Simplified posterior sciatic nerve block at mid gluteofemoral dulcus: comparison of different 1% lidocaine volumes

Abstracts

JUSTIFICATIVA E OBJETIVOS: O bloqueio do nervo isquiático por via subglútea foi descrito com sucesso em estudo anterior, sendo mais uma opção entre as várias abordagens possíveis. O nervo isquiático torna-se superficial na borda inferior do músculo glúteo máximo, permitindo seu acesso com fácil localização, pouco desconforto e baixo risco de punção acidental de grandes vasos. O objetivo deste estudo foi avaliar o bloqueio do nervo isquiático por esta abordagem simplificada com diferentes volumes de lidocaína a 1%. MÉTODO: Foram estudados 40 pacientes com intervenções cirúrgicas na perna ou no pé distribuídos em dois grupos. Após monitorização, eles foram posicionados em decúbito ventral e realizado bloqueio no ponto médio do sulco glúteo-femoral, com auxílio de neuroestimulador e agulha de 5 cm eletricamente isolada, utilizando 300 mg (G1) ou 200 mg (G2) de lidocaína a 1% sem adrenalina. RESULTADOS: Obteve-se anestesia adequada em todos os casos com o volume e a concentração usados. O tempo de execução do bloqueio foi de 8,6 ± 5,7 min (G1) e 5,6 ± 5,7 min (G2). A latência foi de 5,98 ± 1,4 min (G1) e 6,7 ± 2,9 min (G2). A duração sensitiva e motora do bloqueio foi de 243 ± 37 min e 152 ± 30 min (G1) e 235 ± 39 min e 149 ± 59 min (G2), respectivamente. Não foram observadas diferenças estatísticas significativas entre os grupos estudados. CONCLUSÕES: Essa abordagem é eficaz e de fácil execução, podendo a dose total de anestésico ser reduzida sem comprometimento da qualidade.

ANATOMIA; ANESTESIA, Regional; ANESTÉSICOS, Local; TÉCNICAS ANESTÉSICAS, Regional

SCIENTIFIC ARTICLE

Simplified posterior sciatic nerve block at mid gluteofemoral dulcus: Comparison of different 1% lidocaine volumes^*

Bloqueo del nervio isquiático por abordaje posterior simplificado en el punto medio del surco glúteo-femoral: Estudio con diferentes volúmenes de lidocaína a 1%

Neuber Martins Fonseca, TSA^I; Beatriz Lemos Mandim, TSA^II; Roberto Araújo Ruzi, TSA^II; Fabiana Rosa Tavares^III

^IProfessor Doutor da Disciplina de Anestesiologia e Responsável pelo CET/SBA da FM-UFU. Membro da Comissão de Normas Técnicas Segurança em Anestesiologia/SBA

^IICo-responsável pelo CET/SBA da FM-UFU

^IIIAnestesiologista do Serviço de Anestesiologia (SEANE) do HCFM-UFU

^{Correspondence to}

SUMMARY

BACKGROUND AND OBJECTIVES: Subgluteus sciatic nerve block has been successfully described in a previous study and is one more option among several possible approaches. The sciatic nerve becomes superficial at inferior gluteus maximus muscle where it is easily located and accessed with minor discomfort and low risk of accidental great vessels puncture. Our study aimed at evaluating this simplified sciatic nerve block approach with different 1% lidocaine volumes.

METHODS: Participated in this study 40 patients submitted to leg or foot procedures, who were distributed in two groups. Patients were placed in the prone position after monitoring and blockade was induced at mid gluteofemoral sulcus with the aid of neurostimulator and with beveled insulated 5 cm needle, with 300 mg (G1) or 200 mg (G2) of 1% plain lidocaine.

