- contra-indication to prone position including pregnancy - presence of pacemaker - severe hypoxemia with pao2/fio2 < 100 mmhg - evidence of clinical signs of respiratory distress with high probability of intubation in the next two hours

- contra-indication to prone position including pregnancy - presence of pacemaker - severe hypoxemia with pao2/fio2 < 100 mmhg - evidence of clinical signs of respiratory distress with high probability of intubation in the next two hours