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Print version ISSN 0034-7094
Rev. Bras. Anestesiol. vol.54 no.3 Campinas May/June 2004
Low isobaric 0.5% bupivacaine doses for unilateral spinal anesthesia*
Bajas dosis de bupivacaína a 0,5% isobárica para raquianestesia unilateral
Luiz Eduardo Imbelloni, TSA, M.D.I; Lúcia Beato, TSA, M.D.II; M.A. Gouveia, TSA, M.D.III
IDiretor do Instituto de Anestesia
Regional, Anestesiologista da Casa de Saúde Santa Maria e Clínica
São Bernardo. Rio de Janeiro
IIAnestesiologista da Casa de Saúde Santa Maria e Clínica São Bernardo. Rio de Janeiro
IIIDiretor do Instituto de Anestesia Regional, Chefe do Serviço de Anestesiologia do Hospital Central do IASERJ, Rio de Janeiro
BACKGROUND AND OBJECTIVES: Unilateral
spinal anesthesia may be advantageous, especially in the outpatient setting.
Low local anesthetic doses, slow spinal injection rate and the lateral position
have been related to the easiness of inducing unilateral spinal anesthesia.
This study aimed at investigating the possibility of inducing unilateral spinal
anesthesia with isobaric 0.5% bupivacaine.
METHODS: Spinal anesthesia with 1 mL isobaric 0.5% bupivacaine (5 mg) was induced through 27G Quincke needle in 25 physical status ASA I and II patients undergoing orthopedic procedures. Dural puncture was performed with patients in lateral decubitus with the limb to be operated facing upwards. One mililiter of isobaric bupivacaine was injected in 30 seconds. Sensory and motor blocks were compared between the operated and the contralateral side.
RESULTS: Motor and sensory blocks on operated and contralateral sides were significantly different in all studied moments. All patients presented surgical anesthesia in the operated limb. At 20 minutes, nine patients presented sensory block in the contralateral side; at 40 minutes they were 18 and at 60 minutes they were 17 patients. So, unilateral block was present in seven patients (28%) and bilateral block was present in the remaining 18 patients (72%). No patient developed post-dural puncture headache.
CONCLUSIONS: Isobaric bupivacaine (5 mg) provides predominant unilateral block after 20 minutes in the lateral position. Isobaric bupivacaine moves in the CSF after 20 minutes resulting in just 28% unilateral blocks. Major advantages of unilateral spinal anesthesia are hemodynamic stability and short duration and it might be a new alternative for outpatient procedures.
Key Words: ANESTHETICS, Local, bupivacaine; ANESTHETIC TECHNIQUES, Regional: spinal block
JUSTIFICATIVA Y OBJETIVOS: La raquianestesia
unilateral puede presentar diversas ventajas, principalmente en el paciente
ambulatorial. Bajas dosis de anestésicos locales, lenta velocidad de inyección
subaracnóidea y posición de decúbito lateral son relacionados
con la facilidad de producir distribución unilateral en la raquianestesia.
En este estudio, fue verificada la posibilidad de obtenerse raquianestesia unilateral
con bupivacaína a 0,5% isobárica.
MÉTODO: La raquianestesia con 1 ml de bupivacaína isobárica a 0,5% (5 mg) fue realizada a través de aguja 27G Quincke en 25 pacientes, estado físico ASA I y II sometidos a cirugías ortopédicas. La punción subaracnóidea fue realizada por vía lateral con el paciente en decúbito lateral, con el miembro a ser operado vuelto para arriba, y 1 ml de bupivacaína hipobárica fue inyectado en la velocidad de 1 ml.30s-1. Bloqueos sensitivo y motor (picada de aguja y escala de 0 a 3) fueron comparados entre el lado a ser operado y el contralateral.