RESULTS: Used volumes and concentrations have promoted adequate anesthesia in all patients. Blockade time was 8.6 ± 5.7 min (G1) and 5.6 ± 5.7 min (G2). Onset time was 5.98 ± 1.4 min (G1) and 6.7 ± 2.9 min (G2). Sensory and motor block duration was 243 ± 37 min and 152 ± 30 min (G1), and 235 ± 39 min and 149 ± 59 min (G2), respectively. There were no statistically significant differences between groups.

CONCLUSIONS: This is an effective and easy approach and total anesthetic dose may be decreased without impairing quality.

Key Words: ANATOMY: sciatic nerve; ANESTHESIA, Regional; ANESTHETICS, Local: lidocaine; ANESTHETIC TECHNIQUES, Regional: sciatic nerve block

RESUMEN

JUSTIFICATIVA Y OBJETIVOS: El bloqueo del nervio isquiático por vía subglútea fue descrito con éxito en estudio anterior, siendo una opción más entre los varios abordajes posibles. El nervio isquiático se hace superficial en el borde inferior del músculo glúteo máximo, permitiendo su acceso con fácil ubicación, poca incomodidad y bajo riesgo de punción accidental de grandes vasos. El objetivo de este estudio fue el de evaluar el bloqueo del nervio isquiático por este abordaje simplificado con diferentes volúmenes de lidocaína a 1%.

MÉTODO: Se estudiaron 40 pacientes con intervenciones quirúrgicas en la pierna o en el pie, distribuidos en dos grupos. Después de la monitorización, fueron colocados en decúbito ventral y realizado el bloqueo en el punto medio del surco glúteo-femoral, con auxilio de neuroestimulador y aguja de 5 cm, eléctricamente aislada, utilizando 300 mg (G1) o 200 mg (G2) de lidocaína a 1% sin adrenalina.

RESULTADOS: Se obtuvo anestesia adecuada en todos los casos con el volumen y la concentración utilizados. El tiempo de ejecución del bloqueo fue de 8,6 ± 5,7 min (G1) y 5,6 ± 5,7 min (G2). La latencia fue de 5,98 ± 1,4 min (G1) y 6,7 ± 2,9 min (G2). La duración sensitiva y motora del bloqueo fue de 243 ± 37 min y 152 ± 30 min (G1) y 235 ± 39 min y 149 ± 59 min (G2), respectivamente. No se observaron diferencias estadísticas significativas entre los grupos estudiados.

CONCLUSIONES: Ese abordaje es eficaz y de fácil ejecución, pudiendo la dosis total de anestésico ser reducida sin el comprometimiento de la calidad.

INTRODUCTION

Some conditions are needed to routinely adopt peripheral nerve block in the anesthetic practice. It has to be technically simple, reference points have to be easily identified and approaches should not be uncomfortable for patients, promoting adequate anesthesia. Notwithstanding several proposals with different access pathways for sciatic nerve block ^1-8 it is seldom performed due to lack of adequate training or to technical difficulties ^9-11. Another limiting factor is the lack of access pathway standardization and patients' discomfort with some techniques. Some acceptance limitations are related to difficulties in identifying landmarks (especially in obese patients), while others are related to technical difficulties because blockade is induced with long needles which have to cross thick muscles, such as the gluteus, before reaching the blockade point. Others require multiple injections with tibial and fibular nerves block in the popliteal fossa.

Recent studies ^12,13 have proposed a simplified sciatic nerve block technique with single injection, short beveled insulated needle, by posterior approach at mid gluteofemoral sulcus, identifying the nerve with the aid of peripheral nerve stimulator. These techniques consider the anatomy of the sciatic nerve, which emerges from the sacral plexus, is formed by ventral roots L₄ to S₃, emerges from the pelvis through greater sciatic foramen, passes below the piriform muscle, goes down between the greater femoral trocanter and the sciatic tuberosity and along the dorsum of the thigh, anterior to femoral biceps and semitendinous muscles, going toward the popliteal fossa, where it is divided into two major branches called tibial and common fibular nerves. This anatomic position allows it to be accessed by different routes, from the parasacral space to the popliteal fossa.

