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Brown: Atlas of Regional Anesthesia, 3rd ed., Copyright © 2006 Saunders, An Imprint of Elsevier
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Chapter 2 – Continuous Peripheral Nerve Blocks

André P. Boezaart, M.D., Ph.D.

Peripheral nerve blocks can provide analgesia in patients with acute and chronic pain for many hours after a single local anesthetic injection. Many clinical settings, however, require even more than the 12-hour or longer nerve blocks after a single injection. The requirement for longer analgesia without the potential for neuraxial side effects accelerated the development of continuous nerve blocks. Research into reversible yet long-acting local anesthetics is also ongoing, but to date no effective reversible, extremely long-acting local agent is available. Thus, physicians are left with continuous nerve blocks via perineural catheters as an effective means of pro-viding ongoing analgesia. Advances in perineural techniques have focused on improving catheter placement, thereby reducing analgesia fade following the initial bolus injection. There are two primary techniques for placing perineural catheters: the nonstimulating technique and the stimulating catheter technique. Although a number of stimulating catheters are available, for the sake of clarity in this chapter the stimulating catheter technique covered is the StimuCath technique (Arrow International, Reading, PA, USA). One should remember that the principles outlined can be used with other manufacturers’ devices.

When using the nonstimulating technique, an insulated needle (usually a Tuohy needle) is advanced near a nerve with nerve stimulator guidance. Once the physician is satisfied with the position of the needle tip, saline or local anesthetic agent is injected through the needle to expand the potential perineural space. A typical (usually multiorifice) epidural catheter is then advanced through the needle. This technique is relatively easy to perform and usually provides an adequate initial block when the local anesthetic agent is injected through the needle prior to catheter placement. The success rate of the secondary block (when local anesthetic agent is infused through the catheter) is, however, quite variable.

During a stimulating catheter technique, an insulated needle (typically a Tuohy needle) is similarly placed near the nerve to be blocked with nerve stimulator guidance. With this technique, no bolus injection is made at the time of needle placement; rather, a catheter with an electrically conductive tip is advanced through the needle while being stimulated. This technique has a few more steps to perform than a nonstimulating method, although it appears manageable even in the training setting. The primary success rate with this technique probably equals that of the traditional technique but with a theoretically higher secondary block success rate owing to more precise catheter placement. Completed formal outcome comparisons are needed.

NONSTIMULATING CATHETER TECHNIQUE

The insulated stimulating needle is directed to the peripheral nerve to be blocked with a stimulator current output of 1.5 mA. The final needle position is confirmed by observing an appropriate motor response with the nerve stimulator current output set at 0.3 to 0.5 mA, a frequency of 1 to 2 Hz, and a pulse width of 100 to 300 μsec. The needle is often attached to a syringe via tubing from a side port ( Fig. 2-1 ). This arrangement allows the physician to aspirate blood or cerebrospinal fluid during needle placement to minimize unintentional intravascular or intrathecal injection. Once the needle position is finalized, the needle is held steady and the bolus of local anesthetic solution is injected in divided doses. Saline (5–10 mL) is sometimes used rather than a bolus injection of local anesthetic, which many believe eases passage of the subsequently placed catheter and minimizes confusing bolus local anesthetic effects from those of the catheter injection. The catheter is typically a 19- or 20-gauge epidural (multiorifice) catheter that is advanced 5 to 10 cm past the distal end of the needle. After catheter insertion the needle is removed, and the catheter is secured with the operator’s preferred technique, possibly a medical adhesive spray, Steri-strips, and a transparent occlusive dressing. Some physicians tunnel the catheter to secure it. A variety of local anesthetic solutions have been described, with many preferring ropivacaine. For emphasis, typically with this method a bolus (20–40 mL) of the local anesthetic is injected through the needle providing the primary block, followed by catheter placement and infusion of a local anesthetic solution through the catheter. This infusion produces what many call the secondary block (see Fig. 2-1 ).

Click to view full size figure

Figure 2-1  Side-port device used during catheter placement for infraclavicular block. A, Localization of the correct needle site via nerve stimulator guidance. B, Injection of local anesthetic to distend the perineural space prior to catheter insertion. C, Insertion of a catheter without additional guidance.


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