Determination of the minimum effective volume of 0.5% bupivacaine for ultrasound-guided axillary brachial plexus block

Abstracts

Background and objective:

The use of ultrasound for needle correct placement and local anesthetic spread monitoring helped to reduce the volume of local anesthetic required for peripheral nerve blocks. There are few studies of the minimum effective volume of local anesthetic for axillary brachial plexus block. The aim of this study was to determine the minimum effective volume (VE90) of 0.5% bupivacaine with epinephrine (1:200,000) for ultrasound guided ABPB.

Method:

Massey and Dixon's up-and-down method was used to calculate the minimum effective volume. The initial dose was 5 mL per nerve (radial, median, ulnar, and musculocutaneous). In case of blockade failure, the volume was increased to 0.5 mL per nerve. A successful blockade resulted in decreased volume of 0.5 mL per nerve to the next patient. Successful blockade was defined as a motor block ≤2, according to the modified Bromage scale; lack of thermal sensitivity; and response to pinprick. The achievement of five cases of failure followed by success cases was defined as criterion to complete the study.

Results:

19 patients were included in the study. The minimum effective volume (VE90) of 0.5% bupivacaine with 1:200,000 epinephrine was 1.56 mL (95% CI, 0.99-3.5) per nerve.

Conclusion:

This study is in agreement with some other studies, which show that it is possible to achieve surgical anesthesia with low volumes of local anesthetic for ultrasound-guided peripheral nerve blocks.

Regional anesthesia; Brachial plexus; Minimum volume; Ultrasound; Bupivacaine

Justificativa e objetivo:

o uso do ultrassom para acompanhar o correto posicionamento da agulha e a dispersão do anestésico local permitiu a redução do volume de anestésico local necessário para o bloqueio de nervos periféricos. Existem poucos trabalhos sobre o volume mínimo efetivo de anestésico local para o bloqueio do plexo braquial via axilar (BPVA). Este estudo foi conduzido com o objetivo de determinar o volume mínimo efetivo (VE90) de bupivacaína 0,5% comadrenalina (1:200.000) para o BPVA guiado por ultrassom.

Método:

o método up-and-down proposto por Massey e Dixon foi usado para o cálculo do volume mínimo efetivo. A dose inicial foi de 5 ml por nervo (radial, mediano, ulnar e musculocutâneo). No caso de falha do bloqueio, o volume era aumentado em 0,5 mL por nervo. O sucesso do bloqueio resultava na diminuição do volume em 0,5 mL por nervo para o paciente subsequente. O sucesso do bloqueio foi definido como bloqueio da função motora ≤ 2 segundo a escala de Bromage modificada, ausência de sensibilidade térmica e de resposta ao pinprick. Foi definido como critério para término do estudo a obtenção de cinco casos de falha seguidos de casos de sucesso.

Resultados:

foram incluídos 19 pacientes no estudo. O volume mínimo efetivo (VE90) de bupi-vacaína 0,5% com 1:200.000 de adrenalina foi de 1,56 ml (IC 95% 0,99-3,5) por nervo.

Conclusão:

este trabalho corrobora alguns estudos que mostram que é possível obter anestesia cirúrgica com baixos volumes de anestésico local para bloqueios de nervo periférico guiados por ultrassom.

Anestesia regional; Plexo braquial; Volume mínimo; Ultrassom; Bupivacaína

Justificación y objetivo:

el uso del ultrasonido para acompanar el correcto posicionamiento de la aguja y la dispersión del anestésico local ha permitido la reducción del volumen de anestésico local necesario para el bloqueo de los nervios periféricos. Existen pocos trabajos sobre el volumen mínimo efectivo de anestésico local para el bloqueo del plexo braquial vía axilar. Este estudio fue llevado a cabo con el objetivo de determinar el volumen mínimo efectivo (VE90) de bupivacaína al 0,5% con adrenalina (1:200.000) para el bloqueo del plexo braquial vía axilar guiado por ultrasonido.

Método:

el método up-and-down propuesto por Massey y Dixon fue usado para el cálculo del volumen mínimo efectivo. La dosis inicial fue de 5mL por nervio (radial, mediano, cubital y musculocutáneo). En el caso de fallo en el bloqueo, el volumen se aumentaba a 0,5 mL por nervio. El éxito del bloqueo traía la disminución del volumen en 0,5 mL por nervio para el paciente posterior. El éxito del bloqueo se definió como bloqueo de la función motora < 2 según la escala de Bromage modificada, ausencia de sensibilidad térmica y de respuesta al pinprick. Quedó definido como criterio para el término del estudio la obtención de 5 casos de fallo seguidos de casos de éxito.

