Anesth Analg 2004;98:831-834
© 2004 International Anesthesia Research Society
doi: 10.1213/01.ANE.0000099368.62200.01
REGIONAL ANESTHESIA
Continuous Parasacral Sciatic Block: A Radiographic Study
Elisabeth Gaertner, MD*,
Pablo Lascurain, MD*,
Cyrille Venet, MD
,
Xavier Maschino, MD*,
Alina Zamfir, MD*,
Radu Lupescu, MD*, and
Admir Hadzic, MD PhD
Section Editor
*Service d’Anesthésie Réanimation Chirurgicale Hôpital de Hautepierre, Strasbourg, France;
Service d’Anesthésie, Clinique des Eaux Claires, Grenoble, France; and
Department of Anesthesiology, St. Luke’s-Roosevelt Hospital, New York, New York
Address correspondence and reprint requests to Elisabeth Gaertner, MD, Service d’Anesthésie-Réanimation Chirurgicale, Hôpital de Hautepierre, 1 Avenue Molière, 67098 Strasbourg, France. Address email to e.gaertner{at}evc.net
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Abstract
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Parasacral sciatic blockade results in anesthesia of the entire sacral plexus. In this study we sought to determine the spread of the local anesthetic injected through a parasacral catheter, the anatomical location of the inserted catheters, and the extent and reliability of the blockade. In this study, 87 consecutive patients undergoing major lower limb surgery were enrolled. After placement of the catheter and injection of 8 mL of radio-opaque contrast dye, radiographic images were evaluated for dispersion of the injectate. Sensory and motor evaluations were also performed. Radiographic analysis of the injectates revealed that nearly all catheters (86 catheters, 99%) were in the correct anatomical position. The mean volume of local anesthetic injection was 21 ± 3 mL. All patients developed a full sensory block of all three major components of the sciatic plexus (tibial, common peroneal, and posterior cutaneous nerve of the thigh). We conclude that the parasacral sciatic block results in frequent success of blockade of all three major components of the sciatic plexus and it has a small risk of complications. Contrast radiography can be used to document the catheter placement.
IMPLICATIONS: The parasacral sciatic block results in a frequent success rate of blockade of all three major components of the sciatic plexus (tibial, common peroneal, and cutaneous nerve of thigh). A contrast radiography can be used to confirm the proper position of the catheter.
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Introduction
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The sciatic nerve block is a valuable technique to achieve anesthesia or analgesia of the lower extremity. When combined with the femoral or lumbar plexus block, nearly the entire lower extremity can be anesthetized. A parasacral block technique was suggested to block the entire sacral plexus after a single injection of local anesthetic in a fascial plane (1). Its wider coverage gives the parasacral sciatic block a theoretical advantage over the classical, posterior approach and makes the technique particularly well suited for a continuous infusion of local anesthetic (2,3). However, this approach is relatively new and little is known about the mechanics of the blockade or the anatomical location and extent of dispersion of injected local anesthetic. The aims of this study were to determine the spread of local anesthetic injected through the parasacral catheter, the anatomical location of the inserted catheters, and the extent and reliability of the blockade.
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Methods
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In this Institutional Ethics Committee approved, prospective study, all patients of ASA physical status I–III undergoing major lower limb surgery and consenting to continuous sciatic nerve block for postoperative pain management were enrolled. Patients with contraindications to nerve blocks (e.g., infection at the needle insertion site, coagulation disorders, neurological defect) were excluded.
After written informed consent was obtained, patients were premedicated IV with 2 mg of midazolam and positioned in the lateral decubitus position with the limb to be blocked uppermost and flexed in the hip and knee joints.
A line between the posterior superior iliac spine (PSIS) and the ischial tuberosity (IT) was drawn; the point of needle insertion was marked at 6 cm from the PSIS (Fig. 1). After skin infiltration with local anesthetic, a 22-gauge 110 mm insulated needle (ContiplexD; B.Braun®, Melsungen, Germany) connected to a nerve stimulator (HNS 11; B.Braun®) was advanced in a sagittal plane with a slight (10°) caudal angulation. The nerve stimulator was initially set at 2 mA (2 Hz, 0.1 ms). The needle was "walked" off the ridge of the greater sciatic notch until stimulation of the sciatic nerve was achieved. Plantar flexion of either the foot or toes (tibial division of the sciatic nerve) or dorsiflexion/eversion of the foot or toes (peroneal division of the sciatic nerve) at 0.5 mA were accepted. Once motor response was achieved, 20 mL of mixture containing 0.75% ropivacaine and lidocaine 2% with 1:200,000 epinephrine (in a 3:1 proportion) was injected through the needle (the target volume was 0.3 mL/kg; minimal volume was 15 mL and maximum volume was 25 mL). This dosing regimen was chosen based on our standard clinical practice protocol1. After the injection was complete, the needle stylet was removed and the catheter was inserted 2 cm beyond the tip of the cannula. The catheter was fixed to the skin, and a test dose of lidocaine with epinephrine 1:200,000 (lidocaine 2% 2 mL) was administered. When necessary, a femoral or lumbar plexus block was performed to achieve complete surgical anesthesia of the lower limb.
