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REGIONAL ANESTHESIA

Combined Ultrasound and Neurostimulation Guidance for Popliteal Sciatic Nerve Block: A Prospective, Randomized Comparison with Neurostimulation Alone

Eric Dufour, MD^*, Patrick Quennesson, MD, Anne Laure Van Robais, MD^*, Françoise Ledon, MD, Pierre-Antoine Laloë, MD^*, Ngai Liu, MD^*, and Marc Fischler, MD^*

From the *Department of Anesthesiology, Hôpital Foch, Suresnes, France; Departments of Anesthesiology, and Surgery, Clinique La Montagne, Courbevoie, France.

Address correspondence and reprint requests to Prof. M. Fischler, Department of Anesthesiology, Hôpital Foch, 40 rue Worth, 92151 Suresnes, France. Address e-mail to m.fischler{at}hopital-foch.org.

	Abstract

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BACKGROUND: Ultrasound imaging, an effective tool to localize peripheral nerves, may facilitate block performance. However, its usefulness during popliteal sciatic nerve block has not been assessed.

METHODS: In this prospective, randomized, patient-blinded study, we compared the block time (as the primary end-point) of a popliteal sciatic nerve block with double-injection performed using anatomical landmarks and neurostimulation (NS group; n = 30) versus combined ultrasound and neurostimulation guidance (US-NS group; n = 30). Each block procedure was performed by a single operator. Correct needle placement was defined by a minimal stimulating current 0.5 mA, or, in the US-NS group, by mobilization of the nerve by the needle shaft even if the minimal stimulating current >0.5 mA. Ten milliliter levobupivacaine 0.5% was administered separately on the tibial and common peroneal nerves without needle adjustment to improve the spread of anesthetic in the US-NS group. All procedures were video-recorded, and a maximum of 7 min was allowed to perform the block. Successful block was defined as complete loss of cold sensation in the sciatic distribution and an inability to perform a plantar and dorsal flexion of the foot at 30 min.

RESULTS: Five patients in the NS group and three in US-NS group were excluded from the study for prolonged procedure. Block time was not significantly different between groups. The number of needle passes was lower only for the detection of the first nerve in the US-NS group (1 [1–2] vs 2 [1–6]; P < 0.01). A greater success rate was observed at 30 min in the US-NS group (65% vs 16%; P < 0.001).

CONCLUSIONS: Combined ultrasound and neurostimulation guidance does not decrease block time but increases the success rate of popliteal sciatic nerve block observed at 30 min.

	Introduction

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Ultrasound imaging allows direct visualization of nerve structures, needle guidance in real-time to the target, and observation of local anesthetic diffusion.1 Using various techniques of nerve localization, high success rates ranging from 79% to 100% have been reported.2–7 We hypothesized that ultrasound can help localize both branches of the sciatic nerve and decrease block time during popliteal sciatic nerve block with double injection. The present study was designed to compare a conventional technique (anatomical landmarks and neurostimulation) with combined ultrasound and neurostimulation guidance.

	METHODS

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After University Ethics Committee approval and written informed consent, 60 adult patients, ASA physical class I or II, scheduled to receive a sciatic nerve block for foot surgery, were enrolled in this prospective, randomized, patient-blinded study. Exclusion criteria included type 1 and type 2 diabetes mellitus, history of clinical or laboratory evidence of abnormal bleeding, infection at the injection site, allergy to local anesthetics, or preexisting central or peripheral neurological or muscular disease. Patients taking analgesics for neuropathic pain were also excluded. Patients were randomly assigned to the neurostimulation group (popliteal sciatic block guided by anatomical landmarks and neurostimulation, NS group) or to the ultrasound-neurostimulation group (popliteal sciatic block guided by ultrasonic landmarks and neurostimulation, US-NS group) by using a random number table.

All patients were orally premedicated with hydroxyzine 50 mg approximately 60 min before arrival in the operating room.

IV sedation (1 mg of midazolam and 5 µg of sufentanil) was given before the block. No other sedation was administered until the end of the evaluation period. Standard monitors were applied (electrocardiogram, noninvasive arterial blood pressure, and pulse oximetry). Patients were in prone position with the leg fully extended beyond the mattress edge to allow movement of the foot. The entire procedure was video recorded to allow a precise post hoc analysis of needle movements. All blocks were performed using a 20 degree bevel, 22-gauge, 50-mm insulated needle (Temena, Bondy, France) attached to a Stimuplex HNS11® peripheral nerve stimulator (Braun, Boulogne-Billancourt, France).

