|Year : 2008 | Volume
| Issue : 5 | Page : 506
Continuous Peripheral Nerve Block: the Future of Regional Anaesthesia?
Senior Consultant, Department of Anaesthesiology, Ganga Medical Centre & Hospital, 313, Mettupalayam Road, Coimbatore, India
|Date of Acceptance||09-Aug-2008|
|Date of Web Publication||19-Mar-2010|
Ganga Medical Centre & Hospital, 313, Mettupalayam Road, Coimbatore
Source of Support: None, Conflict of Interest: None
Continuous peripheral nerve blocks provide site specific analgesia with least systemic effects. They could be effectively used for intraoperative anaesthesia and as well as for very effective postoperative analgesia. The introduction of ultrasound and peripheral nerve stimulators into clinical practice have aided us to place these catheters in close proximity to the neural bundle. The stimulating catheters have further aided us to be more accurate. This article describes the equipment and the technique involved in performing continuous peripheral nerve blocks.
Keywords: Continuous Peripheral Nerve Block(CPNB), Peripheral nerve stimulator, Stimulating and Nonstimulating catheters.
|How to cite this article:|
Balavenkatasubramanian J. Continuous Peripheral Nerve Block: the Future of Regional Anaesthesia?. Indian J Anaesth 2008;52:506
|How to cite this URL:|
Balavenkatasubramanian J. Continuous Peripheral Nerve Block: the Future of Regional Anaesthesia?. Indian J Anaesth [serial online] 2008 [cited 2020 Jul 3];52:506. Available from: http://www.ijaweb.org/text.asp?2008/52/5/506/60667
| Introduction|| |
The past few years have witnessed a resurgence in the use of regional anaesthetic techniques. Regional anaesthesia per se and as an adjunct to general anaesthesia in providing balanced anaesthesia has greatly influenced the anaesthetic practice in the past decade. It is becoming increasingly evident that regional anaesthesia offers immense benefit to the patient in the perioperative period to the extent that it might decrease the perioperative morbidity and influence the overall outcome.
One of the advances in Regional Anaesthesia is the Continuous Peripheral Nerve Blocks (CPNBs) also known as Continuous Perinueral Blocks. Continuous peripheral nerve blocks offer tremendous advantage in the perioperative period. These techniques offer the possibility of prolonging intraoperative anaesthesia while avoiding the risks and side effects of general anaesthesia and centrineuraxis block. Continuous perineural blocks are site specific and offer superior analgesia than parenteral opioid analgesia and also are not associated with the possible side effects of opioid analgesia including nausea, vomiting, sedation, and respiratory depression  . The quality of analgesia mimicks that of epidural analgesia but it is devoid of ceratin complications associated with epidural anaesthesia like hypotension, urinary retention and pruritus  . There is increasing evidence to indicate that CPNBs aid in early mobilization, decrease incidence of DVT in the perioperative period, aid better sleep pattern and decrease the incidence of cognitive dysfunction in the perioperative period. 
The chemical sympathectomy produced by CPNBs is ideal after microvascular surgery, reimplantation and free flap procedures.  They are also of great use in treating patients with chronic pain syndromes and those requiring palliation for terminal illness.  It also helps to provide immediate pain relief in major trauma just after the initial stabilization of the patient. This could be termed as "on arrival block". It is also becoming evident that it not only provides immediate pain relief to the trauma victim but also considerably attenuates the stress response to tissue trauma. The stress response to tissue injury is mediated through neurohormonal, metabolic and immunological responses which in turn result in the release of plethora of chemical mediators like bradykinin, substance P, leukotrienes and interleukin. These chemical mediators in turn produce changes in the end organs and if unabated might lead to systemic inflammatory response syndrome (SIRS) and occasionally even to multiple organ dysfunction syndrome (MODS). Effective and early analgesia is thought to attenuate this stress response and possibly could prevent the development of SIRS.
The other important factor that is gaining attention is, if acute pain is taken care with adequate analgesia the possibility of developing chronic pain syndromes as a sequlae of the acute trauma might become less.
