Long-Term Follow-up of Nocturnal Ventilatory Assistance in Patients with Respiratory Failure Due: DISCUSSION continue
The lack of change in parameters of pulmonary function and arterial blood gas values during a period of 11 h of spontaneous breathing in four of our patients indicates that our patients remained stable off the ventilator and that blood gas levels obtained at midday or late during the period of spontaneous ventilation are representative of the patients sustained level of ventilation. This stability during the period of spontaneous ventilation also demonstrates that evidence of respiratory muscle fatigue did not occur between intervals of assisted ventilation.
The mechanism by which nocturnal ventilatory assistance reverses hypoventilation is not known with certainty. One theory, proposes that intermittent ventilation provides rest for fatigued respiratory muscles, allowing for greater levels of sustained ventilation after resting. A second theory proposes that Ventilatory assistance at night prevents the nocturnal hypoventilation that blunts respiratory drive, resulting in a gradual resetting of the respiratory center and increasing ventilatory responsiveness to CCV We cannot confirm or disprove either theory based on our study, nor are they mutually exclusive. However, if reversal of hypoventilation is related to reversal of muscle fatigue, one might predict that FVC would improve after a few months of assisted ventilation and that evidence of muscle fatigue would occur after a sustained period of spontaneous ventilation. Although we studied only a small number of patients, we could not confirm these predictions. We cannot exclude the possibility that muscle fatigue develops during longer periods of spontaneous breathing, but nocturnal assisted ventilation had no discernible effect on the parameters of respiratory muscle function that we studied. Prevention of nocturnal hypoventilation, as demonstrated by Goldstein et al, with a gradual downward resetting of the respiratory center, remains a possible explanation for the sustained reversal of hypoventilation in our patients. flomax 0.4 mg
In our eight patients with Duchenne or Duchenne- type muscular dystrophy supported with nocturnal ventilatory assistance over an average of 39 months, we observed an early reversal of hypoventilation and stabilization of the clinical course. However, the underlying muscular dystrophy relentlessly progressed necessitating increased periods of ventilatory assistance and changes to more effacacious and invasive ventilators such as the iron lung or positive pressure ventilation via a permanent tracheostomy. Although the clinical course varied considerably between patients after initiation of nocturnal ventilatory assistance, our findings demonstrate that intermittent noninvasive assisted ventilation in Duchenne muscular dystrophy is of temporary benefit, with most patients requiring almost continuous ventilatory support within a few years. These observations should be useful in counseling patients with muscular dystrophy and their families regarding modes of ventilatory assistance.
Addendum
Since acceptance of this manuscript, patient 4 died suddenly 62 months after initiation of ventilation when his ventilator became accidentally detached from his tracheostomy tube. Autopsy revealed a well-healed tracheostomy without stricture, severe dystrophy of skeletal muscle, and moderate fatty infiltration of the myocardium without evidence of cardiac failure.
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