Abstract
Caring for patients with neuromuscular disease (NMD) is challenging. Respiratory care is of the utmost importance because it is a major determinant of quality of life and survival. Noninvasive ventilation (NIV) is one of the few modalities that has shown survival benefit in the NMD patient population. Newer modes with smart technologies are being developed to assist in better ventilation. Some noninvasive methods have shown success in the management of sialorrhea, which is of paramount importance in the initiation of NIV. This review will summarize the management of respiratory symptomatology in patients with NMD with recent advances made in NIV.
- ventilation
- noninvasive ventilation
- neuromuscular weakness
- chronic respiratory failure
- amyotrophic lateral sclerosis
Introduction
Respiratory muscle weakness is common in patients with neuromuscular disease (NMD).1 Expiratory, inspiratory, or upper airway muscles can be compromised, which can lead to chronic respiratory failure. Dyspnea is the most common presentation, although the pathophysiology may vary depending on the location of the lesion (eg, upper vs lower motor neuron lesion).2 Noninvasive ventilation (NIV) could prolong survival and improve quality of life. A multidisciplinary approach to symptom management not only reduces the hospitalization but also improves the quality of life for these patients.
Sialorrhea
Sialorrhea refers to excessive salivation caused either due to excessive production of saliva or difficulty in saliva clearance. Patients with NMD develop sialorrhea primarily due to bulbar dysfunction with poor coordination of the tongue and palate. This could result in poor performance with NIV and lead to intolerance of a life-prolonging treatment. Anticholinergics form the bedrock of the management of sialorrhea because they block the cholinergic input to the salivary glands and help in drying up the secretions. The most commonly used medications include topical atropine, oral hyoscyamine sulfate, nebulized or subcutaneous glycopyrrolate, oral amitriptyline, and scopolamine patches.3 Atropine and hyoscyamine are efficacious, but they cross the blood–brain barrier and can cause cognitive side effects. Glycopyrrolate is preferred due to a better side effect profile because it doesn't cross the blood–brain barrier, but it may still cause systemic side effects such as constipation and urinary retention. Amitriptyline has been used orally with much success despite the lack of robust evidence in the literature. Scopolamine patches have shown good response in controlling sialorrhea with efficacy as high as 85%.4 These medications can thicken oral secretions, which can make it difficult to mobilize the secretions. Overall, two thirds of patients respond to these medications, but they may not present a sustainable long-term solution due to unwanted adverse effects.
In patients with refractory sialorrhea, botulinum toxin injection in the salivary gland is viewed as the best alternative. Botulinum toxin blocks the presynaptic release of acetylcholine at the parasympathetic ganglia. Therefore, when injected into the salivary glands, it blocks the production of saliva until the presynaptic terminal regenerates.5 Long-term efficacy and safety data with botulinum injection is favorable, with a mean duration of benefit lasting 3.5 months, and after such time the botulinum toxin can be redosed.6 The use of ultrasound guidance to assist with localization of the injection may improve the precision of this procedure.7
External beam radiation with photon- or electron-based therapy can be used in refractory cases of sialorrhea with lasting benefits.8,9 Electron-based therapy is preferred due to its precision in targeting the superficial parotid tissue compared to photon-based therapy.10 Radiation is generally preferred over botulinum injection because it doesn't cause a reduction in oropharyngeal function, which is a distinct advantage in patients with bulbar dysfunction. Radiation is not widely accepted due to the perceived side effect of mucositis, although the recent trials do not report it as a potential limitation.
Surgical interventions are considered when conservative approaches have failed. The range of options includes denervation of the salivary glands, excision or ablation of the salivary glands, ligation of the salivary ducts, and relocation of the ducts. The isolated salivary gland ablation, either by excision or ligation, may prove futile due to compensatory hypersecretion from the other salivary glands.11 Similarly, the denervation of the salivary glands has proven ineffective due to nerve regeneration.12 Recently bilateral submandibulectomy and endoscopic transoral neurectomy of the submandibular gland and sublingual gland have had some success.13 Most of these procedures require pulmonary reserve, which is a limitation in adult neuromuscular patients unless they have longstanding use of tracheostomy or mechanical ventilation. Salivary duct ablation could be attempted with alcohol by interventional radiology, although this technique lacks any significant published detail. Figure 1 summarizes the various management options available for these patients.