Though it became increasingly evident that CPNBs offer great advantage in the management of pain in the perioperative period the main limitation was nonavailability of appropriate equipment. But the past decade has seen a steady growth in the development of catheters and techniques that allow relatively simple, accurate and less invasive catheter placement thus ensuring block effectiveness and decreasing the incidence of secondary block failure.
| Equipments|| |
1. Peripheral Nerve Stimulator:
Peripheral electrical nerve stimulation is currently the most common technique for localizing nerves prior to the injection of the local anaesthetic. The equipment used to perform the peripheral nerve block is a peripheral nerve stimulator
Principle: Depolarising the nerve membrane results in contraction of the effector muscles due to stimulation of motor fibres or in paraesthesia due to the pure sensory fibres along the distribution of the nerve. These responses help us to confirm the proximity of the stimulating needle or the stimulating catheter to the nerve.
Features: The important features of the nerve stimulator include a constant current output and they are designed to deliver a current output from 0.2mA to 5mA, accurate display of the current delivered, an easy method to control the current intensity, a short pulse width of 100 to 200 microsecond, a disconnect or malfunction indicator. The stimulating frequency could be either 1 or 2 Hz, it has to be remembered while using 1 Hz the needle must be advanced very slowly so to avoid missing the nerve. The polarity of stimulating and returning electrode is very important. The negative electrode or the cathode should be connected to the stimulating electrode which is basically the needle or the stimulating catheter and the anode or the positive electrode to the patient's skin. The polarity of the stimulating current is an important aspect of nerve stimulation, when the cathode is used as the stimulating electrode rather than the anode, significantly less current is required to elicit motor response. In the [Figure 1] the various parts of the peripheral nerve stimulator have been marked. Many different models of this [Figure 2] peripheral nerve stimulators are available in the market now.
2. Stimulation needle: The peripheral nerve stimulator is attached to a stimulating needle. The stimulating needle is an insulated needle and it is coated with a layer of nonconducting material like polytetrafluoroethylene or silicon over the entire length of the needle with the exception of the needle tip. Upon stimulation the current density focuses on the uncoated tip of the needle. The advantage of these needles is a low threshold current is sufficient to stimulate the target nerve. For continuous blocks the needle gauge must be large enough to allow the passage of a catheter, currently most clinicians use 18 or 19 gauge needles for continuous blocks which aids us to pass a 20 gauge catheter through the needle. Most of these needles have an extension tubing attached to the needle which facilitates the clinician to aspirate and test for intravascular placement as the needle is advanced towards the nerve and it also helps in injecting the local anaesthetic agents without producing much movement of the needle. One of the common reason for a block failure even after obtaining adequate evoked motor response is the displacement of the needle while injecting the local anaesthetic agent and this is obviated by the addition of this extension tubing.
3. Catheters: The difference between the single shot nerve block and the continuous nerve block is the placement of a catheter. A brief description of the currently available catheters is important. The following systems are available in the catheter through needle system:
| Contiplex A system|| |
This was the first commercially available system for CPNB. It involves a cannula over a short bevel needle and an accompanying catheter.
| Contiplex D system|| |
This is a subsequent modification of contiplex A [Figure 3] system which includes an integrated wire for nerve stimulation and connection tubing for concurrent aspiration and injection.
Miniset system: This system offers the choice of 21 or 24 gauge needle with either Sporette or Facet tip.
| The Contiplex Tuohy system|| |
This system offers the advantage of single operator use. In this apparatus an 18 gauge Tuohy type needle insulated with polytetrafluoroethylene coating along its length with the exception of a pinpoint area at the most distal tip is the hallmark. This Tuohy needle was designed with a Huber tip to facilitate placement of a catheter in a direction parallel with the nerve. The system incorporates a 50cm extension tubing which allows for continuous aspiration for blood and injection of local anaesthetic solution by an assistant and which facilitates an immobile needle technique. The adapter also has a central diaphragm that allows the passage of a catheter through a port separate from where aspiration and injection occurs. This eliminates the need for equipment disconnection and minimizes the likelihood of needle movement, catheter misplacement and secondary block failure. In this system the length of the catheter is 100cm and is made of polyamide nylon, it has centimeter gradations until the 20cm and there are three distal orifices with the tip being closed. The catheter is translucent but it has an incorporated tungsten filament which is not highly radiopaque.
| Plexolong system|| |
This system also contains an 18 gauge Tuohy tip needle but with a sporette tip, it is radiopaque with styletted catheter. There is a large catheter threading assist device which keeps the catheter in sterile coil.
| Prolong system|| |
This system is also a Tuohy tip short bevel tip and a radiopaque catheter without a catheter stylet.
| Stimucath and Polyplex T.|| |
These systems have integrated stimulating wire attached to needle and integrated stimulating wire or alligator added to stimulating catheter [Figure 4].
