P51. Feasibility study of a non-invasive laser-Doppler spectrophotometry system for intraoperative monitoring of local microcirculation

Abstract

Question To evaluate non-invasive measurement of cortical microcirculation using a novel laser-Doppler spectrophotometry system in a surgical setting. Methods Local cerebral microcirculation was measured using the non-invasive laser-Doppler spectrophotometry system “Oxygen-to-see (O2C)” in sixteen patients with incidental aneurysms of the anterior and middle cerebral arterial circulation. A subdural fiber optic probe was placed on the cortex after dural incision. Capillary venous oxygenation (SO2), post-capillary venous filling pressures (rHb), blood cell velocity (velo) and blood flow (flow) were measured in 7 mm tissue depth. The measurement site corresponded to the supply territory of the aneurysmatic blood vessel. For routine monitoring we used both micro-Doppler ultrasound and ICG angiography. Additionally, we performed monitoring of somatosensory evoked potentials (SEP) with median and posterior tibial nerve stimulation. Results The sampling rate was 2 Hz for the spectrophotometry system and 40 Hz for the laser-Doppler flowmeter. Representative recordings were acquired immediately after dural opening over a time span of 42–238 s before surgical manipulation. Normal values (median, SD) for each parameters were, in consecutive order: SO2 39 ± 9.1 %, rHb 51 ± 10.2 AU (arbitrary units), velo 57 ± 10.2 AU, and flow 310 ± 33.8 AU. Statistical analysis proved good reproducibility of the measurement system and the obtained values. SEP monitoring revealed no changes in latency or amplitude of N20 or P40. In all elective microsurgical clippings, no postoperative neurological deficit occurred. Conclusions This combined laser-Doppler flowmetry and spectrophotometry system is able to measure local brain microcirculation with the parameters SO2, rHb, velo and flow. It can be integrated in routine surgical setting. In ongoing studies we will investigate the predictive value in the assessment of microcirculatory insufficiency.