Management of sialorrhea.
Vocal Cord Spasticity
Vocal cord spasticity is seen more commonly in patients with amyotrophic lateral sclerosis (ALS), but it is also seen in patients with spinal muscular atrophy and other neuromuscular conditions. It is frequently reported as a complication in otolaryngology literature, with incidence varying from 4% to 30%.14 Acute onset of dyspnea or stridor in patients with vocal cord spasticity warrants urgent airway management or tracheotomy. Some patients may report nocturnal stridor as the presenting complaint. This is related to the increase in upper airway resistance leading to increases in negative intra-thoracic pressure during inspiration, which contributes to nocturnal stridor. Noninvasive techniques of applying positive pressure with CPAP may be helpful in treating it.15 Benzodiazepines, such as diazepam and lorazepam intensol, can be used to relax the spastic oropharyngeal muscles by presynaptic inhibition. This has not been formally studied for vocal cord spasm in NMD.16 However, given the well described spasticity associated with the upper motor neuron disease, the use of benzodiazepines is a reasonable first step.
Noninvasive Ventilation
Screening for Respiratory Muscle Weakness
The accepted standards for accessing respiratory weakness are transdiaphragmatic pressure and esophageal pressure monitoring. These are invasive and labor-intensive measurements, the repetition of which is impractical in a clinic setting. The surrogate markers for diaphragm weakness include maximum inspiratory pressure (PImax), supine and upright FVC, overnight oximetry, and PaCO2. Some studies have reported supine FVC as the most highly correlated predictor of transdiaphragmatic pressure (R2 = 0.76), although a combination of supine FVC and PImax was better.17 Others have concluded that PImax and nocturnal pulse oximetry were more sensitive in detecting early respiratory weakness compared to FVC.18 Therefore, no single maneuver is likely sufficient to define hypoventilation. It is suggested that optimum monitoring of all the parameters at regular intervals is best for early detection of diaphragm weakness.
Initiation of NIV
NMDs are categorized as restrictive thoracic disorders for Medicare reimbursement for NIV or respiratory assist devices. The minimum requirement for the initial coverage includes symptoms suggestive of hypoventilation (Table 1) and any of the following: awake arterial blood gas CO2 levels ≥ 45 mm Hg, or oxygen saturation (SpO2) of ≤ 88% for at least 5 min of nocturnal recording, or PImax ≥ −60 cm H2O or FVC < 50% predicted performed in the upright or supine position.19 The European guidelines are more tolerant (Table 2).20
Symptoms and Signs of Neuromuscular Disorders
National Institute for Health and Care Excellence Guidelines
ATS guidelines for Duchenne muscular dystrophy (DMD) are more liberal, with the following parameters suggesting the timing of initiation of NIV: signs or symptoms of nocturnal hypoventilation (especially patients with FVC < 30% predicted/FVC < 1.25 L), or apnea hypopnea index of > 10/h or ≥ 4 episodes of SpO2 < 92%, or drops of SpO2 of at least 4% per hour of sleep or baseline SpO2 < 95%, and/or end-tidal CO2 > 45 mm Hg while awake.21
A recent study showed that the frequencies of the respiratory assessments and initiation of respiratory assist devices in patients with DMD is lower than recommended in the guidelines. Pulmonologists and respiratory therapists should collaborate to encourage health care providers caring for patients with DMD to evaluate these patients in timely manner.22
Early Versus Late Initiation of NIV
Figure 2 elaborates a general approach to the initiation of NIV. Early initiation for of NIV has been associated with prolonged survival. A retrospective study showed that early initiation of NIV prolonged the tracheostomy-free survival (median survival 2.7 y vs 1.8 y). In this study, the early NIV group also had higher PImax (−50.4 ± 4.6 cm H2O vs −28.2 ± 2.7 cm H2O, P < .001) and lower PaCO2 (44.9 ± 1.7 mm Hg and 49.3 ± 2 mm Hg), emphasizing that multiple parameters should be assessed while evaluating alveolar hypoventilation.23 This could be postulated to improve lung compliance, decrease work of breathing at nighttime, increase rest of the fatigued diaphragm, and reduce the severity of respiratory acidosis–related muscle fatigue. Current U.S. guidelines suggest initiation of NIV at FVC < 50%, and European guidelines suggest initiation at FVC < 80%, although we anticipate an imminent change in the U.S. guidelines.24
Initiation of noninvasive ventilation (NIV).
