We used a double-stimulation technique for posterior popliteal sciatic nerve block as previously described.1,2,6 Exclusion criteria were contraindication to regional anesthesia: diseases affecting sensory or motor function of the lower extremities (such as multiple sclerosis and amyotrophic lateral sclerosis), coagulation disorders, treatment with anticoagulant medication, infection at the injection site, allergy to local anesthetics, and lack of patient consent.
In the operating room, an 18-gauge IV catheter was placed in the arm opposite to the surgical site, and midazolam 0.03 mg/kg was given IV as a premedication. Standard monitoring including noninvasive arterial blood pressure, heart rate, and pulse oximetry was used throughout the operation and the block procedure. An experienced anesthesiologist skilled in regional anesthesia techniques performed all blocks. The second author of the study, who was blinded to study groups, performed the measurements. Patients were positioned prone for popliteal block.
The needle insertion site was prepared aseptically a few minutes before infiltration with 2 mL local anesthetic before block needle puncture. A standardized local anesthetic mixture containing 15 mL of 2% prilocaine and 15 mL of 0.5% levobupivacaine (total volume 30 mL: 15 mL for tibial nerve and 15 mL for peroneal nerve) was used in all study groups. Patients also received a saphenous nerve block if the surgical site involved the saphenous nerve territory. This procedure was performed by wide subcutaneous infiltration with 5 mL local anesthetic solution in the proximal anteromedial aspect of the tibia. For patients in all groups, the popliteal fossa crease, the tendon of the biceps femoris muscle (lateral), and the tendons of the semitendinosus and semimembranosus muscles (medial) were used for identification. The needle was inserted at a point 7 cm proximal to the knee flexion crease, between the tendons of the semitendinosus and biceps femoris muscles. A nerve stimulator was used for nerve location (Stimuplex, HNS 11; B Braun Medical, Melsungen, Germany) with a 100-mm-long, 21-gauge, short-beveled, Teflon-coated stimulating needle (Stimuplex; B Braun Medical). A pulse duration of 0.1 milliseconds, current intensity of 1 mA, and frequency of 2 Hz were used for the stimulator. The 2 components of the sciatic nerve were identified according to their specific muscular responses (as foot plantar flexion and inversion for the tibial nerve, foot dorsal flexion and eversion for the common peroneal nerve). After the appropriate response, the current was decreased to 0.4 mA. The correct needle position was confirmed by the nerve response fading at lower current intensities. The local anesthetic solution had a total volume of 30 mL, which was incrementally injected after a negative aspiration.
The recorded data were as follows. The block procedure time was the time interval from landmark palpation to the end of local anesthetic. Assessment for sensory and motor block was established every minute for 30 minutes after local anesthetic injection. Both sensory and motor blocks were evaluated for each sciatic branch (tibial nerve and peroneal nerve) by the second author of the study who was blinded to the groups. For the assessment of sensory function, a 22-gauge needle was touched to the plantar skin (nervus tibialis) and dorsal skin (nervus peroneus) of the foot for the pinprick test.5 The level of sensation was evaluated as follows: 0 = no sensation, 1 = decreased sensation, and 2 = normal sensation. The level of motor blockade was evaluated as follows: 0 = normal muscle strength, 1 = incomplete motor block (minor movements of the foot digits or ankle), and 2 = complete block (absolutely no movement of ankle). Patients who had normal sensation and normal muscle strength received general anesthesia. Patients with incomplete sensory or motor blocks and who had pain were first given fentanyl. If they complained of pain after fentanyl administration, they were converted to general anesthesia. The second author of the study made the decisions to give fentanyl and to convert to general anesthesia.
Sensory and motor onset times of the block as well as the duration times, and perioperative need for supplemental IV opioids or general anesthesia, were recorded. Via phone calls, patients' complaints related to a nerve injury, such as hypoesthesia and motor weakness, and their replies regarding satisfaction about the anesthetic technique were recorded on postoperative day 7.
