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)

Use of sequential electrical nerve stimuli (SENS) for location of the sciatic nerve and lumbar plexus.

BACKGROUND AND OBJECTIVES: Conventional electrical stimulation has been done by continuous adjustment of current amplitude at a single, set pulse duration (conventionally, 0.1 ms). This study evaluated a novel technique for nerve location by utilization of a peripheral-nerve stimulator (PNS) programmed to deliver sequential electrical nerve stimuli (SENS). A repeating series of alternating sequential pulses of 0.1, 0.3, and 1.0 ms at 1/3-second period intervals between pulses were generated so that at a greater distance from the nerve, only higher-duration pulses would stimulate the targeted nerve and result in 1 or 2 motor responses (MR) per second. Three MR per second at 0.5 mA or less signified the conventional endpoint for nerve location (

Orthopaedic trauma in the pregnant patient.

Trauma affects up to 8% of pregnancies and is the leading cause of death among pregnant women in the United States. A pregnancy test is mandated for all females of childbearing age who are involved in trauma. Orthopaedic trauma in the pregnant patient is managed similarly to that for all trauma patients. Initial resuscitation efforts should focus on the pregnant patient because stable patient vital signs provide the best chance for fetal survival. In the stable patient, fetal assessment and a pelvic examination are mandatory. Radiographs as well as abdominal ultrasound of the patient and fetal ultrasound are useful. No known biologic risks are associated with magnetic resonance imaging, and no specific fetal abnormalities have been linked with standard low-intensity magnetic resonance imaging. Emergency surgery can be safely performed in most pregnant patients. Avoiding patient hypotension and using left lateral decubitus positioning increase the likelihood of success for the patient and fetus. An experienced multidisciplinary team consisting of an obstetrician, perinatologist, orthopaedic surgeon, anesthesiologist, radiologist, and nursing staff will optimize the treatment of both the pregnant patient and her fetus.

Locked knee during pregnancy.

An acutely locked knee is a painful and debilitating orthopaedic condition usually caused by a loose body or bucket-handle meniscal tear that requires surgery to remove or repair. We describe 2 cases of acute locking of the knee that occurred during pregnancy. Both patients underwent urgent arthroscopic treatment under spinal anesthesia without complication to the patient or fetus. Concerns regarding surgery during pregnancy revolve around the safety for the mother and fetus. Although local and regional anesthetics are safe with proper management, there is a slightly increased risk of spontaneous abortion when general anesthesia is used, especially in the first trimester. Although purely elective surgery is never recommended during pregnancy, arthroscopic knee surgery can be performed safely in emergency situations with proper planning by a coordinated team including the surgeon, anesthesiologist, and obstetrician.

Maximum recommended doses of local anesthetics: a multifactorial concept.

The current recommendations regarding maximum doses of local anesthetics presented in textbooks, or by the responsible pharmaceutical companies, are not evidence based (ie, determined by randomized and controlled studies). Rather, decisions on recommending certain maximum local anesthetic doses have been made in part by extrapolations from animal experiments, clinical experiences from the use of various doses and measurement of blood concentrations, case reports of local anesthetic toxicity, and pharmacokinetic results. The common occurrence of central nervous system toxicity symptoms when large lidocaine doses were used in infiltration anesthesia led to the recommendation of just 200 mg as the maximum dose, which has remained unchanged for more than 50 years. In most cases, there is no scientific justification for presenting exact milligram doses or mg/kg doses as maximum dose recommendations. Instead, only clinically adequate and safe doses (ranges) that are block specific are justified, taking into consideration the site of local anesthetic injection and patient-related factors such as age, organ dysfunctions, and pregnancy, which may influence the effect and the pharmacokinetics of the local anesthetic. Epinephrine in concentrations of 2.5 to 5 microg/mL should be added to the local anesthetic solution when large doses are administered, providing there are no contraindications for the use of epinephrine. As a rule, conditions (eg, end-stage pregnancy, high age in epidural, or spinal block) or diseases (uremia) that may increase the rate of the initial uptake of the local anesthetic are indications to reduce the dose in comparison to one normally used for young, healthy, and nonpregnant adults. On the other hand, the reduced clearance of local anesthetics associated with renal, hepatic, and cardiac diseases is the most important reason to reduce the dose for repeated or continuous administration. The magnitude of the reduction should be related to the expected influence of the pharmacodynamic or pharmacokinetic change.

Spinal anaesthesia for outpatient surgery.

Spinal anaesthesia in the outpatient is characterized by rapid onset and offset, easy administration, minimal expense, and minimal side effects or complications. Spinal anaesthesia offers advantages for outpatient lower extremity, perineal, and many abdominal and gynaecological procedures. Development of small-gauge, pencil-point needles are responsible for the success of outpatient spinal anaesthesia with acceptable rates (0-2%) of postdural puncture headache (PDPH). Compared with peripheral nerve blocks, spinal anaesthesia has a more predictable offset. There are many possible choices of local anaesthetics for outpatient spinal anaesthesia. These include lidocaine, prilocaine, mepivacaine and small doses of bupivacaine. Meperidine has local anaesthetic properties in addition to its opiate properties. It has been used as the sole intrathecal agent for spinal anaesthesia but has no real advantages over lidocaine. Mepivacaine and lidocaine have each been associated with transient neurological symptoms (TNS) following intrathecal administration. This has stimulated development of alternative agents, including combinations of local anaesthetics and opioids. Lidocaine remains the most useful agent for outpatient spinal anaesthesia. For longer procedures, mepivacaine is an excellent spinal anaesthetic agent. Attention to technique, reduction of dose and addition of fentanyl to lidocaine result in effective spinal anaesthesia with rapid recovery and a low incidence of significant side effects or complications.

