A comparison of sensory and motor loss after a femoral nerve block conducted with ultrasound versus ultrasound and nerve stimulation.

BACKGROUND: Controversy exists regarding the need for nerve stimulation when performing an ultrasound (US)-guided peripheral nerve block. We tested the hypothesis that the quality of a femoral nerve block (FNB) performed with US is equivalent to an FNB performed with US and nerve stimulation. METHODS: One hundred seven patients undergoing unilateral total knee arthroplasty were randomized to receive either a US-guided FNB (group US) or a US-guided FNB with nerve stimulation (group USNS). Thirty milliliters of bupivacaine 0.5% was injected in both groups. At 10, 20, 30, and 40 mins after block placement, blinded motor and sensory examinations were conducted. Secondary outcomes included time to perform the block, the number of needle redirections, and 24-hrs intravenously administered morphine equivalent consumption. RESULTS: There were no significant differences in the proportion of patients with either a partial or complete block. At 40 mins, 95.7% of the USNS subjects had a partial or complete sensory block of the femoral nerve (complete in 71.7% and partial in 24%) compared with 88.1% of US subjects (complete in 69% and partial in 19.1%; odds ratio, 2.97; P = 0.19). There were more needle redirections in group USNS (4.1 vs 1.1, P < 0.001), with a higher percentage of patients requiring 2 or more needle attempts (44.2% vs 18.9%, P < 0.01). The time to perform the block in group USNS was longer (188 vs 148 secs, P = 0.01). CONCLUSION: The addition of nerve stimulation to a US-guided FNB did not change preoperative block efficacy.

Ultrasound improves the success rate of a tibial nerve block at the ankle.

BACKGROUND: The tibial nerve provides the majority of sensation to the foot. Although multiple techniques have been described, there exists little evidence-based medicine evaluating different techniques for blocking the tibial nerve at the ankle. We hypothesized that an ultrasound (US)-guided tibial nerve block at the ankle would prove more successful than a conventional approach based on surface landmarks. METHODS: Eighteen healthy volunteers were prospectively randomized into this controlled and blinded study. Each subject was placed prone, and one ankle was randomly assigned to receive either an US-guided tibial nerve block (group US) or a traditional landmark-based tibial nerve block (group LM). The subject's other ankle then received the alternate approach. All blocks were performed with 5 mL of 3% chloroprocaine. We evaluated sensory and motor blocks. A successful block was defined as complete loss of sensation to both ice and pinprick at 5 cutaneous sites. Secondary outcome variables included performance times, number of needle passes, participant satisfaction, and presence of any complications. RESULTS: At 30 mins, the block was complete in 72% of participants in group US as compared with 22% in group LM. At all times, the proportion of complete blocks was higher in group US. Ultrasound-guided blocks took longer on average to perform than traditional blocks (159 vs 79 secs; P < 0.001). There were more needle redirects in group US, with 8 subjects requiring 3 or more redirects versus none in group LM. Subjects preferred the US block 78% of the time (95% confidence interval, 52%-95%). CONCLUSIONS: In healthy volunteers, US guidance results in a more successful tibial nerve block at the ankle than does a traditional approach using surface landmarks.

Ultrasound improves the success rate of a sural nerve block at the ankle.

BACKGROUND AND OBJECTIVES: : During ankle block performance, anesthetizing the sural nerve is important for generating complete anesthesia of the lateral aspect of the foot. We hypothesized that an ultrasound-guided perivascular approach, utilizing the lesser saphenous vein as a reference, would prove more successful than a conventional approach based on surface landmarks. METHODS: : Eighteen healthy volunteers were prospectively randomized into this controlled and blinded study. Each subject was placed prone and the right ankle was randomized to receive either an ultrasound-guided perivascular sural nerve block (group US) or a traditional landmark-based sural nerve block (group TRAD). The subject's left ankle then received the alternate approach. The ultrasound technique relied on injecting local anesthetic circumferentially around the lesser saphenous vein. All blocks were performed with 5 mL of 3% chloroprocaine. We evaluated sensory block to ice and pinprick. Secondary outcome variables included performance times, number of needle passes, participant satisfaction, and presence of any complications. RESULTS: : At the midfoot position, testing at 10 minutes after block placement revealed a loss of sensation to ice in 94% (complete in 78% and partial in 16%) in the US group versus 56% in the TRAD group (complete in 28%, partial in 28%) (P <.01). Complete loss of sensation to ice persisted in 33% of the US group as compared with 6% in the TRAD group at 60 minutes (P <.05). A similar pattern was observed when the blocks were tested with pinprick. Ultrasound-guided blocks took longer to perform on average than the traditional blocks (mean difference of 102 seconds, P <.001). The ultrasound block was subjectively felt to be denser by 88% of the subjects (P =.001). CONCLUSIONS: : Ultrasound guidance using the lesser saphenous vein as a reference point results in a more complete and longer lasting sural nerve block than does a traditional approach using surface landmarks.