The Art and Science of Peripheral Nerve Blocks

Abstract

In this issue of Anesthesia and Analgesia, Marhofer et al. (1) have clearly demonstrated both the art and science of peripheral nerve blocks. Their magnetic resonance imaging (MRI) study of the distribution of local anesthetic after three-in-one block has laid to rest one of the most frequently discussed issues in regional anesthesia during the past 25 yr. They demonstrated that local anesthetic spread can be observed on MRI and that, after the injection of the femoral nerve in the inguinal region by using nerve stimulation, it is lateral, caudal, and slightly medial. This finding contradicts the long-standing teaching that the solution reliably spreads cephalad and bathes the lumbar plexus. This is the most objective evidence of local anesthetic distribution after peripheral nerve blockade. MRI opens a window to the rigorous scientific examination of peripheral nerve blockade that has not previously been available. Haven’t you ever wondered why microscopic changes of needle position can change the “twitch” observed with nerve stimulation, what difference bevel orientation makes to the success of peripheral nerve blocks, and whether additives change the distribution of local anesthetics during peripheral nerve blockade? This technology should help answer some of these basic questions. Why do we care about these questions? Regional anesthesia has never been more popular or in more demand by surgeons. Peripheral nerve blocks have enjoyed a resurgence because of their ability to improve home readiness after ambulatory surgery. A variety of factors influence discharge times after ambulatory surgery, but the most common reasons for delay in discharge are persistent pain, nausea, and drowsiness. Peripheral nerve blocks reduce the incidence of these factors by reducing the use of narcotics and eliminating the need for general anesthesia. In a study of factors influencing home readiness, peripheral nerve blockade for upper extremity surgery improved home readiness time by more than 70 min compared with “fast track” general anesthesia techniques (2). D’Alessio et al. (3) documented a 30-min improvement in street readiness after shoulder arthroscopy with interscalene block compared with general anesthesia. For lower extremity surgery, peripheral nerve blockade techniques are less well established but likely to be at least as effective as upper extremity peripheral nerve blockade. Ankle block has long been recognized as a safe and effective technique with a very high patient satisfaction rating (4). Vloka et al. (5) recently compared popliteal block to spinal anesthesia for short-vein stripping. The patients who received peripheral nerve blockade were discharged 70 min faster than those who received spinal anesthesia. Continuous peripheral nerve blocks improve rehabilitation scores and improve patient satisfaction compared with IV narcotic therapy after orthopedic surgery for both upper and lower extremity procedures. Borgeat et al. (6) improved pain scores and improved satisfaction for patients receiving continuous interscalene blockade for analgesia after major shoulder surgery compared with patients receiving IV narcotics. These authors particularly noted the improvement in analgesia during physical therapy. Rehabilitation is particularly important after total knee arthroplasty. Two studies have recently shown improvement in rehabilitation outcome after this procedure when continuous peripheral nerve blockade was compared with IV narcotics analgesia (7,8). Both studies confirmed lumbar plexus blockade to be as efficacious as epidural analgesia after total knee arthroplasty. However, continuous lumbar plexus blockade has several distinct advantages compared with epidural analgesia, including unilateral block, reduced urinary retention, and reduction of the low but real risk of spinal hematoma in the anticoagulated patient receiving epidural analgesia. Clearly, the time to spread the gospel of peripheral nerve blockade techniques has arrived. The importance of these techniques in providing safe and highly effective analgesia is no longer questioned. Our challenge now is to obtain a deeper understanding of the nuances of peripheral nerve blockade in order to demystify it for the rest of the world. Regional anesthesia has enjoyed a unique niche in the anesthesia world. It has defied scientific innovation in our technology-obsessed specialty. It remains a mystery to most of our anesthesia brethren. Regional anesthesia enthusiasts are viewed as part shaman, part acupuncturist, and part artist by many of their colleagues. Nonregional enthusiasts are usually that because of the inconsistencies that have seemed inherent in the practice of regional anesthesia. Even in the study of Marhofer et al. (1), there is objective evidence of local anesthetic distribution encompassing the femoral and lateral femoral cutaneous nerve in all patients. Yet only two of seven patients had complete obliteration of all sensation in the distribution of these nerves. As we are pushed to be more cost effective and time efficient, we must rigorously study the nuances of peripheral nerve blockade technique. Marhofer et al. (1) are to be congratulated for opening this window and shedding some scientific light on this timely topic.