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Print version ISSN 0034-7094
Rev. Bras. Anestesiol. vol.56 no.3 Campinas May/June 2006
Effects of increasing spinal hyperbaric lidocaine concentrations on spinal cord and meninges. Experimental study in dogs*
Efectos de concentraciones crecientes de lidocaína hiperbara, administradas en el espacio subaracnoideo, sobre la médula espinal y las meninges. Estudio experimental en perros
Silvânia R.O. PiresI; Eliana Marisa Ganem, TSAII; Mariângela MarquesIII; Yara Marcondes Machado Castiglia, TSAIV
do Programa de Pós-Graduação em Anestesiologia do Departamento
de Anestesiologia da FMB-UNESP
IIProfessora Adjunta do CET/SBA do Departamento de Anestesiologia da FMB-UNESP
IIIProfessora Assistente Doutora do Departamento de Patologia da FMB-UNESP
IVProfessora Titular do CET/SBA do Departamento de Anestesiologia da FMB-UNESP
OBJECTIVES: Lidocaine concentration potentially able to determine nervous
tissue injury is still not well established. This study aimed at investigating
the effect of increasing spinal lidocaine concentrations in single injection
through Quincke needle.
METHODS: After the Animal Experiment Ethical Committee approval, 40 adult animals were anesthetized with fentanyl and etomidate and submitted to spinal puncture with 22G 21/2 Quincke needle for the introduction of 1 mL of 7.5% glucose solution in 10 seconds Group 1; 5% lidocaine in 7.5% glucose solution Group 2; 7.5% lidocaine in 7.5% glucose solution Group 3; 10% lidocaine in 7.5% glucose solution Group 4. After intravenous anesthesia recovery and in the presence of spinal block, the following parameters were observed: presence of motor block, anal sphincter tone (normal or relaxed) and sensory block level in different cervical, thoracic, lumbar and sacral dermatomes. Animals remained in captivity for 72 hours. Anal sphincter tone, hind paws mobility, painful fore and hind paws and sacral, lumbar and thoracic dermatomes sensitivity were evaluated. Were euthanized by electrocution under anesthesia and spinal cord and meningeal lumbar and sacral portions were removed for histological exam under optic microscopy.
RESULTS: No Group 1 and 2 animal presented clinical or histological injuries. Three Group 3 animals presented hind paws motor changes and anal sphincter relaxation with foci of posterior necrosis (two dogs) and fascial necrosis in all spinal cord surface (one dog). In a different animal of this group in which foci of necrosis were observed in less than 5% histological field, no clinical changes were found. Seven Group 4 animals presented clinical changes (paralysis or decreased muscle strength in hind paws, anal sphincter relaxation) or histological changes (spinal cord surface band necrosis or nervous tissue necrosis foci).
CONCLUSIONS: In this study, spinal lidocaine in concentrations above 7.5% in single injection through Quincke needle has determined histological changes on spinal cord, but not on meninges.
Key Words: ANESTHESIA, Regional: spinal block; ANESTHETICS, Local: lidocaine; ANIMALS: dogs; COMPLICATIONS; neurological injury, neurotoxicity
Y OBJETIVOS: Todavía no ha quedado bien establecida la concentración
de lidocaína que es potencialmente capaz de determinar lesión
en el tejido nervioso. El objetivo de esta pesquisa fue el de estudiar los efectos
sobre la médula espinal y las meninges, de concentraciones crecientes
de lidocaína administrada por vía subaracnoidea, en inyección
única a través de aguja de Quincke.
MÉTODO: Después de la aprobación de la Comisión de Ética en Experimentación Animal, 40 perros adultos fueron anestesiados con fentanil y etomidato y sometidos a punción subaracnoidea con aguja de Quincke 22G 21/2 para introducción de 1 mL, en 10 segundos, de solución glicosada a 7,5% - Grupo 1; lidocaína a 5% en solución glicosada a 7,5 % - Grupo 2; lidocaína a 7,5% en solución glicosada a 7,5% - Grupo 3; lidocaína a 10% en solución glicosada a 7,5% - Grupo 4. Después de la recuperación de la anestesia venosa, se observó, durante el período en que los animales estaban bajo los efectos del bloqueo subaracnoideo, la presencia de bloqueo motor, el tono del esfínter anal (normal o relajado) y el nivel de bloqueo sensitivo en los diferentes dermátomos de las regiones cervical, torácica, lumbar y sacral. Los animales permanecieron en cautiverio por 72 horas. Se evaluaron el tono del esfínter anal, la motricidad de las patas posteriores, la sensibilidad dolorosa en las patas anteriores y posteriores y en los dermátomos sacrales, lumbares y torácicos. Ellos fueron sacrificados por electrocución bajo anestesia y fueron retiradas las partes lumbar y sacral de la médula espinal y de las meninges para examen histológico por microscopía óptica.
