Combined Ultrasound and Nerve Stimulator-guided Deep Nerve Block May Decrease the Rate of Local Anesthetics Systemic Toxicity

A Randomized Clinical Trial

Xu-hao Zhang; Yu-jie Li; Wen-quan He; Chun-yong Yang; Jian-teng Gu; Kai-zhi Lu; Bin Y


BMC Anesthesiol. 2019;19(103) 

In This Article

Block Preparation

LPBs and SNBs were performed preoperatively by 1 of 3 attending anesthesiologists who were skilled in peripheral nerve blocks with both ultrasound guidance (US) and nerve stimulator guidance (NS). All of them had been in clinical practice with a focus on regional anesthesia for at least 5 years. After arriving in the operating room, the patient was placed in the lateral decubitus position with the surgical limb uppermost and monitored continuously via electrocardiography, SpO2 measurements, and non-invasive blood pressure monitoring during the nerve blockade and surgery. Both the ultrasound and nerve stimulation systems were prepared and positioned conventionally in each group. The ultrasound machine and nerve stimulator were turned on, and a grounding lead was placed on the lateral aspect of the leg being blocked for each group. The patient's group allocation was given to the anesthesiologist only after the preparation of both systems and just before the block procedure. The patient was pretreated with 0.05 mg/kg midazolam and 1.5 μg/kg fentanyl. The injection site was prepared with chlorhexidine gluconate. Five millilitres of 0.5% lidocaine was injected subcutaneously at the site of needle insertion. The LA mixture was composed of 200 mg of ropivacaine, 200 mg of lidocaine and 20 ml of 0.9% sodium chloride solution. The concentration of ropivacaine and lidocaine was 0.4%. The total amount of LAs used was determined by the dosage of ropivacaine needed, namely, 3 mg/kg. The patient and investigators assessing the block quality prevented from seeing both the block procedure itself and the sonographic image displayed by an opaque screen. According to the group allocation, the patient received the nerve blocks under one of the following three techniques.

Nerve Stimulation Technique

In the operating room, LPB was performed using Chayen's approach.[13,14] The puncture site was located 4–5 cm lateral to the posterior midline along the intercristal line. A 110-mm, 22-G stimulating needle connected to a nerve stimulator (Stimuplex HNS 11, B. Braun) was advanced perpendicular to the skin. The nerve stimulator was set to a pulse duration of 0.1 ms, current intensity of 1.0 mA, and frequency of 2 Hz. The stimulating intensity was progressively reduced to 0.4 mA or less while maintaining the twitch in the quadriceps distribution. The total volume of LAs was determined by the amount of the LA mixture calculated according to the patient's weight, as mentioned above. Each point was given half of the total calculated volume of the LA mixture. When the correct needle position was achieved based on evoking the desired motor response, the amounts of LAs described above were injected. SNB was performed with the classic Labat approach.[15] The needle was inserted 5 cm below the midpoint of a line connecting the posterior superior iliac spine and the greater trochanter. After an appropriate stimulus was localized in the sciatic distribution, the LAs described above were injected.

Ultrasound-guided Technique

We chose the "Shamrock Method" for the LPBs.[16] A sterile cover was placed on a 3-MHz low-frequency ultrasound probe (LOGIQe 4C-RS, GE Inc., USA). The ultrasound transducer was positioned on the line connecting the subcostal margin and iliac spine and adjusted until a clear view of the psoas, erector muscle and quadratus lumborum appeared. The hyperechoic structure located in the posterior internal quadrant of the psoas was the lumbar plexus. The puncture site was beneath the probe and 4–5 cm lateral to the vertebral body. We chose a subgluteal approach for the SNBs.[17] The ultrasound transducer was positioned perpendicular to the skin on the line connecting the ischial tuberosity and greater trochanter, and a clear transverse image of the hyperechoic sciatic nerve between the ischial tuberosity and greater trochanter was obtained. For the LPBs and SNBs, the needle placement and LA spread were confirmed by ultrasound visualization. After the proper needle placement was confirmed, incremental injection of the same LA solution in the same volume was performed as previously described until circumferential spread around the nerve was obtained. The needle was redirected, when required, to achieve this goal. In group M, initially, needle-to-nerve guidance was applied as in group U. Maintaining the needle nerve position, the nerve stimulator was set as described for group N. When the correct needle position was achieved based on evoking the desired motor response, the LAs described above were injected.