Modes of Ventilation
In neuromuscular patients, ventilator support can be provided with a home mechanical ventilator. Mechanical ventilators for the home are easier to use and have a back-up battery, but they are often bulky and expensive. NIV devices, commonly referred as respiratory assist devices, are more portable and less expensive alternatives that can provide better quality of life.
If a patient with NMD qualifies, he or she can be prescribed NIV without a CPAP trial or a polysomnogram. In these patients, what may appear to be upper airway resistance on a diagnostic sleep study could be related to diaphragm weakness instead of upper airway narrowing. Bi-level devices can either be used in fixed-pressure or self-adjusting (targeted) pressure modes. Fixed inspiratory positive airway pressure and expiratory positive airway pressure (EPAP) with a back-up rate (NIV in the spontaneous/timed mode) has traditionally been used to care for those with NMD. EPAP is often set as low as possible in neuromuscular patients. The only purpose of EPAP during neuromuscular disease is to flush CO2 from the circuit or to address obstructive sleep apnea in the patient. For concomitant obstructive sleep apnea, EPAP is titrated in the usual manner. Recently, however, newer technology has become available. Patients with progressive disease benefit from variable pressure support as their respiratory efforts may change throughout the day and as the disease advances. Volume-assured pressure support (VAPS) bi-level devices target the alveolar ventilation or exhaled tidal volume and work in the self-adjusting pressure mode, which is an option for these patients. Given that the neuromuscular patient will always require a sufficient minimum level of ventilation, VAPS devices should always be set to assure that even the minimum pressure support level is adequate for the patient's baseline need. The addition of VAPS settings should be thought of as a safety net allowing for higher pressure support when needed. The VAPS device should not be set with a low starting pressure support because the device could undershoot the patient's needs. Once the type of device is chosen, clinicians need to determine how the breath needs to be delivered (timed, spontaneous, or spontaneous/timed). Please refer to Table 3 for further description of NIV modes, and keep in mind these points: add a back-up rate, use appropriate Ti min, consider pressure control, and never use adaptive servo ventilation, auto bi-level positive airway pressure, or CPAP. NIV could be used in a spontaneous mode (breaths triggered by the patient only), but this is usually associated with apnea due to respiratory muscle weakness related to failure to trigger. A back-up rate prevents this. A detailed protocol on selecting the appropriate settings with each NIV mode has been discussed in depth elsewhere.25
Modes of Ventilation
Adaptive sero ventilation is a form of NIV that is used for stabilizing of Cheyne-Stokes respiration. This is not appropriate for patients with NMD.
