4.2.1 Preoperative Management

Preoperative evaluation and optimization of comorbidities is critical and hence a multidisciplinary team approach is highly recommended. In our center, the multidisciplinary team is composed of a deformity surgeon, pediatrician, pediatric respiratory physician, cardiologist, experienced anesthetist, and physical therapist. Diagnostic studies routinely include complete blood count, basic metabolic panel, coagulation studies, nutritional studies, gastrointestinal assessment, pulmonary function testing if child is cooperative, or polysomnogram and two-dimensional echocardiography.

Particular attention is paid to the respiratory systems of patients with neuromuscular scoliosis, as the Healthcare Cost and Utilization Project Kids’ Inpatient Database (HCUP KID) showed that patients with neuromuscular scoliosis were 10 times more likely to aspirate and require mechanical ventilation postoperatively, and 5 times more likely to develop pneumonia than patients with AIS undergoing posterior spinal fusion. ^{3 ,​ 4} Pulmonary dysfunction is usually greater in severity and more frequent than in patients with AIS. The high incidence of respiratory complications is due to the frequent involvement of respiratory and pharyngeal musclesas well as the high incidence of sleep apnea in children with neuromuscular scoliosis. ⁵ Progressive deformities cause restrictive lung disease and aggravate chronic respiratory insufficiency. The administration of anesthetic agents that depress the respiratory system contributes to this decompensation, particularly in patients with disturbed neuromuscular transmission. Preoperative optimization of the respiratory system may also be a useful adjunct in patients with neuromuscular scoliosis awaiting spinal surgery. Khirani et al placed 13 patients with planned spinal surgery in a respiratory training program in which noninvasive positive pressure ventilation and mechanical insufflation/exsufflation were used for 30 minutes per day for at least 1 to 4 weeks before surgery. ^{6 ,​ 7} No postoperative respiratory complications were observed in any of the patients, highlighting the potential role of preoperative optimization prior to spinal surgery.

In patients with neuromuscular scoliosis, cardiac arrest is the second most common reason for perioperative and postoperative mortality. ^{2 ,​ 8} Cardiac muscle and conducting pathways are often adversely affected in neuromuscular spinal, even though many patients are asymptomatic. ⁸ neuromuscular spinal patients are often unaware of this underlying cardiac anomaly, as they are unable to exercise vigorously, owing to the muscle disorder. Understanding their functional cardiac reserve using an echocardiogram is important as perioperative and postoperative stress may induce failure in these vulnerable patients. Volatile anesthetics are cardiodepressive because they reduce the availability of both myoplasmic calcium and also decrease the responsiveness of the contractile filaments to calcium. ⁹ Volatile anesthetics may also cause arrhythmia due to the sensitization of the heart to catecholamines and from their inhibitory effects on voltage-gated potassium channels, which are essential for membrane repolarization. Prolongation of the QT interval, in addition to hyperkalemia produced by suxamethonium-induced rhabdomyolysis, may contribute to this arrhythmia. ^{8 ,​ 10} A cardiology examination, in addition to an electrocardiogram, chest radiograph, and echocardiogram would help identify these susceptible patients preoperatively. Patients with a cardiomyopathy should be optimized preoperatively, with the European Alliance of Muscular Dystrophy Associations recommending treatment for 4 months prior to surgical intervention. ¹¹

Bowel function requires assessment, as wheelchair-bound patients have bowel dysmotility. A child with neuromuscular spinal who is constipated with a heavily filled bowel will have reduced pulmonary function. Adequate nutrition is also important, as malnutrition often accompanies children with cerebral palsy (CP) and dystrophic dystrophies, due to the dysfunction of the muscles of mastication and swallowing, in addition to reflux esophagitis. Malnutrition is associated with poor wound healing, infection, fatigue, and apathy.

4.2.2 Perioperative Management

A preoperative assessment for lower and upper extremity contractures guides intraoperative patient positioning. Prone positioning on an open Jackson table is performed for all cases. These frame type spine tables are mandatory to accommodate the low positioning of the hips and knees in the presence of flexion contractures that are routine in these patients. In the presence of flexion contractures of the shoulders and elbows, the arms can be tucked at the sides or placed directly on the frame. An ample number of foam and gel pads must be used to avoid pressure sores.

Neuromuscular spinal surgeries are associated with greater blood loss than AIS surgeries. The authors routinely obtain central line, peripheral line, and arterial line accesses for all cases.

