Print version ISSN 0034-7094
Rev. Bras. Anestesiol. vol.55 no.3 Campinas May/June 2005
Onset of 1% lidocaine for skin infiltrative anesthesia*
Latencia de la lidocaína a 1% para anestesia infiltrativa de la piel
Gustavo Paiva Almeida, M.D.I; Gustavo Luchi Boos, M.D.II; Tiago Gayer de Alencar, M.D.III; Getúlio Rodrigues de Oliveira Filho, TSA, M.D.IV
IME2 CET/SBA Integrado
de Anestesiologia da SES-SC, Florianópolis, SC
IIME3 CET/SBA Integrado de Anestesiologia da SES-SC, Florianópolis, SC
IIIME1 CET/SBA de Anestesiologia do Hospital de Clínicas da Universidade Federal do Paraná, Curitiba, PR
IVResponsável CET/SBA Integrado de Anestesiologia da SES-SC, Florianópolis, SC
BACKGROUND AND OBJECTIVES: Minimum T50
and T95 onsets are the medians of time intervals between end of skin and subcutaneous
tissue infiltration with local anesthetics and a painful stimulation, which
are associated to no pain in 50% and 95% of patients, respectively. This study
has evaluated T50 and T95 of subcutaneous 1% lidocaine for lumbar skin puncture.
METHODS: This was a prospective study with sequential allocation depending on the response of previous patient (Dixon and Massey's up-down method) involving 25 patients submitted to spinal blocks with 25G Quincke needle. Skin and subcutaneous tissue were infiltrated with 3 mL of 1% lidocaine in L3-L4 or L4-L5 interspace with 10 mm 25G needle. Time elapsed between the end of infiltration and 25G Quincke needle puncture was established in logarithmic scale. Initial interval was 30 seconds. Subsequent intervals depended on previous patient's response. If the patient referred pain at 25G Quincke needle puncture, the next patient was allocated to the immediately longer interval; otherwise, the next patient would be allocated to the immediately shorter interval. Dixon and Massey's formulas were applied to calculate T50 and T95.
RESULTS: Medians (95% confidence limits) of T50 and T95 were 25 seconds (20-31 seconds) and 53 seconds (33-85 seconds), respectively.
CONCLUSIONS: To obtain lumbar skin anesthesia before lumbar puncture in 95% of patients, one should wait 33 to 85 seconds after the end of subcutaneous infiltration of 3 mL of 1% plain lidocaine.
Key words: ANESTHETIC TECHNIQUES, Infiltrative; COMPLICATIONS, Pain: lumbar puncture
JUSTIFICATIVA Y OBJETIVOS: Las latencias
T50 y T95 corresponden a las medianas de los intervalos entre el término
de la infiltración de la piel y subcutáneo con anestésico
local y la ocurrencia de estímulo nóxico, que garantizan insensibilidad
en un 50% y en un 95% de los pacientes, respectivamente. Este estudio evaluó
el T50 y el T95 de la infiltración de lidocaína a 1% para punción
de la piel de la región lumbar.
MÉTODO: El estudio fue prospectivo siguiendo la técnica de secuencial dependiente de la respuesta del paciente anterior, incluyendo 25 pacientes sometidos a bloqueos subaracnóideos con aguja de Quincke 25G. Lidocaína a 1%, 3 mL, fue infiltrada en la piel y subcutáneo de L3-L4 ó L4-L5, con aguja de 10 mm 25G. Los intervalos de tiempo decorridos entre el término de la infiltración y la punción con aguja de Quincke 25G fueron establecidos en escala logarítmica. El intervalo inicial fue de 30 segundos. Los intervalos subsiguientes dependieron de la respuesta del paciente anterior. Caso el paciente mencionase haber sentido la punción de la piel con la aguja de Quincke, el tiempo de espera era aumentado para el tiempo inmediatamente superior en el próximo paciente. Caso contrario, era disminuido para el intervalo inmediatamente inferior. El T50 y el T95 fueron calculados por las fórmulas de Dixon y Massey.
RESULTADOS: Las medianas (límites del 95% de confianza) del T50 y del T95 fueron 25 segundos (20 - 31 segundos) y 53 segundos (33 - 85 segundos), respectivamente.
CONCLUSIONES: Para lograr anestesia de la piel de la región lumbar para punción subaracnóidea en un 95% de los pacientes utilizando anestesia infiltrativa con 3 mL de lidocaína a 1%, se debe aguardar de 33 a 85 segundos entre el término de la infiltración y la punción.
Lumbar punctures are common anesthetic procedures very often related to uncomfortable patients' experience, in addition to promoting reflexes peaking with skeletal muscle contractions. The International Association for the Study of Pain defines pain as a disagreeable sensory and emotional experience associated to real or potential tissue damage, or described as such terms 1. Paravertebral muscle reflexes are triggered by painful skin stimulations 2,3 and may change patient's position. Previous studies have shown the importance of adequate position for the success in carring out a neuraxial block 4,5. An effective method to decrease painful sensations and motor reactions inherent to the procedure is skin infiltration with local anesthetics.
Local anesthetic infiltration is described as painful and several studies have tested different strategies to minimize pain during injection. Although infiltration before puncture is a common and effective technique to decrease venous puncture pain scores 6, it is necessary to determine minimum onset for the anesthetic to produce skin insensitivity, which would prevent the association of subsequent painful stimulations. So, at noxious puncture stimulation, one may assure that patient's stimulation conduction is blocked, thus preventing pain at puncture site.
This study aimed at evaluating minimum onset of infiltrative anesthesia with 1% lidocaine to abolish the skin pain during lumbar puncture with 25G Quincke needle.