4. Infusion pumps: The continuous catheters once placed successfully in the proximity of the nerve or the plexus are connected to infusion systems which deliver the chosen local anaesthetic agents as a continuous infusion. There are a variety of infusion systems available, including the simple elastomeric pumps, which are easy for use. These elastomeric pumps are disposable, deliver a fixed rate and are generally inexpensive. The univariate elastomeric pump[Figure 5] that is most suited for CPNB is the one that delivers at a rate of 5ml/hr.Currently multivariate elastomeric pumps are also available and these pumps give the flexibility to alter the rate of infusion. Elastomeric pumps with the option of patient controlled analgesia are also available. Though mechanical, battery-operated pumps offer more flexibility of programming and bolus dosing, they tend to be more costly  . In developing countries when battery operated mechanical pumps are not available freely elastomeric pumps serve as a good alternatives.
| The Continuous Catheter placement techniques|| |
The catheter placement techniques that are currently used to place the CPNBs are the nonstimulating catheter technique described by Steele and colleagues  and the Stimulating catheter technique described by Sarnoff. 
| Nonstimulating catheter technique|| |
In the nonstimulating technique an insulated needle is inserted near a nerve with the aid of a peripheral nerve stimulator. Once the needle tip is advanced near the nerve and the desired evoked motor response is obtained, the local anaesthetic agent is injected through the extension tubing that is attached to the needle to expand the perineural space resulting in the production of the nerve block which is called as the primary block and subsequently the needle is removed and the catheter is passed through the stylet and the local anaesthetic is injected through this catheter which results in further blocking the nerve called as secondary block. The non-stimulating catheter technique is relatively simple to perform and provides a very reliable primary block. In this technique the only limiting factor is the catheter is placed without confirmation of the tip position and thus there is the inability to assess the nerve to the catheter tip position, the success rate of the secondary block which is due to the infusion of the local anaesthetic through the catheter may be lower than the primary block . This is infact the disadvantage of the nonstimulating catheters and this problem has been overcome by using a stimulating catheter.
| Stimulating catheter technique|| |
In the stimulating catheter technique also known as Sarnoff technique, the nerve stimulator is attached to an insulated 17 to 20 gauge needle eg. Stimucath needle and set to deliver a current of 1-1.5 mA. The needle is advanced until a brisk motor response of the desired muscle group is elicited with a current output of 0.4-0.5 mA. The needle is held steady in the stimulating position but no local anaesthetic is injected through the needle. The nerve stimulator is disconnected from the needle and then it is attached to the proximal end of the stimulating catheter. Then the catheter is advanced through the needle to elicit a motor response similar to that elicited by stimulating the needle. Then the catheter is advanced beyond the distal end of the needle while maintaining the desired motor response. In case if the motor response disappears or changes to an undesired quality with advancement of the catheter the catheter is carefully withdrawn inside the shaft of the needle. Now with the catheter in the needle which essentially converts stimulation from the catheter to the stimulation through the needle, the needle is carefully manipulated slightly by rotating clockwise and counterclockwise or by moving a few millimeters inward or outward, while maintaining the desired evoked motor response. Once the desired stimulation is obtained the catheter is advanced 3 to 5cm along the chosen nerve. With this technique, both the bolus dose and the continuous infusion of local anaesthetic are injected through the catheter. The confirmation of the catheter tip position logically should provide a lower risk of secondary block failure due to more accurate placement of the catheter.
| Tunneling|| |
One of the major concerns while using the CPNB catheters has been the ability to secure these catheters in place without accidental dislodgement. Tunneling is a technique that has been widely used for fixing these catheters. In this technique we do not allow the needle to exit from the same exit wound as the catheter. Here we leave a "skin bridge"between the two. This helps in properly securing the peripheral catheters for a longer time without dislodgement. This also makes catheter removal much safer.
