Near-Infrared Spectroscopic Examination of Alterations in Brain Surface Blood Flow following Stellate Ganglion Block

Background: Stellate Ganglion Block (SGB) is used to treat pain and other disorders, but the target diseases of SGB are controversial because the mechanisms underlying SGB remain unclear. Increased cerebral blood flow is one of the processes presumed to be involved. The aim of this study was to clarify the effects of SGB by using nearinfrared spectroscopy to measure brain surface blood flow during and after SGB. Methods: The participants were nine healthy staff volunteers. Near-infrared spectroscopy was applied to subjects’ heads, and the same operator performed a right SGB (1% mepivacaine 4 ml). Changes in oxy-hemoglobin (oxy-Hb) concentration were measured from approximately 30 s before administering SGB until approximately after 30 min. Results: For the mean brain waves between the right (block) side channels, oxy-Hb concentration immediately increased after SGB in four subjects, while it temporarily decreased after SGB and then increased in five subjects. For the mean brain waves between the left (contralateral) side channels, oxy-Hb concentration markedly decreased after SGB in four subjects. In three subjects, it temporarily increased immediately after SGB but decreased after approximately 15 min. almost no change in oxy-Hb concentration was observed in the remaining two subjects. Overall, oxy-Hb concentration increased in all subjects on the right (block) side. Discussion: Increased oxy-Hb concentrations suggest that SGB relaxed vascular tone, increased the capillary bed, and enhanced blood flow. However, oxy-Hb concentration temporarily decreased before it increased in five subjects. We assume that during the temporary decrease, blood flow was unable to keep up with this rate of increase in the capillary bed. In four subjects, oxy-Hb concentration markedly decreased contralateral to the block. This may have been due to higher blood volume on the block side, but the reasons are not fully known.