Non-invasive ventilation (NIV) is recognised as an efficient therapeutic option in patients with chronic respiratory insufficiency due to neuromuscular disorders. However, the long standing clinical experience with NIV contrasts with the absence of validated criteria for initiating this treatment and the paucity of data on its long term physiological and psychometric effects.

Several consensus conferences agree on the value of daytime hypercapnia and an acute exacerbation as criteria for starting NIV because they are characteristic signs of established ventilatory failure.^1–3 However, these two classical criteria are preceded by a variable period of nocturnal hypoventilation during which treatable symptoms—such as frequent arousals, severe orthopnoea, daytime fatigue, and alterations in cognitive function—may cause deterioration in the quality of the patient’s daily life.

The first problem is to decide when to perform polysomnography in a patient with only a few symptoms.⁴ Polysomnography should be undertaken without delay when the patient develops symptoms related to sleep disordered breathing, but patients with neuromuscular disorders tend to underestimate symptoms such as fatigue before using mechanical ventilation. Sleep disordered breathing is difficult to establish in children because of reliance on parents and other caregivers who have a different perception of the child’s disease. Lung function parameters are poor indicators of nocturnal hypoventilation and data are only available for patients with neuromuscular disorders. Indeed, forced expiratory volume in 1 second (FEV₁) has been shown to be inversely correlated with daytime arterial carbon dioxide tension (Paco₂) and base excess in patients with Duchenne muscular dystrophy.⁵ But the recommendation to perform …