RESULTADOS: Los bloqueos motor y sensitivo entre el lado operado y el contralateral fueron significativamente diferentes en todos los tiempos evaluados. En el miembro operado todos los pacientes presentaran anestesia quirúrgica. En el miembro contralateral, a los 20 minutos, 9 pacientes presentaron bloqueo sensitivo; a los 40 minutos 18 pacientes y a los 60 minutos 17 pacientes. Por tanto, el bloqueo sensitivo unilateral ocurrió en 7 pacientes (28%) y en ambos miembros en 18 pacientes (72%). Raquianestesia unilateral fue obtenida en 28% de los pacientes. Estabilidad hemodinámica fue observada en todos los pacientes. Ningún paciente desenvolvió cefalea pós-raquianestesia.
CONCLUSIONES: La bupivacaína isobárica (5 mg) proporciona predominante bloqueo unilateral después de 20 minutos en la posición lateral. La solución isobárica de bupivacaína se moviliza dentro del LCR después de 20 minutos, resultando en un bloqueo unilateral en apenas 28% de los pacientes. La principal ventaja de la raquianestesia unilateral es la estabilidad hemodinámica y su rápida regresión, pudiendo ser una nueva opción para cirugía ambulatorial.
Anesthesiologists are often faced with unilateral surgical procedures on one lower limb, especially during outpatient and orthopedic procedures. In such situations, unilateral spinal anesthesia is advantageous over conventional spinal anesthesia. These advantages include decreased hypotension during spinal anesthesia 1-3, faster anesthetic recovery 2,3 and increased patients satisfaction 2,3. Lateral position, low anesthetic doses, pencil point needles and slow injection rate have been suggested to enhance unilateral spinal anesthesia 4,5.
Theoretically non-isobaric local anesthetic injections may induce unilateral block in patients in the lateral position. Isobaric bupivacaine solutions were compared to hyperbaric 6 and hypobaric 7 solutions to induce unilateral spinal anesthesia.
Our study aimed at evaluating the attempt to asymmetrically distribute blockade between the operated and contralateral limb and its influence in the incidence of arterial hypotension during spinal anesthesia for lower limb orthopedic procedures with low doses of isobaric 0.5% bupivacaine.
After the Clinics Disclosure and Publication Board of Directors approval and their informed consent, participated in this prospective study 25 patient's physical status ASA I and II, aged 21 to 67 years, submitted to elective and urgency orthopedic surgeries involving just one limb. Exclusion criteria were hypovolemia, coagulation disorders, infection and refusal of the method. Monitoring included noninvasive blood pressure, heart rate and pulse oximetry. Patients were not premedicated. Venous access was installed in the operating room with lactated Ringer's solution and 25 to 50 µg fentanyl were injected.
Patients were placed in the lateral position with the limb to be operated facing upwards. Spine was horizontally positioned before spinal puncture and the table was leveled in the horizontal position (zero) throughout the procedure. Paramedian spinal puncture was performed at the L3-L4 interspace with 27G Quincke needle (B. Braun) and 5 mg isobaric 0.5% bupivacaine were injected at the rate of 1 mL.30s-1 with needle tip oriented upwards. Patients were maintained in this position for 20 minutes and then placed in the supine position.
Sensory block was evaluated by loss of sensation to cold (ice) and to a 27G needle pinprick, while motor block was evaluated by Bromage's modified scale (0 = no motor block to 3 = total motor block). Sensory and motor blocks were evaluated in both limbs at 20, 40 and 60 minutes, and at the end of the surgery. Hemodynamic parameters were evaluated at 3-minute intervals during the first 10 minutes after spinal puncture and then at 5-minute intervals until the end of the surgery.
Arterial hypotension was defined as a 30% decrement from baseline values, while bradycardia was defined as HR below 50 bpm. Arterial hypotension was treated with 1 mg boluses of ethylphenylephrine i.v. and bradycardia with 0.5 mg atropine. During surgery, a pneumatic tourniquet was inflated 100 mmHg above systolic blood pressure on the operated limb. Oxygen (2 L.min-1) was administered through nasal catheter or Hudson's mask. Midazolam (1 to 2 mg) was administered after the second evaluation (40 minutes).
Patients were followed until the 3rd postoperative day for information about their satisfaction with the technique, post-dural puncture headache or transient neurological symptoms (TNS), and until the 30th day for permanent neurological complications.
