SPINAL ANESTHETIC AGENTS

Lidocaine, tetracaine, and bupivacaine are the local anesthetic agents most commonly employed for spinal anesthesia in the U.S. Lidocaine provides a short duration of anesthesia and is primarily useful for surgical and obstetrical procedures lasting less than one hour. Tetracaine and bupivacaine are used for procedures lasting 2 to 5 hours. Tetracaine appears to provide a somewhat longer duration of anesthesia and a more profound degree of motor block than does bupivacaine. On the other hand, compared with tetracaine, bupivacaine has been demonstrated to be associated with a decreased incidence of hypotension. In addition, bupivacaine may be better than tetracaine for use in orthopedic surgical procedures since it appears to be associated with a lower incidence of tourniquet pain. Vasoconstrictors can prolong the duration of spinal anesthesia of all three agents. However, the greatest duration is seen when vasoconstrictors are added to tetracaine solutions. Lidocaine and bupivacaine do not appear to benefit as much from the addition of vasoconstrictors. In general, the local anesthetic agents that are currently available for spinal anesthesia provide significant versatility. By carefully considering the planned surgical procedure, the surgeon's requirements, and the patient's characteristics (e.g., age, height, gravidity), and by understanding the factors that influence spinal anesthesia, the anesthesiologist can select a local anesthetic agent that will assure adequate and satisfying spinal anesthesia.