The popliteal sciatic blocks in the NS group were performed by an experienced anesthesiologist (PQ) according to the intertendinous approach.4 Patients were asked to flex their knee. The tendons of the biceps femoris and semitendinosus muscles were palpated and marked. After skin preparation, the needle was inserted perpendicularly to the skin halfway between these two tendons, 7 cm above the popliteal fossa crease. The stimulation frequency was set at 1 Hz, the impulse duration at 0.1 ms, whereas the intensity of the stimulating current initially set to deliver 1.5 mA was gradually decreased to obtain the minimal stimulating current. The needle was repositioned until the minimal stimulating current was 0.5 mA. The two components of the sciatic nerve were identified: plantar flexion for the tibial nerve and dorsiflexion or eversion for the common popliteal nerve. Foot inversion was not considered as an appropriate response because it can result from stimulation of either the tibial nerve or the common peroneal nerve.8 The anesthetic solution consisted of 10 mL of levobupivacaine 0.5% administered separately on the tibial and common peroneal nerves (i.e., 20 mL total volume) after aspiration.

The popliteal sciatic blocks in the US-NS group were performed by an anesthesiologist experienced in regional anesthesia under ultrasound guidance (ED). Patients were positioned as in the NS group. The popliteal region was scanned using a GE Logiqbook® Ultrasound System equipped with a linear 5- to 10-MHz probe (8 L) (GE Medical Systems, Milwaukee, WI). After aseptic preparation of the puncture site, the probe inside a sterile cover was applied horizontally on the posterior thigh 7 cm above the popliteal crease. In a transverse view, the sciatic nerve appeared as a round hyperechoic structure (Fig. 1). To differentiate the sciatic nerve from muscles and to identify its two components from each other, passive movements of the foot were performed during this short axis ultrasound examination. The seesaw sign observed corresponds to a displacement toward the posterior aspect of the thigh (i.e., towards the ultrasound probe) of the tibial nerve and the common peroneal nerve during a dorsiflexion and a plantar flexion, respectively.9 The nerve was located according to the short axis out of plane technique, the needle being advanced just below the midpoint of the ultrasound probe toward each of the two components.1 Simultaneously, a second anesthesiologist operated the nerve stimulator. For the localization of the first nerve, stimulation frequency was set at 2 Hz, the impulse duration at 0.1 ms, and the intensity of the stimulating current at 0.5 mA. The needle was repositioned until the minimal stimulating current was 0.5 mA, and then 10 mL of levobupivacaine 0.5% was administered after an aspiration test to exclude vascular puncture. For the localization of the second nerve, stimulation frequency and impulse duration were not modified, but the initial intensity of the stimulating current was set at 1 mA; the remainder of the procedure was identical (needle repositioning until the minimal stimulating current was 0.5 mA before injection of 10 mL of levobupivacaine 0.5%). If the needle seemed to be in contact with a nerve structure (mobilization of the nerve by the needle shaft) and the intensity of the stimulating current was more than 0.5 mA, the needle was not repositioned. For each injection, the spread of local anesthetic was observed, but the needle was never repositioned to improve its distribution around the nerve.

View larger version (51K): [in this window] [in a new window]   Figure 1. Transverse echographic view of the sciatic nerve.

A maximum of 7 min was allowed to locate and perform the two injections. At that time, ultrasound guidance was used in the NS group as a rescue technique and was continued in the US-NS group.

Patients returned to supine position and an additional saphenous nerve block was performed to prevent tourniquet pain. This nerve was blocked by the approach described by Bouaziz et al.10 with 10 mL of lidocaine 1.5% with epinephrine (1:200.000) or with infiltration at the medial surface of the tibia with 6 mL of the same solution.

Evaluation of sensory and motor block was performed every 5 min in all nerve territories over a 30-min period by an independent observer blinded to the procedure used. Sensory block was evaluated by comparing the cold sensation elicited by ice on the sole of the foot (for the tibial nerve), on the dorsum of the foot (for the superficial peroneal nerve), in the space between the first and second toes (for the deep peroneal nerve), and on the lateral aspect of the foot (for the sural nerve) with the same stimulus delivered to the contralateral side. Sensory block rating was quantified as follows: normal sensation = 0 (no block), reduced sensation = 1 (partial block), or total loss of cold sensation = 2 (complete block). Motor block was evaluated using plantar flexion (tibial nerve) or dorsiflexion (common peroneal nerve), and scored as follows: no loss of force = 0 (no block); reduced force compared with the contralateral foot = 1 (partial block); total immobility = 2 (complete block). A block was considered successful when sensory and motor scores were each complete [i.e., = 2] in the distribution of both tibial and common peroneal nerves at the end of the 30-min period.

