ventilatory Support |
|---|---|---|---|---|
| Idiopathic | ||||
| Infantile <3 years | Repeat operations, small size | ✓ | ✓ | |
| Juvenile 3–9 years | ||||
| Adolescent 9–18 years | Regarded as cosmetic by patient; perfect result expected | |||
| Congenital | ||||
| Bony abnormalities | Acute angle deformity; high risk of spinal cord injury, genitourinary malformations | |||
| Neural tube defects | ||||
| Meningomyelocele, spina bifida, syringomyelia | Latex allergy, pressure sores, hydrocephalus, Arnold-Chiari and Chiari malformations (avoid neck extension) | |||
| Neuromuscular | ||||
| Neuropathic | ||||
| Upper motor neuron | ||||
| Cerebral palsy, cerebral hypoxia | Upper airway obstruction, recurrent pneumonia, postoperative pain management | ✓✓ | ✓✓ | |
| Lower motor neuron | ||||
| Poliomyelitis | ||||
| Myopathic | ||||
| Progressive | ||||
| Duchenne muscular dystrophy | Cardiomyopathy, mitral valve prolapse, conduction abnormalities | ✓ | ✓✓ | ✓✓ |
| Spinal muscular atrophy | Electrocardiographic abnormalities | ✓ | ✓ | ✓ |
| Facioscapulohumeral muscular dystrophy | Hypertrophic cardiomyopathy, cardiac failure | ✓ | ||
| Other | ||||
| Friedrich ataxia | ✓ | |||
| Neurofibromatosis | Hypertension, other neurofibromas | |||
| Mesenchymal | ||||
| Marfan syndrome | Mitral and aortic regurgitation | |||
| Mucopolysaccharidoses (e.g., Morquio syndrome) | Atlantoaxial subluxation, difficult intubation | |||
| Arthrogryposis | Difficult intubation, severe contractures | ✓ | ||
| Osteogenesis imperfecta | Small size | |||
| Trauma | ||||
| Tumor | ||||
✓, anesthetic risk is likely; ✓✓, anesthetic risk is very likely.
The Lenke classification system, developed in 2001 for idiopathic scoliosis, provides a means to categorize curves and guide surgical treatment. It is increasingly used by the surgeons as an integral part of their decision making. Major and structural minor curves included in the instrumentation and fusion are used for the classification, and the nonstructural minor curves are excluded. The system has three components: curve type, a lumbar spine modifier, and a sagittal thoracic modifier. The resulting six curve types have specific radiographic characteristics that differentiate structural and nonstructural curves as proximal thoracic, main thoracic, and thoracolumbar/lumbar regions such that the number, curve type, and main structural curves are related as follows:
-
Type 1, main thoracic: single; main thoracic structural curve
-
Type 2, double thoracic: double; proximal, and main thoracic structural curves
-
Type 3, double major: double; main thoracic (major curve) and thoracolumbar/lumbar structural curves
-
Type 4, triple major: triple; all three structural curves
-
Type 5, thoracolumbar/lumbar: single; thoracolumbar/lumbar structural curve
-
Type 6, thoracolumbar/lumbar main thoracic: double; thoracolumbar/lumbar (major curve) and main thoracic structural curves
In types 1 through 4, the main thoracic curve is the major curve, and in types 5 and 6, the thoracolumbar/lumbar curve is the major curve.
Pathophysiology and Natural History
Vertebral rotation and rib cage deformity usually accompany any lateral curvature. With progression of the curve, the vertebral bodies in the area of the primary curve rotate the convex aspect of the curve and the spinous process to the concave side. This vertebral rotation can be determined by measurement of the position of the pedicles from the midline (i.e., Moe method). The vertebral bodies and the discs develop a wedge-shaped appearance, with the apex of the wedge toward the concave side. On the convex side of the curve, the ribs are pushed posteriorly, which narrows the thoracic cavity and causes the characteristic hump. On the concave side, the same rotation forces the ribs laterally, with consequent crowding toward their lateral margins ( Fig. 32.2 ). These changes result in an increasingly restrictive lung defect. Exactly when this becomes a problem depends on the child's accompanying pathology. The thoracic and lumbar regions are the most common sites of the primary curve. In children in whom the primary curve is in the lumbar region, the rotation of the vertebral bodies and spinous processes should be taken into consideration when spinal or epidural insertion is attempted because the spinal canal is relatively displaced toward the convex aspect of the curve.
The physical distortion in the thorax results in restriction of lung volumes and function. Ventilation depends on the mobility of the thoracic cage, the volume of each hemithorax, and the muscle power and elastic forces required to move the thorax. Children with idiopathic scoliosis with a mild decrease in vital capacity also have reduced forced expired volume at 1 second (FEV 1 ), gas transfer factor, and maximal static expiratory airway pressures (P e max) (see Fig. 13.4 and Table 13.2 ). The predominant deformity of lateral flexion and vertebral rotation results in the lung on the concave side being able to achieve a near-normal end-expiratory position but not end-inspiratory position, whereas the lung on the convex side achieves a normal end-inspiratory position but cannot reach a normal end-expiratory position. The concave side contributes less than normal at total lung capacity, resulting in a decrease in P e max. Similarly, because the convex side does not reach a normal end-expiratory position, the intercostal muscles and hemidiaphragm will be less efficient, resulting in a reduced maximum static inspiratory airway pressure (P i max), although this reduction may not be quite so marked. The main effect of scoliosis on respiratory function is mechanical, and the anatomic changes in the chest wall cause impaired movement and reduced compliance. Potential long-term respiratory problems when these defects are left untreated include hypoxemia, hypercarbia, recurrent lung infections, and pulmonary hypertension.
Congenital, Infantile, and Juvenile Scoliosis: Early-Onset Scoliosis
Congenital spinal anomalies are caused by failures of formation and segmentation that result in scoliosis and kyphosis. The hemivertebra, caused by failure of formation, is the most common anomaly. Fully segmented hemivertebrae contribute to progressive deformity during periods of rapid spinal growth (e.g., the first 5 years of life). The most severe deformities are seen in the thoracolumbar spine. Congenital spinal anomalies may be associated with malformations of the ribs, chest wall, and hemifacial microsomia. Children with congenital scoliosis have an associated 25% risk of urologic and 10% risk of cardiac abnormalities. Bracing or casting techniques are not effective for this form of scoliosis. These children may have obstructive lung disease in addition to their restrictive impairment, possibly owing to mainstem bronchial compression from spine rotation. Surgical options for these children include fusion in situ, convex hemiepiphysiodesis, hemivertebra excision, growing rods, and vertical expandable prosthetic titanium rib (VEPTR) treatment. Although short-term correction is easily achievable, a short thoracic spine or even thoracic insufficiency syndrome (inability of the thorax to support normal breathing and lung growth) can result. Approximately one-half of the children who have extensive thoracic fusions and those whose fusions involve the proximal thoracic spine develop restrictive pulmonary disease (FEV 1 <50%). Expansion thoracoplasty and stabilization using a VEPTR may be used.
