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Print version ISSN 0034-7094
Rev. Bras. Anestesiol. vol.56 no.2 Campinas Mar/Apr. 2006
Influence of lidocaine on the neuromuscular block produced by rocuronium. Study in rat phrenic-diaphragmatic nerve preparation*
Influencia de la lidocaína en el bloqueo neuromuscular producido por el rocuronio. Estudio en preparación nervio frénico-diafragma de ratón
Yolanda Christina S. Loyola, M.D.I; Angélica de Fátima de Assunção Braga, TSA, M.D.II; Glória Maria Braga Potério, TSA, M.D. II; Silmara Rodrigues de Sousa, M.D.I; Samanta Cristina Antoniassi Fernandes, M.D.I; Franklin S. da Silva Braga, M.D.III
do Curso de Pós-Graduação do Departamento de Farmacologia
da FCM da UNICAMP
IIProfª Associada do Departamento de Anestesiologia da FCM da UNICAMP
IIIProf. Dr. do Departamento de Anestesiologia da FCM da UNICAMP
AND OBJECTIVES: The action mechanism of local anesthetics (LA) on neuromuscular
junction motivated seve-ral studies. When administered at low doses, they do not
interfere on neuromuscular transmission. But high doses may compromise neuromuscular
transmission and increase the effects of neuromuscular blockers. The objective
of this study was to evaluate lidocaine interaction with rocuronium on rat diaphragm
through its influence on neuromuscular block degree.
METHODS: Rats, weighing between 250 and 300 g, were used. Preparation was set according to the technique described by Bulbring. Groups were formed (n = 5) according to the drug being studied: lidocaine 20 µg.mL-1 (Group I); rocuronium 4 µg.mL-1 (Group II), and rocuronium 4 µg.mL-1 with lidocaine 20 µg.mL-1 (Group III). The following items were assessed: 1) the extent of diaphragm muscle responses to indirect stimulation, both before and 60 minutes after adding lidocaine and a neuromuscular blocker; 2) membrane potentials (MP) and miniature end-plate potentials (MEPP); 3) the effectiveness of neostigmine, and 4) aminopyridine on neuromuscular blockage reversal.
RESULTS: When administered separately, lidocaine did not alter the extent of muscular responses. With the previous use of lidocaine, rocuronium neuromuscular blockage was 82.8% ± 1.91%, with a significant difference (p = 0.0079) when compared to the group with isolated rocuronium (57.8% ± 1.9%). Blockage was both partially and fully reverted by neostigmine and 4-aminopyridine, respectively. Lidocaine did not alter membrane potential and caused an initial increase on MEPP, followed by a blockage.
CONCLUSIONS: Lidocaine increases the neuromuscular blocking produced by rocuronium. MEPP modifications identify a presynaptic action. The complete antagonism of 4-aminopyridine indicates a presynaptic component. This idea is supported by the partial antagonism through neostigmine.
Key words: ANESTHETICS, Local: lidocaine; ANIMALS: rats; NEUROMUSCULAR BLOCKERS, Nondepolarizing: rocuronium.
Y OBJETIVOS: El mecanismo de acción de los anestésicos locales
(AL) en la junción neuromuscular motivó la realización de
varios estudios. Con dosis bajas, los mismos no interfieren en la transmisión
neuromuscular, altas dosis pueden comprometer la transmisión neuromuscular
y potenciar los efectos de bloqueadores neuromusculares. El objetivo del estudio
fue evaluar en diafragma de ratón, la interacción entre la lidocaína
y el rocuronio a través de la influencia en el grado del bloqueo neuromuscular.
MÉTODO: Fueron utilizados ratones, con peso entre 250 y 300 g. La preparación fue montada de acuerdo con la técnica descripta por Bulbring. Se formaron grupos (n = 5) de acuerdo con la droga en estudio: lidocaína 20 µg.mL-1 (Grupo I); rocuronio 4 µg.mL-1 (Grupo II) y rocuronio 4 µg.mL-1 con lidocaína 20 µg.mL-1 (Grupo III). Fueron evaluados: 1) la amplitud de las respuestas del músculo diafragma a la estimulación indirecta, antes y 60 minutos después de la adición de la lidocaína y del bloqueador neuromuscular; 2) los potenciales de membrana (PM) y potenciales de placa terminal en miniatura (PPTM); 3) la eficacia de la neostigmina y 4) aminopiridina en la reversión del bloqueo neuromuscular.
