ABSTRACT
Local Anesthetic Solution The choice of local anesthetic and the addition of adjuvants for lower extremity peripheral nerve block are dependent on the anticipated duration of operation, the need for prolonged analgesia, and the timing of ambulation and weight bearing postoperatively. Prolonged blockade for 24 hours (or longer) may occur with long-acting agents such as bupivacaine, levobupivacaine, or ropivacaine. Although this feature may result in excellent postoperative pain relief for the inpatient, it may be undesirable or a cause for concern in the ambulatory patient because of the potential for falls with a partially insensate or weak lower extremity. A medium-acting agent may be more appropriate in the outpatient setting for orthopedic procedures associated with minimal to moderate postoperative pain. In general, equipotent concentrations of the long-acting amides have a similar onset and quality of block. However, bupivacaine may have a slightly longer duration than levobupivacaine or ropivacaine. Likewise, higher concentrations are more likely to be associated with profound sensory and motor block, whereas infusions of 0.1% to 0.2% bupivacaine or ropivacaine often allow complete weight bearing without notable motor deficits. Recent investigations have suggested that increasing the local anesthetic concentration alters the character (i.e., degree of sensory or motor block) but not the duration.