Data were analyzed using SPSS 16.0 for Windows (SPSS, Inc., Chicago, IL). Significance was assumed at P < 0.05. In the current study, our primary outcome was sensory block onset time. We predicted a 25% to 30% decrease in sensory block onset time in groups 2 and 3 compared with group 1. Therefore, to reach a statistically significant difference among the 3 groups, sample size was calculated by accepting an α risk of 5% and a power (1 − β) of 95%. From this calculation, we would need 30 subjects in each group to detect a significant difference.
The Shapiro-Wilk test was used for determining normal distribution, whereas between-group differences were evaluated by an analysis of variance test for normally distributed variables, and a Bonferroni correction was also applied. For abnormal distribution, Kruskal-Wallis analyses of variance and Mann-Whitney U test were used. Nominal and ordinal variables were gathered in tables according to the groups while a χ2 test was applied. Statistical significance was established at P < 0.05.
Methods for Pilot Dye Study
Before the study, after giving written informed consent, 3 patients were included in a dye study to test our hypothesis. The patients in the dye study were randomly distributed into groups 1, 2, and 3 (1 patient in each group) to test our hypothesis and to demonstrate the spread of the injected local anesthetic, including 3 mL radiocontrast dye (gadopentetate dimeglumine [Magnevist]; Bayer, Germany) in the positions (neutral, leg-up, and tourniquet) described in the study protocol. C-arm scopy (GE OEC Medical Systems, Inc., Germany) was used to show the distribution of local anesthetic in the 3 patients. No additional patients were enrolled in the dye study, and those patients' data were not included in the statistical analysis of the current study.
One hundred five patients underwent foot and ankle surgery during the study period. Fifteen were excluded from the study (13 patients refused to participate and 2 were using anticoagulant medication). Ninety patients were recruited into the current study. There was no difference in patient demographics (Table 1). The onset times for the sensory and motor blocks were shorter, and the time to recovery of both blocks was longer, in groups 2 and 3 (P < 0.001, P < 0.001, respectively; Table 2). There was no difference between groups 2 and 3. Motor block was found to be complete for 26 group 1 patients and for 27 group 2 patients, whereas 29 group 3 patients had complete motor block (P > 0.05). One patient in each group was found to have no motor block whereas 3 patients in group 1 and 2 patients in group 2 had incomplete motor block and pain caused by tourniquet application for surgery, which was treated with IV opioids.
All patients were evaluated by the second author of the study for complications and complaints related to the block procedures. No seizures, arrhythmias, problems with consciousness, or hemodynamic status changes were observed in any patients. One patient in group 1 experienced puncture of the popliteal artery during block application. All patients were evaluated for complications after the surgery and by a phone call 7 days after surgery. Two patients in group 2 complained of hypoesthesia in the area innervated by the sciatic nerve below the knee, which was evaluated with electromyography, and the results were normal.
Regarding the dye study, leg flexion of 45 degrees at the hip immediately after the block resulted in more centrally oriented distribution of the local anesthetic as compared with the neutral position (Figs. 3 and 4). A similar local anesthetic distribution effect seemed more prominent (Fig. 5) when a distal tourniquet was applied during injection of local anesthetic.
This study demonstrated that modifying both leg position and application of a tourniquet under the knee in sciatic nerve block by the popliteal approach decreased sensory and motor block onset times and prolonged sensory and motor block durations compared with leg placement in a neutral resting position.
The effect of positioning in the axillary brachial plexus has been evaluated. The degree of sensory and motor block was influenced by spread of local anesthetic within the axillary neurovascular sheath in the study of Yamamoto et al.5 Abduction of the arm further impaired circumferential spread of local anesthetic to the radial nerve. The axillary brachial plexus block was also improved when the injection was performed with the arm in neutral position.5 The effect of position was also shown by Orlowski et al.4 when 20-degree Trendelenburg and lateral positions improved sensory block of the radial nerve to 100% in patients who were left in that position for 30 minutes after a perivascular axillary block with a single-injection technique.
