The investigators justify the need of our study based on the positive results of two recent clinical trials: (i) Meijvis et al (Lancet 2011) showed that dexamethasone (5 mg/day) for 4 days was able to reduce length of hospital stay in 304 patients with bacterial pneumonia when added to the conventional treatment; (ii) Azoulay et al (Eur Respir J 2011) showed that dexamethasone (10 mg/6h), when added to chemotherapy and conventional ICU management, caused less respiratory deterioration and lower ICU mortality in 40 patients with acute lung injury resulting from leukaemia.