HOBOE (head-of-bed optimization of elevation) study: association of higher angle with reduced cerebral blood flow velocity in acute ischemic stroke

Background: Cerebral autoregulation can be impaired after ischemic stroke, with potential adverse effects on cerebral blood flow during early rehabilitation. Objective: The objective of this study was to assess changes in cerebral blood flow velocity with orthostatic variation at 24 hours after stroke. Design: This investigation was an observational study comparing mean flow velocities (MFVs) at 30, 15, and 0 degrees of elevation of the head of the bed (HOB). Methods: Eight participants underwent bilateral middle cerebral artery (MCA) transcranial Doppler monitoring during orthostatic variation at 24 hours after ischemic stroke. Computed tomography angiography separated participants into recanalized (artery completely reopened) and incompletely recanalized groups. Friedmantests were used to determine MFVs at the various HOB angles. Mann-Whitney U tests were used to compare the change in MFV (from 30° to 0°) between groups and between hemispheres within groups. Results: For stroke-affected MCAs in the incompletely recanalized group, MFVs differed at the various HOB angles (30°: median MFV=51.5 cm/s, interquartile range [IQR]=33.0 to 103.8; 15°: median MFV=55.5 cm/s, IQR=34.0 to 117.5; 0°: median MFV=85.0 cm/s, IQR=58.8 to 127.0); there were no significant differences for other MCAs. For stroke-affected MCAs in the incompletely recanalized group, MFVs increased with a change in the HOB angle from 30 degrees to 0 degrees by a median of 26.0 cm/s (IQR=21.3 to 35.3); there were no significant changes in the recanalized group (-3.5 cm/s, IQR=-12.3 to 0.8). The changes in MFV with a change in the HOB angle from 30 degrees to 0 degrees differed between hemispheres in the incompletely recanalized group but not in the recanalized group. Limitations: Generalizability was limited by sample size. Conclusions: The incompletely recanalized group showed changes in MFVs at various HOB angles, suggesting that cerebral blood flow in this group may be sensitive to orthostatic variation, whereas the recanalized group maintained stable blood flow velocities.