Head Down Tilt 15° to Increase Collateral Flow in Acute Ischemic Stroke

Inclusion Criteria: * Acute ischemic stroke due to left or right MCA occlusion of the M1 segment (excluding occlusion of the internal carotid artery terminus + M1) * Decision to treat with mechanical thrombectomy (with or without intravenous thrombolysis) * Informed consent obtained from patient or patient's next of kin, or emergency consent procedure Exclusion Criteria: * Impaired consciousness, defined as NIHSS score of 2 or 3 of the item 1a (level of consciousness): not alert, requires repeated stimulation or unresponsive. * Vomiting upon stroke onset. * History of glaucoma. * History or imaging findings of intracranial hypertension of any aetiology * Major breath disorders, defined as follows: * oxygen saturation ≤92% in room air at admission * severe chronic obstructive pulmonary disease (COPD) treated with long-term oxygen therapy. * severe heart failure with NYHA class 3 or 4 (breathlessness during ordinary physical activity or at rest). * Severe obesity, defined as body mass index (BMI) \> 35. * Patients participating in another interventional trial that would interfere with this study. * Female patients who are pregnant