Lower limbs regional anesthesia will become routine, as it is currently observed with neuraxial anesthesia, when its advantages are well established, especially with less adverse effects. This has been observed by Fonseca et al. ¹² who have obtained good results with the technique in patients with cardiopulmonary disorders without increasing morbidity-mortality rates.

With this technique, with simplified approach at mid gluteofemoral sulcus, landmarks are easily identified, as opposed to the proposal of di Benedetto et al. ⁸, who adopt bone references, such as greater trocanter and sciatic tuberosity, disregarding the individual biotype. Another advantage is the low risk of vascular accident and the impossibility of total spinal or epidural anesthesia, as it is the case with the access proposed by Mansour and Bennetts ¹⁴.

The large sciatic nerve diameter at the level of the gluteofemoral sulcus could make blockade onset less predictable as compared to other peripheral blocks. This has not been confirmed by Fonseca et al. ¹² who have shown relatively shorter onset as compared to other studies with other access pathways and different anesthetic agents ^7,8,15-18.

The intermuscular space in which the sciatic nerve is located in the gluteofemoral sulcus is small and involved by a small amount of connective tissue. This may favor nervous bundle impregnation with local anesthetics. So, it is possible to suppose that it is easily blocked with low anesthetic doses and concentrations, further decreasing the possibility of anesthetic intoxication, already described during sciatic nerve block ^19,20.

This study aimed at evaluating sciatic nerve block by the simplified technique described by Fonseca et al. ¹², investigating its behavior with different 1% lidocaine volumes.

METHODS

After the Clinical Research Ethical Committee, Hospital de Clínicas, Faculdade de Medicina, Universidade Federal, Uberlândia approval and their informed consent, participated in this study 40 patients of both genders, physical status ASA I to IV, aged 21 to 82 years, weighing 50 to 90 kg, scheduled to be anesthetized with posterior sciatic nerve block and to be submitted to leg or foot procedures. Patients were randomly distributed in two equal groups. Group 1 (G1) received 30 mL of 1% plain lidocaine (300 mg) and Group 2 (G2) received 20 mL of 1% plain lidocaine (200 mg). Exclusion criteria were patients counterindicated for regional anesthesia, with psychiatric diseases or history of drug abuse.

Venous access was established before anesthetic block with 18G catheter in forearm vein and lactated Ringer's infusion. Patients were monitored with continuous ECG at D_II or CM5 lead, peripheral hemoglobin oxygen saturation (SpO₂), and automatic blood pressure by the oscilometric method during blockade and in the intraoperative period. Blockade was induced after sedation with 1 to 3 mg intravenous midazolam. Additional midazolam and fentanyl dose, in the ratio of 1 mg and 50 µg, respectively, was prepared to administer to patients complaining of discomfort or needing additional anxiety relief.

Blockade was induced in the prone position in all patients. Anatomic criteria for the procedure were those proposed by Fonseca et al. ¹². Puncture was performed at the gluteofemoral sulcus. The mid point of this sulcus was adopted as landmark for needle introduction. After antisepsis and skin and subcutaneous tissue anesthesia with 1% plain lidocaine (20 mg), a short bevel, 5 cm insulated needle with Teflon (Stimuplex A 50^â, B.Braun) connected to peripheral nerve stimulator (TOF-WATCH^â) was introduced perpendicular to skin. Needle was gradually introduced aiming at reaching the sciatic nerve located anteriorly to the semitendinous muscle, crossing the sulcus delimited by the semitendinous, gluteus maximus insertion and vastus lateralis muscles. Electrical stimulation was initially adjusted to 1 Hz frequency and 1 mA current. At the depth of 3 to 5 cm, stimulation response of the tibial component of the sciatic nerve (foot inversion and plantar flexion) or of the common fibular nerve (dorsoflexion of foot eversion) was observed. Since foot movement represented motor response to electric stimulation, current was decreased to 0.5 mA.