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.

Peripheral nerve blocks for anaesthesia and postoperative analgesia.

PURPOSE OF REVIEW: Perioperative analgesia is a major concern for the patient and for the anesthesiologist, whose task is to avoid pain and all related complications on immediate outcome and healing. Regional anesthesia, alone or combined with general anesthesia, is becoming a preferred technique in a variety of surgical procedures. There is increasing interest in peripheral nerve blocks, single or continuous, mainly for perioperative treatment of unilateral surgery. Specificity of analgesic area combined with decreased complications, including spinal or epidural hematoma, urinary retention, or hemodynamic alterations, are advantages of the peripheral nerve block over more central neural blocks. RECENT FINDINGS: Insertion of catheters near neural plexuses or in the vicinity of single nerves are being continuously developed and improved. The appearance of new techniques and devices is increasing. Percutaneous electrode guidance, ultrasonographic localization of neural structures, and the use of stimulating catheters represent the newest advances in this area. Use of enantiomeric local anesthetic drugs permits a safer and wider range of postoperative treatment, which includes continuous analgesia administered in the patient's home. Use of patient-controlled analgesia, through electronic or elastomeric pumps, is recommended for postoperative pain control. Peripheral nerve block is the standard for anesthesia or analgesia in ambulatory surgery. Complications of the technique have been examined in large clinical studies which have recently been published. Results of such studies highlight the effectiveness and safety of peripheral blocks. These results have given new strength to arguments for regional anesthesia and analgesia and led to the increase in popularity of regional techniques. The articles considered below have, in summary, the main purpose of enhancing safety, as well as dissemination and education regarding regional anesthetic techniques. SUMMARY: Possibilities afforded by the use of peripheral nerve blocks mainly consist of prolonged analgesia, selective area of action, and fewer collateral effects when compared with general anesthesia or more central neural blockade. Introduction of new devices and new techniques are increasing, as evidenced by the large number of studies which have appeared in the literature during the past year.

Percutaneous electrode guidance: a noninvasive technique for prelocation of peripheral nerves to facilitate peripheral plexus or nerve block.

BACKGROUND AND OBJECTIVES: Typically, peripheral nerve block is done by approximating nerve location, usually by use of anatomical landmarks. Precise nerve location has been done by needle exploration. A new method, percutaneous electrode guidance (PEG) of the block needle, was performed. A transcutaneous stimulating cylindrical electrode was used to indent the skin, locate the underlying nerve, and guide a block needle near it. METHODS: PEG was used to prelocate the desired nerve or neural plexus by use of a shielded cylindrical electrode with a 1-mm-diameter conductive area of skin contact at the distal end, the center of which contained a 22-gauge (1/2 mm) hole, which precisely matched a shielded conventional block needle. Transcutaneous stimulation began at less than 10 mA and was decreased to minimal amperage that elicited the desired motor response. Electrode position was fixed, and electrode current was discontinued. A shielded 22-gauge block needle was advanced through the electrode guide to near the underlying nerve. Initial needle current was only 0.5 mA. Local anesthetic was injected to block the targeted nerve or nerves. Standard sensory/motor testing was performed at 20 minutes. RESULTS: Nine upper or lower extremity blocks were performed on 7 patients. All were successful. Minimal stimulating currents were 1.3 to 8.2 mA for transcutaneous electrode stimulation and 0.20 to 0.70 for needle stimulation. Needle depth was 0.4 to 1.1 cm beyond the electrode tip and correlated with minimal electrode stimulating current. CONCLUSIONS: A smooth, metal-tipped electrically shielded skin electrode probe can be used to comfortably and accurately indent the skin over a desired nerve or plexus, define its anatomical course, and subsequently guide a block needle near it.

Inability to consistently elicit a motor response following sensory paresthesia during interscalene block administration.

BACKGROUND: Two methods of nerve block based on eliciting neural feedback with the block needle currently exist. The paresthesia technique uses sensory feedback to ascertain that the needle tip is close to the nerve. By contrast, a peripheral nerve stimulator makes use of motor responses to electrical stimulation. The relation of motor responses to an electrical peripheral nerve stimulator and sensory nerve contact (paresthesia) had not been studied. METHODS: Thirty consecutive unpremedicated patients who presented for shoulder surgery with interscalene block anesthesia were prospectively studied. Interscalene block was performed by the single paresthesia method of Winnie, using an insulated or non-insulated needle connected to a peripheral nerve stimulator with the power off. At the precise point of paresthesia, the peripheral nerve stimulator was turned on, and the current was slowly increased to 1.0 mA with a pulse width of 0.2 ms. Presence and location of any motor responses were observed and recorded. RESULTS: All patients had easily elicited paresthesias. The site of first paresthesia was to the shoulder in 73% of patients. Only 30% of patients exhibited any motor response to electrical stimulation up to 1.0 mA. There was no relation between site of paresthesia and associated motor nerve response. CONCLUSION: Elicitation of paresthesia does not translate to an ability to elicit a motor response to a peripheral nerve stimulator in the majority of patients.