pressure may reveal upper airway collapsibility.This is especially useful for detecting obstructive sleep apnoea syndrome in obese snorers [4,10].Thus, in the present case, the NEP technique would have allowed the recognition of extrathoracic EFL, which may have contributed to our patient's hypoxaemia.However, when this phenomenon extends to the whole expiration during NEP, it may preclude the detection of intrathoracic EFL with this method [10].Actually, it is unlikely that upper airway collapse may account for the acute cardiorespiratory disaster experienced by our patient.The patient was awake, he was moved and positive pressure NIV was continuously applied with 8 cmH 2 O PEEP during this period.Finally, a growing body of evidence suggests that the deterioration of pulmonary gas exchange that occurs when obese patients are lying down may be the result of ventilation/perfusion mismatch rather than a consequence of hypoventilation [7,8].When morbidly obese patients are lying down, their small airways may extensively collapse in the posterior dependent lung zones.These nonaerated pulmonary areas are well perfused in the supine position and may rapidly lead to severe refractory hypoxaemia [8].To summarise, it is noteworthy that the sitting position not only ensures comfort but may also be part of a strategy preventing severe cardiorespiratory complications in superobese patients.