Effective volume of local anesthetics for fascia iliac compartment block: a double-blind, comparative study between 0.5% ropivacaine and 0.5% bupivacaine

Abstracts

JUSTIFICATIVA E OBJETIVOS: O bloqueio do compartimento da fáscia ilíaca é amplamente empregado como parte das técnicas anestésicas para intervenções cirúrgicas de quadril, coxa e joelho. A maioria dos estudos tem utilizado volumes fixos de ropivacaína ou de bupivacaína. Este estudo teve como objetivo calcular os volumes de ropivacaína a 0,5% e de bupivacaína a 0,5% efetivos em 50% (VE50), 95% (VE95) e 99% (VE99) dos casos para realização de bloqueios do compartimento da fáscia ilíaca. MÉTODO: Cinqüenta e um adultos agendados para intervenções cirúrgicas eletivas do quadril, diáfise femoral e joelho foram submetidos ao bloqueio do compartimento da fáscia ilíaca. Os pacientes foram aleatoriamente distribuídos e receberam ropivacaína a 0,5% (n = 25) ou bupivacaína a 0,5% (n = 26). O sucesso do bloqueio foi definido como bloqueio sensitivo completo das regiões anterior, medial e lateral da coxa. O volume anestésico foi determinado pelo método up-and-down de Massey e Dixon e os volumes efetivos foram calculados pelas fórmulas de Massey e Dixon (VE50) e por regressão de probits (VE50, VE95 e VE99). RESULTADOS: Os volumes anestésicos capazes de produzir bloqueio nervoso efetivo em 50% dos casos, calculados pela formula de Massey e Dixon, foram 28,79 mL (IC 95%: 26,31 - 31,5 mL) para ropivacaína e 29,56 mL (IC 95%: 25,22 - 34,64 mL) para bupivacaína (p = 0,62). Os volumes efetivos de ropivacaína capazes de bloquear 50%, 95% e 99% dos casos foram estimados pela regressão de probits como 28,8 mL (27,2 - 30,4), 34,3 mL (32,5 - 37,3) e 36,6 mL (34,3 - 40,5), respectivamente. Os volumes correspondentes de bupivacaína foram 29,5 mL (28,1 - 31,1), 36,1 mL (33,5 - 38,1), e 37,3 mL (35,1 - 41,3) (p < 0,05). CONCLUSÕES: Os volumes necessários de ropivacaína a 0,5% e bupivacaína a 0,5% com adrenalina 1:200.000 para o bloqueio do compartimento da fáscia ilíaca são similares.

ANESTÉSICOS, Local; ropivacaína; TÉCNICAS ANESTÉSICAS, Regional

SCIENTIFIC ARTICLE

Effective volume of local anesthetics for fascia iliac compartment block: a double-blind, comparative study between 0.5% ropivacaine and 0.5% bupivacaine^*

Volúmenes efectivos de anestésicos locales para el bloqueo del compartimiento de la fascia ilíaca: estudio comparativo doblemente encubierto entre ropivacaína a 0,5% y bupivacaína a 0,5%

Pablo Escovedo Helayel, TSA, M.D.^I; Giovanni Lobo, M.D.^II; Roberta Vergara, M.D.^III; Diogo Brüggemann da Conceição, M.D.^IV; Getúlio Rodrigues de Oliveira Filho, TSA, M.D.^V

^IInstrutor Co-Responsável, Coordenador do Núcleo de Ensino e Pesquisa em Anestesia Regional (NEPAR) do CET/SBA Integrado de Anestesiologia da SES-SC

^IIME₃ do CET/SBA Integrado de Anestesiologia da SES-SC

^IIIME₂ do CET/SBA Integrado de Anestesiologia da SES-SC

^IVAnestesiologista do Hospital Governador Celso Ramos, Pesquisador do NEPAR

^VResponsável do CET/SBA Integrado de Anestesiologia da SES-SC

^{Correspondence to}

SUMMARY

BACKGROUND AND OBJECTIVES: Fascia iliac compartment block is widely used as one of the anesthetic techniques used for surgical interventions of the hip, thigh, and knee. The majority of the studies have used fixed volumes of ropivacaine or bupivacaine. The objective of this study was to calculate the effective volume of 0.5% ropivacaine and 0.5% bupivacaine in 50% (EV50%), 95% (EV95), and 99% (EV99) of the cases to achieve fascia iliac compartment block.

