Inclusion Criteria:  Severe ARDS: PaO2/FiO2 <200, resistant hypoxemia and tachypnoea (RR > 40 breath/minute) Not relieved by high frequency nasal canula or CPAP. Need for invasive mechanical ventilation (uncooperative)  Exclusion Criteria:  Patient relatives' refusal Not mechanically ventilated. Combination of female, corticosteroids administration and vecuronium muscle relaxant. Neuromuscular diseases (especially demyelinating diseases).