Estimulación nerviosa periférica: análisis de la respuesta motora en diferentes circunstancias experimentales / Peripheral nerve stimulation: motor response analysis in different experimental circumstances

Introducción. Con una aguja aislada, en aparente contacto nervioso testeado por ultrasonido (US) o por la referencia de una parestesia, no se consigue respuesta motora (RM) a la estimulación nerviosa en un porcentaje variable de casos. El objetivo de nuestros estudios fue observar el comportamiento de la RM a valores < 1mA / 0.1 mseg en diferentes circunstancias experimentales. Aportar evidencia científica que contribuya determinar si con técnica usual de estimulación nerviosa (NS) un nervio puede contactarse o penetrarse sin obtenerse antes una RM. Material y Métodos. Bajo visión directa, doce nervios ciáticos de diferentes animales fueron expuestos y estimulados en dos mitades imaginarias. Observadores ciegos a la intensidad utilizada, consignaron la RM obtenida con 1 mA / 0.1 mseg sin y con contacto nervioso; y con 0.5 mA en contacto; el valor mínimo de intensidad en contacto con que aparece una RM y se obtiene una RM Grado 2, el comportamiento de la RM con la inyección anestésica local (AL) extraneural y la necesidad de aumentar o no la intensidad para obtener una RM de igual intensidad. Luego de colocar la aguja intraneural, se aumentó la intensidad hasta obtener una primer RM y una RM Grado 2. Finalmente se inyectó el AL intraneural y se consignó el comportamiento de la RM. Resultados. Sin contacto nervioso con 1 mA, se obtuvo RM en el 91.6 por ciento de los intentos en ambas mitades del nervio ciático y en el 100 por ciento con contacto neural. Con 0.5 mA en contacto, no se consiguió RM en una mitad en 33.3 por ciento de los intentos (8/24), al recolocarse la aguja, se obtuvo una RM en el 91.6 por ciento en ambas mitades (22/24), en un nervio no se obtuvo RM en ninguna mitad (2/24)... (TRUNCADO)

Introduction. With a needle apparently in contact with a nerve, tested by US or with the reference of a paresthesia, a MR is not observed during nerve stimulation in a variable percentage of the cases. The object of this study was to experimentally observe the behavior of MR within values + 1mA / 0.1 mseg in different circumstances. Provide scientific evidence to contribute to determine if, with the usual nerve stimulation technique (NS) a nerve can be contacted or penetrated without obtaining before a MR. Material and Methods. Under direct visualization, twelve sciatic nerves from different animals were exposed and stimulated in two imaginary halves. Blinded Observers to the intensity, classified the MR at 1 mA/0.1 mseg, with and without nerve contact and with 0.5 mA in contact. Also, minimum intensity value in contact in which a MR appears and when a MR G2 is obtained was determined, the behavior of the MR with the injection of the LA (local anesthetic), extra-neural and the need to increase or not the intensity to obtain a MR at same intensity. After introducing the needle intraneurally, the intensity was increased until a first MR and a Grade 2 was obtained. Finally, LA was injected intraneurally and the behavior of the RM was observed. Results. RM was obtained with 1 mA in 91.6 per cent of the cases in both halves of the Sciatic nerve without contact, and 100 per cent in contact. With 0.5 mA in 33.3 per cent (8/24) of the cases, MR wasn't observed in one half of the nerve. In one case, MR wasn't obtained in any half. After relocalizing the needle a MR was obtained in 91.6 per cent of the cases in both halves (22/24). The mean minimum intensity in contact for a first MR was of 0.16 + 0.08 mA, and 0.36 + 0.08 mA for a MR Grade 2. An intraneural MR was found in 92 per cent with a mean minimum value of 0.19 + 0.08 mA... (TRUNCADO)

Com uma agulha isolada em aparente contato com o nervo, conforme teste de ultra-som (US) ou presença de parestesia, nao é conseguida resposta motora (RM) a estimulação nervosa em uma porcentagem variável de casos. O objetivo de nossos estudos foi observar o comportamento da RM a valores < 1 mA /0.1 mseg em diferentes circunstancias experimentais. Proporcionar evidencia científica que ajude a determinar se com a técnica usual de estimulação nervosa (NS) é possível contatar ou penetrar um nervo sem antes se obter RM. Material e métodos. Sob visão direta, doze nervos ciáticos de diferentes animais foram expostos e estimulados em duas metades imaginárias. Observadores cegos a intensidade utilizada consignaram a RM obtida com 1 mA/0.1 mseg com e sem contato nervoso, e com 0.5 mA em contato; o valor mínimo de intensidade em contato ao qual aparece uma RM e é obtida uma RM grau 2; o comportamento da RM com injeção anestésica local (AL) extraneural e a necessidade de aumentar ou nao a intensidade para se obter uma RM de igual intensidade. Colocada a agulha intraneural, aumentou-se a intensidade até se obter uma primeira RM e uma RM grau 2. Finalmente, foi injetado o AL intraneural e registrado o comportamento da RM. Resultados. Sem contato nervoso e com 1 mA, obteve-se RM em ambas metades do nervo ciático em 91.6 por cento dos intentos, e com contato neural em 100 por cento. Com 0.5 mA em contato, nao se obteve RM em uma metade em 33.3 por cento dos intentos (8/24); recolocada a agulha, obteve-se RM em 91.6 por cento em ambas metades (22/24), e em um nervo nao foi obtida RM em nenhuma metade (2/24). A intensidade mínima em contato para uma primeira RM foi de 0.14 + 0.07 mA, e de 0.31 + 0.11 mA para uma RM grau 2. Houve RM intraneural em 92 por cento com valor mínimo de 0.19 + 0.08 mA. A RM desapareceu com a injeção de anestésico local; nao foi observado deslocamento do nervo da ponta da agulha. (TRUNCADO)

Relationship between evoked motor response and sensory paresthesia in interscalene brachial plexus block.

BACKGROUND AND OBJECTIVES: This study sought to define the relationship between a paresthesia and a motor response (MR) to electrical nerve stimulation using a peripheral nerve stimulator (PNS) during interscalene block. We sought to determine if at a low amperage (< or =1.0 mA) a MR would precede a paresthesia. METHODS: Twenty-two interscalene blocks were performed using insulated needles and a PNS. A MR was obtained at 0.5 mA and then the PNS was turned off. The needle was further advanced until a paresthesia was elicited. The PNS was again turned on, the needle held immobile, and the amperage increased in 0.1 mA increments up to 0.5 mA, or an MR obtained, whichever occurred first. If no MR was obtained, the needle was withdrawn at 0.5 mA in the same direction as it entered until MR was again observed. RESULTS: A MR was obtained at 0.5 mA in all the patients. After the PNS was turned off and the needle further advanced, a paresthesia was elicited in 21 patients. When the PNS was turned on again, a MR was produced at 0 to 0.5 mA in 13 patients. In a subset of 8 patients without a second MR to stimulation up to 0.5 mA, the needle was withdrawn at that amperage. A MR was subsequently obtained during withdrawal in each patient in this subset. CONCLUSIONS: MR preceded paresthesia in every patient. The most likely explanation for this observation is that MR can be achieved at a small distance from the nerve, whereas elicitation of mechanical paresthesia requires either nerve contact or more intimate location of the needle's tip relative to the nerve. Another possible explanation is that motor fibers are located in a more superficial position and are therefore encountered first. Motor and sensory responses are separate and discrete phenomena.