Effect of Vasoconstrictor Agents on the Duration of Action of Intrathecal Tetracaine, Bupivacaine and Lidocaine in the Dog

Both epinephrine and phenylephrine are capable of prolonging the duration of anesthesia when added to solutions of tetracaine intended for intrathecal use. Conflicting data exist concerning the relative efficacy of vasoconstrictor agents added to lidocaine and bupivacaine solutions intended for intrathecal use. The present investigation was initiated to study the comparative efficacy of epinephrine and phenylephrine in combination with tetracaine, lidocaine, and bupivacaine employing a model for spinal anesthesia in the dog. The results indicate that epinephrine and phenylephrine are capable of significantly prolonging the duration of motor blockade induced by tetracaine in the dog. When compared to plain solutions, no significant prolongation of motor blockade was observed following intrathecal administration of either lidocaine or bupivacaine with epinephrine and phenylephrine.