RESULTADOS: Ningún animal de los Grupos 1 y 2 presentó lesiones clínicas o histológicas. Tres animales del Grupo 3 presentaron alteraciones motoras en las patas posteriores y relajamiento del esfínter anal. En ellos se observaron focos de necrosis en la región posterior (dos perros) y necrosis en faja en toda la superficie medular (un perro). En otro animal de ese grupo, en el cual se observó focos de necrosis, en área inferior a 5% del campo histológico, no se encontraron alteraciones clínicas. Siete animales del Grupo 4 presentaron alteraciones clínicas (parálisis o disminución de fuerza muscular en las patas posteriores, relajamiento del esfínter anal) e histológicas (necrosis en faja de superficie medular o focos de necrosis de tejido nervioso).
CONCLUSIONES: En ese estudio, la lidocaína en concentraciones superiores a 7,5%, en inyección única, administrada en el espacio subaracnoideo a través de aguja de Quincke, determinó alteraciones histológicas sobre la médula espinal, pero no sobre las meninges.
The narrow therapeutic index of 5% hyperbaric lidocaine on neuroaxis has been shown since the early 1990, when Cauda Equina syndrome was associated to its spinal administration via microcatheter in continuous infusion 1,2, after single pencil point needle injection 3,4 and repeated injections due to blockade failure 5.
Lidocaine concentration potentially able to determine nervous tissue injury is still not well established. Experimental studies in rats, in which the anesthetic was administered via spinal catheter, have shown neurotoxicity in concentrations varying from 2.5% 6 to 7.5% 7,8. The criticism to this model is that it does not reproduce the anesthetic technique used in the clinical practice 6.
This study aimed at investigating the effect on spinal cord and meninges of increasing spinal lidocaine concentrations in single injection through Quincke needle.
After the Animal Experiment Ethical Committee approval, 40 adult mixed-breed dogs of both genders, weighing 7 to 12 kg and with spinal length of 60 to 68 cm were involved in this study. Exclusion criteria were unhealthy animals or those needing more than one spinal puncture, in addition to those in which hemorrhagic CSF was obtained, characterizing puncture accident. Dogs were randomly distributed in four groups of 10 animals, according to the spinal solution, that is: Group 1 (control) 7.5% glucose solution, Group 2 5% lidocaine in 7.5% glucose solution; Group 3 7.5% lidocaine in 7.5% glucose solution; Group 4 10% lidocaine in 7.5% glucose solution.
The same experimental sequence was performed in all animals. After 12-hour fast with free access to water, dogs were anesthetized with intravenous fentanyl (0.005 mg.kg-1) and etomidate (2 mg.kg-1). Then they were placed on Claude Bernard trough in the prone position and the distance between occipital protuberance and lumbo-sacral space was measured to obtain spinal length.
Skin and fur were cleaned with soap and water in an area of 10 cm around L6-L7 interspace, followed by washing with water, antisepsis with topic 2% chlorexidine gluconate and placement of sterile drapes.
Lumbo-sacral space was identified after palpation of both iliac bone tuberosities and last lumbar vertebra spinous process immediately below. Sliding the index finger in the cephalad direction, the next interspace was L6-L7. Spinal puncture was performed by introducing through median access with approximately 45º inclination angle a disposable 22G 21/2 Quincke needle with local anesthetic administration orifice in the cephalad direction. After crossing the arachnoid membrane, needle's mandrel was removed and CSF flow was obtained.
After obtaining CSF, the solution of each group was spinally injected with 3 mL syringes in 10 seconds. Administrated volume was 1 mL.
After intravenous anesthesia recovery, in approximately 20 minutes, and in the presence of spinal block, the following parameters were observed: presence of motor block, anal sphincter tone (normal or relaxed) and sensory block level evaluated by the presence of pain in different cervical, thoracic, lumbar and sacral dermatomes, with the aid of haemostatic clamp, by closing the first lock. Pain was defined as skin contraction at painful stimulation of head movement trying to byte.
After spinal anesthesia recovery, animals remained in captivity under clinical observation for 72 hours. The following parameters were evaluated: anal sphincter tone, hind paws mobility by walking profile (normal walk, walk with limitations, unable to sustain paws, inability to walk), ability to move tail, and changes in pain sensitivity. Sensitivity was investigated by pain sensation (paw retraction, postural change, anguished face) after pressure by closing clamp teeth on interdigital hind and fore paw membranes and on skin in the region corresponding to sacral, lumbar and thoracic dermatomes.
Animals were euthanized by electrocution after previous anesthesia with sodium pentobarbital and spinal cord lumbar and sacral portions were removed in less than three minutes and fixed with 10% formalin for histological exam.
Nervous tissue and meningeal cross sections were obtained starting approximately 5 cm above spinal puncture site going toward the end of cauda equina in 1-cm intervals.
Cross-sections were stained with hematoxylin-eosin and were examined under optic microscopy without knowing to which experimental group the specimen belonged.
Analysis of Variance was used to evaluate weight and spinal length homogeneity among groups, considering significant p < 0.05.
Statistical analysis has shown homogeneity among groups in weight and spinal length (Table I).
All animals were healthy with no spinal puncture difficulty and clear CSF.
After intravenous anesthesia recovery, Groups 2, 3 and 4 animals presented hind paws motor block, sensory block varying from T11 to L1 and relaxed anal sphincter with spontaneous loss of feces.
