Spinal cord blood flow after intrathecal injection of ropivacaine and bupivacaine with or without epinephrine in rats

Background: Ropivacaine is a new local anaesthetic available for spinal and epidural anaesthesia. When new drugs are being introduced for spinal application, their effect on spinal cord blood flow (SCBF) should be studied for safety and toxicological aspects. In the present study, SCBF was studied after intrathecal (i. t.) application of ropivacaine and bupivacaine with and without epinephrine.
Method: SCBF was measured continuously in spontaneously breathing, enflurane/N₂O anaesthetized rats, using laser-Doppler flowmetry technique. The spinal cord was exposed by laminectomy at the L₁-L₂ level, and a laser-Doppler probe was placed over the dorsal horn, allowing on-line registration of SCBF in a tissue hemisphere of 1–2 mm. Relative changes in SCBF were then measured on-line after i. t. administration of increasing doses of ropivacaine, bupivacaine or bupivacaine with epinephrine.
Results: Ropivacaine and bupivacaine decreased SCBF in a dose-dependent manner. In contrast, the reduction in SCBF produced by bupivacaine + epinephrine (Bupi+Epi) was equal for all doses of bupivacaine. The order of magnitude of SCBF decreases was Bupi + Epi >ropivacaine>bupivacaine. The maximal decrease in SCBF at the highest concentration given (10 mg/ml) was 37±6% for ropivacaine, 27±7% for bupivacaine and 40 ±6% for bupivacaine + epinephrine.
Conclusion: Ropivacaine and bupivacaine produce a dose-related, transient decrease in SCBF following i. t. administration in anaesthetized rats. However, the decrease in SCBF produced by both ropivacaine and bupivacaine was less than that produced by bupivacaine, when epinephrine was added in a concentration of 5 μg/ml. These results suggest that ropivacaine, like bupivacaine, may be used for spinal anaesthesia without important effects on SCBF.