| Pharmacological agents for CPNB|| |
| Local anaesthetic agents|| |
The long acting local anaesthetic agents are preferred for continuous nerve blocks because they produce a differentiation in sensory and motor blocks and thus it is an important endpoint in providing adequate postoperative analgesia. The drugs of choice are 0.125% to 0.25% bupivacaine, 0.2% ropivacaine and 0.125% levobupivacaine. At these concentrations they provide a postoperative analgesia without impairement of motor function. The infusion rates of these solutions have been found to be effective between the rate of 510ml/hr. Though theoretically continuing infusion of a local anaesthetic solution after surgery may be associated with a risk of drug accumulation, pharmacokinetic studies during continuous nerve blocks reported the safety of this technique, with the unbound plasma concentrations of local anaesthetic remaining well below the threshold levels for systemic central nervous system toxicity.
| Additives|| |
Additive drugs when used alongwith the local anaesthetics prolong the duration of the local anaesthetics and also increase the quality of analgesia. The commonly used additives are epinephrine, sodium bicarbonate, clonidine and opioids.
| Vasoconstrictors|| |
Epinephrine in a dose of 5mcg/ml reduces the absorption of local anaesthetics, increasing their concentration at the intended target nerves increasing the duration and intensity of the block.
| Alkalinisation|| |
The alkalinisation of local anaesthetic solutions usually obtained by adding 1mEq of sodium bicarbonate to 10ml of lidocaine and mepivacaine reduces the onset time of a nerve block. This however does not happen when sodium bicarbonate is added to bupivacaine and ropivacaine. Though changing the pH may shorten the onset of the block there are not clinically relevant advantages when a continuous peripheral nerve block is used.
| Clonidine|| |
Clonidine added to the local anaesthetic solution improves the duration and the quality of analgesia of the peripheral nerve block. The recommended dose of clonidine is 1mcg/ml and for a continuous block the infusion rate would be 5-7ml/hr.
| Peripheral opioids|| |
Opioid agents are known to exert their effects peripherally. Adding small doses of opioids to local anaesthetic solutions for peripheral blocks have resulted in improvement in the onset time, quality and duration of nerve block. Small concentrations of fentany1 12mcg/ml, sufentanil 0.1mcg/ml or morphine 0.03mg/ ml have been suggested for continuous infusion. Tramadol has a local anaesthetic effect on peripheral nerves and this could provide potentially a synergistic effect in continuous infusion as an additive to local anaesthetic agent.
| Common guidelines for CPNB|| |
- The continuous peripheral nerve block is an advanced regional anaesthesia technique, and adequate experience with the single shot technique is necessary to ensure its efficacy and safety.
- CPNB should be performed in a place where facilitiy for standard monitoring, oxygen source, suctioning, resuscitation equipment and emergency drugs are available.
- Placement of the catheter should occur under sterile conditions, using, at a minimum, sterile gloves and sterile drapes. A typical block tray is as shown in [Figure 6].
- After identification and locating the landmarks, site of needle insertion should be infiltrated with local anaesthetic.
- As needle is advanced towards the target nerve the initial current is set between 1.0-1.5mA and we should constantly watch for the desired evoked motor response (EMR) and once the desired motor response is obtained the current strength is gradually decreased until 0.4mA and if the same EMR persists it is indicative that the needle tip is close to the nerve.
- Local anaesthetic is injected only after making sure that the catheter is not intravascular confirmed by negative aspiration for blood. Before initiating the infusion of local anaesthetic, the catheter is first checked for patency, and then the intravascular placement is ruled out by administering a small volume (2-3 mL of 1% lidocaine with epinephrine 1:300,000) and observing for any change in the heart rate.
- Tunneling is preferred option for securing the catheter without dislodgement.
- The catheter is secured using a benzoin skin preparation, followed by application of a clear dressing. The infusion port should be clearly marked as "continuous block".
- The patient has to be explained and a consent should be obtained before performing the procedure. The procedure has to be documented in the anaesthesia chart.
