Location, location, location: Continuous peripheral nerve blocks and stimulating catheters.

C ontinuous peripheral nerve blocks offer the potential benefits of extended site-specific postoperative analgesia, few side effects, improved patient satisfaction , and accelerated functional recovery after extremity surgery. 1 Continuous peripheral nerve blocks provide superior analgesia compared with intravenous patient-controlled analgesia and a lower incidence of side effects compared with either intravenous patient-controlled analgesia or continuous lumbar epidural analgesia. 2-5 Prospective, randomized clinical studies have demonstrated the effectiveness of ambulatory continuous peripheral blocks after painful orthopedic procedures. 6,7 A major concern with the use of continuous peripheral nerve block is placement of the catheter close enough to the nerve to allow effective analgesia with the small amounts of dilute local anesthetic solutions utilized for the " secondary analgesic block " after the initial primary anesthetic block has resolved. Large case series have demonstrated failed secondary block in up to 10% of patients, despite receiving a large bolus of concentrated local anesthetic. 8,9 Recent studies using injected contrast media exiting at the catheter tip have demonstrated that despite the ease of " successful insertion, " the direction of continuous femoral catheters is unpredictable. 9,10 Given the expected increase in the clinical use of continuous peripheral blocks, a reliable method to immediately verify correct peripheral catheter position is needed to prevent secondary analgesic block failures. Otherwise, patients will be subject to a technique with possible risks, but no benefit. Traditionally, correct catheter placement has been confirmed by testing for a clinical effect of satisfactory analgesia and or by sensory modality testing within the desired sensory distribution. Many continuous studies have initiated primary block via the stimulating needle, followed simply by blind insertion of the peripheral catheter 5 to 15 cm beyond the needle tip. Communication with colleagues who have significant experience in placing peripheral catheters reveals up to 40% secondary analgesic block failure rate (via the peripheral catheter infusion). My personal experience with placing continuous peripheral catheters confirms this impression. In order to avoid secondary block failure, the primary block can be injected through the peripheral catheter. Lack of satisfactory anesthesia after injection of local anesthetic would then indicate an improperly positioned catheter prior to initiating continuous perineural analgesia. However, even this approach may require several attempts to localize the peripheral nerve and then correctly place the catheter, as well as injection of an additional bolus of local anesthetic. In this issue of Regional Anesthesia and Pain Medicine, Pham-Dang et al. 11 …