Infantile and juvenile scoliosis are part of the spectrum of idiopathic scoliosis but are considered here because they manifest and require treatment at an early age. Infantile scoliosis accounts for less than 1% of idiopathic scoliosis and is defined as scoliosis appearing between birth and 3 years of age. It usually occurs in the thoracic spine, and the curve is usually convex to the left. Bracing and serial casting techniques are used for infantile scoliosis; improvement and resolution in some cases have been achieved at 9-year follow-up.
Treatment of infantile scoliosis may begin as early as 4 to 5 months of age or as soon as the diagnosis of scoliosis has been made. Body casting appears useful in selected children, such as those with smaller, flexible spinal curves, but curve progression and the need for secondary treatments affect a significant proportion of these children. Bracing is considered when the curve reaches 30 degrees. Success has also been reported for more severe curves (60 degrees) when casting was started before 20 months. After induction of anesthesia, the child is positioned on the frame (first described by Cotrel and Morel ), securing the pelvis to the caudal end of the frame and tethering the head by a chin strap to the rostral end. The spine is mildly distracted, but the main maneuver derotates the spine through the ribs ( Fig. 32.3A ). General anesthesia with tracheal intubation is required to facilitate positioning the child, stretching the spine, and molding the body cast. Hemoglobin desaturation frequently occurs when the cast is molded to correct the spinal deformity. Hypoxemia or breathlessness may occur following cast application. Peak Inspiratory pressure (PIP) may double if using positive-pressure ventilation intraoperatively; this can be partially improved by cutting a window in the cast.
An oral airway is also needed to prevent compression of the tracheal tube after the chin strap is applied and tightened ( Fig. 32.3A ). After the cast has hardened, it is cut back and trimmed to maintain the correction to the spine while facilitating breathing, gastrointestinal function, and day-to-day living (see Fig. 32.3B ). Halo traction may be used to stretch and improve the curves but infections occur in ~50%.
Juvenile idiopathic scoliosis represents 10% to 15% of idiopathic scoliosis and is defined as scoliosis that is first diagnosed between the ages of 4 and 10 years. Approximately 20% of these children and those with infantile scoliosis with a curve greater than 20% have an underlying spinal condition, most commonly Arnold-Chiari malformation and syringomyelia. Although bracing is used to manage these curves, almost all children in this group with curves greater than 30% require surgical intervention.
Growing rods may be used for congenital, infantile, or juvenile scoliosis to maintain the correction obtained at initial surgery while allowing spinal growth to continue. Several procedures are required before a definitive fusion. All the systems (i.e., growing rods and VEPTR) have a moderate complication rate (i.e., rod breakage and hook displacement).VEPTR systems are being used to correct large-magnitude curves in this group of children when conservative treatment is inadequate.
Idiopathic Scoliosis
Although adolescent idiopathic scoliosis is relatively common, severe morbidity is seen only in children with early-onset (infantile or juvenile) idiopathic scoliosis. Respiratory deterioration alone is seldom the reason for surgery in those who develop scoliosis after the age of 5 years. This is explained by the fact that the respiratory alveoli are mature by this age.
Scoliosis evolves during growth spurts. The earlier the age of onset and the more immature the bone growth at the time the process begins, the more severe the outcome. The relentless progression of infantile-onset idiopathic scoliosis with rapidly deteriorating curves and lung function is often not amenable to surgery. Treatment involving spinal instrumentation and anterior epiphysiodesis does not prevent the reappearance of the deformity or the decrease in pulmonary function.
Pulmonary impairment correlates directly with the magnitude of the thoracic curve. Severity of the scoliosis is the most accurate predictor of impaired lung function. The morphology of the thoracic curve, the number of vertebrae in the major curve, and the rigidity of the curve also are associated with deteriorating pulmonary function. Conventional wisdom has held that there is minimal impact on the vital capacity until the curve exceeds 60 degrees, with clinically relevant decreases in respiratory function occurring only after the thoracic scoliosis has progressed beyond 100 degrees. However, children with adolescent idiopathic scoliosis may have pulmonary impairment that is disproportionate to the severity of the scoliosis since it occurs before the curve reaches 100 degrees. Forced vital capacity (FVC) may decrease below normal (<80% of predicted) after the magnitude of the thoracic curve exceeds 70 degrees; FEV 1 decreases below normal after the main thoracic curve exceeds 60 degrees. Twenty percent of children with a thoracic curve of 50 to 70 degrees have moderate or severe pulmonary impairment (i.e., <65% of predicted) ( Fig. 32.4A ). Those with thoracic hypokyphosis are more likely to have moderate or severe pulmonary impairment; complex curves have a greater prevalence of moderate or severe pulmonary impairment, and the number of vertebrae in the thoracic curve is the most significant predictor of impaired respiratory function (see Fig. 32.4 ). Children with a structural cephalad thoracic curve, a major thoracic curve spanning eight or more vertebral levels, or thoracic hypokyphosis are at increased risk for moderate to severe pulmonary impairment. Bracing patients with adolescent idiopathic scoliosis (AIS) decreases the progression of high risk curves but is associated with worse pulmonary function test (PFT) results at the time of surgery.
Neuromuscular Scoliosis
Children with neuromuscular scoliosis have the burden of deteriorating muscle function in addition to mechanical distortion. Crowding of the ribs on the concave side of the curve limits chest wall expansion, and the sitting posture restricts diaphragmatic excursion. This inevitably leads to more rapid deterioration in the curve and respiratory function. These children also have the potential for rapid and unpredictable deterioration of the curve. It is important to consider the natural history of the specific neuromuscular disease when trying to balance the risks of surgery against conservative management.
Children with Duchenne muscular dystrophy (DMD) suffer from progressive muscular weakness and increasing disability until death occurs, usually by the beginning of the third decade. These children tend to become wheelchair-bound by 8 to 10 years of age because of increasing motor muscle weakness. Scoliosis then progresses with an acute deterioration during the growth spurt between the ages of 13 and 15 years, such that it becomes difficult or impossible to sit unaided. After the lumbar curve exceeds 35 degrees, further progression becomes inevitable. A normal cough requires an inspiratory effort of more than 60% of total lung capacity and effective glottic closure to produce an effective peak flow (more than 160 L/minute in adults). Forced expiratory flows are typically reduced in proportion to the decrease in lung volume. As muscle weakness progresses, patients hypoventilate, initially at night. If nocturnal ventilatory support is not provided at this stage, diurnal hypercapnia will result.