Sites of Continuous Perineural Block:
The commonly used sites for CPNB include:
- Continuous Interscalene Block
- Continuous Supraclavicular block
- Continuous Infraclavicular Block
- Continuous Femoral Block
- Continuous Sciatic Nerve Block
- Continuous Popliteal Nerve Block
- Continuous Thoracic Paravertebral Block
- Continuous Lumbar Paravertebral Block
- Continuous Lumbar Plexus Block
| Continuous Interscalene Block|| |
Placement of the catheter in the interscalene groove may be one of the more challenging continuous block techniques, although the single-shot interscalene block is one of the easiest to perform and master. This discrepancy is mostly due to the shallow position of the brachial plexus and difficulties in stabilizing the needle during catheter advancement. In addition, there is a difference in stimulating characteristics between the smaller-caliber single shot and larger caliber Tuohy style tip needles. The technique is otherwise similar to the single shot injection with the exception that the needle is inserted at a lower angle so that threading of the catheter becomes easy. This technique provides excellent analgesia in patients after shoulder, arm and elbow surgery.
| Procedure|| |
The patient is positioned in the same position as in the single-shot technique. The subcutaneous tissues at the projected site of needle insertion are anaesthetized with local anaesthetic. The needle is attached to the nerve stimulator (1.0 mA, 2 Hz, 100µsec) and to a syringe with local anaesthetic. With this technique, it is imperative that the palpating hand firmly stabilizes the skin to facilitate needle insertion and insertion of the catheter. A 5-cm block needle is inserted at a slightly caudal angle[Figure 7] and advanced until the brachial plexus twitch is elicited at 0.2 to 0.5mA while paying meticulous attention to the position of the needle, the catheter is inserted some 2-3cm beyond the tip of the needle[Figure 8].
| Continuous Supraclavicular Technique|| |
Traditionally the supraclavicular technique has not been considered an optimal choice for placement of catheters. The great mobility of the neck at this location carries a risk for catheter dislodgement. Tunnelling of the catheter to the infraclavicular level could help to make the catheter more stable; however this does not seem to be the preferred technique at present.
| Continuous Infraclavicular Technique|| |
The infraclavicular block[Figure 9] has a particular advantage over the axillary approach for continuous pain management. With the infraclavicular approach, catheter management is simplified by its easy accessibility. The catheter is easier to care for and observe and there is less inherent movement than the axillary area, so there is less chance for dislodgement. Patient comfort is greater with an infraclavicular catheter rather than with a dressing in the axillary area.
Different approaches have been utilized successfully with a continuous infraclavicular technique but there is no overwhelming evidence that favours a particular approach. ,,, One could postulate that the lateral sagittal approach or the modified Raj approach might offer an advantage because the catheter would not be required to make a 90-degree turn from the surface.
| Continuous Axillary Block|| |
Continuous axillary brachial plexus block is similar to the single-injection technique, nerve stimulation technique is typically used and catheter is advanced 58 cm cephalad into the neurovascular sheath. When a stimulating catheter is used, a non-conducting solution (eg 5% dextrose) , can be injected through the catheter to dilate the sheath and facilitate insertion of the catheter. However as mentioned earlier fixing the catheter is a challenge while using the axillary approach.
| Continuous Femoral Block|| |
Continuous femoral block is one of the most commonly performed lower extremity block.
The primary indication of continuous femoral nerve block is pain management after major femur or knee surgery  In addition, when compared with a single dose technique continuous femoral nerve block significantly reduces postoperative opioid consumption in patients after total hip replacement  Continuous femoral nerve block provides excellent analgesia in patients with femoral shaft or femoral neck fractures  Its relative simplicity makes it uniquely suitable for analgesia in the emergency room and facilitate physical and radiologic examinations as well as manipulations of the fractured femur or hip of a trauma victim.
For knee surgery, continuous femoral block is as effective as continuous lumbar plexus block or continuous epidural analgesia, with fewer risks of complications. Because this technique results in faster postoperative knee rehabilitation than IV PCA with morphine and fewer side effects than epidural analgesia, continuous femoral nerve block is probably the analgesic technique of choice in patients after total knee arthroplasty. 
The choice of local anaesthetic depends on the duration of surgery and whether the catheter is planned for surgical anaesthesia or for postoperative analgesia alone. In our institution, for surgical anaesthesia we use 0.25% Bupivacaine whereas for postopertaive analgesia we use a combination of 0.125% bupivacaine with fentanyl, 2µg/ml and the infusion rate ranging between 5-7ml/h.
| Procedure|| |
The patient lies in supine position. The ipsilateral extremity is abducted 10 - 20 degrees. The site of needle insertion is 1cm below the inguinal ligament and 1 cm lateral to the femoral artery. The needle is introduced at an angle of 45 degrees to the skin [Figure 10]. The more distal needle insertion site prevents the possibility of insertion of the needle into the pelvis and allows insertion of the needle more tangentially and thus facilitates insertion of the catheter with ease. After passage through the fascia lata, the needle is advanced to elicit a patellar twitch using a current output between 0.2 - 0.5 mA (0.1 msec). After obtaining this response the catheter is inserted 5-10 cm beyond the tip of the needle or introducer. It is secured in place with a stitch tunneling and/or a dressing.