METHODS: Fifty-one adults scheduled for elective surgical interventions of the hip, femoral diaphysis, and knee underwent fascia iliac compartment block. Patients were randomly assigned to receive either 0.5% ropivacaine (n = 25) or 0.5% bupivacaine (n = 26). The success of the block was defined as a complete sensitive block of the anterior, medial, and lateral regions of the thigh. The volume of the anesthetic was determined by Massey and Dixon's up-and-down method, while the effective volume was calculated by Massey and Dixon's formula (EV50) and by probits regression (EV50, EV95, and EV99).

RESULTS: The volume of anesthetic capable of producing an effective nervous anesthesia in 50% of the cases, calculated by Massey and Dixon formula, were 28.79 mL (CI 95%: 26.31 – 31.5 mL) for ropivacaine, and 29.56 mL (CI 95%: 25.22 – 34.64 mL) for bupivacaine (p = 0.62). The effective volumes of ropivacaine capable of producing a blocking in 50%, 95%, and 99% of the cases were estimated by probits regression as 28.8 mL (27.2 – 30.4), 34.3 mL (32.5 – 37.3), and 36.6 mL (34.3 – 40.5), respectively. The corresponding volumes of bupivacaine were 29.5 mL (28.1 – 31.1), 36.1 mL (33.5 – 38.1), and 37.3 mL (35.1 – 41.3) (p > 0.05).

CONCLUSIONS: The volumes of 0.5% ropivacaine and 0.5% bupivacaine with adrenaline 1:200,000 for the fascia iliac block are similar.

Key Words: ANESTHETICS, Local: bupivacaine; ropivacaine; ANESTHETIC TECHNIQUES, Regional: fascia iliac compartment block

RESUMEN

JUSTIFICATIVA Y OBJETIVOS: El bloqueo del compartimento de la fascia ilíaca es ampliamente empleado como parte de las técnicas anestésicas para intervenciones quirúrgicas de la cadera, muslo y rodilla. La mayoría de los estudios han utilizado volúmenes fijos de ropivacaína o de bupivacaína. Este estudio tuvo como objetivo calcular los volúmenes de ropivacaína a 0,5% y de bupivacaína a 0,5% efectivos en 50% (VE50), 95% (VE95) y 99% (VE99) de los casos para la realización de bloqueos del compartimento de la fascia ilíaca.

MÉTODO: Cincuenta y un adultos con cirugías marcadas electivas de la cadera, diáfisis femoral y rodilla se sometieron al bloqueo del compartimento de la fascia ilíaca. Los pacientes fueron aleatoriamente distribuidos y recibieron ropivacaína a 0,5% (n = 25) o bupivacaína a 0,5% (n = 26). El éxito del bloqueo fue definido como bloqueo sensitivo completo de las regiones anterior, media y lateral del muslo. El volumen anestésico fue determinado por el método up-and-down de Massey y Dixon y los volúmenes efectivos fueron calculados por las formulas de Massey y Dixon (VE50) y por regresión de probits (VE50, VE95 y VE99).

RESULTADOS: Los volúmenes anestésicos capaces de producir bloqueo nervioso efectivo en 50% de los casos, calculados por la formula de Massey y Dixon, fueron 28,79 mL (IC 95% : 26,31 – 31,5 mL) para ropivacaína y 29,56 mL (IC 95% : 25,22 – 34,64 mL) para bupivacaína (p = 0,62). Los volúmenes efectivos de ropivacaína capaces de bloquear 50%, 95% y 99% de los casos se estimaron por la regresión de probits como 28,8 mL (27,2 – 30,4), 34,3 mL (32,5 – 37,3) y 36,6 mL (34,3 – 40,5), respectivamente. Los volúmenes correspondientes de bupivacaína fueron 29,5 mL (28,1 – 31,1), 36,1 mL (33,5 – 38,1), y 37,3 mL (35,1 – 41,3) (p > 0,05).

CONCLUSIONES: Los volúmenes necesarios de ropivacaína a 0,5% y bupivacaína a 0,5% con adrenalina 1:200.000 para el bloqueo del compartimento de la fascia ilíaca son semejantes.

INTRODUCTION

Fascia iliac compartment block is widely used as one of the anesthetic techniques for surgery of the hip, thigh, and knee. Most studies have used fixed volumes of ropivacaine and bupivacaine. Effective anesthetic volumes of 0.5% ropivacaine and 0.5% bupivacaine for femoral nerve block are similar in 50% of the cases ¹.

In peripheral nerve block, the volume injected and the mass of the local anesthetic are crucial factors that affect the success rate and the level and safety of the anesthesia ^1,2. The objective of this double-blind, prospective study was to determine the minimum volume of 0.5% ropivacaine and 0.5% bupivacaine for an effective fascia iliac compartment block in 50%, 95%, and 99% of the patients.

