Role of Non-invasive Ventilation in Amyotrophic Lateral Sclerosis: Volume Versus Pressure Mode

Background

Non-invasive mechanical ventilation (NIV) has been increasingly used as a treatment of chronic hypercapnic respiratory failure. Its use in patients affected by chronic obstructive pulmonary disorders is still controversial, while most of the studies performed in restrictive thoracic disorders (RTD), and in particular in neuromuscular patients, suggested alleviation of the symptoms of chronic hypoventilation in the short term, and in two small studies survival was prolonged. As a matter of fact a recent Cochrane review stated that "long-term mechanical ventilation should be offered as a therapeutic option to patients with chronic respiratory failure due to neuromuscular diseases". Recurrent episodes of nocturnal desaturation especially during REM sleep may deeply influence the prognosis of patients affect by these disorders (i.e. ALS), and they are often associated with hypercapnia, so that the correction of nocturnal hypoventilation seems to be the major goal to achieve with the ventilatory treatment.

A very recent randomized controlled trial show that in ALS without severe bulbar dysfunction, NIV improves survival with maintenance of, and improvement in, quality of life, including sleep quality. The survival benefit from NIV in this group is much greater than that from currently available neuroprotective therapy, like riluzole.

Most of the studies performed in RTD disorders were performed using a pressure assisted mode (i.e Pressure Support Ventilation), because of the supposed better tolerance of the patients and easy of settings for the operators, even though this has never been scientifically proven.

In the terminal phase of the disease, when the respiratory muscles became weaker it is very likely that the operators need to frequently adjust the level of inspiratory pressure in an attempt to guarantee an adequate tidal volume, so that alveolar hypoventilation may be avoided.