Physiological Effects of Continuous Negative External Pressure for Acute Hypoxemic Respiratory Failure

Inclusion Criteria:

1. Age 18 years or older
2. Acute hypoxemic respiratory failure
3. Non-cardiogenic airspace opacities on chest radiograph or computed tomography (CT) scan
4. High-flow nasal cannula (flow ≥ 30 LPM) initiated within last 96 hours (4 days)
5. FiO2 ≥ 40%
6. SpO2 ≥ 92%

Exclusion Criteria:

1. Do-not-intubate order
2. Anatomical factor predisposing to poor fit of cuirass (e.g. severe kyphosis or scoliosis)
3. Use of cuirass precluded, e.g. due to:

   * Clinically prescribed prone positioning
   * Tense ascites
   * Severe abdominal pain
   * Abdominal wound or surgery, symptomatic abdominal aortic aneurysm, or other unstable or high-risk intra-abdominal pathology
   * Pregnancy
   * Agitated delirium
   * Body weight \> 180 kg
   * Burned skin or draining wounds under the planed cuirass area
   * Indwelling tube/drain entry sites within the planned cuirass seat path
4. Prior intubation during hospital stay
5. Cardiogenic pulmonary edema
6. Exacerbation of asthma or COPD
7. Chronic lung disease, including:

   * Interstitial lung disease
   * Cystic fibrosis
   * Lung mass, lung cancer, or metastasis to the lung
   * Lung transplant recipient
   * Any disease that requires home oxygen
8. Glasgow coma score \< 15
9. Chest tube, pneumothorax, or pneumomediastinum
10. Hemodynamic instability, defined as any of:

    * Heart rate \< 50 beats/minute
    * Mean arterial pressure \< 55 mmHg
    * Norepinephrine-equivalent vasopressor requirement \> 0.1mcg/kg/min
11. Implantable electrical device (e.g. pacemaker, defibrillator, neurostimulator)
12. Unreliable pulse-oximetry tracing
13. Imminent intubation
14. Anticipated lack of patient availability to complete study procedures (e.g. due to planned clinical procedure such as CT scan or dialysis during potential time of study)
15. Attending physician refusal
16. Lack of capacity for direct consent