Temperature measurement and control is also extremely important, as patients with neuromuscular spinal are susceptible to thermodysregulation. ⁵ Temperature probe is recommended for all cases. Hypothermia may develop due to reduced heat production from immobile muscles, which may be compounded by the peripheral vasodilation that occurs with general anesthesia. Patients should be normothermic prior to induction, and their temperature maintained with forced air warming systems and warmed fluids, if necessary. ¹² In some neuromuscular disorders, hypothermia can exacerbate myotonia and potentially aggravate rhabdomyolysis. Hyperthermia may occur secondary to increased muscle activity, associated with myotonias and malignant hyperthermia. A high index of suspicion should exist for patients with muscular dystrophies and myotonias for concomitant malignant hyperthermia. Unexplained tachycardia with an increase in end tidal carbon dioxide concentration should alert the anesthetist to a potential hyperthermic complication. ^{13 ,​ 14}

The use of volatile agents for general anesthesia is controversial. Volatile agents have been contraindicated in the past because of their association with malignant hyperthermia, in conditions such as Duchenne muscular dystrophy (DMD). Although this link is now thought to be tenuous, a total intravenous anesthetic with a clean anesthetic machine is recommended to avoid the development of rhabdomyolysis. ¹⁵ Nitrous oxide, potent inhalation agents, and muscle relaxants have been demonstrated to compromise neurophysiological signals. ^{16 ,​ 17} In addition to this, cardiovascular decompensation may be caused by volatile agents due to their cardiodepressive and arrhythmogenic properties. Intravenous anesthesia offers many benefits to patients with neuromuscular disorders, as the agents are short acting. However, care must be taken due to the potential for autonomic dysfunction and cardiovascular collapse.

Perioperative antibiotic coverage with clindamycin with repeat doses every 6 hours and changes of gown and gloves after 3 to 4 hours are routinely performed. ¹⁸

4.2.3 Postoperative Management

Patients with neuromuscular disorders in the postoperative period are at an increased risk of cardiorespiratory complications, autonomic dysfunction, myotonias, and rhabdomyolysis. ^{2 ,​ 6} Respiratory failure is the most common cause of death in these patients, with bulbar muscle weakness leading to aspiration, poor pharyngeal and respiratory muscle tone, and obstructive sleep apnea all contributing to the development of this problem. ⁶ Extubation should be achieved as early as possible to prevent further weakening of the respiratory musculature but considered against the risk of atelectasis, aspiration, infection, and respiratory failure. The rate of extubation in the operating room (OR) is variable and highly patient dependent, but it is generally around 70 to 80% at our institution. The decision for immediate postoperative extubation should take into consideration the patient’s baseline pulmonary status, the difficulty of intubation at the outset of surgery, and the availability of a team skilled at obtaining an emergent airway. Patients with DMD, preoperative FVC < 30% of predictive, hemodynamic instability and prolonged surgery greater than 8 to 10 hours are more prone to require postoperative ventilator support. Cardiomyopathies and conduction abnormalities may predispose to morbidity and mortality in the postoperative period. ^{2 ,​ 3} As a result, a patient with neuromuscular spinal should be treated as a high cardiac risk, with appropriate invasive monitoring in situ, and inotropic drugs administered if required.

Autonomic dysfunction is not uncommon and can be responsible for hypotension on induction. Gastric dysmotility can lead to regurgitation and aspiration during general anesthesia. ¹⁹ Sympathomimetic drugs need to be available for use, but the doses modified due to the increased sensitivity of alpha and beta receptors in patients with NMS. Myotonic contractures can occur with the dystrophic and nondystrophic myotonias. The contractures are caused by repeated action potentials that lead to sodium influx and chloride efflux, rendering the neuron hyerexcitable. ¹⁰ Myotonic contractures can be caused by a number of agents including opioids, anticholinesterases, and succinylcholine. Environmental factors may also be responsible, including acidosis, alterations in ambient temperature, and shivering. If a myotonia is triggered, agents that block sodium channels, such as antiarrhythmic agents and local anesthetics, should be administered.

Rhabdomyolysis may be associated with volatile agents, myotonias, and depolarizing neuromuscular blocking agents. ¹⁵ Signs of rhabdomyolysis include metabolic acidosis, hyperkalemia, myoglobinuria, and elevated creatinine kinase. Treatment involves cessation of the causative agent and correction of the hyperkalemia.