Effect of tetracaine-induced spinal anesthesia on pial microcirculation in pentobarbital anesthetized rats

Local anesthetic is administrated intrathecally to produce spinal anesthesia. This study examines the effect of spinal anesthesia induced by intrathecal tetracaine on cerebral pial microcirculation in rats. We monitored changes in the mean arterial pressure, internal diameter (ID) of the pial arteriole, intracranial pressure, and red blood cell velocity. The regional cerebral blood flow was calculated from the product of cross sectional area and red blood cell velocity. To induce spinal anesthesia, tetracaine was administered via a polyethylene tube at the L4-5 intervertebral space after laminectomy. Arterial blood pressure was monitored via a catheter in the femoral artery. A left parietal craniotomy with an encapsulated cranial window was prepared for biomicroscopy. Change in the arteriolar ID was measured by image shearing. Red blood cell velocity was measured by the dual-slit photometric method and correlation technique. Three levels of spinal anesthesia were evaluated. Tetracaine at 0.1 and 0.2 mg/kg, which produced T10 and T6 sensory block, respectively, did not cause significant change of ID of the pial arteriole and red blood cell velocity. Tetracaine (0.3 mg/kg) produced total spinal block, resulting in a significant decrease of the calculated cerebral blood flow and caused brief pial arteriolar vasodilation followed by vasoconstriction. Our results show that total spinal anesthesia with tetracaine causes significant changes in rat cerebral microcirculation.