Answer: The contraindication: “Major trauma or burns to the head and torso” refers to new or acute traumas, and not any previous or remote trauma issue.
The concerns stem from the suspected pneumothorax in acute trauma (sometimes we only see them on the CT scan), difficult patient assessment, impending airway problems with a patient with major burns to head and torso, basal skull fracture or intracranial injury which could limit the ability to cooperate. Also generally it is hard to sit major trauma patients upright with possible concern about spine injury.