METHODS

After approval by the Ethics Committee of the Hospital Governador Celso Ramos, and after signing an informed consent, 51 patients with ages between 18 and 65 years, of both genders, physical status ASA I and II, that were scheduled to undergo elective surgeries of the hip, femoral diaphysis, and knee under fascia iliac compartment block combined with general anesthesia, were included in the study prospectively. Exclusion criteria included patients with respiratory, liver, and heart disease; diabetes mellitus or peripheral neuropathy; patients receiving medication for chronic pain; and patients with known allergy to the drugs used in the study.

Patients were randomly assigned to each group according to numbers generated electronically. The R Group (n = 25) received 0.5% ropivacaine, while the B Group (n = 26) received 0.5% bupivacaine. Adrenaline (5 µg mL^-1) was added to the bupivacaine. After venous cannulation in the forearm with a 18G catheter, every patient received a standardized premedication composed of IV midazolam (0.05 mg.kg^-1) 10 minutes before the anesthesia was performed. Syringes containing the local anesthetics were prepared, in a double-blind fashion, by an investigator that was not involved in the subsequent evaluation of the patient. All fascia iliac compartment blocks were performed by an investigator that did not know which local anesthetic was being injected at least 45 minutes before the beginning of the surgery.

To perform the anesthesia, the entry point of the needle was marked approximately 1 cm below the limit between the outer and middle thirds of the inguinal ligament. The skin in this area was anesthetized with 2 mL of 1% lidocaine with a 25G needle; afterwards, a 17G Tuohy needle (Pericanâ, B. Braun, Melsungen, Germany) was introduced at a 75° angle. The first resistance break (pop) was felt when the tip of needle went through the fascia lata. The needle was introduced in the same angle until the break of a second resistance, corresponding to the perforation of the fascia iliac. The angle with the skin was, then, reduced to 30° and the needle introduced 1 cm cephalad. The local anesthetic was injected during a 2-minute period. Afterwards, an 18G epidural catheter was introduced 15 cm beyond the tip of the needle with its bevel was oriented cephalically. The end of the administration of the anesthetic was considered moment zero for evaluating the effectiveness of the anesthesia. An observer that was not present during the administration of the local anesthetic and that did not know the volume and type of anesthetic used evaluated the nervous blocks. Sensitive anesthesia was evaluated by the loss of pinprick sensation with a 22G needle using a 3-point scale (0 = normal sensitivity, 1 = decreased sensitivity, and 2 = complete sensitivity loss) on the anterior, medial, and lateral aspects of the distal thigh. A total score of the effectivity of the block was obtained by the sum of the scores of the three regions. The score varied from 0 (lack of sensitivity block in all three regions) to 6 (total block in the anterior, medial, and lateral aspects of the distal thigh).

A block was considered successful when the patient presented an effectivity score of 6 thirty minutes after the injection of the local anesthetic. A score smaller than 6, was considered a failure according to the objectives of the study. In case a total effectivity score of zero occurred 30 minutes after the anesthesia, 20 mL of 2% lidocaine with adrenaline 1:200,000 were injected through the catheter. If anesthesia of any one of the territories was obtained, a failure would be confirmed and the next patient would receive a larger dose, as described ahead. If there was no skin anesthesia 15 minutes after the lidocaine rescue, the case would be rejected and the same volume of local anesthetic would be administered to the next patient.

The volume of local anesthetic administered to the first patient of each group was 20 mL. The success or failure determined the reduction or increase in the volume of local anesthetic administered to the next patient. To calculate the interval among the volumes that should be administered in each sequence, the initial volume (20 mL) was normalized by transforming it in its natural logarithm ^3,4. By adding or subtracting 0.1 mL to the normalized volume administered to the previous patient, we obtained the normalized volume to be administered to the next patient. The volumes administered were calculated by the transformation of the normalized volumes in their respective antilogarithms, approximated to zero.

In a previous study ¹, the standard deviation of the effective volume of the local anesthetic in 50% of the cases (s) was 2 mL and the standard error of the estimation (sx) was 0.4 mL. The number of patients in each group necessary to obtain a similar standard error was calculated as n = (s/sx)² = (2/0.4)² = 25 cases ⁴. Sample size for comparisons between groups was calculated to detect a difference of 2 mL, assuming 1 - b = 0.8 and a - 0.05, leading to an estimation of at least 10 patients per group.

