- prior intubation during this hospital admission - cardiopulmonary arrest - glasgow coma scale <12 - tracheostomy - upper airway obstruction - active epistaxis - requirement for more than one vasopressor to maintain mean arterial pressure > 65 mm hg - pregnancy - imminent intubation - patients with do not intubate orders or equivalent - enrolled in another trial for which co-enrolment is not approved including trials on mechanical ventilation - patients already treated with helmet - patients with chronic carbon dioxide retention (paco2 >45) - previous enrolment in this trial - the primary cause of respiratory failure is not heart failure as judged by the treating team

- prior intubation during this hospital admission - cardiopulmonary arrest - glasgow coma scale <12 - tracheostomy - upper airway obstruction - active epistaxis - requirement for more than one vasopressor to maintain mean arterial pressure > 65 mm hg - pregnancy - imminent intubation - patients with do not intubate orders or equivalent - enrolled in another trial for which co-enrolment is not approved including trials on mechanical ventilation - patients already treated with helmet - patients with chronic carbon dioxide retention (paco2 >45) - previous enrolment in this trial - the primary cause of respiratory failure is not heart failure as judged by the treating team

- prior intubation during this hospital admission - cardiopulmonary arrest - glasgow coma scale <12 - tracheostomy - upper airway obstruction - active epistaxis - requirement for more than one vasopressor to maintain mean arterial pressure > 65 mm hg. - pregnancy - imminent intubation - patients with do not intubate orders or equivalent - enrolled in another trial for which co-enrolment is not approved including trials on mechanical ventilation - patients already treated with helmet - patients with chronic carbon dioxide retention (paco2>45) - previous enrolment in this trial - the primary cause of respiratory failure is not heart failure as judged by the treating team

- prior intubation during this hospital admission - cardiopulmonary arrest - glasgow coma scale <12 - tracheostomy - upper airway obstruction - active epistaxis - requirement for more than one vasopressor to maintain mean arterial pressure > 65 mm hg. - pregnancy - imminent intubation - patients with do not intubate orders or equivalent - enrolled in another trial for which co-enrolment is not approved including trials on mechanical ventilation - patients already treated with helmet - patients with chronic carbon dioxide retention (paco2>45) - previous enrolment in this trial - the primary cause of respiratory failure is not heart failure as judged by the treating team

- prior intubation during this hospital admission - cardiopulmonary arrest - glasgow coma scale < 12 - tracheostomy - upper airway obstruction - active epistaxis - requirement for more than one vasopressor to maintain mean arterial pressure > 65 mm hg. - pregnancy - imminent intubation - patients with do not intubate orders or equivalent - enrolled in another trial for which co-enrolment is not approved including trials on mechanical ventilation

- prior intubation during this hospital admission - cardiopulmonary arrest - glasgow coma scale < 12 - tracheostomy - upper airway obstruction - active epistaxis - requirement for more than one vasopressor to maintain mean arterial pressure > 65 mm hg. - pregnancy - imminent intubation - patients with do not intubate orders or equivalent - enrolled in another trial for which co-enrolment is not approved including trials on mechanical ventilation