In vivo diffusion-weighted magnetic resonance microscopy of rat spinal cord:: Effect of ischemia and intrathecal hyperbaric 5% lidocaine

Background and Objectives. Pathophysiologic mechanisms underlying persistent neurologic deficits after continuous spinal anesthesia using hyperbaric 5% lidocaine are still not well understood. It has been suggested that high-dose intrathecal lidocaine induces irreversible conduction block and even ischemia in while matter tracts by breakdown of the blood-nerve barrier. In this study, we use diffusion-weighted magnetic resonance microscopy to characterize the effect of intrathecal hyperbaric 5% lidocaine in rat spinal cord. The parameter measured with DWM, is an "apparent diffusion coefficient," (ADC), which can be used to exclude the presence of ischemia. Methods. Female Fischer CDP rats were used. Group 1 (n = 5) was exposed to ischemia, group 2 (n = 7) was exposed to intrathecal 5% hyperbaric lidocaine, and group 3 (n = 5) was exposed to intrathecal 7.5% glucose. Diffusion-weighted MR images in group 1 were acquired before and after ischemia induced by cardiac arrest and in groups 2 and 3 rats prior to and during perfusion of the spinal catheter with either 5% hyperbaric lidocaine or 7.5% glucose. Results. Ischemia decreased the ADC by 40% in gray matter and by 30% in white matter of spinal cord. Continuous intrathecal anesthesia with hyperbaric 5% lidocaine did not affect the spinal cord ADC. Further, 7.5% intrathecal glucose had no effect on ADCs in gray or while matter of spinal cord. Conclusions. Ischemia reduced the ADC in both spinal cord white and gray matter. Hyperbaric 5% lidocaine did not affect the spinal cord ADC during the first 1.5 hours. We suggest that 5% hyperbaric lidocaine does not induce irreversible neurologic deficits by causing spinal cord ischemia.