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Figure 1. Landmarks for the parasacral nerve block. PSIS = posterior iliac spine; IT = ischial tuberosity.
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Postoperatively, 8 mL of radio-opaque dye was injected through the catheter (Omnipaque®; Nycomed Imaging, Oslo, Norway) and a series of radiographs in the anterior-posterior projection (AP) were taken. The radiographic images were evaluated for dispersion of the injected contrast media and catheter tip location. The presence of a spindle 2 to 3 cm in length with an oblique orientation and crossing the sciatic notch on the AP radiograph (Fig. 2a) and/or shadowing of the sacral roots (Fig. 2b) were considered to indicate injection into the correct plane and adequate placement of the catheter. These radiographic findings were deemed indicative of correct catheter placement based on a high correlation of these findings with the computed tomography (CT) images of the injectate in our internal clinical series. All radiographic evaluations were performed by a radiologist blinded as to the study goals. Successful catheter placement was determined by the radiographic appearance of the injected contrast and documented blockade (motor or sensory block in the sciatic distribution) after injection of local anesthetic. The patients then received a continuous infusion of ropivacaine 0.2% at a rate of 8 mL/h with or without a patient-controlled analgesia bolus.
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Figure 2. a, typical radiographic image after an injection of a radio-opaque dye through the parasacral sciatic catheter. B, the roots of the sacral plexus seen as a "negative" contrast within the injectate.
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The following additional data were recorded: patient demographics, ASA classification, specific motor response, minimal current intensity (mA) at which the stimulation was obtained, and daily visual analog pain scores during four postoperative days. In addition, the success rate of achieving sensory analgesia in the distribution of the tibial, common peroneal, and posterior cutaneous nerve of the thigh was documented (pinprick method). Motor block was assessed on a three-point scale as follows: 0 = no block; 1 = mild motor block (able to lift against gravity but unable to lift against resistance); 2 = dense motor block (unable to move the extremity). Postoperatively, the efficacy of the catheter in providing sensory anesthesia was assessed twice a day using the pinprick sensory test. All adverse events were recorded, and patients were systematically asked whether they had hypoesthesia, paresthesia, or pain in the sciatic area 1 day after catheter removal.
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Results
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Eighty-seven consecutive patients (40 men and 47 women) undergoing lower extremity surgery were studied. Mean age, weight, and height were 59 ± 19 (16–85) years, 74 ± 12 (42–98) kg, and 170 ± 8 (152–185) cm, respectively. Twenty-two patients (25%) were ASA I, 49 (56%) were ASA II, and 16 (19%) were ASA III. The surgical procedures are listed in Table 1. The parasacral catheter was combined with the femoral or lumbar plexus blocks in 71 patients (82%). The most frequent response to nerve stimulation was that of the tibial nerve (71%). The common peroneal response was obtained in 26% of patients. Motor response could not be obtained in 2 (3%) patients despite several attempts. In these patients, twitch of the piriformis muscle (abduction of the thigh) was accepted instead. The mA at which the local anesthetic was injected was 0.5 ± 0.1 (range, 0.2–1.1) for the tibial response and 0.6 ± 0.1 (range, 0.3–0.8) for the common peroneal response. The mean volume of local anesthetic injection was 21 ± 3 mL. All patients developed full sensory block of all three major components of the sciatic plexus (tibial, common peroneal, and posterior cutaneous nerve of the thigh).
All parasacral catheters, except one that required repositioning, provided effective postoperative analgesia and sensory distribution in the expected dermatomes (Table 2). The catheters were kept 24–384 h (median, 72 h). None of the patients developed infectious, neurologic or systemic toxicity complications.
Radiographic analysis of the injectates revealed that nearly all catheters (86 catheters, 99%) were in the correct anatomical position. The position of one catheter was found to be intrapelvic (subperitoneal) (Figure 3). Indeed, a CT scan study of this patient’s pelvis demonstrated the pooling of the contrast medium in the presacral area (Figure 4). This was likely attributable to the placement of the catheter too deep and within the fascia of the obturator internis muscle. In this patient, the catheter was withdrawn 2 cm; the consequent reinjection resulted in the expected, typical spread of the contrast media with a successful block. There were no complications as the result of the intrapelvic placement of the catheter.
