When should home mechanical ventilation be started in patients with different neuromuscular disorders?

Current international consensus guidelines identify a number of indicators for the establishment of home mechanical ventilation (HMV) for patients with neuromuscular diseases but do not address the possible clinical differences between each of the underlying disorders. This study assessed the differences in the physiological parameters of patients with neuromuscular disease commenced on HMV for the treatment of symptomatic chronic hypercapnic respiratory failure.

Patients commenced on HMV for the treatment of symptomatic chronic hypercapnic respiratory failure over a 9-year period were studied. Physiological parameters at the time of referral for HMV, impact of HMV and survival were analysed.

The study recruited 66 patients with neuromuscular disease. Thirty-one patients had rapidly progressive disease: amyotrophic lateral sclerosis (ALS, n = 19), Duchenne muscular dystrophy (DMD, n = 12) and 35 patients had slowly progressive disease. Mean FVC at HMV onset was 40.3 +/- 17.5% predicted in all patients, but was >50% predicted in eight patients (12%). ALS patients were more hypercapnic (P = 0.03) and more hypoxaemic (P < 0.001), but had better FEV(1) at HMV onset, compared with DMD patients (P = 0.005). Maximal inspiratory mouth occlusion pressure (PImax) was 3.0 +/- 1.6 kPa in all patients, but values were lower compared with international consensus guidelines (5.88 kPa). Median survival in DMD, slowly progressive diseases and ALS was 132, 82 and 16 months, respectively (P < 0.001).

Blood gases and lung function parameters vary substantially between patients with differing underlying neuromuscular disorders when commenced on HMV for the treatment of symptomatic chronic hypercapnic respiratory failure. In contrast, PImax is equally reduced in all patients and more severely reduced compared with consensus guidelines. The specific underlying neuromuscular disease has a major impact on outcome. Specific selection criteria are needed for the use of HMV in the different diseases that comprise neuromuscular disorders.