In the absence of movement, needle position was adjusted to maintain muscle response with low current (< 0.5 mA), and this was considered the optimum point for local anesthetic injection. Blockade was performed without investigating paresthesia and total programmed dose was only administered after a test dose of 2 mL anesthetic solution to rule out the possibility of intraneural anesthetic injection (acute pain simultaneous to anesthetic injection). At every 5 mL, syringe was aspired to confirm that the needle remained in the extravascular region.

All blockades were induced by the authors. When there was indication, the saphenous nerve was also blocked (sensory branch of the femoral nerve). Saphenous nerve was approached at the level of the knee and 3 mL of 1% lidocaine (30 mg) were injected.

Patients were considered ready for the surgical procedure when they presented total loss of painful sensation at pinprick at the distribution of tibial and fibular nerves, confirmed by the inability to effective move ankle and foot.

An independent observer, not involved with the blockade, observed time between needle introduction and adequate motor response to electric stimulation (blockade time), time between end of anesthetic injection and the moment considered adequate for the procedure (onset), number of needle repositionings to obtain desired motor response, and depth in which there was electric stimulation response. The same independent observer recorded the need for additional analgesia or sedation.

After blockade, patients were asked to evaluate their discomfort during the procedure using a 3-point scale (1 = no pain, 2 = moderate pain, 3 = extremely painful). All surgical procedures were performed with no need for anesthetic supplementation. Sensory block was confirmed by applying ice on foot dorsum (common fibular nerve) and plantar region (tibial nerve), being considered complete when cold was not felt. Motor block was confirmed by asking patients to move foot planta and dorsum, and was considered complete in the lack of movement. Motor and sensory block duration was defined as the period between anesthetic injection and motor and sensory function recovery. Patients' satisfaction with the technique was evaluated 24 hours post-procedure through a 2-point scale: 1 = satisfied – "if needing a new surgery, I would accept the same type of anesthesia"; 2 = unsatisfied – "if needing a new surgery, I would prefer a different type of anesthesia".

Fisher Exact or Chi-square tests were used to evaluate blockade success rate, gender and physical status (ASA) between groups. Age, weight, surgical procedure duration, electric stimulation intensity and number of needle repositioning for the blockade were evaluated by Student's t test for analysis of data related to two samples presented with interval or ratio scale. Mann-Whitney U test was used to compare sensory and motor onset between groups. Null hypothesis rejection level was 5% for all tests.

RESULTS

Sciatic nerve was identified in all 40 patients with minimum stimulation response of 0.5 mA. There were no differences in stimulation of sciatic nerve, tibial and common fibular branches and there were no reports of discomfort with any need for sedative supplementation to perform the anesthetic procedure. Demographics data are shown in table I with no significant differences between groups.

Anesthetic behavior of sciatic nerve block is shown in tables II, ^III and ^IV. There has been significant difference in sciatic nerve identification in G2, without any other difference between groups.

No blood aspiration, paresthesia or clinical signs of anesthetic intoxication during or after sciatic nerve block were observed. There were no hemodynamic changes. There has been no sensory or motor deficit after total blockade recovery.

DISCUSSION

The investigation developed in this study to decrease anesthetic dose without impairing sciatic block quality via subgluteus has shown satisfactory and promising results.

A large number of patients presented peripheral vasculopathy due to pathological complications, especially diabetes mellitus, thus being chronically ill patients with diversified treatment modalities with the involvement of several organs. Although sciatic nerve block is seldom performed in the clinical practice, it may be useful and the best option for some patients, especially those with major cardiopulmonary disorders. Patients' satisfaction with blockade was gratifying due to suffering relief with fast recovery without hemodynamic changes. Although it has not compared this technique to other sciatic nerve block techniques, this observation confirms results of other authors ^8,13,21.