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Figure 3. Intrapelvic, subperitoneal catheter placement with pooling of the contrast in the presacral space.
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Figure 4. Computed tomography scan of the tip of the parasacral catheter. 1 = gluteal muscle; 2 = catheter; 3 = tip of the catheter within the obturator internis aponevrosis; 4 = piriformis muscle; 5 = pooling of the contrast medium in the presacral area.
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Discussion
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Our results indicate that the parasacral sciatic block results in frequent success of blockade of all three major components of the sciatic plexus (tibial, common peroneal, and cutaneous nerves of thigh). The technique provided consistent analgesia and allowed predictably accurate placement of the nerve block catheters without significant complications.
In the single shot technique of the parasacral block, the patient is in the lateral position and the needle is directed perpendicular to the skin and horizontally to the table plane. However, with the continuous technique, the needle is inserted at a slight caudad angulation (10°–15°) to facilitate insertion of the catheter. In our study there was no difference in the block success rate between the stimulation of the common peroneal or tibial nerves and a single injection was sufficient to block both components of the sciatic nerve, as well as the posterior cutaneous nerve of the thigh (4). Therefore, a multiple stimulation technique is not necessary with this approach because all three major branches of the sciatic nerve emerge together within the same fascial sheath above the piriformis muscle (5). The catheter is inserted in the space formed by the pelvic fascia medially, piriformis muscle dorsally, and internal obturator muscle laterally. Ideally the catheter is introduced 2 cm beyond the tip of the needle, cephalad to the emergence of the posterior cutaneous nerve of the thigh to assure blockade of this nerve before it leaves the sciatic trunk above the piriformis muscle. Remarkably, a relatively small dose of local anesthetic (e.g., 20 mL) is sufficient to achieve reliable blockade of all three major branches.
In our practice, catheter location is routinely confirmed using contrast radiography. A typical radiographic feature after an injection resembles a spindle 2 to 3 cm in width, with an oblique orientation and crossing the sciatic notch. The roots of the sacral plexus can often be seen as a "negative" contrast within the injectate (Fig. 2).
Care should be taken to avoid insertion of the needle too deeply to avoid intrapelvic placement of the needle and catheter and possible injury to the anteriorly positioned ureter and other pelvic organs. The hypogastric, gluteal, sacral, ischial, and pudendal vessels are all located near the sacral plexus. Therefore, a careful and slow injection with frequent check for intravascular placement of the needle or catheter is necessary to decrease the risk of systemic toxicity.
Our study has several important limitations. First, the injection of the dye postoperatively might not necessarily represent the spread of the fluid injected preoperatively. Second, a follow-up radiographic study to test for inadvertent misplacement of the catheters was not done; therefore we cannot conclude with certainty that the catheters remained in their original position. Nevertheless, the excellent efficacy of analgesia suggests that the infusion remained effective throughout the study period. Finally, it is possible that the use of additional blocks (i.e., femoral and lumbar plexus blocks) may have contributed to the adequacy of analgesia. However, the sensory distribution of the additional blocks is clearly different from that obtained with parasacral blocks; therefore the additional blocks alone would be unlikely to provide adequate surgical anesthesia or quality postoperative analgesia.
In summary, the parasacral sciatic block results in frequent success and a predictable spread of local anesthetic within the sheath of the sciatic plexus (6,7). An additional advantage of this technique is the ability to achieve anesthesia of all three branches of the sciatic nerve (tibial, common peroneal, and posterior cutaneous nerve of the thigh) with a single injection of local anesthetic. Plane contrast radiography can be used to confirm its proper position by demonstrating a typical distribution of the injected contrast.
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Footnotes
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1 http://www.nysora.com, March 18, 2002. 
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References
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- de Visme V, Picart F, Le Jouan R, et al. Combined lumbar and sacral plexus block compared with plain bupivacaine spinal anesthesia for hip fractures in the elderly. Reg Anesth Pain Med 2000; 25: 158–62.[ISI][Medline]
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- Ho AM, Karmakar MK. Combined paravertebral lumbar plexus and parasacral sciatic nerve block for reduction of hip fracture in a patient with severe aortic stenosis. Can J Anaesth 2002; 49: 946–50.[Abstract/Free Full Text]
Accepted for publication September 17, 2003.
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Abstract
Introduction
