Head Positioning in Patients With Acute Ischemic Stroke: Does it Matter?

By Stephanie Abbuhl, MD, FACEP, Vice Chair, Department of Emergency Medicine, The Hospital of the University of Pennsylvania; Associate Professor of Emergency Medicine, University of Pennsylvania School of Medicine, Philadelphia, PA Dr. Abbuhl reports no relationships with companies having ties to the field of study covered by this CME program.

Source: Wojner-Alexander AW, et al. Heads down: Flat positioning improves blood flow velocity in acute ischemic stroke. Neurology 2005;64:1354-1355.

The purpose of this study was to determine if middle cerebral artery flow velocity could be augmented by simple head-of-the-bed (HOB) positioning during acute stroke while avoiding arterial flow compromise as might occur with an increase in intracranial pressure (ICP). Transcranial Doppler (TCD) was used to measure mean flow velocity (MFV) and indirectly estimate flow changes in association with HOB positioning. In a repeated measures design, the effect of 30°, 15°, and 0° HOB elevation on residual arterial flow signals was measured in 20 awake patients within the first 24 hours of acute ischemic stroke symptoms. Patients with hemorrhagic or posterior circulation stroke were excluded from the study, and no patient received thrombolytic therapy prior to, or at the time of, TCD measurements.

The mean age of the patients was 60 ± 15 years with 14 men and 6 women. Median National Institute of Health Stroke Scale score at the time of initial TCD was 14 points (range 3 to 24 points). All patients had middle cerebral artery MFV improvement with lowering the head position. The mean difference in MFV from HOB 30° to HOB 0° was -8.2 cm/s ±8.2 (95% CI -12.0 to - 4.28). On average, the middle cerebral artery MFV increased 20% (12% from 30° to 15° and 8% from 15° to 0°; p < 0.025). No significant difference was measured in mean arterial pressure and heart rate for any HOB position change throughout the intervention. Pulsatility index, a measure of resistance to flow, remained unchanged at each HOB position. Immediate neurologic improvement occurred in three patients after lowering the head position.

Commentary

This study found that decreasing HOB elevation from the 30° to the 0° position resulted on average in a 20% increase in the mean velocity of the residual arterial blood flow at the affected artery following acute ischemic stroke. At the same time, the pulsatility index remained unchanged within low resistance parameters suggesting no increase in resistance due to a potential increase in ICP. While this study is limited by its small size, the results suggested that zero-degree head positioning may improve residual flow in the affected middle cerebral artery. One explanation is that simple gravitational force may augment the local perfusion pressure gradients. It also is possible that the velocity increase may be due to improved collateral flow.

It should be cautioned, however, that TCD MFV is only a surrogate marker of cerebral blood flow. There is no direct way of measuring blood flow volume with TCD, and the velocity measurement is limited to the horizontal portion of the middle cerebral artery. Ultimately, all these measurements are only surrogate markers for the most important outcome: clinical functional status. A large study comparing these simple HOB maneuvers with clinical outcomes would be helpful in guiding both prehospital and emergency department management. Certainly, not all patients can tolerate zero-degree positioning due to poor cardiopulmonary status and/or the risk of pulmonary aspiration, and patients with hemorrhagic stroke might do worse. The optimal beneficial time frame for this position and the question of any further benefit with the Trendelenburg position are unknown.

Yet, until we have more data, this study—along with a prior paper1 that directly measured ICP and middle cerebral artery flow velocity in patients with large hemispheric stroke—suggested that cerebral perfusion pressure may be maximized by simple zero-degree HOB positioning in patients with acute ischemic stroke. It will be interesting to see if the next set of American Heart Association/American Stroke Association guidelines recommend a flat position if tolerated.

References

1. Schwarz S, et al. Effects of body position on intracranial pressure and cerebral perfusion in patients with large hemispheric stroke. Stroke 2002;33:497-501.