Quantitative variables were analyzed in terms of descriptive statistics with means ± standard deviation, minimum, maximum and median - when this was the best alternative. Blockades on both limbs were compared by non-parametric sign test, and correlations were evaluated by Pearson's correlation coefficient. Significance level was 5%.
Demographics data are shown in table I.
Unilateral block was induced in 64% of patients at 20 minutes. At 40 and 60 minutes, just 28% of patients remained with unilateral block. At the end of the surgery, 32% of patients presented unilateral block. Total blockade regression time was 2.34 ± 0.33 h on the operated limb and 1.64 ± 0.67 h on the contralateral limb. There were no significant differences in total blockade regression according to gender (p = 0.95, operated; p = 0.97, contralateral), or to surgery duration (p = 0.86). Females were older as compared to males (p = 0.028).
Sensory block spread in the operated limb varied from T8 through L1 and on the contralateral limb from T12 through L3, showing a clear between-limb dissociation. At 20 minutes, 9 patients exhibited sensory block on the contralateral limb; at 40 minutes 18 patients, and at 60 minutes 17 patients exhibited sensory block on the contralateral limb. Unilateral blocks occurred in 7 patients (28%) while blocks were bilateral in the remaining 18 patients (72%). Blocks were significantly higher on operated limbs (p < 0.0001), as shown on figures 1 through 4. There was linear correlation between sensory block spread in both limbs, as shown in figures 1 to 4.
At 20 minutes, total motor block (grade 3) of the operated limb was noted in 21 patients, and grade 2 blocks occurred in 4 patients. At 40 minutes, two additional patients exhibited total motor block. Total motor block of the contralateral limb occurred in 1 patient, grade 2 in 5, grade 1 in 3 and no motor block in 16 patients, at 20 minutes. At 40 minutes, total motor block was noted in 2 patients, grade 2 in 12, grade 1 in 5, and no motor block in 6 patients (Figure 5). Unilateral motor block was present in 16 patients (64%) at 20 minutes and in 6 patients (24%) at 40 minutes. Motor block on the operated limb was higher as compared to the contralateral limb in all evaluations (p < 0.0001).
Spinal anesthesia was satisfactory, as no patient needed general anesthesia complementation. One patient referred tourniquet pain after 65 minutes of surgery. Two out of the 6 patients without contralateral limb blockade have referred loss of proprioception. No blood pressure and or heart rate changes were noted. No urinary retention was observed and no patient developed post-dural puncture headache. No back, buttock or leg pain has been referred that could be classified as TNS. No late neurological complications occurred.
All patients were satisfied with the technique. All 6 patients with unilateral spinal anesthesia referred a nice sensation of being able to feel the contralateral limb.
Low doses of isobaric bupivacaine (5 mg) at the rate of 1 mL.30s-1 through 27G Quincke needle induced total unilateral block in 64% of patients at 20 minutes, but this figure evolved to just 28% at 40 minutes, showing that isobaric bupivacaine moves in the CSF in this time-frame. Unilateral spinal anesthesia has shown to be safe for single limb orthopedic procedures, decreasing the hemodynamic impact of neuraxial blocks 1,2,8 and increasing patients' satisfaction with the technique.
The density of 0.5% bupivacaine at 37 ºC is 0.9993 g.mL-1 9. By definition, baricity is the ratio between injected solution density and CSF density. Mean CSF density is 1.00059 ± 0.00020 g.mL-1 10. The density of 0.5% bupivacaine is slightly hypobaric.
Unilateral spinal anesthesia has been increasingly used in recent years for inducing unilateral short-lasting motor block, allowing patients' comfort and preventing hemodynamic changes. Isobaric 0.5% bupivacaine is a long-lasting local anesthetic, which is usually overdosed during short orthopedic procedures. The dose of 5 mg of isobaric 0.5% bupivacaine has allowed a recovery time of 2.15 hours in the operated limb and of 1.65 hours in the contralateral limb, shorter than 2.93 hours obtained with 6 mg isobaric 0.5% bupivacaine 7, and shorter than the 2.32-hour duration with the same dose of hypobaric 0.15% bupivacaine 3.