Peripheral nerve block with neurostimulator allows the exact location of the nervous fascicle with no need for investigating paresthesia ²². Single injection associated to peripheral stimulation is associated to higher blockade success rate. There are virtually no blockade failures when solution is injected after the induction of muscle contractions with electric current equal to or below 0.5 mA, as shown in a previous study ¹² and confirmed by this study, resulting in the same blockade quality even with decreased local anesthetic volume.

Some studies state that multiple injections technique is better as compared to neurostimulator ²², which is contradictory due to higher theoretical risk of needle-induced neurological trauma. There is virtually no risk of neurological injury when adequate material is used, with short beveled insulated needles connected to adequately adjusted peripheral nerve stimulator ^22,23. However, studies have shown that some patients may have symptoms in the first three weeks, even after total blockade recovery, and that the vast majority goes unnoticed due to spontaneous resolution within up to 10 weeks, being mistaken with other diagnoses ²³ since mechanisms are in general multifactoral ²⁴. So, any statement of lower risk of neurological complications by the studied technique would be premature because patients were not followed-up and there were no comparisons with other techniques.

Sciatic nerve block by other techniques has been referred as uncomfortable especially due to the thick muscle layer the needle has to cross to reach regions close to the sciatic nerve ²³. The study results have shown that the posterior approach via gluteus sulcus is effective for sciatic nerve block, being well tolerated by patients (^{Tables III} and ^IV).

The large sciatic nerve diameter may make blockade onset less predictable as compared to other peripheral blocks. Although this pharmacological effect is influenced by chemical anesthetic properties, such as concentration and volume ¹¹, others may also interfere, such as type of motor response obtained with the neurostimulator ^22,23 or the current intensity used to stimulate the nerve ^22-26.

In this study, there has been no significant difference in onset between groups, but it was relatively faster as compared to previous studies using other anesthetic agents and different routes, such as ropivacaine, the mean onset of which was 10 to 25 minutes ^13,14, or levobupivacaine ^8,13,22. Since these factors were maintained constant in our study, volume has not influenced results.

The sciatic nerve is made up of L₄ to S₃ fibers. Two separate nervous branches, tibial and common fibular nerves, are involved by an epineural sheath and are distinct since their origin in the sacral plexus. These two branches leave the pelvis through the greater sciatic foramen and become superficial at the end of the gluteus maximum muscle. Then they go to the popliteal fossa where they divide into two major branches called tibial and common fibular nerve. There is anatomic demonstration of the continuity of the connective tissue sheath involving nervous branches making up the sciatic nerve until its division in the popliteal fossa ²⁷.

This anatomic uniqueness is fundamental to justify the lower anesthetic volume proposed in our study, when no cephalad or caudal anesthetic spread would be needed for an effective blockade, because the small intermuscular space in which the sciatic nerve is inserted in the subgluteus region, associated to small amount of connective tissue, may favor nervous bundle impregnation by local anesthetics. This may also be the possible reason for the fast onset and the lack of perioperative analgesic supplementation, differently from what has been reported by other authors ¹⁴

Similar to previous study ¹², there was no anesthesia in the region corresponding to the posterior cutaneous nerve of thigh. The technique has substantial advantages, such as easy landmark, low risk of venous injury and impossibility of complications such as total spinal or epidural anesthesia described in Mansour and Bennetts ¹⁴.

The conclusion of this prospective study is that the sciatic nerve may be blocked by the posterior pathway, with lower local anesthetic volume than that initially proposed.

REFERENCES

Submitted for publication 19 de julho de 2005

Accepted for publication 13 de fevereiro de 2006

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*

Received from Serviço de Anestesiologia (CET/SBA) da Faculdade de Medicina da Universidade Federal de Uberlândia (FM-UFU), Uberlândia, MG.

Publication Dates

• Publication in this collection
  29 May 2006
• Date of issue
  June 2006

History

• Accepted
  13 Feb 2006
• Received
  19 July 2005