A Pilot Study Comparing Oxygen Delivery Via Helmet Interface Versus High Flow Nasal Cannula

Inclusion Criteria: 1. Age ≥ 18 years 2. AHRF defined as: A ratio of partial pressure of oxygen (PaO2) to fraction of inspired oxygen (FiO2) between 100 - 250 mm Hg while breathing O2 from Venturi mask, or other delivery system that allows quantification of FiO2 such as Mask-NIPPV or HFNC. When no arterial blood gas (ABG) result available, use transcutaneous oxygen saturation measurement (SpO2) to impute PaO2 (Appendix A.2 for Table of PaO2 / FiO2 imputed from SpO2 \[Brown 2017\]. If no oxygenation data prior to use of Mask-NIPPV or HFNC are available, then P/F ratio 100 - 250 on Mask-NIPPV or HFNC meets this criterion. 3. Respiratory rate (RR) ≥24 /min and/or subjective shortness of breath (Modified Borg Dyspnea Scale ≥ 2) Exclusion Criteria: 1. P/F Ratio \< 100 (Severe ARDS) on quantifiable FiO2 2. More than 24 hours has elapsed since the patient met criteria for AHRF (Inclusion #2 and 3, above) 3. Urgent need for intubation Criteria for intubation: i. RR\>40 ii. Lack of improvement of respiratory muscle fatigue iii. Copious tracheal secretions that require frequent suctioning iv. Acidosis with a potential Hydrogen (pH) \<7.35 v. Acute hypercarbia (PaCO2 \> 45 mm Hg) vi. SpO2 \< 88% for more than 5 minutes despite FiO2 and non-invasive support vii. Respiratory or cardiac arrest viii. Glasgow Coma Scale ≤ 8 4. Contraindication to HFNC, Helmet-NIPPV, or Mask-NIPPV 5. Upper airway obstruction, facial trauma 6. Copious secretions, airway bleeding, epistaxis or vomiting 7. Primary cause of respiratory failure is exacerbation of chronic obstructive pulmonary disease (COPD) or asthma 8. Elevated intracranial pressure \>20 mm Hg 9. Home mechanical ventilation except for CPAP/BiPAP used solely for sleep disordered breathing 10. Persistent hemodynamic instability (systolic blood pressure (SBP)\<90 or mean arterial pressure (MAP)\<60 despite IV fluid resuscitation, or norepinephrine dose \> 0.1 mcg/kg/min or equivalent vasopressor dose) 11. Plan for procedure during which NIPPV or HFNC is contraindicated. Okay to enroll if procedure is complete and AHRF persists within 24 hours. 12. Absence of airway protective gag reflex or cough 13. Tracheostomy 14. Lack of informed consent 15. Pregnancy 16. Actual body weight exceeding 1 kg per cm of height 17. Diffuse alveolar hemorrhage 18. Severe acute pancreatitis as etiology for hypoxemia 19. Recent upper gastrointestinal surgical anastomosis within the past 30 days 20. Enrollment in another clinical trial within the past 30 days 21. Unsuitable for non-invasive ventilation in the judgment of the treating MD 22. Decision to withhold life-sustaining treatment. Patients with Do-Not-Resuscitate (DNR) or No Cardiopulmonary resuscitation (No CPR) order may be enrolled. 23. Do not intubate order