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A 58-year-old man with progressive weakness has noted difficulty sleeping, headache on awakening in the morning, and a lack of refreshing sleep. He becomes dyspneic lying supine and has been sleeping in a reclining chair. According to his wife, he used to snore, but no longer does so. He has no swallowing difficulty, but slurs his speech slightly.
On physical examination, he has a respiration rate of 24/min; his palate elevates normally, but there are some tongue fasciculations, and he manifests dyspnea and abdominal paradox when lying flat. Nighttime pulse oximetry with the patient breathing room air reveals episodes of oxygen desaturation in the range of 85% to 88%, some episodes lasting longer than 5 minutes. Forced vital capacity is 46% of predicted when upright, 34% of predicted when supine. Arterial oxygen saturation is normal during the day, and the patient can walk slowly without difficulty.
Which of the following is the most appropriate management at this time?
A Continuous positive airway pressure (CPAP) by mask at night
B Tracheostomy and nighttime mechanical ventilation by assist/control mode
C Noninvasive positive airway pressure ventilation by mask at night
D Low-flow oxygen supplementation by nasal cannula at night
E An oral hypnotic
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Answer and Critique (Correct Answer = C)
Early morning headache and a lack of refreshing sleep are symptoms of nocturnal hypercapnia caused by hypoventilation in neuromuscular disease patients like this one, who most likely has amyotrophic lateral sclerosis. Nocturnal hypoxemia is also present in this patient during episodes of hypoventilation. The episodic nature of the hypoxemia raises the possibility of obstructive sleep apnea, which may complicate neuromuscular diseases. The resolution of snoring is a common observation in these patients, may be related to decreasing airflow as weakness progresses and does not mean obstructive sleep apnea is less likely. CPAP alone is therefore a consideration, but this patient's respiratory abnormalities are secondary to neuromuscular weakness and CPAP alone is unlikely to reverse the hypoventilation effectively. The history of orthopnea, abdominal paradox and drop in FVC >25% when the patient goes from the upright to supine position are diagnostic of diaphragm paralysis. Such individuals are excellent candidates for nocturnal noninvasive positive airway pressure to augment their ventilation during sleep. The increased ventilation provided by this modality will likely prevent nocturnal hypercapnia and hypoxemia, something that can be assessed using a follow-up nocturnal oximetry. As the patient's incipient bulbar involvement progresses, tolerance of NPPV may become more difficult, as swallowing and control of secretions become problematic. If hypoxemia persists, it can be corrected with supplementation of inspired oxygen via the noninvasive positive airway pressure apparatus, but this should not be the case if the problem is entirely related to the neuromuscular disease. Use of oxygen or an oral hypnotic alone without ventilatory assistance in such a patient can precipitate severe carbon dioxide retention, and is contraindicated. Tracheostomy and full mechanical ventilation are not required at this point in the patient's course. Although this aggressive therapy will be considered at some point as the disease progresses and the bulbar involvement becomes severe, most patients in the United States (95% in most series) decide against this option because it does nothing to slow the progression of the disease, may lead to a locked-in state, and poses enormous psychological and financial burdens for family members.
Key Points
* A history of orthopnea, abdominal paradox, and a decrease in forced vital capacity >25% when the patient goes from the upright to supine position are diagnostic of diaphragm paralysis.
* Patients with hypoventilation secondary to diaphragm paralysis should be treated with nocturnal noninvasive positive airway pressure to augment their ventilation during sleep.
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NONINVASIVE POSITIVE AIRWAY PRESSURE BY MASK AT NIGHT ...FOR PATEINT WITH OBSTRUCTIVE SLEEP APNEA
The history of orthopnea, abdominal paradox and drop in FVC >25% when the patient goes from the upright to supine position are diagnostic of diaphragm paralysis