There have been two significant changes in the overall management of children with DMD: the use of steroids and the earlier use of nocturnal noninvasive positive-pressure ventilation (NPPV). Steroid treatment in the early phase of the disease appears to slow disease progression for a few years; treatment with prednisone can stabilize strength and function for 6 months to 2 years. This may delay the presentation of children for corrective surgery. Earlier adoption of nocturnal NPPV for nocturnal hypoventilation improves survival and quality of life. Clinically unsuspected nocturnal hypoventilation occurs in about 15% of patients with DMD and can be predicted by moderate impairment according to PFT results (FVC <70% and FEV 1 <65% of predicted) and scoliosis. Those with nocturnal hypoventilation have increased gas trapping, decline of muscle strength, and worse perception of health status despite NPPV.
A 2007 multidisciplinary “Consensus Statement on the Respiratory and Related Management of Patients with Duchenne Muscular Dystrophy undergoing Anesthesia or Sedation” provided recommendations to standardize the approach to these patients and others with flaccid neuromuscular diseases undergoing anesthesia. The most important of these recommendations are as follows: an FVC <50% of predicted indicates an increase in postoperative respiratory complications; an FVC <30% suggests a further increase in risk. PFTs should be part of the preoperative evaluation when possible and should include FVC, PImax, PEmax, peak cough flow, oxygen saturation by pulse oximetry (Sp o 2 ) on room air, and partial pressure of carbon dioxide (Pa co 2 ) if the Sp o 2 value is less than 95%. Consider preoperative training and postoperative use of NPPV if FVC is less than 50% of predicted, and strongly consider NPPV if FVC is less than 30%. Consider preoperative training and postoperative use of manual and mechanically assisted cough in those with impaired cough. In older children, this can be predicted by a peak cough flow less than 270 L/minute or maximal expiratory pressure less than 60 cm H 2 O. Strongly consider planning to extubate the trachea directly to NPPV when the FVC is less than 30%.
Dilated cardiomyopathy occurs in up to 90% of DMD individuals older than 18 years of age; the severity of their physical disability often masks the clinical symptoms of cardiac failure. Cardiomyopathy is responsible for 20% of deaths, but this proportion may increase in the future for individuals in whom NPPV prevents respiratory-related mortality (see also Chapter 23 ).
Risk Minimization and Improving Outcome From Surgical Intervention
Respiratory Function and Other Complications in the Early Postoperative Period
Decreases in lung volumes and flow rates similar to thoracic and upper abdominal surgery occur after scoliosis surgery. The FVC and FEV 1 decrease with a nadir at 3 days and are about 60% of preoperative values 7 to 10 days after surgery ( Fig. 32.5 ). It is not until 1 to 2 months after surgery that PFTs approach baseline values. The magnitude of this decrease is not affected by the type of surgery performed or whether the scoliosis has an idiopathic or neuromuscular cause. Surveys from the British Scoliosis Society and Scoliosis Research Society report mortality rates of 1.5 to 1.9 per 1000 cases, with a smaller rate in children with AIS (0.4 per 1000) and a greater rate in those with neuromuscular disease (3.6 per 1000). Overall, deep infections occurred in 2.8% and permanent neurologic defect in 0.45% of children.
Early-Onset Scoliosis
Early-onset scoliosis (EOS) has a dismal prognosis when untreated, and repeated spinal lengthening procedures are associated with a complication rate of 80% and a mortality rate of 18%. Magnetic growing rods, by reducing the number of operative interventions, may be associated with fewer complications and improved pulmonary function.
Idiopathic Scoliosis
Complications in children with AIS are uncommon but an increased body mass index is associated with a threefold increase in postoperative adverse events. Instrumentation of more than 13 segments and operation times longer than 6 hours are associated with an increased length of stay. Any complication during the hospital stay is associated with readmission; the most common cause is surgical site infection (SSI). Scheuermann kyphosis is associated with an 8- to 10-fold increase in major complications, SSI, and reoperations compared with AIS.
Neuromuscular Scoliosis
Children with neuromuscular disease are more likely to require prolonged mechanical ventilation after spinal surgery because of more severe preoperative respiratory impairment. The marked decrease in vital capacity and peak flows is undoubtedly related to the risk of postoperative complications, but determining when it is no longer safe to anesthetize those with a restrictive lung defect remains an imperfect science.
Equipment is available to assist the postoperative management of children with impaired respiratory function. The routine use of NPPV and cough augmentation therapy should be planned if the preoperative FVC is less than 30%. Cough augmentation can be provided manually by hyperinflation and forced expiration, alone or together, and by mechanical insufflation-exsufflation (MIE) therapy. The effectiveness of MIE may be limited in children with a weak or enlarged tongue if it blocks exsufflation flow.
Less extensive surgery with the newer pedicle screw systems decreases the need for pelvic fixation to correct pelvic obliquity. The procedures require less extensive surgery and shorter operating times, which may benefit children with impaired respiratory function.
Respiratory complications after surgery for AIS are relatively uncommon; however, these complications are fivefold greater in children with neuromuscular scoliosis. Anterior spinal procedures are associated with a greater incidence of complications than posterior spinal fusion; some consider this to be the main risk factor for postoperative respiratory complications. Current pedicle screw systems may decrease the need for anterior procedures, thereby decreasing the complication rate.
Atelectasis, infiltrates, hemothoraces, pneumothoraces, pleural effusions, and prolonged intubation have the greatest incidence, whereas pneumonia, pulmonary edema, and upper airway obstruction occur less frequently. These problems are more common when the scoliosis is associated with developmental delay; the greatest complication rate is in those with cerebral palsy and flaccid neuromuscular scoliosis. Respiratory complications increase as the severity of scoliosis and degree of respiratory impairment increase but complication rates vary considerably. Children with neuromuscular scoliosis have a respiratory complication rate of 15% to 30% and minimal mortality. One study, which separated three groups according to respiratory impairment (FVC <30%, FVC = 30% to 50%, FVC >50%), reported an overall complication rate of 31% independent of the degree of respiratory impairment, perhaps reflecting improvement with modern management techniques ( Table 32.2 ).
