Background and Purpose- Hypercapnia can induce intracranial blood-flow steal from ischemic brain tissues, and early initiation of noninvasive ventilator correction (NIVC) may improve cerebral hemodynamics in acute ischemic stroke. We sought to determine safety and tolerability of NIVC initiated on hospital admission without polysomnography study. Subjects and Methods- Consecutive acute ischemic stroke patients were evaluated for the presence of a proximal arterial occlusion, daytime sleepiness, or history of obstructive sleep apnea, and acceptable pulse oximetry readings while awake (96%-100% on 2 to 4 L supplemental oxygen delivered by nasal cannula). NIVC was started on hospital admission as standard of care when considered necessary by treating physicians. NIVC was initiated using bilevel positive airway pressure at 10 cmH2O inspiratory positive airway pressure and 5 cmH2O expiratory positive airway pressure in combination with 40% fraction of inspired oxygen. All potential adverse events were prospectively documented. Results- Among 356 acute ischemic stroke patients (median NIHSS score, 5; interquartile range, 2-13), 64 cases (18%) received NIVC (median NIHSS score, 12; interquartile range, 6-17). Baseline stroke severity was higher and proximal arterial occlusions were more frequent in NIVC patients compared to the rest (P<0.001). NIVC was not tolerated by 4 patients (7%). Adverse events in NIVC included vomiting (n=1), aspiration pneumonia (n=1), respiratory failure/intubation (n=1), hypotension requiring pressors (n=1), and facial skin breakdown (n=3). The in-hospital mortality rate was 13% in NIVC patients and 8% in the rest (P=0.195). Neurological improvement during hospitalization tended to be greater in the NIVC group (median NIHSS score decrease, 2 points; interquartile range, 0-4) compared to the rest (median NIHSS score decrease, 1; interquartile range, 0-2; P=0.078). Conclusions- In acute ischemic stroke patients with proximal arterial occlusion and excessive sleepiness or obstructive sleep apnea, NIVC can be initiated early with good tolerability and a relatively small risk of serious complications. © 2011 American Heart Association. All rights reserved.