24.1.1 Mechanical Ventilation and Pulmonary Support

Patients with idiopathic scoliosis are often healthy preoperatively, and therefore experience a complication-free surgery. As a result, they commonly tolerate extubation immediately postoperatively or on the same day of surgery. For those patients with neuromuscular scoliosis, comorbidities including cerebral palsy, seizure disorder, congenital anomalies, cardiac anomalies such as Fontan patients, myopathies, and muscular dystrophies such as Duchenne’s muscular dystrophy increase the likelihood that they will require respiratory support postoperatively in the ICU.

Mechanical ventilation in the postoperative period may be required for a variety of reasons including airway control, inappropriate oxygen delivery, abnormal lung function, inadequate cardiac output and fluid overload, significant abdominal distension, residual anesthesia, and neurologic complications. It has been shown that scoliosis surgery produces immediate and transient decrease of up to 40% in vital capacity (VC) in almost all patients undergoing surgery. ¹ The reasons for this decline are many, including the duration of the operation, patient positioning, and surgical trauma to various muscle groups (especially with thoracotomy). Given that the VC is usually much lower than normal before surgery, any further reduction can easily lead to respiratory failure. This risk is significantly higher in patients with neuromuscular scoliosis.

An early goal of ICU care is to proceed with a safe and expedited wean from mechanical ventilation. A systematic review of the criteria for extubation is performed (Table 24‑3). Chest radiographs, blood gas sampling, pulse oximetry, end tidal carbon dioxide, lung mechanics, and physical examination are the parameters used to determine the weaning from mechanical ventilation and pulmonary adequacy. Dexamethasone is sometimes initiated to prevent airway edema, while diuretics may be started to achieve a negative fluid balance prior to extubation.

After weaning from mechanical ventilation, aggressive pulmonary toilet should be initiated to prevent atelectasis, which is more commonly seen in patients with neuromuscular scoliosis or myopathies. Patients at risk for postextubation atelectasis are weaned to noninvasive ventilation (bilevel positive airway pressure [BiPAP], nasal continuous positive airway pressure [NCPAP]), frequent chest percussion treatments and postural drainage are provided, and routine chest radiographs are performed to assess lung expansion. The efficacy of noninvasive ventilation in prevention of tracheal intubation due to respiratory failure is well supported. ^{2 ,​ 3} Patients who require noninvasive ventilation at home should be placed on noninvasive ventilation via BiPAP or NCPAP immediately following extubation. Over the course of a few days, the noninvasive ventilation can be weaned as patient strength improves and pain is reduced.

Pleural effusions may develop in response to the fluids administered in the operating room. A chest tube may be placed in the operating room or a thoracentesis may need to be performed prior to extubation for resolution of the pleural effusion and optimization of functional residual capacity. Postsurgical thoracotomy complications including air leak, hemothorax, and persistent chest pain ⁴ are commonly observed, whereas chylothorax has been noted much less frequently and is most often associated with an anterior surgical approach. ⁴

Halo placement and cervical fusion pose unique challenges to the anesthesiologists and intensivists while securing an airway. Fixed position, limited access to the face, and immobilization of neck due to halo and cervical fusion make it difficult to visualize the larynx, thus increasing the level of difficulty for successful tracheal intubation, as well as increasing the upper airway obstruction following tracheal extubation. Patients placed in a halo vest sometimes experience a decrease in VC that may reduce their pulmonary reserve and ability to tolerate any pulmonary insult. ⁵

Prior to tracheal extubation, patients must be able to maintain their airway, demonstrate adequate gag reflex and cough, and be able to manage secretions, as well as demonstrate adequate strength to support spontaneous respirations. The intubation and anesthetic record should be reviewed prior to extubation. For patients with pre-existing pulmonary disease or airway control issues, preoperative PFTs, chest X-rays, and medications should be reviewed. Prolonged mechanical ventilation can be necessary in patients with severe restrictive lung disease prior to scoliosis repair. Based on these considerations, if it has been determined safe, experienced personnel (intensivists, anesthesiologists, ear nose throat specialists if difficult airway) should be readily available at the time of extubation. If there is concern that the patient’s trachea may need to be re-intubated due to weakness, excessive secretions, or known future procedures such as staged repair, extubation should be postponed. It should be noted that one should have a low threshold for re-intubating these patients under more controlled and elective circumstances. In these situations, a fiberoptic bronchoscope, glidescope, or laryngeal mask airway may be helpful.

24.1.2 Cardiac Support

Support of the cardiovascular system is directed at optimizing cardiac output and oxygen delivery. This is achieved by optimization of preload, afterload, and inotropy, and is guided by invasive, noninvasive, and laboratory monitoring.

Requirement for cardiac support in patients with no associated heart diseases, such as cardiomyopathy, is minimal. Hypovolemia is the most commonly recognized complication following scoliosis surgery and results from inadequate replacement of intraoperative fluid losses, as well as from fluid third spacing. Unless there are complications associated with loss of motor evoked potential (MEP) and somatosensory evoked potential (SSEP) in the operating room, patients do not routinely require vasopressor support.

For patients who experienced loss of MEP and SSEP during scoliosis surgery, support of blood pressure is achieved using vasopressors and fluid replacement to optimize nerve and spinal cord perfusion. SSEP and MEP are particularly sensitive to blood pressure changes and can be used quite effectively to titrate the degree of hypotensive state that the spinal cord will withstand. ⁶ At the time of transfer to the pediatric intensive care unit (PICU), anesthesiologists will report the use of vasopressor support intraoperatively, and will note the mean arterial pressure utilized to preserve evoked potentials during surgery. In these patients, the mean arterial blood pressure is usually maintained at a slightly higher-than-normal value by administering intravenous fluids, intravenous calcium, and vasopressor therapy. Dopamine is commonly used; however, epinephrine and norepinephrine can be added if there is a need to increase systemic vascular resistance.

Patients with pre-existing heart disease, such as Duchenne muscular dystrophy, are maintained on their preoperative medications. It is pertinent to review the preoperative echocardiogram and utilize invasive and noninvasive monitoring to follow hemodynamics. Prior to induction of anesthesia, every effort should be made to obtain a baseline echocardiogram so that baseline cardiac function may be well understood and to determine what cardiac support the patient will need in the perioperative period.