The most appropriate respiratory management for this patient is nocturnal noninvasive positive pressure ventilation (NPPV). He has chronic respiratory failure due to progressive muscular weakness. Although there are no clear guidelines regarding when to institute respiratory support in patients with progressive muscle weakness, this patient's inability to breathe while lying flat is highly suggestive of diaphragm weakness, and his low vital capacity is below the threshold at which most patients require mechanical support. Frequently used clinical indicators for the need of ventilatory assistance include an FVC less than 50% of predicted, a vital capacity below 60% of predicted (or 1 L), or a maximal inspiratory pressure of less than −30 cm H₂O. In patients requiring ventilator support, NPPV is the usual initial method used, typically on an intermittent, nocturnal basis. NPPV has been shown to improve quality of life and delay the progression of respiratory failure in patients with progressive neuromuscular disease.

Nocturnal continuous positive airway pressure is typically used in patients with upper airway obstruction such as obstructive sleep apnea, but it would not improve this patient's respiratory mechanics and ventilatory impairment.

Nocturnal oxygen therapy is not indicated and would not be expected to be helpful in this patient with adequate arterial oxygenation despite his chronic hypoventilation.

Continuous mechanical ventilation, usually through a tracheostomy, is generally indicated for patients with a contraindication to NPPV or for those requiring continuous mechanical ventilation for an extended period of time. This patient does not have a contraindication to noninvasive ventilation, and his response to a trial of NPPV therapy is not yet known. Therefore, pursuing tracheostomy and continuous mechanical ventilation would be premature in this patient. It should be noted that he will probably eventually require a tracheostomy, and this would be a good time to introduce that idea for ongoing discussion.