TABLE 32.2
Incidence of Pulmonary Complications
| Forced Vital Capacity | Total Number of Patients | Patients With Pulmonary Complications | Pneumonia | Atelectasis | Pneumothorax | Ventilator Care (>3 days) |
|---|---|---|---|---|---|---|
| <30% | 18 | 6 | 3 | 0 | 1 | 2 |
| 30%–50% | 18 | 7 | 3 | 1 | 0 | 4 |
| >50% | 38 | 10 | 2 | 1 | 0 | 7 |
Children with cerebral palsy have additional problems associated with their lack of muscular control (e.g., swallowing incoordination, excessive salivation, gastroesophageal reflux) and sometimes have developmental delay that contributes to a postoperative complication rate of 30%. Nonambulatory children and those with curves greater than 60 degrees are at increased risk for major complications; nonambulatory patients are almost four times more likely to have a major complication. Gastrointestinal dysmotility in cerebral palsy patients can be exacerbated after scoliosis surgery and cause persistent vomiting and bloating. Pancreatitis may occur in up to 30% of cerebral palsy patients after surgery, with a greater incidence among those with documented gastroesophageal reflux and reactive airway disease.
Surgical Site Infection
SSI results in high morbidity and cost. Rates are much greater after non-idiopathic scoliosis repair, increasing from 2.6% with AIS to 9.2% with neuromuscular scoliosis. The most common pathogens are Staphylococcus aureus, coagulase-negative staphylococci, and Pseudomonas aeruginosa . Almost half of the infections in children with neuromuscular scoliosis contain at least one gram-negative organism. Despite this, there is little evidence to support the use of intravenous (IV) vancomycin or gentamycin powder to the surgical site or graft. More severe curves, nonambulatory status, and increased length of stay increase the risk of infection.
Long-Term Changes
Idiopathic Scoliosis
Improvements in pulmonary function are not impressive after correction of idiopathic scoliosis. Early studies suggested that spinal fusion stabilized the respiratory dysfunction that existed preoperatively but failed to offer any improvement. Improvements are possible in certain subgroups of patients with some surgical techniques, but it takes months to years for pulmonary function to improve. Children with a preoperative curve less than 90 degrees undergoing a posterior procedure experienced an increase in vital capacity of slightly greater than 10%, maximum voluntary ventilation, and maximum respiratory mid-flow rate after 2 years; this improvement did not occur in those who underwent anterior surgery. Harrington rod instrumentation in children with idiopathic scoliosis resulted in only a small improvement in vital capacity.
The newer instrumentation systems (e.g., Cotrel-Dubousset instrumentation) allow segmental realignment and approximation, resulting in further improvements in pulmonary volumes. Pulmonary function returns to preoperative values within 3 months after the posterior approach using the newer instrumentation systems, with additional improvements occurring and being sustained for 2 years. Pedicle screws provide greater curve correction in AIS, with a trend toward improved pulmonary function after 2 years compared with other instrumentation techniques. Lung volumes measured by 3D computed tomographic scans do not change even with an increase in patient height, suggesting a dynamic improvement from hemithoracic symmetry rather than a static benefit. A 10-year follow-up analysis demonstrated an absolute increase in the FVC (3.66 L from 3.25 L) and FEV 1 (3.10 L from 2.77 L) but no changes in percent of predicted values in children who underwent a posterior fusion only. In the same analysis, those with chest wall disruption experienced no change in FVC and FEV 1 over 10 years, but a significant decrease in predicted FVC (79% vs. 85%,) and FEV 1 values (76% vs. 80%).
Chest cage disruption (i.e., thoracoplasty or anterior thoracotomy) is associated with reduced pulmonary function at 3 months and a 10% to 20% decrease in total lung capacity (TLC) and FVC. These values do not return to baseline until 1 to 2 years after surgery. Improvements in lung function with this approach rarely occur. Video-assisted thoracoscopic surgery (VATS) for anterior release and instrumentation results in less pulmonary morbidity and a smaller decrease in pulmonary function at 3 months. One year after surgery, values for children treated thoracoscopically return to baseline, but this did not occur for those undergoing open thoracotomy ( Fig. 32.6 ). Two- and five-year follow-up evaluations of those undergoing VATS showed no significant changes with regard to the correction of the major Cobb angle (56% ± 11% and 52% ± 14%, respectively) or average predicted TLC (95% ± 14% and 91% ± 10%).
Changing surgical techniques may challenge these findings in the future because some surgeons think that anterior fusions with modern systems offer short-term benefits of reduced blood loss and transfusion and long-term benefits owing to shorter fusions, better maintenance of thoracic kyphosis, and improved spontaneous lumbar curve correction. A 2-year postoperative study concluded that VATS for thoracic curves and open procedures for thoracolumbar curves resulted in minimal to no permanent pulmonary impairment 6 months after the procedure compared with posterior spinal fusion, despite a short-term decrease observed after VATS.
Neuromuscular Scoliosis
Improvements in the scoliosis angle and the degree of pelvic obliquity are achieved after spinal instrumentation in children with neuromuscular disease. Significant improvement in the quality of life perceived by the child or caregiver and in the ability to sit unaided, particularly if children are unable to do so beforehand. There is little evidence for any improvement in respiratory function in this group of children, although there may be a period of delay or even stabilization of the inevitable deterioration of respiratory function. Other investigators have shown no difference in respiratory function after 5 years compared with patients managed conservatively or an early loss in vital capacity after surgery with a progressive decrease of 25% over 4 years, with 66% of children requiring mechanical respiratory assistance by that time. A Cochrane review failed to find any data evaluating the effectiveness of scoliosis surgery in patients with DMD, leaving them to suggest: “Patients should also be informed about the uncertainty of benefits on long-term survival and respiratory function after scoliosis surgery.”
Some retrospective analyses, however, deserve consideration. A review of the long-term survival of children with DMD after spinal surgery and nocturnal ventilation demonstrated that those having spinal surgery and ventilation had a median survival of 30 years, whereas those receiving nocturnal ventilation only survived to 22.2 years. This result occurred despite a decrease in mean vital capacity from 1.4 L to 1.13 L in the first postoperative year. Posterior spinal fusion for scoliosis in DMD was associated with a significant slowing in the rate of decrease in respiratory function; the rate of 4% per year before surgery decreased to 1.75% per year (over 8 years) after surgery. In a study of 14 children with DMD and an FVC of less than 30%, the mean rate of decrease in percent of FVC after surgery was 3.6% per year. Most children and parents thought scoliosis surgery improved their function, sitting balance, and quality of life and gave it high satisfaction scores.
