Equipment for Continuous Peripheral Nerve Blocks.

Figure 48–1.A: Apparatus consists of a 10-mL Luer-lock syringe and the two-way valve as used in the Hingson-Edwards continuous caudal method. The tubing can be of any desired length (18 inches is sufficient). A malleable needle (Becton-Dickinson & Company ) is used, which has been filed to a blunt end to prevent perforation of blood vessels. A cork stopper from an ether can completes the apparatus. B: Apparatus with needle through the cork, usually 4-6 cm. C: Close view of blunted needle through the cork guard. The cork, when placed flush with the skin in the supraclavicular area, prevents the needle from going in deeper. D: Needle in place in the supraclavicular area. The cork prevents displacement inward and holds it upright. E: Pulsation of the needle, indicating its close apposition to the subclavian artery. If the needle is placed lateral to the artery and on top of the first rib, it is of necessity in close proximity to the plexus. Injection of 30-40 mL of 1% procaine induces anesthesia within 15 minutes. F: Apparatus in place and ready for fractional injections. The adhesive strapping over the cork keeps the needle in place and prevents its outward displacement. The cork firmly holding the needle prevents its inward displacement. (Reprinted, with permission, from Ansbro FP: A method of continuous brachial plexus block. Am J Surg 1946;71:716-722.)

In 1951, Sarnoff and Sarnoff²⁶ published one of the first reports involving the use of a flexible indwelling catheter for CPNB. They performed continuous phrenic nerve blocks on patients with intractable hiccups. They used a 2-in., 18-gauge needle to locate the nerve and subsequently threaded a 9-in. piece of polyethylene tubing (inner diameter 0.023 in.; outer diameter 0.038 in.) with an inner stylet. A blunt 23-gauge needle was fit into the proximal end of the tubing and attached to a needle stopper to occlude the opening between local anesthetic injections. It is interesting to note that in their early trials these investigators used Vinylite tubing for the indwelling catheter but discovered that it became brittle and less pliable over time. They presumed that this was due to the material–s inherent solubility in animal fat and so abandoned it in favor of polyethylene.

The next report occurred almost a quarter century later when DeKrey et al.²⁷ described their experience using continuous subclavian perivascular blocks intraoperatively for upper extremity surgery of long duration. They used a 15- to 18-gauge Rochester-type plastic needle. After elicitation of paresthesia, they advanced the overlying plastic part of the needle (cannula) into the brachial plexus sheath and removed the inner metal stylet. A total of 25 patients received intermittent local anesthesia boluses for up to 9 hours. Shortly thereafter, Winnie²⁸ outlined continuous interscalene block using similar equipment. He described using a small “extra- cath” intravenous-type needle and cannula set. After identification of the brachial plexus with the paresthesia technique, the inner metal needle was removed while the outer plastic cannula was advanced. The cannula was subsequently used for repeated doses of local anesthesia. Selander²⁹ published one of the first reports of continuous axillary brachial plexus blocks in a series of 137 patients having hand surgery. He used an intravenous needle (external diameter 0.65 mm) and cannula (external diameter 1 mm; length 47 mm) and identified the axillary sheath with the fascial pop method (Figure 48–2). The cannula was threaded off the needle and into the sheath to provide a more secure attachment for a syringe containing local anesthesia and, consequently, to minimize the risk of block failure due to needle movements. The catheter was dosed with intermittent boluses of mepivacaine and left in place for up to 24 hours.

Although these early accounts primarily involved “cannula-over-needle” devices, subsequent descriptions also included “catheter-through-needle” equipment. In the earliest report of a continuous lower extremity block, Brands and Callahan³⁰ provided details of a series of 21 patients who received continuous lumbar plexus blocks for 72 to 96 hours after femoral neck fractures. An intravenous cannula had insufficient length for this block and would likely have been too susceptible to kinking when inserted at 90 degrees to the course of the plexus. Consequently, these authors used a 15-cm, 18-gauge needle and the loss-of-resistance method to identify the lumbar plexus psoas compartment. They subsequently threaded an epidural catheter through the needle. Rosenblatt³¹ described another technique to facilitate catheter placement when the block needle approaches the neural structures perpendicularly. They reported using a Seldinger technique for a continuous interscalene brachial plexus block. After using a 25-gauge single-injection needle to identify the brachial plexus, an 8.9-cm, 18-gauge epidural needle was inserted. After injection of local anesthesia, a 0.53 mm diameter, 35-cm long spring guidewire was threaded through the needle and into the sheath about 4 cm. The epidural needle was subsequently removed and a 5-cm, 18-gauge diameter catheter was threaded over the guidewire into place. The guidewire was then removed and bupivacaine 0.25% was given as a continuous infusion at 10 mL/h to provide 24 hours of analgesia.

