 The 1999 consensus for NIV selected classical criteria to consider NIV in patients with respiratory symptoms suggesting hypoventilation: daytime hypercapnia PaCO2 45 mmHg, nocturnal SaO2 89 more than 5 consecutive minutes and for progressive neuromuscular disorders NMD mainly ALS, a vital capacity VC 50 pred or a PImax 60 cmH2O. 