Abstract
The authors have developed a brain retractor with optical probes for monitoring the oxygenation state of living tissue for the purpose of preventing tissue damage during brain retraction. In neurosurgical operations, brain retraction is an essential technique. If the mechanical stress induced on the brain tissue during retraction is too high, blood vessels can become occluded and the resultant blocking of blood flow could cause low oxygen saturation (SO2), which may damage the brain tissue. Neurosurgeons know the safety limit for retraction based on past experience, however a technique to monitor the oxygenation state of retracted tissue is required. We have developed a retractor with optical probes that enables the quantitative measurement of SO2 in the retracted tissue. One optical fiber that emits near infrared light and three optical fibers for detecting the light reemitted from the brain surface are built into the retractor. The emitted light propagates in the brain tissue through absorption and scattering. The absorption of light occurs in the endogenous chromophores of the tissue, such as oxyhemoglobin, deoxyhemoglobin or cytochrome oxidase. The intensities of the reemitted light are measured (λ=780, 805, 830nm) and processed to calculate the SO2 in the brain tissue by means of spatially resolved spectroscopy. The relationship between mechanical stress and SO2 in a piglet brain has been obtained experimentally, and the feasibility of SO2 measurement using the retractor with optical probes during brain retraction has been confirmed by experiments using phantoms and piglet brains.