Figure 48–2. A and B: The Venflon cannula. C and D: Schematic views of the introduction of the Venflon catheter into the axillary neurovascular sheath. (Reprinted, with permission, from Selander D: Catheter technique in axillary plexus block. Presentation of a new method. Acta Anaesthesiol Scand 1977;21 [4]:324-329.)

The identification of important neuroanatomic features occurred concurrently with the description of these early CPNBs and was instrumental in the further understanding of plexus anatomy and the development of continuous regional anesthesia techniques. Landmark papers were published by Winnie²⁸ as well as Thompson and Rorie³² outlining the existence of a brachial plexus sheath and suggesting the potential for continuous plexus anesthesia. Tuominen et al.³³ provided early evidence of the safety of continuous plexus infusions of local anesthesia when they studied blood levels of bupivacaine during continuous axillary brachial plexus infusion.

Reflecting the popularity of the paresthesia, fascial pop and loss-of-resistance techniques from the 1970s through the early 1990s, most subsequent reports of CPNBs also involved the use of intravenous-type needles and cannula (“cannula-over-needle” devices)^33–38 as well as epiduraltype needles and catheters (“catheter-through-needle” equipment).^3,4,39–42 In the late 1970s, however, concern surfaced in the regional anesthesia literature over the association between long-bevel needles used for peripheral nerve blocks and the occurrence of neurologic complications.⁴³ Consequently, the use of short-bevel needles was suggested to decrease the risk of intraneural injections. For example, Buttner et al.⁴⁴ described a modification of intravenous-type equipment to include an inner metal stylet with a 45-degree or short-bevel needle.

Concerns over neurologic injury from the elicitation of paresthesia⁴⁵ together with the introduction of nerve stimulator techniques⁴⁶ led to a decline in the popularity of the paresthesia method in favor of identification of neural structures by electrolocation. Although uninsulated needles could be used with nerve stimulators, insulated needles were found to provide more focused current output and consequently more accurate localization of neural structures.⁴⁷ As nerve stimulator techniques came into more widespread use in the 1990s, commercially insulated single-injection needles became available, but the design of CPNB needles and catheters was unsuitable. To circumvent this obstacle, regional anesthesia practitioners assembled intravenous access and spinal and epidural equipment to create their own CPNB apparatus.

There are numerous reports of various adaptations used for connecting an intravenous needle and cannula to a current source to enable nerve stimulation. Smith et al.¹ provided one of the first descriptions of a CPNB using an “insulated needle” and a nerve stimulator. They connected the metal trocar of a 16-gauge intravenous needle—catheter assembly (Medicut) to a low-powered nerve stimulator. On appropriate sciatic nerve stimulation, the trocar was removed and local anesthesia injected through the cannula. A 16-gauge epidural catheter (Simms-Portex, UK) was threaded through the cannula, and the cannula was subsequently removed. Anker-Moller et al.⁴⁸ used a similar system that consisted of a 14-gauge intravenous needle and cannula set (Viggo). After identification of the femoral nerve with a nerve stimulator, the inner needle was removed and a 16-gauge epidural catheter (Portex) inserted through the intravenous cannula (Figure 48–3). In a unique adaptation of intravenous equipment, Ben-David et al.⁴⁹ inserted the metal needle of a 20-gauge intravenous catheter (Venflon, Viggo) inside the proximal end of a 16-gauge central venous pressure needle (Secalon, Viggo). They attached the negative electrode of the nerve stimulator to the exposed metal needle of the 20-gauge intravenous catheter and obtained appropriate stimulation during lumbar plexus block. The over-the-needle central venous cannula was then advanced beyond the tip of the needle and used for continuous lumbar plexus block (Figure 48–4). Using an innovative design, Concepcion⁵⁰ described wrapping the stylet of a 26-gauge spinal needle around the metal introducer of a typical intravenous over- the-needle cannula. An alligator clip was then attached to the stylet to allow electrical stimulation using a nerve stimulator (Figure 48–5).

Figure 48–3. A: Placement of the infusion cannula. Nerve stimulator attached to the trocar (lateral view). B: The catheter is inserted through the infusion cannula (lateral view). (Reprinted, with permission, from Anker-Moller E, et al: Continuous blockade of the lumbar plexus after knee surgery: A comparison of the plasma concentrations and analgesic effect of bupivacaine 0.250% and 0.125%. Acta Anaesthesiol Scand 1990;34[6]: 468-472.)

Figure 48–4. Assembly shows a 21-gauge needle inserted into the proximal end of the 16-gauge Secalon (Viggo) central venous pressure catheter. Metal contact of the smaller needle inside the larger needle allows an electrical impulse to be conveyed to the Secalon needle tip. An alligator clip from the electrical stimulator is attached to the shaft of the 21-gauge needle. Intravenous extension tubing inserts into the hub of the 21-gauge needle. (Reprinted, with permission, from Ben-David B, Lee E, Croitoru M: Psoas block for surgical repair of hip fracture: A case report and description of a catheter technique. Anesth Analg 1990;71 [31:298-301.)

