Stroke monitoring: NIR gets in the patient's head

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  • Published: Apr 1, 2014
  • Author: David Bradley
  • Channels: Infrared Spectroscopy
thumbnail image: Stroke monitoring: NIR gets in the patient's head

Stroke heads-up

A near-infrared monitoring device has been developed by scientists at the University of Pennsylvania, Philadelphia. The system could be used for bedside monitoring of cerebral blood flow in ischemic stroke patients with a view to ensuring optimal treatment and improved outcomes in a potentially debilitating and often lethal condition.

A near-infrared monitoring device has been developed by scientists at the University of Pennsylvania, Philadelphia. The system could be used for bedside monitoring of cerebral blood flow in ischemic stroke patients with a view to ensuring optimal treatment and improved outcomes in a potentially debilitating and often lethal condition.

Most patients admitted to hospital with an acute ischemic stroke are kept supine for at least 24 hours in an effort to increase cerebral blood flow to vulnerable brain regions surrounding the tissues damaged by the stroke. Now, researchers have used a device designed and patented by researchers at the University of Pennsylvania to non-invasively and continuously monitor CBF in such patients. The team from Penn Medicine and the Department of Physics & Astronomy are discovering exactly how "head-of-bed" positioning affects blood flow and thus outcome for stroke patients. Their initial findings suggest that for about three-quarters of patients a flat head-of-bed position increased blood flow to the damaged hemisphere, but for a proportion, there was a quite paradoxical response in that optimal blood flow was seen if their head were at an elevated angle.

"HOB positioning is just one of several interventions commonly used in the treatment of stroke patients to increase CBF," Detre told SpectroscopyNow. "Others include giving fluids and withholding antihypertensive agents.  All of these interventions can theoretically improve CBF and therefore stroke outcomes, but there is really little data to show whether they work or in whom. We chose to look at HOB because a HOB position change is easy to study at the bedside in a short period of time."

Insult and injury

Stroke, also known as cerebrovascular insult (CVI), occurs when blood supply to the brain is disrupted acutely. A blockage (thrombosis, arterial embolism), or a haemorrhage in the brain or intracranial blood vessels is the usual cause, although the latter is not considered in this present research. Damage to the brain usually results and commonly leaves patients that survive with speech problems or paralysis down one side of their bodies, depending on which parts of the brain are affected. It can also cause cognitive deficit and problems with vision.

Rapid and appropriate treatment can minimise the effects of stroke. As such, an optical and non-invasive device for monitoring of blood flow at the patient's bedside is proving to be a boon to healthcare workers treating such patients. The key technology development is a near-infrared probe that is simply placed on the surface of the patient's head, the probe emits NIR and detects the reflections from within the brain, these fluctuate depending on the flow of red blood cells through the tissues within. This diffuse correlation spectroscopy (DCS) matches blood flow precisely, the team says, much more so than Transcranial Doppler (TCD), ultrasound scanning, which uses acoustic waves to quantify blood flow in the larger arteries supplying the brain.

"This study illustrates the potential of using advanced technology to make individualized treatment decisions in real time" explains senior author John Detre. "While, on average, our findings support current guidelines to lay patients flat following stroke, they also suggest that for some stroke patients, lying flat may be either unnecessary or even harmful. Future studies examining clinical outcomes after stroke and using optical CBF measurements to guide management will be needed to confirm this."

Improving outcomes at a stroke

Arjun Yodh adds that, "We believe that these optical CBF measurements are detecting brain tissue blood flow of local microvasculature that might differ due to injury." The team showed that for all patients, blood flow was reduced by 9 percent to the brain hemisphere with the stroke damage if the head-of-bed was elevated 15 degrees, but 17 percent lower when elevated to 30 degrees. But, in 29 percent of the patients, CBF improved with head elevation although no clinical nor radiological differences predicted this unexpected response.

"Our study suggests that it would be impossible for stroke clinicians to know whether HOB flat is optimal without actually measuring the response," stroke neurologist Michael Mullen explains. This may also be true for other clinical interventions such as administration of fluids, withholding antihypertensive therapies, or using medications to raise blood pressure. "The ability to measure cerebral blood flow continuously has tremendous potential and may one day allow clinicians to individualize therapy for each patient," he adds.

"We are currently using the technology to evaluate the effects of an intravenous saline bolus (fluids)," Detre told us. "Other future technical work includes improving the probes further, and expanding the number of probes.  For this study we only had two probes - one over each frontal lobe. Obviously it would be good to have more coverage over the brain."

Related Links

Stroke, 2014, online: "Optical Bedside Monitoring of Cerebral Blood Flow in Acute Ischemic Stroke Patients During Head-of-Bed Manipulation"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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