Perioperative Management of Patients With Neuromuscular Disorders

Introduction

Patients with neuromuscular disorders (NMDs) are at increased risk for complications during or immediately after surgery; they share a common risk of respiratory failure, atelectasis, and pneumonia and may have longer hospital stays and increased risks of morbidity, as compared with those without neuromuscular diseases ( ; ).

Hypoventilation can occur due to respiratory muscle weakness. Increased chest wall compliance in younger patients can contribute to atelectasis. Upper airway obstruction is common, due to pharyngeal and laryngeal muscle weakness/discoordination. Macroglossia, as in the case of Duchenne muscular dystrophy (DMD) or Pompe disease, can complicate intubation and contribute to airway obstruction.

Aspiration is a significant risk for these patients. Oropharyngeal weakness and incoordination, as well as failure to protect the airway opening, can lead to aspiration, which can be compounded by abdominal muscle weakness with an ineffective cough.

The patient’s characteristics may vary with localization of the primary lesion ( ), and those with upper motor lesions are more likely to be associated with chest wall immotility and increased tone, whereas lower motor neuron lesions are more likely to be associated with chest wall mobility and flaccid paralysis.

Characteristics of Physiologic Abnormalities

Those with NMDs typically have inspiratory and expiratory muscle weakness, but all aspects of the respiratory physiology could be altered. Early, children could have excessive chest wall compliance. Some have chest wall deformity ( ), such as pectus excavatum. Development of scoliosis can lead to decreased chest wall compliance ( ), as can intercostal muscle fibrosis (commonly seen in DMD).

Respiratory control is also altered in many patients, particularly in those with mitochondrial myopathy ( ).

With chronic carbon dioxide retention, the characteristic hypercarbic ventilatory response can be diminished. Without hypoventilation, however, even patients with significant weakness do not necessarily develop a blunted respiratory drive ( ). Chronic respiratory acidosis from hypoventilation is offset by a compensatory metabolic alkalosis which in turn blunts respiratory drive. Sleep disordered breathing is common ( ).

Recognition of impaired cough is also key to the prevention of respiratory complications in neuromuscular diseases. Each phase of cough can be affected by weakness ( ). The inspiratory phase of cough is affected by diaphragm weakness. Glottic closure is limited by bulbar dysfunction, and the expiratory phase of cough is restricted from both thoracic and abdominal muscle weakness.

Preoperative Management

Prior to surgery, a patient with significant neuromuscular weakness should undergo pulmonary assessment. The simplest pulmonary test is a pulse oximetry, and if this reveals SpO ₂ under 95%, measurement of carbon dioxide in the blood or end-tidal (or transcutaneous) CO ₂ should be obtained ( ). When conducting blood gas measurement, sampling from the arterial circulation is preferable as it permits A-a gradient calculation, but capillary gas measurement can be reliable, especially in younger patients. Hypoxemia in the presence of normal carbon dioxide levels, particularly in those individuals with neurocognitive disabilities, is strongly suggestive of ventilation-perfusion mismatch, and suggests chronic aspiration or atelectasis.

Pulmonary function testing (spirometry, plethysmography, and measurement of CO ₂ ) should be performed in patients capable of participation. The risks and complications of pediatric neuromuscular diseases have best been described in DMD. Forced vital capacity (FVC) has predictive value in DMD and can be used to assess risk for respiratory complications. DMD patients with an FVC under 50% of predicted are at increased risk of respiratory complications when undergoing a procedure, and those with an FVC of under 30% are at higher risk ( ). Vital capacity can also be shown to predict daytime ventilation in patients with DMD. noticed that vital capacity below 680 mL was very sensitive to threshold for detection of daytime hypercapnia.

In patients with NMDs with the risk of hypoventilation as assessed by FVC, the clinician should consider perioperative training with noninvasive positive pressure ventilation (NPPV). Perioperative training can increase the likelihood of successful postoperative NPPV use ( ; ). Patients with an ineffective cough, history of recurrent pneumonia, and loss of expiratory muscle strength, as measured by maximum expiratory pressure (MEP; i.e., below 60 cm of H ₂ O) ( ), should receive preoperative training with a mechanical insufflation-exsufflation device ( ).

Cardiovascular Assessment

Cardiovascular involvement occurs in different neuromuscular diseases, particularly DMD, and some limb-girdle dystrophies and may have dilated cardiomyopathy, and dysrhythmias and surgery could predispose to heart failure ( ). Preoperative cardiology consultation with echocardiography and electrocardiogram is especially important in patients with DMD. Treatments with angiotensin-converting enzyme inhibitors, beta-blockers, and even corticosteroids can be beneficial. Cardiovascular dysfunction (particularly dysrhythmia) is also common in myotonic dystrophy (DM) and accounts for 20% of deaths in these patients.

Nutritional Assessment

Malnutrition adversely affects respiratory muscle strength ( ). It is reasonable to suggest that a cachectic patient with these disorders is not an appropriate candidate for surgery, particularly elective surgery.

Malnutrition puts the patient at risk of perioperative loss of skin integrity due to pressure ulceration, and patients may need a feeding tube prior to consideration for surgery such as spinal fusion.

