Our main objective is to collect feasibility data on helmet NIPPV and other clinical elements in to eventually prepare for a full scale randomized trial based on findings of this pilot study.

Patients with acute hypoxemia leading to respiratory failure are frequently supported by endotracheal intubation and mechanical ventilation. Unfortunately an invasive approach to support is associated with risks of lung injury, infection, need for heavy sedation, and increased mortality. Non-invasive oxygen delivery, by mask (BiPAP or CPAP), high flow nasal cannula or helmet interface, is better tolerated and reduces risks associated with invasive mechanical ventilation. A growing body of medical literature and clinical experience suggests that non-invasive oxygen delivery can prevent the need for endotracheal intubation in some patients. This proposal will compare two different modes of non-invasive oxygen delivery: helmet and 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