Chapter 49. Stimulating Catheters

It has been well established that peripheral nerve blocks and neuraxial blocks provide superior analgesia for the treatment of acute pain, especially postoperative pain. The main limitation of these modalities is that acute postoperative pain usually outlasts the relief afforded by single-injection techniques. As a result, continuous peripheral nerve blocks have been developed to overcome these limitations, to extend analgesia beyond duration of a single-injection method, and to allow for greater ability to titrate sensory–motor differentiation of the blockade. Unlike the case for single-injection techniques, continuous nerve block via a perineural catheter, can be discontinued or the infusion changed if unwanted side effects occur. The main emphasis during the past decade has been to develop catheters and techniques that allow relatively simple, accurate, and noninvasive catheter placement to ensure effectiveness and to reduce secondary block failure. These aims have been largely accomplished in the past decade; the current efforts seek to define indications and infusion strategies for continuous peripheral nerve blocks, especially in the setting of outpatient surgery.

Two techniques are currently used to place perineural catheters: the nonstimulating catheter technique described by Steele and colleagues1 and the stimulating catheter technique.2 With a nonstimulating technique, an insulated needle (usually a Tuohy needle) is inserted near a nerve with the aid of a nerve stimulator. Saline or a local anesthetic agent is then injected through the needle to “expand” the perineural space, and a catheter (usually an epidural, multiorifice catheter) is inserted. This technique is relatively simple to perform and provides a reliable primary block (local anesthetic agent injected through the needle). However, because the catheter is placed without confirmation of the tip position, the success rate of the secondary block (infusion through the catheter) may be lower than for the primary block.

With the stimulating catheter technique, an insulated needle (typically a Tuohy needle) is inserted close to a nerve, and a nerve stimulator is used, similar to the procedure for a nonstimulating technique (Figure 49–1). Once the nerve or plexus is electrolocalized, a catheter with an electrically conductive connection to the tip of the catheter (a spring wire2 or a steel stylet3) is then inserted through the needle (Figure 49–2). This allows stimulation of the nerve via the catheter to ensure accurate positioning. With this technique, both the bolus dose and continuous infusion of local anesthetic are injected through the catheter. This technique requires a few extra steps; however, the confirmation of the needle tip position logically should provide a lower risk of secondary block failure due to more accurate catheter placement.4

F. Paul Ansbro5 is credited with the first use of a continuous nerve block in 1946, although he did not use a perineural catheter. Instead, he inserted a blunt needle lateral to the subclavian artery in contact with the first rib after eliciting paresthesia in the patient's arm (Chapter 48). He then secured the needle by inserting it through a cork and strapping the cork to the skin with adhesive tape. The needle was connected with a rubber tube to a 10-mL Luer-Lok syringe for repeated injections of a local anesthetic agent. The objective of the continuous nerve block was to increase the duration of action of the 1% procaine that was used. The author presented 27 cases in which the average duration of the anesthesia was 2 h, ranging from 90 min to 4 h and 20 min. This was a significant improvement over the usual 15-min duration obtained with a single injection of 1% procaine.

Interestingly, the earliest recorded uses of electrical nerve stimulation for peripheral nerve block3 and neuraxial block6 were in 1951 and 1949, respectively, to assist in accurate placement of catheters for continuous block and not for needle placement (Chapters 5 and 17). Stanley and Lili-Charlotte Sarnoff pioneered the use of nerve stimulation for continuous peripheral perineural and subarachnoid block for the accurate placement of catheters. In the midst of the polio epidemic of the late 1940s and early 1950s, the Sarnoffs worked on the development of the “Electrophrenic Respirator” at the Harvard School of Public Health.7 This device was capable of eliciting breathing by stimulating the phrenic nerve transcutaneously in cases of bulbar polio in which respiration could not be established by the iron lung. At the time, the couple's daughter, Daniela, was stricken by bulbar polio and saved by this method. This event made worldwide news under the headline “The Device (that) Cheats Death.”

Armed with this knowledge and previous experience of precise placing of intrathecal catheters with nerve stimulation,6 Stanley Sarnoff was confronted with a patient suffering from intractable hiccups.3 He placed a “prolonged peripheral nerve block” catheter to continuously and accurately block the patient's phrenic nerve by stimulating it via the catheter. In his description of the technique he stated that “The accurate placement of the tip of the needle and catheter is important to the success of the procedure … we adapted a previously described method of electrical localization of catheters to the purpose … by applying an electrical potential to the tip of the catheter by way of its stylet in the subarachnoid space. The same principle was used in localizing the tip of the needle in relation to the phrenic nerve in this study.”

Indeed, early on nerve stimulation in nerve block was used to accurately place catheters for continuous blockade of a motor nerve—the phrenic nerve. Paradoxically, the nonstimulating catheter technique is often referred to as the “classical technique,” when in fact the stimulating technique was the technique that was described first.