Another cause of low weight is chronic respiratory failure, and patients with respiratory failure lose weight either due to insufficient intake with chronic dyspnea or due to increased energy expenditure with increased work of breathing ( ; ; ). Malnutrition in some patients with neuromuscular diseases may be an indication for implementation of NPPV ( ) and consideration for gastrostomy placement.

Advance Directives

Many neuromuscular diseases are progressive and fatal, and goals of care should be discussed in detail, and advance directive status should be well documented ( ).

Intraoperative Management

Major surgery in patients with neuromuscular diseases involving general anesthesia requires a well-trained team ( ), including an anesthesiologist that should, particularly in these disorders, have experience with these patients, and the respiratory therapist should have experience in pediatrics and NPPV and airway clearance techniques. An intensive care unit (ICU) should be readily accessible to manage a potentially prolonged postoperative course ( ). Sedation should be performed by an anesthesiologist and full monitoring ( ; ). In addition to pulse oximetry and cardiac monitoring, the ability to measure carbon dioxide levels and end-tidal transcutaenous CO ₂ is advised.

Respiratory Support During Induction Maintenance and Recovery

Intubation in these patients can be affected by abnormalities of the airway, for example, those with Duchenne’s dystrophy who have an enlarged tongue. Neck and shoulder rigidity can also limit the extension of necks. Jaw ankylosis is also common in DMD, which can make intubation difficult. A protocol for respiratory support should be followed.

Anesthesiologists should consider interoperative noninvasive ventilation depending on the procedure ( ; ), and neuromuscular patients with chronic respiratory insufficiency may benefit with additional ventilation support during induction and recovery.

Manual positive pressure breaths can be delivered via resuscitation bags if there is a prolonged period of recovery, and the patient may require full noninvasive respiratory support from a conventional ventilator ( ; ), depending on the degree of baseline respiratory compromise as measured by FVC, for example. It is reasonable to expect that patients will need to be extubated directly to NPPV, commonly via full face mask ( ; ).

Postoperative Management

Patients with respiratory insufficiency, including those who use NPPV at baseline, are more likely to require extubation to NPPV ( ; ). NPPV can be weaned postoperatively to baseline levels, as tolerated ( ). Return to baseline support often takes much longer than the immediate recovery from anesthesia ( ). This is particularly seen in patients with DM.

Surgeries that affect chest wall shape and have significant postoperative pain such as spinal fusion may be beneficial with support above baseline ( ). In addition, narcotic pain medication affects respiration and cough. NPPV can help to avoid the need to prolong intubation or tracheostomy in high-risk patients ( ).

If the patient uses NPPV at home, it is reasonable to attempt to use this on interphase in the hospital as well ( ; ). If a patient is extubated to NPPV, it is advisable to perform it in the ICU ( ).

It is advisable to assess levels of carbon dioxide in the blood or with end-tidal or transcutaneous CO ₂ measurement prior to initiating increasing levels of oxygen supplementation. Neuromuscular patients with respiratory insufficiency are at high risk of hypercapnia ( ; ; ). The optimal management of hypercapnia is respiratory support rather than supplemental oxygen, which can suppress respiratory drive and lead to respiratory failure.

An escalating oxygen requirement in patients with neuromuscular diseases can also suggest other etiologies. Atelectasis is common in postoperative patients ( ; ). Aggressive treatment of atelectasis includes use of mechanical insufflation/exsufflation. Aspiration can increase with hypoxemia ( ) and necessitates assistive cough therapy.

Sedating analgesics may have an additive effect on baseline respiratory insufficiency in patients with neuromuscular disease, but adequate pain management is essential ( ; ), even if sedating analgesia necessitates prolonged intubation or NPPV use. It is worth considering other measurements such as nerve blockade that can reduce need for analgesia ( ).

Assistive Cough and Airway Clearance

Many patients with neuromuscular disease have an ineffective cough. Inadequate cough strength can be indicated by low peak cough flow or peak flow on spirometry and diminished MEP on pulmonary function testing ( ; ).

Patients with impaired cough should have access to a mechanical insufflation and exsufflation device. This form of augmented airway clearance provides cycles of positive pressure followed by negative pressure. Patients and families need to be introduced to the idea of mechanical insufflation-exsufflation prior to surgery.

Cough assistive technology is also used when surgical pain limits effective postoperative cough, and it is generally well tolerated even in patients who have undergone thoracic and abdominal surgeries.

Impaired mucociliary clearance should be considered in some neuromuscular patients. In one study, 66% of patients with chronic pulmonary aspiration were found to have bronchiectasis ( ). For these patients, chest physiotherapy is helpful, such as use of a high-frequency chest wall compression vest device if the procedure allows this therapy. Newer airway clearance therapies to augment mucociliary clearance include intrapulmonary percussive ventilation (IPV®, Percussionaire) and the MetaNeb® (HillRom) system (a high-frequency airway oscillation and positive expiratory pressure device used in hospitalized patients who cannot tolerate chest wall compression therapy).