Several authors prefer pencil point needles for directing anesthetic flow to induce unilateral spinal anesthesia 1,6,7,11-13. Others 2,14-16, however, prefer cutting-tip needles (Quincke) due to the potential hazard of slow caudal injections promoting high hyperbaric anesthetic concentrations. Quincke needles allow for fast CSF flow 17, do not promote poor local anesthetic distribution 18 and are associated with low incidence of headache 19.
Mean time to reach maximal level of analgesia after 5 mL of 0.5% plain bupivacaine has been shown to be 17.3 minutes 20. Upper sensory level increases more than four dermatomes when patients are positioned in 30º head-up position for 80 to 115 minutes 21. In this study, patients remained in horizontal lateral decubitus for 20 minutes and the sensory level on the operated limb ranged from T8 to L1, while on the contralateral limb sensory block ranged from T12 to L3. In a study in which 5 mg hypobaric bupivacaine was used and patients remaining in lateral position for the same 20 minutes, upper sensory level varied from T7 through L1 3.
Unilateral spinal anesthesia may be induced with hypobaric, isobaric, or hyperbaric solutions and the incidence of unilateral spinal anesthesia varies according to the study. With isobaric solutions the incidence is 37% 6, or higher than our 28%.
One objective of unilateral spinal anesthesia is to decrease hypotension, which may happen during spinal anesthesia, a fact that was confirmed when conventional anesthesia was compared to asymmetric anesthesia 1. Hyperbaric solutions for unilateral spinal anesthesia are associated with an incidence of 10% 15 to 20% 12 of arterial hypotension, regardless of injection rate. Hypobaric solutions 2,6,22,23 result in lower incidence. With isobaric solutions, the incidence has been of 5% 6 and 6.7% 7, higher results than those found in our study where no arterial hypotension episode was observed.
The regression of two segments with low doses of hyperbaric 0.5% bupivacaine varies from 67 1 to 99 18 minutes. With hypobaric bupivacaine, regression was present at 53 minutes and patients were released after 180 to 190 minutes postoperatively 24. Two segments regression was not evaluated in our study, but rather total blockade regression, which varied from 110 to 180 minutes in the operated limb and from 95 to 155 minutes in the contralateral limb, what suggests that 5 mg isobaric bupivacaine may be a good indication for outpatient procedures.
Pencil point needle and slow injection rate may contribute for the occurrence of transient neurological symptoms, especially when hyperbaric lidocaine is used 25. No neurological symptoms have been observed in our study with cutting point needles and bupivacaine, in agreement with other authors 26,27 who have evaluated the influence of hyperbaric 0.5% bupivacaine injection rate on lateral distribution.
Cutting point needles are associated with low incidence of headache 18, which was confirmed in our study where no headache has been observed, similarly to a previous study with 2 and without 3 removal of 3 to 5 mL CSF.
The maintenance of the lateral position for 20 minutes may be a precious time for outpatient anesthetic practice, but this disadvantage may be overcome by advantages. When high isobaric 28 or hyperbaric 29 bupivacaine doses are used, anesthetic depth and unilaterality may change after moving the patient 60 to 120 minutes after injection. Our study has confirmed that low isobaric solution doses move after 20 minutes in the CSF.
In conclusion, this study has shown that unilateral spinal anesthesia with 5 mg isobaric 0.5% bupivacaine results in intense motor block with total regression in 115 minutes on the operated side and in 99 minutes on the contralateral side. Isobaric bupivacaine moves in the CSF after 20 minutes resulting in unilateral block in just 28% of patients. Major advantages of unilateral spinal anesthesia with 5 mg isobaric bupivacaine are its cardiocirculatory stability and fast regression, and it might be a new alternative for outpatient procedures.
We acknowledge Prof. José Antonio Cordeiro for his valuable guidance during statistical analysis.
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Dr. Luiz Eduardo Imbelloni
Av. Epitácio Pessoa, 2356/203 Lagoa
22471-000 Rio de Janeiro, RJ
Submitted for publication May 30, 2003
Accepted for publication August 18, 2003
* Received from Casa de Saúde Santa Maria, Clínica São Bernardo e Hospital IASERJ, Rio de Janeiro, RJ