Surgery was performed 45–75 min after sciatic block completion. Propofol was administered in case of surgical (sciatic or saphenous territory) or tourniquet-induced pain, or because of anxiety (patient's request).

The primary end-point of the study was block time (i.e., the interval between the first needle insertion and its removal at the end of the block). Other measured outcomes were as follows: preparation time (i.e., time necessary to draw surface landmarks in the NS group and to perform ultrasound nerve visualization in the US-NS group, the latter excluding skin and probe preparation), quality of ultrasound sciatic image during a static and a seesaw sign examination (using the following scale: good = nerve outline clearly circumscribed, fair = nerve outline not entirely visualized and poor = doubt as to the nature of the image), number of skin punctures and needle passes required to obtain the appropriate needle placement (a needle pass corresponded either to the initial needle insertion or to a subsequent forward movement of the needle preceded by its slight withdrawal; the number of needle passes was the sum of all forward movements), minimal stimulating current, incidence of paresthesia, pain intensity during the procedure (assessed at the end of the performance of the block using a 0–10 verbal score with end points labeled "no pain" and "worst pain possible"), complete sensory block and complete sensory motor in sciatic distribution at 30 min, and successful block. In addition, we recorded the duration of postblock analgesia (i.e., interval between block completion and the first analgesic demand), the satisfaction with the anesthetic technique evaluated the following day using a 10-cm visual analog scale with end-points labeled "dissatisfied" and "very satisfied" and the incidence of postblock neurologic complications during a surgical consultation 2 to 4 wk later.

The required number of patients to be included in the study was calculated from a preliminary study, block time (double-injection technique with neurostimulation) being 280 ± 90 s on 19 consecutive patients. We assumed that the combination of neurostimulation and ultrasound guidance could reduce the block time by 25%. Assuming a two-tailed error of 5% and a β error of 10%, a sample size of 27 patients per group was calculated. We planned to recruit 30 patients in each group to allow for patient drop-out.

Discrete categorical data are presented as number or % of total patients in each group; continuous data are given as mean ± sd. Numbers of needle passes are presented as median and range. Intergroup differences were compared using unpaired Student's t-test, ² or Fisher's exact probability test as appropriate. The proportion of patients with successful block was evaluated with survival curves and was compared by using the Kaplan–Meier log-rank test. A P value <0.05 was considered significant. Data analysis was performed using SPSS® version 11.0 (SPSS Science Inc., Chicago, IL).

	RESULTS

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Five patients were excluded from the NS group because the procedure time exceeded 7 min. Four patients were excluded in the US-NS group: 1 due to missing data and 3 due to prolonged procedures (lack of visualization of the peroneal nerve).

Patient characteristics were comparable, and surgical procedures were evenly distributed in both groups (Table 1).

Block time did not differ significantly between groups (Table 2). The number of total needle passes was not significantly different in both groups, but the number of needle passes to localize the first nerve was higher in the NS group (P < 0.01). Minimal stimulating current of the first nerve was not significantly different. However, minimal stimulating current of the second nerve was higher in the NS-group (P < 0.001). The minimal stimulating current of the second nerve was calculated in the US-NS group from 16 patients, the 10 other patients having injection on visual criteria and minimal stimulating current >0.5 mA.

At 30 min, a complete sensory block was obtained in 32% of the patients in the NS group and in 85% in the US-NS group (P < 0.0002), and a complete motor block in 16% of the patients in the NS group and in 65% in the US-NS group (P < 0.001). The success rate at 30 min was lower in the NS group (16% vs 65%, P < 0.001) (Fig. 2). Among the 10 patients of the US-NS group who underwent injection with visual criteria and minimal stimulating current >0.5 mA, 6 had a successful block and 8 had a complete sensory block in sciatic distribution at 30 min. The relative proportions for each nerve territory of complete, partial, and no blockade observed at the end of the 30-min evaluation period are presented Figure 3. There was no conversion to general anesthesia but six patients in NS group and five US-NS group required sedation with propofol.

