Inclusion criteria:

1. Age ≥18
2. Ischemic stroke (as defined in the outcome section84), within the prior 7 days.
3. NIHSS ≥1

Exclusion criteria:

1. Pre-event inability to perform all of own basic ADLs
2. Unable to obtain informed consent from subject or legally authorized representative
3. Incarcerated
4. Known pregnancy
5. Current mechanical ventilation (can enroll later if this resolves) or tracheostomy
6. Current use of positive airway pressure, or use within one month prior to stroke
7. Anatomical or dermatologic anomaly that makes use of CPAP interface unfeasible
8. Severe bullous lung disease
9. History of prior spontaneous pneumothorax or current pneumothorax
10. Hypotension requiring current treatment with pressors (can enroll later if this resolves)
11. Other specific medical circumstances that conceivably, in the opinion of the site PI, coul render the patient at risk of harm from use of CPAP
12. Massive epistaxis or previous history of massive epistaxis
13. Cranial surgery or head trauma within the past 6 months, with known or possible CSF leak or pneumocephalus
14. Recent hemicraniectomy or suboccipital craniectomy (i.e. those whose bone has not yet been replaced), or any other recent bone removal procedure for relief of intracranial pressure
15. Current receipt of oxygen supplementation >4 liters per minute
16. Current contact, droplet, respiratory/airborne precautions