| Continuous Sciatic block|| |
This technique can be used for surgery and postoperative pain management in patients undergoing a wide variety of lower leg, foot, and ankle surgeries. Perhaps the single most important indication for use of this block is for amputation of the lower extremity.
| Procedure|| |
The continuous sciatic block technique is similar to the single-shot technique. Proper positioning at the outset and maintenance of the position during the continuous sciatic nerve block are crucially important to allow for precise catheter placement. A slight forward pelvic tilt prevents the "sag" of the soft tissues in the gluteal area and significantly facilitates block placement.  With the patient in the lateral decubitus position and a slight forward pelvic tilt, the landmarks are identified and marked with the pen. After a thorough skin cleaning with antiseptic solution, the skin at the needle insertion site is infiltrated with local anaesthetic. A 10-cm long continuous block needle is connected to the nerve stimulator (1.5mA) and inserted at an angle perpendicular to the skin sphere. The opening of the needle should face distally (pointing toward the patient's foot) to facilitate catheter insertion. The initial intensity of the stimulating current should be 1.0-1.5 mA. As the needle is advanced, the first twitches obtained are from the gluteus muscle. Deeper needle advancement results in stimulation of the sciatic nerve. The best results are obtained when we get the inversion and not eversion as the evoked motor response. After obtaining the appropriate twitches, manipulate the needle until the desired response is seen or felt using a current of 0.20.5mA. At this point, a bolus of local anaesthetic is injected (20 mL) after negative aspiration for blood. This is followed by insertion of the catheter 5-10cm catheter beyond the needle tip. One of the commonest concern while using sciatic catheters has been the accidental dislodgement of the catheter.
| Continuous Popliteal Block|| |
This technique can be used for surgery and postoperative pain management in patients undergoing a wide variety of lower leg, foot, and ankle surgeries.
| Procedure|| |
The continuous popliteal block technique is similar to the single-shot technique. With the patient in the prone position, the skin is infiltrated with local anaesthetic using a 25-gauge needle at the injection site which is 7cm above the popliteal fossa crease and between the tendons of biceps femoris and semitendinosus muscles. A 5 to 10cm needle connected to the nerve stimulator (1.5mA current) is inserted at the midpoint between the tendons of the biceps femoris and semitendinosus muscles.  The block needle is advanced slowly with a slight cranial direction while seeking a plantar or dorsiflexion of the foot or toes. After obtaining appropriate motor response, the needle is manipulated until the desired response is seen or felt using a current of approximately 0.5mA.The catheter should be advanced some 5cm beyond the needle tip.
Continuous Popliteal Block through the lateral approach.
With the patient in the supine position, the skin is infiltrated with local anaesthetic at the injection site 8cm above the popliteal fossa crease and in the groove between the biceps femoris and vastus lateralis muscle using a 25-gauge needle  . A 10-cm Tuohy-style tip needle for continuous nerve block is connected to the nerve stimulator (at 1.5mA current intensity) and inserted to contact the femur [Figure 11]. Once the femur is contacted the needle is withdrawn to the skin and redirected in a slight cranial and posterior direction relative to the plane in which the femur was contacted (usually 30 degrees to the horizontal plane).
The needle is advanced slowly while seeking a plantar flexion or dorsiflexion of the foot or toes. After obtaining appropriate twitches, the needle is manipulated until the desired response is seen or felt using a current of 0.4mA. The catheter should be advanced some 5-7cm beyond the tip of the needle and secured and fixed[Figure 12].
| Conclusion|| |
The advances in the techniques and technologies pertaining to regional anaesthesia offer an entirely a new spectrum of anaesthesia delivery system to the patients. Site specific analgesia would be probably the most preferred anaesthetic technique of the next decade. The development of stimulating catheters has significantly improved the precision with which these catheters are placed near the peripheral nerves and plexuses and thus increasing the success rate. It offers a promise for the future as these continuous perineural catheters might greatly influence the perioperative outcome.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10], [Figure 11], [Figure 12]