RESULTADOS: La lidocaína aisladamente no cambió la amplitud de las respuestas musculares. Con el uso previo de lidocaína, el bloqueo neuromuscular del rocuronio fue del 82,8% ± 1,91%, con diferencia significativa (p = 0,0079) con relación al grupo con rocuronio aislado (57,8% ± 1,9%). El bloqueo fue parcial y totalmente revertido por la neostigmina y la 4-aminopiridina, respectivamente. La lidocaína no cambió el potencial de membrana y causó un aumento inicial en la frecuencia de los PPTM, seguido de bloqueo.
CONCLUSIONES: La lidocaína potenció el bloqueo neuromuscular que el rocuronio produjo. Los cambios del PPTM identifican una acción presináptica. El antagonismo completo de la 4-aminopiridina sugiere un componente presináptico, idea apoyada por el antagonismo parcial de neostigmina.
Pharmacological properties of neuromuscular blockers (NMB), such as onset of action, neuromuscular blockage degree and action length depend on several factors. These factors include: cardiac output, muscle circulatory time, muscular blood flow, affinity for the action site, power and administered dose1. There are also evidences stating that high doses of local anesthetics may compromise neuromuscular transmission and increase neuromuscular blockage produced by a low dose of nondepolarizing and depola-rizing neuromuscular blocker 2.
Local anesthetics, especially aminoamides such as lidocaine and bupivacaine, are pharmaceuticals widely-used at clinical practice in epidural anesthesia associated to general anesthesia. Intravenously administered, lidocaine is used during anesthetic induction to attenuate reflex responses unchained by laryngoscopy and tracheal intubation maneuvers and also as an auxiliary drug to treat cardiac dysrhythmia on intrao-perative 2-7. Rocuronium is a nondepolarizing neuromuscular blocker aminosteroid with a fast onset of action. This feature differentiates rocuronium from other nondepolarizing blockers and also makes it an alternative agent for succinilcoline in situations of rapid sequence induction 7-9.
Several mechanisms are admitted in order to explain the interaction between local anesthetics and neuromuscular blockers, such as presynaptic action, inhibiting acetylcholine release and postsynaptic action through a postjunctional membrane stabilization, and also interference with the muscular fiber exciting-contraction mechanism 10-14.
Research studies point to a possible interaction between lidocaine and neuromuscular blockers, increasing the effects of neuromuscular blockers 4,10. Although local anesthetics produce neuromuscular blockage only at high doses, the interaction with neuromuscular blockers, particularly the nonde-polarizing ones, becomes clinically relevant and demands a careful observation when it comes to simultaneous use of these agents or in situations on which the safety margin of neuromuscular transmission is reduced 2,15.
This study aimed at evaluating the effect of lidocaine on neuromuscular transmission on an experimental model and also assess its influence on neuromuscular blockage produced by rocuronium.
An experimental study was performed with compliance to the ethical principles of the - COBEA (Brazilian Association for Laboratory Animal Science) which were approved by Ethical Commission of Animal Experimentation from Biology Institute UNICAMP (Universidade Estadual de Campinas).