Block Evaluation

Evaluation of the nerve blocks was performed by an investigator blinded to those who administered the LPBs and SNBs. The motor and sensory responses in the nerve distribution area were assessed every 5 min until complete motor and sensory effects were achieved. If it took more than 30 min to achieve sensory loss in both distributions after the end of the LAs injection, the block was considered to have failed. The attending anesthesiologist had the right to perform general anesthesia, rescue block, or supplementation with a local field block in case of a failed block. The motor block was assessed with a modified Bromage scale: 2, full motor strength; 1, decreased strength; and 0, no strength. Similarly, the sensory block was evaluated with ice: 2, full sensation (no change); 1, decreased sensation; and 0, no sensation.

Postoperative follow-ups were performed in the post-anesthesia care unit and by telephone within 72 h after the procedure by clinical personnel in addition to study-related procedures.


The primary outcome was the incidence of LAST. LAST can present with clinical manifestations related to both the central nervous system (CNS) and the cardiovascular system (CVS). CNS symptoms include tongue numbness, tinnitus, light-headedness, metallic taste, nystagmus, confusion, tremors, agitation, seizures, coma, and respiratory arrest.[18] CVS symptoms include tachycardia, arrhythmias, hypertension, and later toxic symptoms, such as bradycardia, cardiac depression, cardiovascular collapse, and asystole.[18] The secondary outcomes were the quality of the nerve block and associated risk factors. The quality of the block included the number of needle redirections, motor and sensory block onset and restoration times in the lumbar and sciatic nerve distributions. The associated risk factors included age, sex and comorbidities. The number of needle redirections was counted as the number of times the needle was withdrawn by at least 10 mm with subsequent forward movement. The upper limit of redirections was 20, but if necessary, the needle was allowed to be redirected as many times as possible to achieve proper placement, as previously described. The onset of motor and sensory block was assessed using the modified Bromage scale as mentioned above for the distributions of both the lumbar plexus and sciatic nerves. The onset time was measured between the final LA injection and the first observation of a 0 score. During the phone follow-up interviews, the patient provided the time of first return of sensation and any block-related complications on postoperative day 1. The block duration time was defined as the interval between block completion and the first return of sensation. Any reported complications were recorded.

Statistical Analysis

The statistical analyses were performed using Statistical Package for the Social Sciences (Windows Software, version 19.0; SPSS Inc., Chicago, IL) and Power Analysis and Sample Size (Windows Software, version 11.0; NCSS Inc., Utah).

Demographic and perioperative data are expressed as the mean and standard deviation. Parametric and non-parametric Kolmogorov–Smirnov tests were applied to assess normality. The primary outcome (incidence of LAST) and potential risk factors were compared by χ 2 test or Fisher exact test when appropriate (n < 5 in any field). In the χ 2 test, we tested whether there were differences in the incidence of LAST and the odds ratios of potential risk factors among different groups. The demographics and secondary outcomes were compared among the three groups by one-way ANOVA, followed by multiple comparisons using the LSD test or Welch and Dunnett's T3 test for unequal variances. Using one-way ANOVA, we tested whether there were differences in the patient characteristics and block quality among the three groups. This analysis was followed by the determination of 95% CIs with Bonferroni's correction to adjust for multiple comparisons (three different methods for nerve block for motor and sensory onset, restoration time and demographics) to minimize the chance of a type I error (0.05). For all comparisons, 2-tailed P values < 0.05 were considered statistically significant.

The incidence of LAST is low according to published data. Therefore, we performed a test to determine the power of the analysis regarding the incidence of LAST in the three groups after the experiment. In the current study, 319 patients were randomly allocated to the three groups. Finally, data from 100 patients for each group were analysed. We performed a test to determine the power of the analysis regarding the primary outcome after the experiment. We calculated the effect size (0.182) using PASS software. Then, we set the significance level to 0.05. We found that when the total sample size was 300, the power(1-β) of the test was 0.81.