View larger version (7K): [in this window] [in a new window]   Figure 2. Proportion of patients in each group with successful block (survival curve). Solid line: ultrasound-neurostimulation group; dashed line: neurostimulation group.

View larger version (14K): [in this window] [in a new window]   Figure 3. Sensory and motor blockade in sciatic distribution at the end of the 30-min evaluation period. The relative proportions of complete, partial, and no blockade for each nerve territory are expressed as percentage. NS = neurostimulation group; US-NS = ultrasound-neurostimulation group; TN = tibial nerve; SPN = superficial peroneal nerve; DPN = deep peroneal nerve; SN = sural nerve; CPN = common peroneal nerve.

	DISCUSSION

Top Abstract Introduction METHODS RESULTS DISCUSSION REFERENCES

 
Although ultrasound imaging can depict variability in sciatic nerve division11 and an unusual relationship between its two components,12 this prospective, randomized study demonstrated that combined ultrasound and neurostimulation guidance did not reduce block time of sciatic block at the popliteal level, despite good sciatic ultrasound visualization in most cases.

Block time using a single-injection technique with the posterior approach to the popliteal fossa is extremely variable ranging from 1 to 16 min.4 Block time is increased using a double-injection technique,13 although typically the success rate is improved and onset time is decreased.14,15 In our study, the success rate at 30 min in the NS-group was lower than that previously reported using a double-stimulation technique. However, the block techniques differed; we used a small volume of local anesthetic and assessed the sensory and motor block only for 30 min after injection. A larger volume of injectate or extending the assessment period may have improved our results.15–18 Likewise, the definition of successful block (surgical anesthesia versus complete sensory/motor block) will also affect the success rate. Of previous investigations,2–4,7,15–18 only Taboada et al.17 used a sensorimotor test, as we did. Using a strict sensorimotor criterion, we reported a higher success rate at 30 min in the US-NS group. But, the presence of surgical anesthesia, which was judged after as long as 75 min after block performance, did not differ significantly between groups. It is possible that less complete blocks could continue to deepen before surgical incision. It would have been useful to increase the objective evaluation period up to the time of surgery.

Several limitations of our methodology may have impacted the results. First, we chose to limit the block time to 7 min, a value close to the mean block time + 2sd measured during the preliminary study, based on patient discomfort and for clinical feasibility. Second, injection was performed despite a minimal stimulating current >0.5 mA for 10 patients of the US-NS group. Block time would have been longer in these cases if we had continued to modify the needle position to obtain minimal stimulating current 0.5 mA. However, using visual criteria for injection, complete sensory block was obtained in most of these patients. Third, the probe was placed and fixed at 7 cm above the popliteal fossa crease to set an identical level of puncture between the two groups. Nerve visibility may have been improved by free search for optimal placement of the probe. Another limitation is that the needle was never repositioned to improve local anesthetic distribution around the nerve. Such an adjustment would have prolonged the block time and increased the number of needle passes, but it may have increased success. Chan et al.19 discussed the need for performing one additional injection in case of asymmetric local anesthetic spread. Finally, some neurostimulation variables were different between groups. We used a smaller initial stimulating current (0.5 mA) in the US-NS group instead of 1.5 mA for the NS-group and increased the frequency of stimulation (2 Hz) for the US-NS group compared with 1 Hz for the NS group to increase the safety of the procedure, since a higher frequency increases the capability to depict motor response more quickly during needle progression. In addition, the initial intensity of the stimulating current was increased to 1 mA for the localization of the second nerve in the US-NS group because the first local anesthetic injection may have decreased the current density at the stimulating needle tip, as suggested by Tsui and Kropelin.20 The effect of these differences in technique between the two groups on block time and success is unknown.

In conclusion, this prospective, randomized study demonstrated that combined ultrasound and neurostimulation guidance ultrasound did not allow a reduction in block time of sciatic nerve block performed with double injection. Enhanced sensorimotor block success at 30 min using the combined technique should be confirmed by further studies.

	Footnotes

 
Accepted for publication December 21, 2007.

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This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a colleague Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (6) Citing Articles via Google Scholar Google Scholar Articles by Dufour, E. Articles by Fischler, M. Search for Related Content PubMed PubMed Citation Articles by Dufour, E. Articles by Fischler, M. Related Collections Anesthetic Techniques Regional Anesthesia Technology