Statistical analysis was done with the Statistica 6.0 program (Statsoft Inc, Tulsa, OK). The continuous variables were analyzed by the non-paired test t Student. The categorical data were analyzed by the Fisher's Exact test. The effective volumes of ropivacaine and bupivacaine were estimated by Massey and Dixon's up-and-down sequence according to the formulas proposed by Massey and Dixon, focusing on testing a minimal volume of anesthetic with a probable effective nervous block equal to 50%. Calculations were performed on MS Excell (Microsoft Corp., Redmond, WA). Sequences were also examined by the probits regression to determine the effective volumes in 50%, 95%, and 99% of the cases. The resulting volume-response curves were compared on the points corresponding to EV50 (SSPS v. 12 SSPS Inc., Chicago). Critical values for a were established in 0.05.

After evaluating the nervous block, general anesthesia was induced by the anesthesiologist responsible for the case. Postoperative analgesia was done by continuous infusion of 0.2% ropivacaine (0.1 mL.kg^-1.h^-1) through the catheter placed on the fascia iliac compartment.

RESULTS

There were no significant differences between both groups regarding the demographics data (Table I).

Ten patients in the R Group (ropivacaine) (40%) and 15 patients in the B Group (bupivacaine) (42%) had effective nervous blocks 30 minutes after the injection. Figure 1 shows the sequence of effective (success) and ineffective (failure) blocks in both groups. No patients were rejected in either group. The effective volume in 50% of the cases was 28.79 mL (CI 95%: 26.31 – 31.5 mL) for ropivacaine and 29.56 mL (CI 95%: 25.22 – 34.64 mL) for bupivacaine (p = 0.62). Table II shows the effective volumes calculated by the probits regression. There were no statistically significant differences between the groups.

DISCUSSION

Fascia iliac compartment block was described by Dalens et al. ⁵ in children based on the hypothesis that if sufficient doses of local anesthetics were injected immediately posterior to the fascia iliac, they could disperse in the internal layers of this fascia, reaching the femoral, lateral femoral cutaneous, genitofemoral, and obturator nerves. This hypothesis was later confirmed by radiographical analysis ⁶.

When compared to the 3-in-1 block, the fascia iliac compartment block is associated with success indexes similar to those of the femoral, genitofemoral, and obturator nerves. However, it is more efficient to block the lateral femoral cutaneous nerve than the 3-in-1 block ⁶. Fascia iliac compartment blocks by a single injection are easily done, have a relatively low cost, and promote a highly effective postoperative analgesia. By placing catheters in the fascia iliac compartment, local anesthetics can be infused to achieve postoperative analgesia in hip, thigh, and knee surgeries ^7-10. Its applicability and efficiency has also been demonstrated for analgesia of fractures of the femur diaphysis in the pre-hospital setting ¹¹.

Relatively high volumes of bupivacaine or ropivacaine have been used to obtain effective fascia iliac compartment blocks ^5,9,12. However, the effective volumes of 0.5% ropivacaine or 0.5% bupivacaine are unknown.

Massey and Dixon's up-and-down method has been used to calculate the concentration, volume, or dose of local anesthetics, effective in 50% of the cases ^1,13-16. The need for smaller sample sizes, compared with randomized allocation methods, and the reduction in the number of failures are the greatest advantages proposed by the method ^3,4,17. However, this method does not reliably estimate the volumes of local anesthetics capable of promoting complete anesthesia in 95% and 99% of the patients, which is more clinically relevant⁴. For this reason, the estimation of the effective volumes for 95% and 99% of the cases were calculated by probits regression ¹⁸.

Massey and Dixon's up-and-down method is based on binary responses ³. For this reason, the criteria of success was defined as a complete block of skin sensitivity of the lateral, anterior, and medial regions of the distal thigh. Neither series had patients with a total effectivity score of zero. Failures were due to incomplete block in one or two regions of the thigh.

Effective volumes of ropivacaine capable of blocking 50%, 95%, and 99% of the cases were 28.8 mL (27.2 – 30.4), 34.3 mL (32.5 – 37.3), and 36.6 mL (34.3 – 40.5), respectively. The corresponding bupivacaine volumes were 29.5 mL (28.1 – 31.1), 36.1 mL (33.5 – 38.1), and 37.3 mL (35.1 – 41.3).

We concluded that similar volumes of 0.5% ropivacaine and 0.5% bupivacaine with adrenaline 1:200,000 are necessary for the fascia iliac compartment block.

REFERENCES

Submitted for publication 05 de dezembro de 2005

Accepted for publication 08 de junho de 2006

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*

Received from Hospital Governador Celso Ramos, CET/SBA Integrado de Anestesiologia da SES-SC, Florianópolis, SC

Publication Dates

• Publication in this collection
  22 Sept 2006
• Date of issue
  Oct 2006

History

• Accepted
  08 June 2006
• Received
  05 Dec 2005