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Raman probe can help pinpoint epidural injections

05 Apr 2016

MIT group led by Peter So develops optical technique to reduce complications from misplaced anesthetic delivery.

by Matthew Peach in Brussels
The Raman4Clinics conference at Photonics Europe 2016 yesterday heard how a fine Raman probe fitted inside a standard “gauge 17” epidural needle can improve the positional accuracy of the injection of anesthetic, such as is used to relieve labor pain in childbirth. A prototype system has been developed by the team of Professor Peter So at MIT, which he is hoping to see commercialized and in clinical use “within the next year or so.”

He introduced his presentation with some facts and figures about the frequency and purposes of epidural procedures in the US: “About five million epidural catheters are inserted per year, typically for labor or surgical pain control. Currently epidural catheter placement relies on the clinician’s experience; feeling the sensation of loss of resistance (LOR) to the needle in the tissues surrounding the spinal cord.”

This subjective approach and variability of patient tissues, considering factors such as age and obesity, leads to complications arising from needle tip misplacement, including: failed block (no or low pain relief) typically in 5-10% of cases; postdural puncture headaches due anesthetic entering the wider neural system (1-3%); and serious neurological injury (rare).

So said, “Epidural catheter placement would benefit from the ability of the clinician to distinguish different tissue types at the tip of the needle. Spectroscopic tissue diagnosis, using Raman spectroscopy, is a method to differentiate these types of tissue the needle passes through.”

“To develop ours systems we have dissected the tissue overlapping the spinal cord and applied Raman spectroscopy to develop characteristic spectra for the different tissues,” he said. The layers include skin, fat, muscle, ligament and the spinal cord itself. The ideal position to deliver the anesthetic drug is in the epidural space, located between the vertebrae and the spinal cord.

Raman spectroscopy can identify every tissue layer from the skin through to the spinal cord. The epidural space can be precisely identified based on Raman spectroscopy signal collected by a narrow probe contained within the needle itself.

This combined approach would mean that the clinician could still rely on his or her experience of the LOR while benefiting from the positional information indicated by the Raman probe.

Recent developments

So’s group has set up a company called Biosight, which has applied for NIH, NSF, STTR business development development grants. Biosight was selected as one of the finalists in the MIT $100K startup competition. “We are currently negotiating a deal with medical device and pharmaceutical companies regarding licensing. The way that we expect to commercialize this will be that it will be a joint procedure – in conjunction with the surgeon’s LOR approach."

So anticipates that following refinement of the technology and the procedure, which will involve in vivo animal research (early spectral tests have been conducted on pig spinal columns) followed by human cadaver studies. “Our Raman-assisted epidural procedure could be developed as a clinical procedure within a year or so. But developing this as a product will depend on whether we can raise enough funds.”

About the Author

Matthew Peach is a contributing editor to optics.org.

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