Less outcome information is available for children with cerebral palsy. Surgery is perceived as having a positive impact on patients' quality of life, overall function, and ease of care by parents and other caregivers, despite the high complication rates described earlier. A 3-year follow-up after a pedicle screw construct for scoliosis, which reduced the mean Cobb angle to 31 degrees, demonstrated improved functional ability in 42% of children. Most children had improved sitting balance and nursing care requirements. A 32% complication rate occurred; most were pulmonary in origin but ultimately reversible. One study reported two perioperative deaths and one transient neurologic deficit caused by screw impingement among 56 patients.
Less morbidity has been claimed for the same-day (one-stage) surgery compared with the two-staged approach in children with neuromuscular disease requiring anterior and posterior spinal surgery. However, it seems reasonable to avoid anterior thoracotomy in neuromuscular patients in view of the poor respiratory function after chest cage disruption. Currently, pedicle screw systems in children with neuromuscular scoliosis produce outcomes similar to those of earlier systems but with shorter operating times and less blood loss.
Spinal Cord Injury During Surgery
Etiology
Spinal cord injury can occur by four main mechanisms: direct contusion of the cord during surgical exposure; contusion by hooks, wires, or pedicle screws; distraction by rods or halo traction; and reduction in spinal cord blood flow. Epidural hematoma should be included in the differential diagnosis of deficits occurring postoperatively. The areas of the spinal cord most vulnerable to ischemic injury are the motor pathways, which are supplied by a single anterior spinal artery. This is fed in a segmental manner by the radicular arteries that arise from the vertebral, cervical, intercostals, lumbar, and iliolumbar arteries. The largest radicular artery is the artery of Adamkiewicz, which arises between T8 and L4. A watershed area between T4 and T9 is prone to ischemia because the blood supply in this region of the cord is poorest. Paraplegia is the most feared neurologic complication, but partial spinal cord injury resulting in areas of localized weakness and numbness as well as bladder and bowel disturbances also have been reported.
The increasing use of pedicle screws in spinal surgery raises the possibility of increased risk to individual nerve roots. A systematic review of pedicle screw complications that involved a total of 4570 pedicle screws in 1666 patients reported an overall 4% malposition rate that increased to 16% in studies that systematically examined their patients postoperatively. Eleven patients required revision surgery for the malpositioned screws, and there was one temporary neurologic complication (i.e., epidural hematoma). No vascular injuries were reported, although six cases of aortic abutment were described.
Risk of Spinal Cord Injury and Spinal Cord Monitoring
Surveys undertaken by the Scoliosis Research Society investigating idiopathic scoliosis reported in 1975 an incidence of neurologic impairment of 0.72%, which in 2000 had decreased to 0.3%. All of the deficits were partial cord lesions. Patients with curves greater than 100 degrees, congenital scoliosis, kyphosis, and postirradiation deformity appear to be at greatest risk for complications. The use of pedicle screws may have increased the immediate neurologic complication rate. In 2007, 9 neural complications were reported among 1301 patients, for an incidence of 0.69%. Three thecal penetrations occurred, two as a result of pedicle screws, all without sequelae. There were two nerve root injuries and four spinal cord injuries, all of which resolved within 3 months.
A retrospective review of 19,360 cases of pediatric scoliosis showed significantly different overall complication rates among idiopathic (6.3%), congenital (10.6%), and neuromuscular (17.9%) scoliosis. Neurologic deficits had a different distribution, with the greatest rate among congenital cases (2%), and smaller rates with neuromuscular (1.1%) and idiopathic scoliosis (0.8%). Mortality rates of 0.3% were observed for neuromuscular and congenital scoliosis, with an idiopathic scoliosis rate of 0.02%. Rates of new neurologic deficits were greater with anterior screw–only constructs (2%) or wire constructs (1.7%) than with pedicle screw constructs (0.7%). Surgery for high-grade spondylolisthesis appears to be associated with a particularly high risk of neurologic deficit with a rate of 11.5%.
Spinal cord function is monitored to ensure that the complication rate is as small as possible. The Scoliosis Research Society issued a position statement concluding that neurophysiologic monitoring can assist in the early detection of complications and can possibly prevent postoperative morbidity. For any monitoring technique to be effective, it needs to have a sensitivity and specificity that allows true changes to be immediately recognized with very low false-negative and false-positive results to allow the problem to be reversed or prevented. Recognition of the limitation of individual techniques has seen the development of increasingly sophisticated monitoring systems to identify and minimize this risk. Older tests, such as the wake-up test and ankle clonus test, have largely been superseded by monitoring of SSEPs, MEPs, and triggered electromyographic (EMG) techniques The importance of using a multimodal approach is increasingly recognized ; the capabilities and limitations of the various techniques are summarized in E-Table 32.1 .
E-TABLE 32.1
Intraoperative Electrophysiologic Monitoring in Spinal Surgery
Modified from Malhotra NR, Shaffrey CI. Intraoperative electrophysiological monitoring in spine surgery. Spine 2010;35:2167–2179.
| Modality | Anatomy | Not Addressed | Anesthetic Concerns | Temporality | Risks |
|---|---|---|---|---|---|
| Wake-up test | Gross motor function | Nerve roots, sensation | Only short-acting, reversible agents should be used | 1 point, difficult to repeat | Self-extubations, missed focal deficit, delayed warning |
| SSEP | Ascending pathways; dorsal column proprioception and vibration | Focal motor pathway injury, nerve roots | Muscle relaxants helpful, volatile anesthetics inhibit, balanced by <50%; no dose-related barbiturate inhibition | 3- to 5-minute summation | Missed focal motor and nerve root injury; delay in warning during summation |
| tcMEP | Anterior spinal grey matter of descending pathways; 4%-5% of motor neuron pool in corticospinal tract | Sensation, complex motor movement | TIVA best, limited muscle relaxant (CMAP) | 1 point, easily repeated | Concern for patient movement |
| nMEP | Whole cord with significant antidromic column component | Nerve roots, possibly no true motor data | Inhaled anesthetics acceptable; however, no muscle relaxant if CMAP recording | 1 point, easily repeated | Possible lack of true motor data |
| sEMG | Nerve root: assessment in selected myotomes | Sensation, anterior descending motor pathways | No muscle relaxants, inhalational anesthetic okay | Continuous | |
| tEMG | Nerve root: stimulator (pedicle screw) to end muscle | Sensation, anterior descending motor pathways | No muscle relaxants, inhalational anesthetic okay | 1 point, easily repeated | Concern about patient movement |
CMAP , compound motor action potential; nMEP , neurogenic (spinal cord) motor evoked potentials; sEMG , spontaneous electromyography; SSEP , somatosensory evoked potentials; tcMEP , transcranial motor evoked potentials; tEMG , triggered electromyography; TIVA , total intravenous anesthesia.
