Inclusion Criteria:  • Ischemic stroke symptoms consistent with large artery occlusion  Baseline non-contrast head CT (or MRI) negative for hemorrhage or mass- effect Evidence of arterial occlusion on standard of care CT angiography or MR angiography or NIHSS 10 or more points Alberta Stroke Program Early Computed Tomography Score [ASPECTS] >6 Patients treated with IV-tPA, mechanical thrombectomy or both Pre-stroke baseline modified Rankin Score (mRS) <1 Ability to enrol, randomize and begin the intervention within the Emergency Department  Exclusion Criteria:  • Pregnancy or suspicion of pregnancy  Evidence or suspicion of vomiting any time prior to consent which could predispose to aspiration pneumonia and therefore confound determination of protocol safety Evidence of evolving malignant infarction on admission noncontrast CT (or MRI) Need for intubation with mechanical ventilation, or non-invasive ventilatory support with either bi-level positive airway pressure (BiPAP) or continuous positive airway pressure (CPAP) Inability to tolerate zero-degree positioning due to congestive heart failure, preexisting pneumonia, chronic obstructive pulmonary disease, or other medical condition Admission chest radiograph positive for pleural effusion, pulmonary edema, pneumonia, or other pulmonary condition that may confound determination of protocol safety Abnormal breath sounds on that may confound determination of protocol safety