The study was performed with male rats from Wistar lineage, weighing between 250 and 300 g, sacrificed under anesthesia with 10% chloral hydrate (250 mg.kg-1) intraperitoneal, injection, and bleeding by means of neck vessels section. Preparation was mounted according to the technique described by Bulbring 16. The hemidiaphragms with corres-ponding phrenic nerves were removed and placed on a vat containing 40 mL of Tyrode nourishing solution, composed of the following elements in mM: NaCl 137; KCl 2.7; CaCl2 1.8; NaHCO3 11.9; MgCl2 0.25; NaH2PO4 0.3, and glycose 11. This solution was constantly aerated with carbogen (95% O2 + 5% CO2) and kept at 37ºC (99ºF). The nerve was placed onto platinum electrodes connected to a S48 Grass stimulator. Diaphragm was maintained by its tendinous portion under constant tension (5.0 g), through a wire connected to a Load Cell BG50 GMS isometric transducer, and subjected to an indirect stimulation of 0.1 Hz frequency and lasting 0.2 msec. Tension variations produced by diaphragm contractions were registered on a Gould RS 3400 physiograph. Groups were formed (n = 5), according to the drug added to the preparation: Group I lidocaine (20 µg.mL-1); Group II - rocuronium (4 µg.mL-1); Group III - rocuronium (4 µg.mL-1) on a preparation previously exposed to lidocaine (20 µg.mL-1). On Group III (lidocaine-rocuronium), rocuronium was added to the preparation 30 minutes after the addition of lidocaine. Muscular responses to indirect stimulation were registered during 60 minutes after adding the drugs. To revert the neuromuscular blockage caused by lidocaine-rocuronium association, neostigmine (2 µg.mL-1) and 4 aminopyridine (4AP) (20 µg.mL-1) were used, added to the preparation 60 minutes after the NMB. The phrenic-nerve preparation was also employed to study the lidocaine effects on miniature endplate potentials and membrane potentials. The assessed items are: 1) the extent of diaphragm muscle response to indirect stimulation, both before and 60 minutes after adding lidocaine; 2) the extent of diaphragm muscle response to indirect stimulation, both before and 60 minutes after adding a neuromuscular blocker; 3) the membrane potentials (MP) and miniature endplate potentials (MEPP); 4) the effectiveness of neostigmine and 4-aminopiridine on neuromuscular block reversal.
The results were expressed on mean and standard deviations. For a statistical analysis, the Mann-Whitney and Wilcoxon tests were used for paired samples. A significant level of 5% (a = 5%) was assumed. The power of test was calculated and a value of b > 20% was found (power > 80%).
At the concentration studied and separately used on phrenic-nerve preparation rat diaphragm, lidocaine did not cause any reduction on the muscular response extent to indirect electrical stimulation
On preparations previously exposed to lidocaine, the blockage produced by rocuronium was 82.8% ± 1.91%, with a significant difference (p = 0.0079) when compared to the blockage produced by rocuronium employed separately (57.8% ± 11.9%), figures 1, 2 and 3, respectively.
It was not noted any significant statistical difference on the lidocaine effect on membrane potentials. The effects on miniature endplate potentials initially featured a frequency increase, noted 30 minutes after the addition of the drug, followed by a blockage at 60 minutes (Figure 5).
The effects of local anesthetics on neuromuscular junction and its influence on the blockage produced by non-depolarizing neuromuscular blockers arte still subjected to few investigations. However, this interaction has been observed on clinical practice 2,4-6.
These clinical discoveries were confirmed on experimental works, which have as a bigger advantage compared to clinical researches, the possibility to eliminate the enormous individual variability of sensibility to neuromuscular blockers 10,17-19.
This present study was made on phrenic-nerve preparation rat diaphragm and showed that lidocaine at the studied concentration and separately used did not exert any effects at the neuromuscular junction. However, it increased the blockage produced by rocuronium. These results are similar to the ones found by other authors, since they also reported the absence of effect of local anesthetics on neuromuscular transmission, but they noted an increase of different neuromuscular blockers when local anesthetics were used through other forms of administration 4-6,10,17,19.
At the 1950 decade, Ellis et al. 17, were working with experiments performed on cats and noted that procaine, although not having an effect on neuromuscular transmission, enhanced the blocking produced by d-tubocurarine and succinilcoline. These results were confirmed in other works which also reported this interaction as true for other local anesthetics and neuromuscular blockers 10,19. Matsuo et al. 10 assessed the associated action of d-tubocurarine to different local anesthetics such as procaine, lidocaine e etidocaine using phrenic-nerve rat diaphragm. They noted that even in concentrations considered ineffective, local anesthetics significantly decreased the ED50 of neuromuscular blockage agents. And those agents, administered in effective concentrations in order to generate neuromuscular blockage, also caused a similar decrease of ED50 from local anesthetics. Thus, the authors concluded that the interaction between neuromuscular blockers and local anesthetics can be followed by the true increase caused by the action of both types of drug on different spots of neuromuscular junction.
During experiments performed on cats, the neuromuscular blockage produced by lidocaine-pancuronium association was 20% higher, with a significant statistical difference when compared to the results observed when pancuronium was employed separately 18. On a similar way, lidocaine at a 5 mg.kg-1 intravenous dose increased the neuromuscular blockage produced by d-turbocurarine in 25%19. On human beings, the effects of vecuronium and atracurium were extended by bupivacaine administrated on the epidural space. Rocuronium has its pharmacological duration increased by intravenous lidocaine administration 4-6.
