A random number generator will be used to assign whether the patient is to be in the control or PRP group. The computer programme will help to randomize subjects in equal opportunity in either group but taking into account 5 factors: age (< 70 years or ≥ 70 years),sex, length of hospital admission (< 7 days or ≥ 7 days), 6 minute walk test ( < 100 metres or ≥ 100 metres), and predicted FEV1 (< 30% or ≥ 30%). This method is adapted by the study of Man et al.