Mask Fitting and Desensitization
There are many challenges to fitting a mask in patients with NMD. Neuromuscular weakness can involve the masseter muscle, which can lead to mouth to remain open during sleep. Second, patients who are initiated on NIV at a younger age may have failure of mid-face development, which makes mask fitting even more challenging.26 Therefore, finding the perfect mask interface is essential but difficult. Clinicians could try to use pediatric masks with adult patients or use chin straps with nasal pillows. Elevating the tubing to support the weight of the tubing and prevent the tubing from pulling the mask may minimize the leaks from the mask. Please refer to Table 4 for further management options. Caution needs to be used when applying an oronasal mask because this could paradoxically worsen the upper airway resistance. There is evidence of posterior displacement of the tongue causing partial obstruction of the oropharyngeal airway as seen on a nasal endoscopy during a CPAP titration.27 Whereas nasal masks are thought to produce a differential pressure gradient between the nasopharynx and oropharynx, thus causing pneumatic splinting, this pushes the soft palate and the tongue anteriorly away from the posterior pharyngeal wall.28 Other drawbacks of using an oronasal mask include increased risk of aspiration, increased risk of aerophagia, limited ability for the patient to call care givers for help/assistance, and increased upper-airway obstruction.
Tips to Enhance Adherence With NIV
Desensitization to masks could be achieved by allowing the patient to play with the mask during the day, and then use the NIV with the mask for few hours in the beginning, then during naps and subsequently nocturnally. This has been elaborated in great detail in a recent review.29
Polysomnogram
Polysomnography is not needed to diagnose alveolar hypoventilation in most adults, although this can be helpful in children. Titration polysomnograghy can be performed as an overnight study. This helps in determining an end-expiratory airway pressure required to overcome any upper airway obstruction, the appropriate pressure support needed to alleviate hypoventilation and ameliorate signs of respiratory distress (ie, tachypnea). More recently a short PAPNAP ambulatory study30 has been proposed as an ambulatory 4-h visit instead of an overnight polysomnogram. In this model, the patients were able to go home with the NIV on the same day, which reduced the time between diagnosis and initiation of a life-prolonging treatment. In the near future, with the advent of auto-titration software, titration may not be needed at all in these patients.
Monitoring
There are no consensus guidelines for NIV regarding an optimal monitoring strategy, compliance goals, or the best follow-up testing. The parameters elaborated in Table 5 could be monitored through tele-monitoring, but this should not replace the in-person interview. Arterial blood gas monitoring or transcutaneous CO2 monitoring have become much more available and in the future may have a more specific role for routine care.
Monitoring Parameters
Resupply of the equipment is very important in the long-term success of NIV. Based on Medicare guidelines, Table 6 outlines the frequency of replacement for various respiratory assist devices.36
Resupply Schedule per Medicare Guidelines
Cough Augmentation
Patients with NMD often have difficulty clearing secretions due to poor cough. Effective cough can be measured in the patients by assessing cough peak flow, which is the maximum expiratory flow generated by a patient after a forceful cough. A value < 160 L/min is considered ineffective for airway clearance. Cough augmentation can assist in increasing the cough peak flow. This is achieved with the help of breath-stacking, mechanical cough augmentation, or manual chest and abdominal compression (ie, manually assisted cough). Sequential breath-stacking (lung volume recruitment) utilizes a hand-held resuscitator with a 1-way valve, which increases lung volume. As a consequence of lung volume recruitment, atelectasis of the bases is prevented and the chest wall remains more flexible due to an increased range of motion. These factors reduce the work of breathing and improve cough strength in patients with NMD. It has been shown to decrease the number of hospitalizations and to improve voice volume and dyspnea. Manually assisted cough can be administered while a patient is either seated or recumbent at 30°. The patient is asked to take a deep inspiration, and then the provider gives a rapid abdominal thrust below the xyphisterum. This increases alveolar and pleural pressures, improving cough peak flow and thus clearance of secretions.37 Mechanical in-exsufflation therapy generates a pressure-limited insufflation in the lung followed by a quick reversal of the negative pressure, leading to the generation of expiratory flow sufficient to clear secretions. The pressure setting recommended for mechanical in-exsufflation in NMD patients is +40/−40 cm H2O for effective cough.38,39 A respiratory therapist at the bedside should also consider the effectiveness of any setting with a mindful eye to the exhaled cough volume and peak flow. Mechanical in-exsufflation has been shown to prevent intubation, tracheostomy, and hospitalizations. Recent literature suggests that the application of higher insufflation pressures may be counterproductive in patients with progression of ALS, especially with the onset of the bulbar symptoms.40 The combination of the cough augmentation techniques is recommended because they are able to enhance cough peak flow even further. A clinical approach to cough augmentation is outlined in Figure 3. A recent systematic review showed weak evidence in support of the continued use of mechanical in-exsufflation in NMD patients; the absence of alternatives makes this a difficult treatment decision.41 A randomized, controlled, crossover, single-center trial with 40 subjects with NMD showed that a combination of mechanical in-exsufflation in conjunction with manual thrust improved cough peak flow to a mean of 202.4 L/min versus mechanical in-exsufflation alone (177.2 L/min).42 A randomized, controlled trial showed improved survival at 12 months in subjects enrolled in a breath-stacking group when compared to mechanical in-exsufflation, although the difference was not statistically significant. In a subgroup analysis, improved survival was even seen in patients with severe bulbar dysfunction in the breath-stacking arm.43 A randomized, controlled trial done in quadriplegic spastic cerebral palsy children showed that mechanical in-exsufflation shortened the duration of therapy for airway clearance when compared to chest physiotherapy and was a safe and efficient alternative for airway clearance.44 While these techniques are helpful, they have limitations in patients who have severe bulbar paralysis, COPD, or severe chest wall restriction.
Approach to cough augmentation.
High-frequency oscillatory ventilation could also be used to reduce pneumonia and hospitalization. The use of high-frequency oscillatory ventilation in ALS patients has been shown to reduce breathlessness with stabilization of FVC in patients who had FVC of 40–70% of predicted.45 A recent cohort study of patients with NMD showed that the total medical costs, hospitalization, and pneumonia after high-frequency oscillatory ventilation were reduced.46
End of Life Care
As an NMD progresses, patients require ventilator support 24 h/d. It is a common practice to recommend invasive ventilation at this stage, although this increases the frequency of institutional care. Continuous NIV with mouthpiece ventilation during the day and NIV during the night has increased in popularity as a safe alternative in patients with NMD.47 This is not a new approach, dating back to post polio patients in 1960s. In a prospective trial done on DMD subjects, 24-h NIV was shown to be a safe alternative in prolonging survival with stabilization of vital capacity.48 Mouthpiece ventilation allows patients to be interface free during the day, resulting in better quality of life. Mouthpiece ventilation is best delivered in the volume-cycle mode. Effective airway clearance and the availability of a home caretaker is of great importance in the success of 24-h NIV.
Dyspnea is the most common complaint of ALS patients in hospice. NIV has been shown to alleviate the dyspnea in these patients but can be challenging in patients with severe bulbar dysfunction. Narcotics remain the cornerstone in management. A prospective non-randomized trial involving patients with ALS showed that extended-release morphine relieved dyspnea without a significant rise in transcutaneous CO2 levels.49 On the other hand supplemental oxygen was not any better than room air in relieving dyspnea in subjects with life-limiting illnesses.50 Therefore, given the high risk of CO2 retention as well as the inability to palliate symptoms of dyspnea, supplemental oxygen should not be used in patients with NMD.
Summary
Supportive care in patients with NMD has demonstrated improved outcomes, and the management of respiratory symptoms is a crucial component that affects quality of life. NIV has shown the largest impact on survival and quality of life in patients with ALS. The advent of a VAPS algorithm as an option for an auto-titration algorithm for NIV will reduce the time between diagnosis and initiation of life-prolonging treatment. The increased popularity of 24-h NIV is likely to improve patient quality of life.
Footnotes
- Correspondence: Ashima S Sahni MD, Division of Sleep Medicine, Department of Neurology, Feinberg School of Medicine at Northwestern University, 676 N St Clair Street, 7th floor, Chicago, IL 60611. E-mail: 1984ashima{at}gmail.com.
Dr Wolfe presented a version of this paper at the Year in Review Symposium of the AARC Congress, held October 4-7, 2017, in Indianapolis, Indiana.
The authors have disclosed no conflicts of interest.
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