Resultado:

se incluyeron 19 pacientes en el estudio. El volumen mínimo efectivo (VE90) de bupivacaína al 0,5% con 1:200.000 de adrenalina fue de 1,56 mL (IC 95%: 0,99-3,5) por nervio.

Conclusiones:

este trabajo corrobora algunos estudios que muestran que se puede obtener la anestesia quirúrgica con bajos volúmenes de anestésico local para bloqueos de nervio periférico guiados por ultrasonido.

Anestesia regional; Plexo braquial; Volumen mínimo; Ultrasonido; Bupivacaína

Introduction

Brachial plexus block is an anesthetic technique often used for upper limb surgical procedures. Axillary brachial plexus block (ABPB) is one of the most commonly used techniques to achieve upper limb regional anesthesia and it is performed by blocking the terminal branches of the brachial plexus, which include the musculocutaneous, ulnar, median, and radial nerves. It was believed that the failures or incomplete blockade due to this technique were the result of needle malposition or brachial plexus septa in the axillary region.^1-3 To increase the success rate, volume up to 80 mL have been reported.⁴ However, the use of large volumes of local anesthetic increases the likelihood of systemic toxicity.^5,6 Thus, a possible technique to prevent this complication and increase patient safety would be to reduce the mass of the local anesthetic used during the procedure.

Currently, technologies such as peripheral nerve stimulator and ultrasound ensure the needle correct positioning in relation to the complex and reduce the need for high volumes of local anesthetic.^7-13 Some studies have shown that the use of ultrasound reduced the volume of local anesthetic for interscalenic brachial plexus block, femoral nerve block, and ilioinguinal/iliohypogastric nerve block without compromising the quality. However, there are few studies of the minimum effective volume of local anesthetic for ABPB. Therefore, this study was performed in order to calculate the minimum effective volume of 5% bupivacaine in 90% (VE90) of cases receiving ultrasound-guided axillary brachial plexus block.

Method

Study conducted at the surgical center of the Hand and Upper Limb Unit, with the coordination of the anesthesia service for the anesthesiology, intensive care and pain discipline, Universidade Federal de São Paulo/Escola Paulista de Medicina, from December 2011 to June 2012. The study was registered at Clinicaltrials.gov under the number NCT01421914.

After approval by the Ethics Committee of the Universidade Federal de São Paulo, patients scheduled to undergo hand surgery were invited to participate in the study. Inclusion criteria were age over 18 and under 65 years, informed consent (IC) signed by the patient, indication for brachial plexus block (anesthesia and analgesia) in candidates for elective hand surgery lasting less than 2 h, ASA physical status I or II according to the American Society of Anesthesiologists, and body mass index (BMI) <35 kg/m². Exclusion criteria were cognitive impairment or active psychiatric condition, infection at the blockade puncture site, bleeding disorders, and history of allergy to bupivacaine.

Protocol design

After inclusion in the study, all patients had their demographics recorded, followed by routine surgical monitoring with ECG, noninvasive blood pressure, and pulse oximetry. Intravenous access was made in the upper limb contralateral to the procedure and maintained with crystalloid infusion.

Axillary brachial plexus block was performed using ultrasound (M-Turbo R System with HFL 38× linear transducer 6-13 MHz, SonoSite, Bothell, WA USA) and a peripheral nerve stimulator (Stimuplex R DIG RC, B. Braum, Mellsung, Germany), with the patient in the supine position. The needle used was a 22 G × 50 mm (AEQ2250, BMD Group, Venezia, Italy). After disinfection and skin antisepsis with chlorhexidine, the puncture site was infiltrated with 1% lidocaine. After brachial plexus nerve visualization using ultrasound, the identification of structures was confirmed with a peripheral nerve stimulator. A starting dose of 5 mL of 0.5% bupivacaine with 1:200,000 epinephrine was injected around each nerve. The needle was repositioned during local anesthetic injection, and epidural injection was ensured by ultrasound image. The patient would have been removed from the study if there were a visual change in nerve diameter or if there were a significant pain during injection. In these cases, patients were followed postoperatively for possible intraneural injection.

The end of local anesthetic injection was considered time zero to assess the blockade effectiveness. An observer who was not present during the procedure and was blinded to the volume of anesthetic used evaluated the nerve blocks studied. This assessment was done every five 5 min until surgical anesthesia was achieved or up to 30 min after local anesthetic injection.

The blockade success or failure led to the reduction or increase in the volume of local anesthetic for the next patient, respectively. When the blockade was considered effective, the subsequent patient received a reduction of 0.5 mL in the local anesthetic volume. In case of blockade failure, patients received supplemental block at the elbow level, and the local anesthetic volume for the next patient was increased by 0.5 mL. After blockade evaluation, the patients were released to the surgical procedure. During the surgical procedure, patients received propofol 15-25 mcg/kg/min for sedation. Moreover, if the patient reported pain during the procedure, the blockade was considered as a failure and general anesthesia was performed.

