Long-Term Follow-up of Nocturnal Ventilatory Assistance in Patients with Respiratory Failure Due: DISCUSSION
In our series of eight patients with Duchenne or Duchenne-type muscular dystrophy with respiratory failure, we found, as others have, that nocturnal ventilatory assistance using noninvasive ventilators brought about a sustained reversal of hypoventilation and improvement in symptoms of chronic hypercarbia. The clinical course was stabilized in most patients who required infrequent hospitalizations despite minimal pulmonary reserve. Although our patients tried a variety of negative and positive pressure ventilators, they preferred negative pressure ventilators and particularly the tank ventilator because it was effective, comfortable and left the upper airway free. Recently, however, as others have reported, we have had success in assisting ventilation in patients with muscular dystrophy and other restrictive lung diseases using positive pressure ventilation administered via a nose mask.
Our patients initiated use of assisted ventilation when they had developed symptomatic hypercarbia prior to the onset of superimposed acute respiratory failure. By beginning assisted ventilation at this phase of their illness, we were able to initiate ventilatory assistance gradually and hypercarbia was reversed very slowly over a period of weeks. Splaingard et al have advocated a similar approach, arguing that a lengthy and expensive hospitalization for an eventual acute deterioration could thereby be avoided. generic propecia
Although the reversal of hypoventilation in our patients was sustained, we detected a gradual and progressive loss of pulmonary function, amounting to approximately 33 percent of vital capacity over the three and one-quarter year follow-up period. In order to compensate for this loss of function and maintain a stable PaC02, patients gradually increased the duration of ventilatory assistance so that after the extended follow-up period, the duration of daily use was more than double that at the early follow-up period. In addition, patients gradually retreated to more effective and invasive forms of assisted ventilation including the iron lung and positive pressure administered via a permanent tracheostomy.
Lacking a control group in our study, we cannot ascertain whether long-term noninvasive ventilatory assistance was influencing the rate of loss of vital capacity in any way or whether survival was prolonged. No other controlled trials addressing these issues have been reported. However, prior studies on pulmonary function in patients with Duchenne muscular dystrophy not given ventilatory support have rarely detected chronic hypercarbia, even in patients with severe restriction, and have considered elevation of PaC02 a preterminal and irreversible event. Rideau et al have described ascending, plateau and descending phases for alterations of vital capacity in Duchenne muscular dystrophy, the onset of the latter phase presaging terminal respiratory insufficiency within several years at an average age of 20 years. A decline in vital capacity to less than 500 ml has been associated with imminent death in untreated patients. Considering these observations on the natural history of respiratory insufficiency in Duchenne muscular dystrophy, it seems highly likely that survival was prolonged in at least some of our patients, particularly in patients 1 and 8, who have lived for more than five years following the onset of hypercarbia. Furthermore, our patients sought treatment for worsening symptoms. Withholding a treatment that has been shown to reliably reverse symptoms and hypercarbia when the prognosis without intervention is so poor seems unjustifiable. On the other hand, controlled studies are needed to determine whether or not nocturnal ventilatory assistance initiated prior to the onset of hypercarbia slows deterioration of pulmonary function, as some have suggested.
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Others have reported nocturnal arterial oxygen desaturations due to upper airway obstruction in patients with neuromuscular diseases (only one with muscular dystrophy) using negative pressure ventilators. We observed no significant nocturnal oxygen desaturations in our series, although we were able to monitor only three patients. We encountered no difficulty reversing hypoventilation or symptoms, nor were there any indications of upper airway obstruction during hospitalizations in the remaining five patients. Although we may have missed desaturations in these remaining patients, upper airway obstruction during ventilator use did not perceptibly interfere with our patient management. It is possible that patients with Duchenne muscular dystrophy are less susceptible to this problem than those with other neuromuscular diseases.
