Skip to Main Content

Introduction

Patients with ventilatory impairment due to ventilatory muscle dysfunction are often evaluated and managed according to practices developed for patients with chronic lung diseases. However, pulmonary function laboratories, designed primarily for assessment of lung diseases, do not evaluate lung volume recruitment capacities or cough flows that are important in the assessment of patients with inspiratory and expiratory muscle dysfunction. In the setting of ventilatory muscle dysfunction polysomnograms may be misinterpreted as central or obstructive apneas and hypopneas rather than hypoventilation due to inspiratory muscle dysfunction, and continuous positive airway pressure (CPAP) or nocturnal bilevel positive airway pressure (BiPAP) prescribed. In the context of ventilatory muscle dysfunction CPAP does not increase tidal volumes, and may actually reduce them by causing them to approach maximum lung capacity for these patients with severe pulmonary restriction while BiPAP is often used at pressures inadequate to support alveolar ventilation, provide inspiratory muscle rest, or assist in coughing.1 In addition, the patients are often treated with supplemental oxygen to correct hypoxemia when efforts to improve oxygenation should be directed at normalizing alveolar ventilation and clearing airway secretions. With advancing inspiratory and expiratory muscle weakness, the common scenario is that respiratory failure ensues and is treated by mechanical ventilation via endotracheal intubation. When ventilator weaning fails, a tracheostomy is performed and mechanical ventilation is continued indefinitely, often in an institution.

Therapeutic modalities commonly used for respiratory diseases can have adverse effects in patients with neuromuscular disorders. Bronchodilator therapy can augment the anxiety and tachycardia that are common in myopathic patients, many of whom have cardiomyopathies. Oxygen therapy increases the risk of pulmonary morbidity, rate of hospitalizations, and mortality by comparison with the use of ventilator assistance or with no treatment at all.2 As noted earlier, oxygen therapy may obscure recognition of mucus plugging because it alleviates oxyhemoglobin desaturation without attention to the expulsion of airway mucus. Oxygen therapy may also prolong hypopneas and apneas during rapid eye movement (REM) sleep,3 and it appears to suppress the reflex muscular activity needed for effective noninvasive intermittent positive pressure ventilation (IPPV) during sleep.4 Translaryngeal intubation, tracheostomy, and tracheal suctioning continue to be used for patients with neuromuscular diseases even though noninvasive IPPV, noninvasive suctioning, and mechanically assisted coughing (MAC) can be more effective and comfortable.

Despite the proven effectiveness of measures to support ventilation noninvasively for long periods even in the absence of respiratory muscle function, these therapeutic modalities have yet to be adopted by many physicians. In Great Britain, 82% of patients with amyotrophic lateral sclerosis (ALS) die receiving morphine and 64% receive benzodiazepines, while few are provided with respiratory muscle aids to prevent respiratory failure.5 This approach both smoothes and hastens passage to the grave by leading to CO2 narcosis.6,7 Often, without consulting the patient, the physician judges the patient’s quality of life to be unacceptable and the disease terminal, ignores options that prevent respiratory ...

Pop-up div Successfully Displayed

This div only appears when the trigger link is hovered over. Otherwise it is hidden from view.