Our dye study suggests that the enhanced onset is attributable to proximal spread of the local anesthetic due to either gravity (limb elevation) or compression (tourniquet inflation). This improvement of block efficacy by facilitating proximal flow of the local anesthetic solution was also suggested for axillary catheters, which allowed injections while the arm was adducted.7,8 One of the limitations of the current study was that in only 3 patients did we demonstrate the spread of the injected local anesthetic, including 3 mL radio contrast dye, during leg positions and during distal tourniquet application described in the study protocol. There is no evidence to suggest that the images of 3 patients represent a typical spread until we show that those images are reproduced consistently for all patients. Consequently, the reason(s) for our decreased onset and prolonged duration of blockade remains speculative.
One limitation of our study is that the time needed for leg elevation (15 minutes) exceeded the period of time gained by enhanced block onset. This limitation does not diminish the interest of the finding, but it may limit the clinical utility of the technique. However, despite the negative net gain in onset time, the duration was still markedly increased.
We conclude that elevated limb positioning or distal tourniquet application in sciatic nerve block by a popliteal approach may lead to a more proximal distribution of local anesthetic and may result in increased efficacy determined by faster onset of sensory and motor blocks as well as longer duration of both block times.
Name: Nezih Sertoz, MD.
Contribution: This author helped design the study, conduct the study, analyze the data, and write the manuscript.
Attestation: Nezih Sertoz has seen the original study data, reviewed the analysis of the data, approved the final manuscript, and is the author responsible for archiving the study files.
Name: M. Nuri Deniz, MD.
Contribution: This author helped design the study, conduct the study, and write the manuscript.
Attestation: M. Nuri Deniz has seen the original study data, reviewed the analysis of the data, approved the final manuscript, and is the author responsible for archiving the study files.
Name: H. Omer Ayanoglu, MD.
Contribution: This author helped design the study, analyze the data, and write the manuscript.
Attestation: H. Omer Ayanoglu has seen the original study data, reviewed the analysis of the data, approved the final manuscript, and is the author responsible for archiving the study files.
This manuscript was handled by: Terese T. Horlocker, MD.
1. Perlas A, Brull R, Chan VW, McCartney JL, Nuica A. Ultrasound guidance improves the success of sciatic nerve block at the popliteal fossa. Reg Anesth Pain Med 2008;33:259–65
2. White P, Issioui T, Skrivanek G, Early JS, Wakefield C. The use of a continuous popliteal sciatic nerve block after surgery involving the foot and ankle: does it improve the quality of recovery? Anesth Analg 2003;97:1303–9
3. Ababou A, Marzouk N, Mosadiq A, Sbihi A. The effects of arm position on onset and duration of axillary brachial plexus block. Anesth Analg 2007;104:980–4
4. Orlowski O, Bullman V, Vieth V, Filler T, Osada N, Aken HV. Perivascular axillary brachial plexus block and patient positioning: the influence of a lateral, head-down position. Anesthesia 2006;61:528–34
5. Yamamoto K, Tsubokawa T, Ohmura S, Kobayashi T. The effects of arm position on central spread of local anesthetics and on quality of the block with axillary brachial plexus block. Reg Anesth Pain Med 1999;24:36–42
6. March X, Pineda O, Garcia M, Carames D, Villalonga A. The posterior approach to the sciatic nerve in the popliteal fossa: a comparison of single- versus double-injection technique. Anesth Analg 2006;103:1571–3
7. Winnie AP, Radonjic R, Akkineni SR, Durrani Z. Factors influencing distribution of local anesthetic injected into the brachial plexus sheath. Anesth Analg 1979;58:225–34
© 2011 International Anesthesia Research Society
8. Koscielniak-Nielsen ZJ, Horn A, Nielsen PR. Effect of arm position on the effectiveness of perivascular axillary nerve block. Br J Anaesth 1995;74:387–91