The interaction between local anesthetics and neuromuscular blockers is not complacently explained and several mechanisms can be held responsible for the potentiation once observed. Theoretically, these agents may interfere in some stage involved on neuromuscular transmission. Through presynaptic action, local anesthetics selectively depress conduction on motor fibers and diminish the acetylcholine release during nervous stimulation 12,20,21. By means of a presynaptic action, they may be able to connect to different specific acetylcholine sites. It results on desensibilization of these receptors, and they also can occlude the nicotine receptors channels on a temporary basis 13,14,22,23.
Lidocaine may completely block nerve conduction and also depress the conduction of both pre and postjunctional impulse24. A study correlates the molecular structure of seve-ral lidocaine derivates with its respective neuromuscular transmission inhibitory properties and with its local anesthetic power. The research shows that molecular properties of these derivates related with the compromise of neuromuscular transmission are similar to the properties involved on acetylcholine receptors activation and not with the properties associated with its local anesthetic power. These results indicate that lidocaine produces neuromuscular blockage by means of mechanisms diverse than its action mechanism as a local anesthetic 24.
Neuromuscular blockage caused by lidocaine-rocuronium association was reversed by neostigmine and 4-aminopiridine. Neostigmine was less effective than 4-aminopiridine to reverse the blockage. With the latter, the extent of muscular response to phrenic nerve stimulation exceeds the extent of responses considered as a control group. When neostigmine inhibits acetyl cholinesterase, it increases the neurotransmitter concentration on synaptic gap, being able to competitively dislocate the agents causing blockage. Besides the inhibitor effect of endplate nicotine receptors desensibilization, 4-aminopiridine causes a huge increase on the acetylcholine quanta. This increase comes from two distinct actions on nerve-ending membranes: inhibition of potassium channels, which increases the lasting of action potential and a greater inflow of calcium ions to motor nerve-endings during the membrane depolarization 25-30. Although the subsynaptic mechanism by which 4-aminopiridine increases the transmitter release is not fully explained yet, the effectiveness of the drug as an antagonist of both pre and postsynaptic neuromuscular blockage has been proved on experimental tests 10,25-31. However, its clinical use is not advocated since it easily crosses the blood-brain barrier with central nervous system stimulation and may cause convulsions 30.
When evaluating bioelectrical potentials, it was noted that the employed concentration of lidocaine does not change the membrane potential of muscular fibers. Therefore, it proves that lidocaine does not present a depolarizing action over skeletal muscle fiber. Although lidocaine did not have any effect over muscle fiber, the studies on bioelectrical potential proved that, on the concentration employed, this drug does interfere on miniature endplate potentials (MEPP). Initially an increase on MEPP frequencies was verified, which can be attributed to presynaptic action increasing the neurotransmitter release and reducing its extent, probably due to postsynaptic action.
Results show that lidocaine at the studied concentration and separately employed did not compromise neuromuscular transmission, but increased the neuromuscular blockage produced by rocuronium. Changes on miniature endplate potentials indicate a presynaptic action altering the acetylcholine quanta release. The absence of changes on membrane potential demonstrates that on this concentration, lidocaine does not have a depolarizing action over muscle fiber and that the probable action site is at neuromuscular junction, particularly on motor endplate. The full antagonism obtained with 4-aminopiridine indicates that interaction between lidocaine and rocuronium has a presynaptic component related to the acetylcholine release decreasing. The partial antagonism of neostigmine supports this idea, since the anticholinesterasics are only effective at the postsynaptic blockage reversal.
It is probable that the power of local anesthetics on neuromuscular junction may differ between different species and, although the extrapolation of these results to the human species is not quantitatively similar, the clinical implications of this interaction make evident the need to monitor neuromuscular blockage and also reduce the dose of neuromuscular blockers when simultaneously used with those agents.
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Dra. Angélica de Fátima de Assunção Braga
Rua Luciano Venere Decourt, 245
13084-040 Campinas, SP
for publication 18 de agosto de 2005
Accepted for publication 19 de dezembro de 2005
* Received from Departamento de Farmacologia da Faculdade de Ciências Médicas da Universidade de Campinas (UNICAMP), Campinas, SP