Methods of Monitoring Spinal Cord Function
Wake-Up Test
The wake-up test measures gross motor function of the upper and lower extremities. The test requires limiting or reversing muscle relaxation and reducing the depth of anesthesia sufficiently to enable the patient to follow commands during the surgery; failure to move the feet and toes while being able to squeeze a hand suggests a problem with the spinal cord. When the test was initially described, 3 of 124 patients were identified as having no movement and were saved from paraplegia. A major concern is that the test is conducted after maximal spinal correction, which may occur after any neurologic insult has occurred; however, removal or modification of the spinal instrumentation within 3 hours of the onset of the neurologic deficit has been reported to prevent permanent neurologic sequelae. However, the wake-up test is unlikely to detect isolated nerve root injury or sensory changes and is limited to patients with an appropriate developmental age who can follow instructions.
With the clinical application of SSEP and MEP monitoring ( Fig. 32.7 ) well established and in the absence of intraoperative changes, there is no justification to perform the wake-up test. Nonetheless, some surgeons still regard the wake-up test to be the gold standard, and it may be used to confirm changes demonstrated by SSEP or MEP monitoring. Risks associated with the wake-up test include lack of nerve root and sensory information, accidental extubation, dislodgment of the instrumentation, intraoperative recall with subsequent psychological trauma, air embolism, and cardiac ischemia. If a wake-up test is planned, it is prudent to warn the patient at the preoperative visit that they will be awakened during the surgery (but reassure them that they should not feel pain) and the wound will be filled with saline to reduce the risk of an air embolism.
Ankle Clonus Test
The ankle clonus test uses the clonus that occurs just before consciousness is regained during wakening from anesthesia. Rhythmic muscle contractions are thought to result from spinal reflexes returning while the higher neurologic centers remain inhibited by anesthesia, and the oscillations demonstrate an intact spinal cord. Inability to demonstrate clonus suggests spinal cord injury. Like the wake-up test, it is a post hoc test rather than real-time monitoring. However, in a review of more than 1000 patients undergoing spinal procedures in which six postoperative neurologic deficits occurred, this test identified all the deficits but produced three false-positive findings, giving a sensitivity of 100% and a specificity of 99.7%. In comparison, the wake-up test produced false-negative results for four of the five patients who developed deficits.
Somatosensory Evoked Potentials
SSEPs involve stimulating a peripheral nerve and measuring the response to that stimulation using scalp electrodes (i.e., cortical SSEPs). Alternatively, the response can be measured subcortically near the spinal cord by electrodes placed in the epidural space, interspinous ligament, or spinous processes of the vertebrae. An intranasally placed pharyngeal electrode can act as a surrogate for these. The advantage of the subcortical evoked potential is that the responses are more stable, reproducible, and resistant to the effects of anesthesic agents.
The signal produced with SSEP monitoring travels from the peripheral nerve through the nerve root and up the ipsilateral dorsal column. The impulses then cross over at the level of the brainstem and progress rostrally through the thalamus to the primary sensory cortex. Up to 30% of patients with AIS may have preoperative abnormal SSEP signals.
The rationale for using SSEP to monitor motor deficits is based on the fact that the sensory tracts are in proximity to the motor tracts of the spinal cord. Injury to the motor tracts indirectly affects the sensory tracts and causes changes in the SSEP. When spinal cord function is significantly impaired, there is usually an increase in latency and a decrease in amplitude in the SSEP, with eventual loss of signal. A 10% increase in latency of the first cortical peak (P1) or 50% decreases in the peak-to-peak amplitude (P1N1) constitute an indication for intervention. Although SSEP signals primarily monitor transmission through the sensory dorsal columns, they are effective, and SSEP monitoring is associated with a 50% decrease in the incidence of neurologic deficits.
It is unusual for motor tract injury to occur when SSEPs remain unchanged, but false-positive and false-negative results have been reported. Seventy percent of the postoperative complications were detected by the monitor, but 30% (false negatives) were not detected. Pedicle screw misplacement leading to radiculopathy may not be detected by SSEP monitoring. Several case reports of paraparesis also attest to the limitations of SSEP monitoring. These problems are caused by injury occurring outside the monitored domain of SSEP rather than a failure of this modality. These concerns encouraged development of methods to monitor the motor tracts of the spinal cord. SSEP monitoring is possible in patients with cerebral palsy, whereas MEP monitoring may not be.
Motor Evoked Potentials
The motor pathways can be activated by transcranial stimulation of the motor cortex or by spinal cord stimulation. Transcranial stimulation is achieved using electrical or magnetic stimulation applied to the scalp. Electrical stimulators are most commonly used in spinal surgery and operate by applying high-voltage pulses to the scalp using corkscrew, needle, or surface electrodes. The stimulation pulses can be applied as single stimuli or brief pulse trains with intervals between the pulse trains. Multiple stimuli result in a stronger signal with less variability owing to temporal summation of the excitatory postsynaptic potential. Epilepsy and proconvulsant medicines are considered relative contraindications to MEP monitoring because of concerns about brain injury from prolonged seizure activity caused by the electrical current required for stimulation. Not surprisingly, MEPs may be difficult to record and interpret in patients with cerebral palsy and should not be attempted if the child has seizures.
MEP monitoring may be a problem in younger children, particularly those younger than 6 or 7 years of age. Use of a spatial summation technique in addition to temporal summation increased the success rate from 78% to 98% over all ages. Using this technique along with ketamine anesthesia in children younger than 6 years of age, reliable MEPs were documented in 98% (111 of 113) of children older than 6 years of age and in 86% (18 of 21) in children younger than 6 years of age. There is also evidence that younger children require a greater stimulating voltage and pulse train frequency for MEP monitoring, probably because of immaturity of the central nervous system, specifically the descending corticospinal tracts.
Spinal cord stimulation is achieved electrically and can be applied using electrodes placed outside or inside the spinal cord rostral to the area of interest. Single stimuli rather than brief pulse trains typically are used for spinal cord stimulation. This approach is not commonly used in scoliosis surgery.
Responses can be recorded anywhere distal to the area of interest. They have included the lower lumbar epidural space (i.e., epidural MEP), peripheral nerve (i.e., neurogenic MEP), and peripheral muscles using compound muscle action potential (CMAP) (see Fig. 32.7 ). Each recording site has its limitations regarding the accuracy of the information displayed and the susceptibility to anesthetic drug interference. Epidural MEPs are the least affected by neuromuscular blocking drugs (NMBDs), but they monitor only conduction in the corticospinal tract and provide no information about the anterior horn grey matter. They have a much slower response to acute spinal cord ischemia compared with myogenic responses (i.e., CMAPs). Neurogenic MEPs are also resistant to anesthetic interference but appear to not accurately measure motor conduction. Most of the spinally elicited peripheral nerve responses seen with neurogenic MEPs occur through the dorsal columns in a retrograde fashion and are sensory rather than motor. Anterior spinal cord injury has been demonstrated with normal neurogenic MEPs. CMAPs after transcranial stimulation are thought to be exclusively generated by motor tract conduction, and unlike epidural MEPs, they include the ischemia-sensitive anterior horn alpha motor neurons. These responses are very sensitive to anesthetic agents. The responses obtained with CMAPs after spinal cord stimulation also appear to contain signals that include transmission through the dorsal columns and may represent a mixed response.
