Victor J. Del Brutto, MD
Early in my neurology training, two cases changed my perspective on the importance of patients’ head positioning during the acute phase of cerebral ischemia. The first was a man in his 60s who presented with a right MCA syndrome associated with an acute occlusion of the ipsilateral cervical ICA. When the patient was transitioned to the CT scan table (flat positioning), initial left homonymous hemianopia, left hemi-neglect, left hemiplegia, and right gaze deviation (NIHSS 17) resolved, leaving just a residual left face droop and left arm drift (NIHSS 3). Once the patient was back to the ED, and despite a constantly elevated blood pressure, the variations on his exam associated with the head of bed flat versus elevated was reproducible.
A few weeks later, I was called to evaluate a lady on her eighth decade of life who developed acute onset right-sided weakness. Initial examination showed right ataxic hemiparesis (NIHSS 4). Brain MRI and MR angiogram showed a tiny DWI-positive lesion on the left ventral pons, as well as diffuse intracranial atherosclerosis including a narrow basilar artery. The patient was loaded with antiplatelet agents and admitted to the Stroke Unit. During the wait time in the ED, the patient stood up from the bed in an attempt to go to the bathroom. According to the nurse report, when the patient stood up, she immediately developed right hemiplegia and right gaze preference. On re-examination, the new worsening deficits persisted (NIHSS 11), and a repeated brain MRI showed progression of the infarct involving now the whole left paramedian pons.
These two cases, as well as several others seen during my neurology residency, exemplify the influence of gravitational forces on cerebral blood flow to maintain perfusion of ischemic brain tissue when perfusion is dependent of collaterals and autoregulation is impaired. Furthermore, they suggest that flat positioning might be a simple but important maneuver that could benefit a subset of patients with certain mechanisms of ischemic injury.
On the first section of the current review, the authors present a summary of the studies that have shown that lying-flat position significantly increases cerebral blood flow when compared to upright position as evaluated by differences in the mean arterial velocities using Transcranial Doppler (Figure 1).
The HeadPoST trial  aimed to determine if this physiologic effect was associated with better clinical outcome when applied to a broad range of patients with acute stroke during the early phase of management. Results published in the New England Journal of Medicine (June 2017) showed that there were no differences in clinical outcome at 90 days between patients assigned to lying-flat position versus those assigned to head of bed elevated (Figure 2). In addition, the authors did not find increased risk of adverse events, including episodes of oxygen desaturation or pneumonia, among groups. The neutral results of the HeadPoST trial determined that the routine application of a standard head position for patients with acute stroke is safe, but does not translate in clinical benefit and is otherwise unnecessary.
Despite the compelling evidence on the lack of advantage of stroke patients being on strict flat position in the acute phase, there is still a subgroup of patients with mechanisms of injury particularly vulnerable to changes in cerebral blood flow in which flat positioning might be of critical benefit . Unfortunately, the HeadPoST trial did not routinely screen for this subset of patients. As seen in the two cases presented above, variations in the severity of neurological deficits between different positions is a physiological phenomena that should not be overlooked. As proposed by the group from UCLA , bedside maneuvers based on the neurological examination could be a good screening tool to recognize patients with a “flow dependent exam” in which maneuvers to maximize cerebral perfusion such as strict head of the bed flat are justified.
 Anderson CS, Arima H, Lavados P, Billot L, Hackett ML, Olavarría VV, et al. Cluster-Randomized, Crossover Trial of Head Positioning in Acute Stroke. N Engl J Med. 2017; 376:2437-2447.
 Gauthier A, Gérardin P, Renou P, Sagnier S, Debruxelles S, Poli M, et al. Trendelenburg Positioning in Large Vessel Ischaemic Stroke: A Pre-Post Observational Study Using Propensity Score Matching. Cerebrovasc Dis. 2018; 46: 24-32.
 Ali LK, Weng JK, Starkman S, Saver JL, Kim D, Ovbiagele B, et al. Heads up! A novel provocative maneuver to guide acute ischemic stroke management. Interv Neurol. 2017;6:8–15.