There are some studies that suggest benefit with the use of chest wall vest therapy in the mechanically complex patient, but its use may be limited by operative considerations in cases of abdominal or thoracic surgery ( ).

Cardiovascular Management

An expert panel in the American Academy of Pediatrics has recommended perioperative cardiac evaluation in patients with DMD ( ), and this recommendation is valuable in the preoperative evaluation of all patients with significant weakness.

Neuromuscular patients with normal perioperative ECG and echocardiogram are still at risk of cardiac complications during surgery ( ). Thorough evaluation should be considered and precautionary observation as management.

Cardiovascular complications are well-established complications in myopathies. Fluid shifts associated with surgery can increase the likelihood of heart failure ( ). Judicious management of fluid balance in these patients is essential.

Nutritional Management

Patients with NMDs are often at risk of gastrointestinal dismotility ( ). Following surgery, patients often are immobile and take opioid analgesics, further limiting motility, so establishing a bowel regimen is necessary. Poor nutrition aggravates baseline respiratory insufficiency ( ). Postoperative consideration of enteral feeding tubes or parenteral nutrition can help with these complications.

In the following sections, we will discuss specific issues related to particular NMDs.

Perioperative Management in Specific Neuromuscular Disorders

Motor Neuron Diseases

Adults with motor neuron diseases, particularly amyotrophic lateral sclerosis (ALS), may undergo percutaneous endoscopic gastrostomy (PEG) tube placement and tracheostomy for management of the disorder. They also may undergo general surgical procedures common in those in late adulthood, and these should be performed under careful monitoring.

Dysphagia is a common symptom in patients with ALS, usually developing at about the same time as respiratory insufficiency; for this reason, pulmonary function should be assessed and oxygen saturation carefully monitored during PEG tube placement ( ; ; ), which requires sedation. The procedure is recommended to be done early and in patients whose vital capacity is more than 50% of predicted ( ), although there are insufficient data to suggest a specific timing ( ). The use of noninvasive ventilation in those who are at risk and do not have a tracheotomy appears safe and reduces complications ( ). PEG tube placement does not prevent aspiration pneumonia, but it does improve the patient’s quality of life and nutritional state. In our center, we perform the procedure in the inpatient setting, followed by at least 24 hours of intravenous (IV) fluids until bowel sounds are present and tube feeding can be started.

Tracheostomy should be discussed early, including its complications, and performed in patients who do not tolerate noninvasive respiratory assistance or have inadequate ventilation. The procedure helps to reduce dead space and improves suctioning. Tracheostomy should be done in the hospital setting after proper discussion with the patient and family concerning long-term care and complications, which include infections, excessive bleeding, and mucus plugs. Patients should be observed for at least 24 hours after the initiation of respiratory assistance ( ) (see also Chapter 12, Chapter 2 , and 13 ).

Spinal Muscular Atrophy

Patients with type 1 spinal muscular atrophy (SMA) develop respiratory failure early, and tracheostomy and PEG tube placement are done in those whose parents opt for aggressive management. These procedures and their complications should be discussed as soon as the diagnosis is made. These patients have difficulty swallowing and have an increased risk of complications ( ), and aspiration and nutritional failure are very common. It is reasonable to consider parenteral gastrostomy tube and fundoplication prior to major surgeries such as spinal fusion ( ; ). If necessary, a laporoscopic approach should be considered ( ; ).

Patients with types 2 and 3 SMA may develop respiratory failure later, but tracheostomy and PEG tube placement should be discussed early and performed as soon as they appear necessary ( ). This approach has been shown to prolong survival ( ).

Scoliosis surgery is done in patients with types 2 and 3 SMA, but those with type 1 SMA usually die before the procedure is necessary. The surgery should be performed before the curvature has become severe. Those with vital capacity below 35% usually have a poorer prognosis and might require permanent tracheotomy ( ). Surgical risks are increased for those with frequent respiratory infections ( ). Other orthopedic procedures that may be required by patients with SMA, such as correction of hip deformities, are discussed in Chapter 13, Chapter 9 . These procedures require careful preoperative and postoperative monitoring and management with respiratory therapy, including the use of incentive spirometry, with monitoring of pulse oximetry and arterial blood gases when necessary. Prompt mobilization is recommended.

Friedreich Ataxia

Individuals with Friedreich ataxia may undergo surgery to correct the orthopedic deformities that accompany the disease, such as surgical correction of foot abnormalities to improve ambulation ( ). Scoliosis may cause respiratory complications, and scoliosis surgery is the most important invasive procedure performed in this disorder. It is usually done on individuals who are wheelchair bound, have vital capacities at least 40% of normal, and have a curvature of more than 60% of normal ( ).

Perioperative care of those with Friedreich ataxia is further complicated by diabetes mellitus and hypertrophic cardiomyopathy that frequently accompany the neuromuscular symptoms. Thus, preoperative care of these patients requires not only oximetry but also cardiac assessment and monitoring as well as frequent electrolyte and glucose measurements. Other, more generalized complications are not uncommon in this population; these include aspiration pneumonia and pulmonary embolism ( ).

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