One outstanding problem with MEP monitoring is deciding when and how much change in the signal is indicative of spinal cord ischemia. Some centers use the same criteria they adopted for SSEP monitoring, whereas others require a greater degree of change, such as a 75% decrease in amplitude. An amplitude decrease of 80% at one of six sites using transcranial myogenic MEP monitoring was demonstrated to have a sensitivity of 1.0 and a specificity of 0.91 when used as the sole monitor during spinal surgery. A 65% decrease in amplitude identified all postoperative motor deficits (SSEP changes identified only 43%) in children with idiopathic scoliosis. An alternative technique of measuring MEP has been described in which a minimum threshold for producing a response is established, and a significant increase in that threshold is used to signal a problem. Supportive data for this technique are lacking.
The dorsal columns may be injured without involvement of the motor tract. Occasionally, adverse changes in SSEPs occur without changes in MEPs. Because of these reports, MEP monitoring should be used in addition to SSEP monitoring rather than as a replacement. Whether SSEP monitoring alone is sufficient to reliably identify neurologic deficits remains debatable, with some institutions reporting sensitivity of 95%, specificity of 99.8%, a positive predictable value of 95%, and a negative predictive value of 99.8% for this monitoring. However, multimodal intraoperative monitoring (combination of SSEP and MEP) demonstrated improved sensitivity when compared with either modality alone.
Triggered Electromyographic Techniques
The increasing use of pedicle screws allows greater curve and rotational correction than earlier techniques but has an additional risk of direct nerve root trauma. Triggered EMGs using a monopolar needle or bipolar handheld stimulator have been described, with a threshold stimulation level of more than 8 mA considered to be normal, 5 to 8 mA to be critical, and less than 5 mA to be pathologic, indicating that there was not enough distance between the screws and the neural tissue. This technique requires monitoring rectus abdominis or intercostal muscles when used for thoracic curves.
Preoperative Assessment and Postoperative Planning
Respiratory Assessment and Planning for Postoperative Ventilatory Support
The preoperative pulmonary assessment should identify patients at increased risk for postoperative respiratory compromise. Since patients with idiopathic scoliosis generally have less compromised pulmonary function, most studies have focused on non-idiopathic patients. The rate of postoperative pulmonary complications correlates broadly with the decrease in vital capacity. Vital capacity less than 30% to 35% of predicted values indicates marginal respiratory reserve and a level at which complications and a need for postoperative respiratory support are likely. Many patients with these low vital capacities are unable to cough effectively, rendering them prone to postoperative atelectasis, pneumonia, and respiratory failure.
Studies of a mixed population of disorders (but a limited number with neuromuscular disorders) with a vital capacity less than 40% reported that despite the occurrence of short-term and middle-term pulmonary complications, these patients can be successfully discharged home, although some require prolonged postoperative ventilation. Modest numbers with a vital capacity less than 25% of the predicted value are included in these studies and do not have greater complication rates than those with greater vital capacities. Anterior or combined approaches increase the likelihood of respiratory complications, particularly owing to pleural effusion.
Children with neuromuscular scoliosis are likely to need postoperative ventilation that is often prolonged. These patients may also have abnormalities in the central control of breathing and impaired airway defense mechanisms. Impaired coordination of laryngeal and pharyngeal muscles may result in impaired swallowing and inadequate cough with increased risk of aspiration. Initial research suggested that as the vital capacity decreased to less than 35% of predicted, most patients would need a brief period of postoperative ventilation. The earlier use of nocturnal NPPV and use of NPPV in the postoperative period may alter our perception of this risk by decreasing the impact or severity of postoperative respiratory complications while allowing children with increasingly severe respiratory impairment to be considered for surgery. Scoliosis surgery can be successfully undertaken in patients with a vital capacity less than 35% of predicted, often with no more than 24 hours of planned ventilation followed by a period of noninvasive ventilation (e.g., bilevel positive airway pressure [BiPAP]). In one study ( n = 30), the overall complication rate was similar whether the FVC was greater than or less than 30%, and the average hospital stay was approximately 3 weeks (see Table 32.2 ). Tracheostomy was required in two children, and the overall pulmonary complication rate was 30% ; similar results are reported by others. It seems reasonable to anticipate using noninvasive ventilator support for several days after spine stabilization surgery in children with a vital capacity less than 25% of predicted values. Children with a mean FVC of 20% of predicted have been successfully managed with a brief period of postoperative ventilation and transition to BiPAP within 48 hours.
Whether a child should be denied surgery requires consideration of individual patient factors. The successful management of children with a vital capacity of 15% to 20% of predicted has been reported, although the sample size was small. Although the risk of an unsuccessful outcome can increase at this level of pulmonary dysfunction, individual circumstances may justify the risk. The successful introduction of perioperative NPPV will likely lead to children who were previously considered unsuitable for surgery now being offered surgery, challenging the established limitations.
Cardiovascular Assessment
Many children with complex cardiac comorbidities can successfully undergo scoliosis surgery as a result of improvements in understanding, monitoring, anesthesia, and surgical techniques. A greater need for blood transfusion should be expected. A preoperative curve greater than 80 degrees is a risk factor for major complications in children who have had congenital cardiac defects corrected. Children with residual cardiac abnormalities will require prolonged stays in the intensive care unit and hospital. Those with single ventricle or Fontan physiology have increased morbidity and mortality. Increased bleeding is almost always a problem because of high venous pressures; the need for inotropic support and the occurrence of arrhythmias and pleural effusions are common.
Muscle disorders may affect the myocardium and the skeletal system. Children with DMD develop a cardiomyopathy in the second decade that may be difficult to evaluate because the child is wheelchair bound by that age. Sinus tachycardia is an early manifestation. Cardiac function deteriorates during early adolescence as more than 90% of adolescents with DMD have subclinical or clinical cardiac involvement. Echocardiography is an essential aspect of the preoperative evaluation of any wheelchair-bound patient presenting for scoliosis surgery (see also Chapters 17 and 23 ). Cardiac magnetic resonance imaging may be better than echocardiography for assessment of children with DMD.