There were histological changes in four Group 3 animals and clinical changes in three of them. The fourth animal, in which posterior, anterior and lateral spinal cord necrosis foci were found in approximately 5% of the histological specimen, has presented no clinical changes. The remaining three animals showed clinical changes characterized by anal sphincter relaxation and decreased hind paws muscle strength leading to paralysis in one animal. Histological changes varied from band necrosis in all spinal cord surface (15% of histological specimen) to necrosis foci in different spinal cord regions with predominance of the posterior region (Table II). Necrosis was characterized by the presence of vacuole, pyknotic nuclei and fibrinoid injuries (Figure 2).
Seven animals in Group 4 presented clinical and histological changes. Six animals presented decreased hind paws muscle strength and three of them had associated anal sphincter relaxation. One animal presented only anal sphincter relaxation.
Histological changes were band necrosis in all spinal cord surface in four animals and foci of necrosis in the anterior, lateral or posterior region, in three dogs (Table III). Necrosis was characterized by confluent vacuolization with loss of substance and presence of pyknotic nuclei (Figure 3).
This study has shown that lidocaine concentrations above 7.5% determine nervous tissue toxicity.
Histological nervous tissue injuries, the presence of vacuoli, axonal degeneration, pyknotic nuclei and fibrinoid injuries are characteristics of necrosis and were more severe in posterior spinal cord, but have extended superficially to lateral and anterior regions. These results are different from those described by some authors 7-9 who have observed histological changes only in posterior spinal cord and dorsal root. However, they are in line with a different study 6 which has observed histological injuries in anterior, lateral and posterior white matter and dorsal and ventral gray matter of rats receiving 10% lidocaine in single injection through spinal catheter.
It has been described that histological changes more frequently affect the posterior region because, in a site close to the posterior root immediately before its entry in the white matter, there is a non-mielinized region with nude neurons. These neurons are more sensitive to toxic effects of drugs injected in the CSF 9. However, it is important to stress that spinal surface is the site of highest contact of the anesthetic drug with the nervous tissue, thus vulnerable to the aggressing agent.
The larger extension of injuries location found in this study may be related to different methodologies. This experiment has used dogs and spinal puncture with Quincke needle and single injection. Other experiments 7-9 have used rats and the anesthetic was administered through a spinal catheter in continuous infusion 10,11 or bolus 6-8, which might have induced different injuries 12
It is well established that to assure lack of toxicity of an agent administered in CSF, this should be checked in several animals of different species 13.
Other studies with the same method have shown that when the injury is very severe it goes beyond the posterior region 14,15.
Our study has not observed clinical or histological changes in all dogs receiving glucose solution and 5% hyperbaric lidocaine. These results are in line with some studies in the literature in which rabbits 16 and rats 7,8,12 presented neurological injuries only when spinal lidocaine was administered in concentrations equal to or above 7.5%. However, in situations favoring local anesthetic build up, such as slow injections (60 seconds), injuries may be present in 5% concentrations 17,18 and in even lower concentrations, after high doses or prolonged exposure of the nervous tissue to the local anesthetic agent 8,10,11,15.
Cauda equina syndrome has been described after spinal administration of large 2% lidocaine volumes which should have been injected in the spinal space 19-21 in humans and experimental animals 15, stressing the effects caused by prolonged contact of the drug with the nervous tissue. This is because the safety margin between lidocaine therapeutic and toxic effects is very narrow.
In isolated nerves of frogs, lidocaine has induced irreversible dose-dependent loss of nervous impulses as from 40 mmol concentrations, corresponding to 1% concentration. Total neuronal activity loss was seen with 80 mmol, that is 2% 22.
In dorsal ganglia neurons of rats it has been observed that 30 mmol concentrations in contact with the nerve for 4 minutes were enough to promote neuronal death 23.
Cell mechanism responsible for local anesthetics neurotoxicity is still not totally understood. It is only known that when there are clinical changes, there are also sufficiently severe injuries to produce conduction loss of some nervous fiber populations 24.
Rapid axoplasmatic transport and nervous conduction block was observed in isolated nerves of rabbits with lidocaine concentrations as low as 0.6% when the contact lasted 60 minutes 25. Rapid axoplasmatic transport is necessary to maintain neuronal viability and structure 26.
A recent in vitro study with dorsal root ganglion cells of rats has shown that lidocaine-triggered neurotoxicity is related to mitochondrial dysfunction with activation of apoptosis pathways 27.
To conclude, one may say that spinal lidocaine in concentrations above 7.5% in single injection through Quincke needle has determined histological spinal cord changes but not meningeal changes in this experimental model with dogs.
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Profª Dra. Eliana Marisa Ganem
Deptº de Anestesiologia da FMB UNESP
18618-970. Botucatu, SP
Submitted for publication
14 de setembro de 2005
Accepted for publication 22 de janeiro de 2006
* Received from Faculdade de Medicina de Botucatu da Universidade do Estado de São Paulo (FMB-UNESP), Botucatu, SP.