Figure 48–5. Assembly of needle and nerve stimulator for continuous brachial plexus blockade using an over-the-needle intravenous catheter: (1) intravenous over-the-needle catheter, (2) stylet from 26-gauge spinal needle, (3) alligator clip attached to the stylet and to the low-output terminal of a nerve stimulator, (4) nerve stimulator, (5) ground wire attached to the common port of the nerve stimulator (marked as “Gen” in the diagram) and to the patient, and (6) extension set and syringe for “immobile needle technique.” (Reprinted, with permission, from Concepcion M: Continuous brachial plexus techniques. In: Ferrante FM, VadeBoncoeur TR [editors]: Postoperative Pain Management. Churchill Livingstone, 1993.)

Spinal and epidural equipment has similarly been adapted for CPNBs performed with nerve stimulators. Several groups^{2, 51} have placed an 18-gauge intravenous cannula over a 22-gauge spinal needle to provide insulation to the distal part of the needle. A current source was then attached to the bare proximal metal needle, and local anesthesia was injected upon identification of neural structures. The cannula was then threaded off the spinal needle into the perineural space and used for continuous infusion of local anesthesia for up to two days. Similarly, our group has placed an intravenous cannula over an epidural needle to insulate the distal part of the needle and has attached a current source to the proximal needle. Upon identification of neural structures, a catheter was threaded through the epidural needle into place. Alternatively, spinal needles and microcatheters have been used. The spinal microcatheters, however, were of such small size that injection was difficult and they were prone to kinking. This equipment was eventually withdrawn from the market because of neurotoxicity associated with continuous spinal anesthesia.

Prosser⁵² devised yet another method to provide nerve stimulation during CPNBs for pediatric patients. This author connected a jackplug electrode into the hub of an intravenous cannula (Abbocath-T Venisystems) to make an electrical contact between the nerve stimulator and the central metal needle of the intravenous set (Figure 48–6). The surrounding Teflon-coated sheath insulated all but the tip of the cannula. This adaptation was successful with 20-, 22- and 24-gauge intravenous catheters and consequently was nearly ideal for the pediatric population.

Further advancing pediatric regional anesthesia, Tan et al.⁵³ used a radial artery catheterization set (#RA-04120; Arrow, Reading, PA) with a 20-gauge cannula over a 22- gauge, thin-walled, short-bevel needle for continuous axillary brachial plexus block. The set had a 0.018-in. integral spring wire that this group connected via an alligator clip to the negative pole of a nerve stimulator to enable electrolocation of the brachial plexus. Using the Seldinger technique, the guidewire was then advanced and used to direct the cannula into the brachial plexus sheath.

Figure48-6. A:Peripheral nerve stimulator lead fitted with standard press stud and jackplug connectors (a); modified connectors, press stud replaced with second jackplug (b). B: Electrical contact between the Abbocath’s central metal cannula and original jackplug from the lead. (Reprinted, with permission, from Prosser DP: Adaptation of an intravenous cannula for paediatric regional anaesthesia. Anaesthesia 1996;51[5]:510.)

Although these designs allowed nerve stimulation through an insulated needle, a number of drawbacks still existed. Several steps were required between identification of the nerve and threading of the catheter. This increased the risk of catheter misplacement and the likelihood of committing a breach in sterility. Despite the insulation provided by an intravenous-type cannula over a metal needle, the uninsulated area of the distal needle tip was of significant size and could adversely affect the accuracy of nerve location. Unfortunately, in these self-assembled systems, the cannula rarely provided a snug fit over the needle. In addition, there was continued concern about the risk of neurologic complications from long-bevel intravenous-type needles. Finally, the shape of the needle tip did not facilitate catheter threading in directions other than parallel with the course of the needle.

Increased effort into the development of CPNB equipment and the introduction of the safer long-acting local anesthesia ropivacaine (Astra, Westborough, MA) in the 1990s further stimulated the expansion of CPNB techniques. The original Contiplex A system (B. Braun-Melsungen AG, Germany) involved a cannula over a short-bevel needle and an accompanying catheter. The advantages of this equipment consisted of components that were designed to fit together, a theoretically less traumatic short-bevel needle (32-degree tip ), and a catheter of compatible size (Figure 48–7 ). Although similar to the early equipment individually assembled and used by many regional anesthesiologists, this became one of the first commercially available CPNB products. This system was subsequently modified to create the Contiplex D model, which included an integrated wire for nerve stimulation and connection tubing for concurrent aspiration and injection. The use of both the Contiplex A and D became popular throughout the 1990s.^{5–7,54–65} Other manufacturers subsequently developed similar systems. Notable among these is the MiniSet (Pajunk, Geisengen, Germany) (Figure 48–8). This system offers the choice of 21- or 24-gauge needles with either Sprotte or Facet tip. These alternatives enhanced the usefulness of this system and made it appealing for use in pediatrics.