Postoperative Pain Management
Scoliosis surgery is associated with severe pain that lasts for at least 3 days. Effective analgesia minimizes postoperative respiratory complications by allowing deep breathing, chest physiotherapy, early ambulation, and rehabilitation. Postoperative pain may be managed with systemic or epidural analgesics. A multimodal approach is likely to be most effective.
Intraoperative Intrathecal and Intravenous Opioids
Intraoperative intrathecal morphine (2–5 µg/kg) has provided potent analgesia during the first 24 hours after spinal fusion in children. Intrathecal morphine also decreases the amount of remifentanil required intraoperatively, contributing to less pain when remifentanil is discontinued. However, perioperative administration of IV morphine, when using remifentanil as part of the anesthesia technique, does not result in any measurable benefit.
Methadone (0.2 mg/kg) decreases pain scores and opioid requirements for 36 hours in children undergoing surgery, but it seems to have been ignored in modern practice. This drug is used in adult spinal surgery and reports of its use in children are increasing. An IV bolus (0.25 mg/kg) followed by an infusion (0.1–0.15 mg/kg per hour) for 4 hours during spinal surgery has been proposed to maintain adequate plasma concentrations for 24 hours.
Nonsteroidal Antiinflammatory Drugs
NSAIDs, but not acetaminophen, impair fracture healing in animal models. Cyclooxygenase-2 (COX-2) activity plays an important role in bone healing, and the use of NSAIDs decreases osteogenic activity that may increase the incidence of nonunion after spinal fusion. The effect on osteogenic activity is dose dependent and reversible. Similar effects have not been demonstrated in humans and the use of these drugs after scoliosis surgery varies in different parts of the world. Nonetheless, based on animal evidence, NSAIDs should be used with caution and in consultation with the surgeon during the first 3 to 5 days after scoliosis surgery.
Systemic Analgesics
Morphine remains the mainstay of systemic analgesic regimens. Morphine infusions of 20 to 40 µg/kg per hour are required during the first 48 hours after surgery. Achieving a balance of effective analgesia while avoiding sedation can be difficult in children with neurodevelopmental delay. Regular evaluation of these children is important if complications are to be avoided. Patient-controlled analgesia (PCA) is appropriate for children older than 6 to 7 years of age. It can be used with a typical bolus dose of 20 µg/kg and a lockout interval of 5 to 10 minutes. The use of a background morphine infusion may be effective in some patients, although its inclusion is controversial. Our preference is to use a nighttime background infusion at 5 to 10 µg/kg per hour but to use PCA alone during the day (see also Chapter 44 ). The addition of acetaminophen improves analgesia but does not decrease opioid requirements. Nurse- and parent-controlled analgesia are effective if the child is too young or unable to use PCA. Intrathecal morphine plus PCA appears to offer the optimal combination of effective analgesia and minimal adverse effects in patients with idiopathic scoliosis compared with PCA morphine alone or epidural morphine. The demands/deliveries ratio of PCA is predictive of increased opioid requirements, with a ratio greater than 1.5 associated with greater pain scores, opioid-related adverse effects, and duration of hospitalization; a ratio greater than 2.5 suggests a benefit from switching opioids.
Low-dose ketamine infusion (0.05-0.2 mg/kg per hour) has been used as an adjunct to morphine infusions or PCA, although its role is debated. Ketamine may be initiated intraoperatively (initial infusion of 5 µg/kg per minute, decreasing to 2 µg/kg per minute at the end of surgery) as part of the anesthetic technique to minimize the hyperalgesia reported after high-dose remifentanil infusions. A postoperative 72-hour ketamine infusion did not decrease morphine consumption or pain scores. Ketamine added to morphine PCA has produced mixed results, with no clear beneficial effect in orthopedic surgery, despite such evidence being apparent for thoracic surgery. If added to PCA, the optimal combination of morphine/ketamine is a 1 : 1 ratio. Although scoliosis is a very painful surgery, it is probably best to reserve the use of ketamine for those with significant preoperative pain or morphine-resistant pain.
Gabapentin and pregabalin may provide some benefit with an opioid-sparing effect, although postoperative nausea and vomiting benefits are limited. Gabapentin (15 mg/kg followed by 5 mg/kg three times daily for 3 days) reduced morphine consumption by about 30% during the study period but without any improvement in morphine's adverse effects. Improved pain relief was observed only until the morning after surgery. All the effects of gabapentin for postoperative pain may have been overestimated by statistically significant small study effects.
Epidural Analgesia
Continuous epidural analgesia using single- and double-catheter techniques may provide effective analgesia after spinal surgery. The single-catheter technique using bupivacaine-fentanyl and sited at T6-7 for patients undergoing a mean 12-level scoliosis surgery resulted in analgesia similar to that of PCA but with more postoperative nausea and vomiting and pruritus. Bowel sounds returned earlier in the epidural group, but liquid intake and hospitalization time were similar. Similar results were reported with a bupivacaine-morphine combination in patients undergoing 10-level spinal fusions. Full diet and discharge from hospital were achieved one-half day earlier with the epidural technique than with PCA. A retrospective review of more than 600 patients treated with an epidural or PCA for analgesia after scoliosis surgery that involved an average 8.5 fused segments confirmed the effectiveness of epidural analgesia. In that study, a bupivacaine-hydromorphone epidural combination effectively controlled the pain, although it was associated with more complications. Respiratory depression and transient neurologic changes were the most common complications observed. Thirteen percent of patients with an epidural catheter required discontinuation of the epidural, most commonly for inadequate pain relief. Effective analgesia and a large incidence of postoperative nausea and vomiting and pruritus have been features of studies that combined bupivacaine and morphine.
Patient-controlled epidural analgesia (PCEA) has been successfully used in children older than 5 years of age for orthopedic surgery and thoracotomies. In scoliosis surgery, the pain score with PCEA with bupivacaine and hydromorphone was slightly superior to that with PCA, although there was a 37% failure rate with the former. PCEA with a single- or double-catheter technique (as discussed later), depending on the number of spinal segments involved, with a combined bupivacaine-fentanyl-clonidine solution effectively controlled pain with a relatively small incidence of complications.
Improved pain control and bowel function with decreased adverse effects may be possible by using a double-epidural technique using moderate amounts of fentanyl and clonidine with local anesthetics. Double-epidural techniques use an upper catheter positioned in the upper to middle thoracic segments and a lower catheter at the upper to middle lumbar level. This technique improved pain control and was associated with fewer gastrointestinal adverse effects when compared with a single epidural catheter and morphine PCA.
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