After surgery, the patient was admitted to the post-anesthesia care unit (PACU) and remained monitored (ECG, noninvasive blood pressure, and pulse oximetry) until meeting the required conditions for outpatient discharge. Postoperative analgesia was assessed in the PACU using a visual analog scale 3 h after the blockade.

Assessment of ABPB success

A successful blockade was considered when there were motor function ≤2 according to the modified Bromage scale, lack of thermal sensitivity and response to pinprick in the regions of the median, ulnar, musculocutaneous, and radial nerves. Furthermore, the procedure should be done without additional analgesia to confirm the anesthetic procedure success.

Assessment of motor function

For motor function evaluation, the modified Bromage scale was used (Table 1).

Table 1
Modified Bromage scale.

Grade	Definition
4	Full muscle strength in relevantmuscle groups
3	Reduced strength, but able to moveagainst resistance
2	Ability to move against gravity, butnot against resistance
1	Discrete movements (trembling) of muscle groups
0	Lack of movement

The following tests were used to assess motor function: finger flexion (median nerve), wrist extension (radial nerve), thumb adduction (ulnar nerve), and elbow flexion (musculocutaneous nerve). Values ≤2 according to the modified Bromage scale were considered successful blockade.

Assessment of thermal sensitivity

The evaluation of upper limb thermal sensation was made with gauze and alcohol to test the sensitivity of the dermatomes innervated by the ulnar (hypothenar eminence), median (thenar eminence), radial (dorsum of the hand), and musculocutaneous (base of the first metacarpal) nerves. The cold sensation was regarded as 1 and lack of cold sensation as 0. A successful blockade was considered when there was no perception of cold in the dermatomes studied.

Assessment of pain sensitivity

The evaluation of upper limb pain sensation was performed with the pinprick test using a 23G needle to test sensitivity at the dermatomes areas of the ulnar, median, musculocutaneous, and radial nerves.

Positive response to pinprick was considered as 1 and lack of response to pinprick as 0. A successful blockade was regarded as the lack pinprick sensation in the dermatomes evaluated.

Criteria to complete the study

The criterion to complete the study was defined as the achievement of five cases of failure followed by success cases.

Statistical analysis

The minimum effective volume of 0.5% bupivacaine was estimated using the up-and-down sequences proposed by Dixon and Massey, focusing on analysis of the minimum effective volume with 50% probability of an effective nerve block.^14,15 Subsequently, the sequences were also evaluated using probit regression to determine the effective volumes in 90% of cases. Nonparametric data were expressed as median and quartiles (P25-P75). Categorical data were expressed as absolute and relative frequencies. Calculations were made in Microsoft Excell spreadsheet for WindowsTM (Microsoft Corp., Redmond, WA, USA) and GraphPad PRISMTM for Windows (GraphPad Software Inc, San Diego, CA, USA).

Results

The study protocol included 19 patients. In all patients it was possible to visualize the anatomical structures relevant to the blockade. The study ended when there was a sequence of five cycles of failure/success. The demographic characteristics of patients and surgical procedures performed are shown in Tables 2 and 3, respectively.

Table 2
Demographic characteristics of patients.

Age (years)		36.5 (27.5-46.5)
Gender (M:F)		14:5 (M-F)
ASA
I		12
II		7

Table 3
Distribution of surgical procedures.

Procedures	n (%)
Metacarpal fracture	5 (26)
Synthesis material removal	1 (5)
Extensor injury	3 (16)
Scaphoid fracture repair	1 (5)
Synovectomy	3 (16)
Dupuytren	2 (11)
Flexor injury	1 (5)
Pseudoarthrosis of the phalanx	2 (11)
Excision of bone tumor	1 (5)
Duration, min (P25-75)	65 (50-77.5)

The sequence of positive and negative responses to the blocks in consecutive patients is shown in Fig. 1. The VE90 of 0.5% bupivacaine with 1:200,000 epinephrine for ultrasound-guided axillary brachial plexus block was 1.56 mL (95% confidence interval [CI]: 0.99-3.5).

Figure 1
Graphical representation of the up-down sequence of subsequent patients. (♦), effective blockade; (◊), blockade failure.

The median latency of effective blockades was 20 min (10-30). When only the blockades with volumes of 1 mL were considered, the median latency was 25 min (20-30). For surgical procedures in which blockades were made with 1 mL per nerve, the median duration was 60 min (35-75). Duration of sensory and motor block was not assessed in this study.

