Air leaks during mechanical ventilation as a cause of persistent hypercapnia in neuromuscular disorders

Objective: This study investigated whether air leaks from the upper airway during assisted ventilatory support are associated with persistent hypercapnia (PaCO2 >45 mmHg) in patients with neuromuscular disorders. Setting: A rehabilitation hospital. Patients: The study was performed in 95 neuromuscular patients; 52 were tracheostomized with a cuffless tracheostomy tube (invasive ventilation), and 43 received noninvasive ventilation. Measurements and results: The volume of air leaked (VL) and arterial carbon dioxide (PaCO2) were routinely measured during mechanical ventilation; PaCO2 was also measured during spontaneous breathing. VL, expressed as a percentage of tidal volume, was higher in the hypercapnic group (32+/-14%, n=20) than the nonhypercapnic group (vs. 20+/-14%). PaCO2 during mechanical ventilation was correlated with both VL and the duration of ventilatory support per day; PaCO2 during spontaneous breathing was correlated only with the volume of air leaked. In stepwise multiple regression analysis, air leaks contributed to 8% of the variance in PaCO2 during mechanical ventilation, and daily duration of ventilatory support contributed 5%. In addition, reduction in VL with normalization of PaCO2 was achieved in five of the noninvasively ventilated patients with persistent hypercapnia by using a chin strap. Conclusions: Air leaks during wakefulness are an important cause of persistent hypercapnia in both invasively and noninvasively ventilated neuromuscular patients. However, simple practical measures to reduce the volume of air leaks improve the efficacy of ventilation in these patients.