After the Ethics Committee, Hospital Governador Celso Ramos approval and their informed consent, participated in this prospective study 25 adult patients of both genders, scheduled for elective surgeries under spinal anesthesia. Exclusion criteria were patients unable to understand or communicate and allergy to lidocaine. Patients were sequentially allocated depending on previous patient's sensory response to puncture (Dixon and Massey's up-down method).
No patient was premedicated. After monitoring with cardioscopy, noninvasive blood pressure, pulse oximetry and venoclysis, patients were placed in the lateral position. Skin and subcutaneous tissue of L3-L4 or L4-L5 interspace were infiltrated with 3 mL of 1% plain lidocaine with 10 mm 25G needle before spinal puncture with 25G Quincke needle.
Initial interval between infiltration and puncture with 25G Quincke needle was defined as 30 seconds. Subsequent intervals were determined a priori, by transforming these 30 seconds into natural logarithm units and adding or subtracting 0.1 logarithm unit up to 10 posts above or below the initial value. Time intervals used in this study were obtained by calculating antilogarithms for each post. After skin puncture with 25G Quincke needle, patient was objectively asked about pain.
If patient referred pain during skin puncture with Quincke needle, the result was considered a failure and time between end of infiltrative anesthesia and Quincke needle puncture for the next patient was increased to the immediately longer time interval. If patient referred no pain, result was considered a success and the interval between infiltration and Quincke needle puncture for the next patient was decreased to the immediately shorter value. Data were collected until the difference between successes and failures was below 2. Effective onsets in 50% (T50) and 95% (T95) of patients were calculated using Dixon and Massey's formulas 7.
The sequence of responses is shown in figure 1. Effective onsets (95% confidence limits) for 50% (T50) and 95% (T95) of patients were 25 seconds (21 to 30 seconds) and 53 seconds (33 to 85 seconds), respectively.
Pain is triggered by direct mechanical or chemical stimulation (release by damaged tissue of substance P such as prostaglandins, histamine, serotonin, bradykinin, 5-hydroxytriptamine, substance P) which may generate action potential in nociceptors. Pain stimulation is transmitted by Ad and C fibers. Ad are fast-conducting myelin fibers, primarily responsible for well localized acute pain. C fibers have no myelin and slow conductance; they are responsible for sensations such as burning, diffuse and poorly localized pain 8. The afference of skin-muscle reflex is promoted by such fibers which transmit stimulation to spinal cord dorsal laminae, where it connects to interneurons and spinal cord ventral region, where the efferent stimulation of this precise and localized reflex is generated 2,3. Response, in case of lumbar punctures, is paravertebral muscle contraction, which may change patient's position. A previous study has shown that the adequate position of the patient is and independent predictor of neuraxial block success, together with other factors, such correct identification of anatomic sites and operator's experience 4. It has also shown that more than one puncture attempt is associated to a higher number of neuraxial block complications.
Subcutaneous infiltrative anesthesia attempts to decrease or suppress painful neuraxial stimulation. Conduction blockade is described as fast with this type of anesthesia, provided dose and volume are adequate 9. Local anesthetic skin infiltration is also painful and is influenced by factors such as anesthetic agent, acidity of the solution, pKa, liposolubility, temperature, technique and presence of adjuvants 6,10-15. However, time needed for blockade installation (onset) has to be determined. Onset should be respected, or else there will be risk of triggering painful stimulation with no benefit for patients.
Some studies have shown that mixing local anesthetic and sodium bicarbonate (alkalinization), may decrease painful sensation 12,13,16-19 and onset 9. Subcutaneous lidocaine infiltration has shown lower pain scores when its pH is close to physiological pH. The first explanation would be that acid pH itself would directly irritate tissue. Another one would be increased proportion of basic form, not electrically charged, derived of increased solution pH. Basic form would be able to more rapidly spread through tissue and nervous membrane, inducing an almost instantaneous blockade 19. In addition to alkalinization, smaller needles may determine lower pain scores at infiltration 14. The association of solution alkalinization and warming to body temperature was synergic in terms of decreasing pain scores at lidocaine infiltration 17.
Onset also depends on some factors, such as intrinsic anesthetic activity of the compound, concentration and total dose, distance between injection and sites of action and anesthetic ability of penetrating the tissue. Tissue penetration ability is the inherent ability of the drug to penetrate fibrous tissues and other structures between injection site and nervous fibers. Lidocaine is classified as fast onset and high penetration agent 20.
Local infiltration allows the drug to rapidly reach small nervous terminals, promptly penetrating adjacent tissues. So, it rapidly reaches axonal membranes where it interferes with sodium conductance. As compared to nerve branch anesthesia, infiltrative anesthesia does not have to penetrate epineuron, perineuron and endoneuron, fat, blood vessels and lymphnodes, which may account for 40% of nervous branch diameter 20.
Dixon and Massey's up-down method was used to calculate T50 (time in which 50% of patients would not refer pain during second puncture) and T95. This method allows for a smaller sample and distributes the sample around the mean 7.
Our study has shown that 1% plain lidocaine minimum onset for lumbar skin infiltration was 33 to 85 seconds for 95% of patients (median of 53 seconds). So, this interval between infiltration and spinal puncture should be respected for painful stimulation blockade to occur. Without it, one runs the risk of adding painful stimulations instead of preventing them.
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Dr. Getúlio Rodrigues de Oliveira Filho
Address: Rua Luiz Delfino, 111/902
ZIP: 88015-360 City: Florianópolis, Brazil
Submitted for publication November 30, 2004
Accepted for publication February 23, 2005
* Received from Hospital Governador Celso Ramos, CET/SBA Integrado de Anestesiologia da SES-SC, Florianópolis, SC