The surgical procedure was uneventful in all patients in whom the blockade was considered successful, and there was no need for additional anesthetic.

Regarding postoperative analgesia, no patient reported pain up to 3 h after the blockade. There were no complications such as vascular puncture or local anesthetic intoxication during the study. All patients were discharged on the same day of the procedure and there was no case of hospital readmission.

Discussion

In modern practice of regional anesthesia, reductions in the volume and dose of local anesthetic have become important strategies to prevent systemic toxicity by local anesthetics.

Therefore, the use of ultrasound to guide the precise location of local anesthetic injection in peripheral nerve blocks has become increasingly frequent. The advancement in ultrasound equipment and methods enabled the identification of vascular and neural structures with high accuracy, benefits compared to classical techniques, lower failure rate, and reduction of local anesthetic dosage.¹⁶

The axillary approach to brachial plexus block was chosen for this study because it is one of the most used techniques in clinical practice. Considering the territory of anesthesia provided by this blockade, only patients undergoing surgical procedures in the hands were selected.

Due to lack of knowledge about the blockade duration with low volumes of bupivacaine, it was decided to select procedures lasting less than 2 h.

This study demonstrated that with the use of ultrasound it is possible to perform the brachial plexus block achieved by axillary approach with a minimum effective volume of 0.5% bupivacaine with 1:200,000 epinephrine (1.56 mL) for each nerve in hand surgery.

O’Donnel and Iohom reported effective blockade of the brachial plexus via axillary route with 1 mL of 2% lidocaine with 1:200,000 epinephrine per nerve. However, one of the study's limitations, reported by the authors, was the choice of superficial procedures such as synovectomy or tenorraphies.¹⁷ Marhofer et al. described the ABPB with similar volumes of 1% mepivacaine. ¹⁸ However, this was just a volunteer study in which surgical anesthesia was assessed only by pinprick test. In our study, even with low doses of local anesthetic, it was possible to perform superficial procedures, such as thumb extensor injury, and surgery with bony structures management, such as third and fourth metacarpal fractures, showing that, despite the decreased dose, it was also possible to perform procedures involving deep structures of the hand.

The choice of bupivacaine was made due to its pharmacokinetic characteristics, which provide longer lasting blockade compared to lidocaine. On the other hand, blockades with higher latency were achieved when compared with the results from the study by O’Donnell and Iohom.¹⁷

According to Hadzic, the use of low volumes of local anesthetic may result in intraneural injection because it is difficult to visualize an increase in nerve diameter in this situation.¹⁹ In order to avoid this complication, the visualization of nerve and adjacent structures, as well as local anesthetic spread by ultrasound, is an important factor.

Our study reaffirms that the minimum effective volume for ABPB is smaller than that described previously. One possible explanation for this fact is that with the aid of ultrasound, it is possible to perform a dynamic blockade, which involves the entire nerve periphery with local anesthetic. The ultrasound allows the anesthesiologist visualization of the nerve during the blockade, which allows redirection of the needle and local anesthetic injection in the entire nerve periphery, allowing effective blockades with low volumes of local anesthetic.

Some studies have shown that low doses of local anesthetic decreased the blockade duration, defined as the time between the onset of blockade installation and the return of motor and sensory functions.²⁰ A limitation of our study was that we did not assess the blockade duration with 0.5% bupivacaine, we just found that the blockades with low doses of local anesthetic were sufficient to perform the procedures with less than 2 h duration and that all blockades had a latency less than or equal to 30 min.

The use of low doses of local anesthetic provides a safer blockade, with less risk of complications, especially related to the systemic toxicity of local anesthetics. Despite the development of effective approaches for treating these complications, such as the use of lipid emulsions, ^21,22 the use of local anesthetics at low doses promotes a blockade with an anesthetic mass with a wide range of safety for the toxic dose.

The use of low doses of local anesthetic provides a safer blockade, with less risk of complications, especially those related to the systemic toxicity of local anesthetics. Despite the development of effective approaches for treating these complications, such as the use of lipid emulsions, ^21,22 the use of local anesthetics at low doses promotes a blockade with an anesthetic mass with a wide range of safety for the toxic dose.

In summary, this study shows that the VE90 ultrasound-guided ABPB is 1.56 mL of 0.5% bupivacaine with 1:200,000 epinephrine per nerve. This corroborates some studies showing that it is possible to obtain peripheral nerve blocks with low volumes of local anesthetic. Additional studies of dose-response should be conducted to assess the influence of bupivacaine concentration for this technique.

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Publication Dates

• Publication in this collection
  Jan-Feb 2014

History

• Received
  19 Dec 2012
• Accepted
  20 Mar 2013