It was only decades later after the use of nerve stimulators for single-injection blocks of peripheral nerves became more popular that the technique of placing catheters for continuous peripheral nerve blocks by stimulating the nerve via both the needle and the catheter was “reinvented.”2,8 In the 30 years after the first descriptions by Sarnoff and Sarnoff, the main focus in the development of continuous peripheral nerve blocks was on the upper extremity, and mainly to improve blood flow by sympathetic block for reimplantations of traumatic amputated parts of the upper limb. Most authors used variations of the axillary perivascular technique in the 1970s and 1980s.9–12 For example, during the Angola Civil War in 1975 the present author, acting as anesthesiologist for the Number 1 Forward Surgical Unit, used a cut-down technique and under direct vision, placed central line catheters in the perivascular space to manage the pain due to severe battlefield injuries of the hand and arm.13 Of note, the main indication for continuous blocks in the 1970s and 1980s was to achieve sympathetic block and improve blood flow; at that time analgesia was considered merely, as an additional “bonus” and did not become the primary goal until the early 1990s.

During the 1990s the emphasis shifted toward the use of continuous nerve blocks to manage acute postoperative pain. This was, among other factors, driven by the quest for cost-effective ambulatory surgery following the exponential escalation of health-care costs in the mid- to late 1980s. Because of the efficiency and relative safety of neuraxial nerve blocks, the lower extremity received little attention during the early development of the technique, and the main focus was on continuous blocks for the upper extremity.14–17 During this era, only the nonstimulating catheter technique was used by most investigators in postoperative treatment of patients undergoing a variety of major surgical procedures on the upper and lower extremities. Francois Singelyn and coworkers18 were the first to demonstrate that continuous femoral nerve block in patients having total knee replacement provides superior pain control to intravenous morphine and epidural analgesia. This report was followed by others also documenting excellent analgesic potential, fewer complications, and faster rehabilitation with continuous nerve blocks.19,20

The secondary failure of continuous nerve block catheters, however, represents a significant obstacle to the ability to reproduce results cited in these and other reports.21–25 Ganapathy and coworkers26 and Klein and colleagues27 alerted practitioners to the importance of ensuring the functionality of the catheters before discharging patients home. Discharging patients from the hospital with continuous nerve blocks that malfunction after the primary block wears off can increase the costs of postoperative management if a patient has to be readmitted to the hospital to treat resulting acute pain.27 It is for these reasons that the concept of the stimulating catheter (or the Sarnoff technique) was revisited in the mid- to late 1990s.2,8

The technique described here is a general description of the stimulator technique applicable to most peripheral nerve blocks; the specifics of the techniques, however, vary somewhat for individual nerve block procedures. Figures 49-1, 49-2, 49-3, 49-4, 49-5, 49-6, and 49-7 illustrate maneuvers specific to the stimulating catheter placement.

Stimulation Through the Needle

• Nerve stimulator is attached to an insulated 17- to 20-gauge needle (eg, StimuCath, Arrow International, Reading PA, USA) and set to deliver 1–1.5 mA (see Figure 49–1).
• The needle is advanced until a brisk motor response of the desired muscle group(s) is elicited with a current output of 0.3 to 0.5 mA (100–300 μsec; frequency 1–2 Hz).
• The needle is then held steady in the stimulating position; no local anesthetic or saline is injected through the needle.
• The nerve stimulator is now disconnected from the needle and attached to the proximal end of the stimulating catheter (see Figure 49–2).

Stimulation Through the Catheter

• The catheter is advanced through the needle to elicit a motor response similar to that elicited by stimulating via the needle (see Figures 49-2, 49-3, and 49-4).
• The catheter is advanced beyond the distal end of the needle while maintaining the desired motor response (the motor response should remain qualitatively similar).
• The depth markings on the catheter should be observed throughout the procedure. One should be familiar with how these depth markings relate to the shaft of the needle (see Figure 49–5). In other words, the operator should always know the depth of the catheter placement (and whether the catheter tip is inside the needle or exited the needle tip).
• The catheter is then connected to an infusio-stimulation port (Figures 49–6 and 49–7).

Catheter-Securing Techniques

Various catheter-securing techniques have been described to prevent dislodgment of the catheters. The catheter can be tunneled subcutaneously to significantly decrease the chance of dislodgment. There are basically two approaches to tunneling the catheter: (1) tunneling without and (2) tunneling with a “skin bridge.” Leaving a skin bridge makes catheter removal easier and is normally used for a short-term (1 to 7 days) catheterization, whereas tunneling without a skin bridge is typically used for long-term infusion (>7 days) catheterization and has the potential advantage of preventing infection. The first method may be associated with more leakage at the skin–bridge area, whereas the latter method may make catheter removal more difficult.

With a commonly used technique, the inner steel stylet of the Tuohy needle is used as a guide. If a skin bridge is planned, the needle enters the skin 2 to 3 cm from the catheter exit site, but through the catheter exit site (taking special care not to damage the catheter) if a skin bridge is not wanted. The stylet is then advanced subcutaneously for approximately 8 to 10 cm. The Tuohy needle is then “railroaded” back over the stylet, the stylet is removed, and the distal end of the catheter advanced retrogradely through the needle. The needle is then removed, and the catheter is tunneled. If a skin bridge is left, a small piece of plastic or silicone tubing can be inserted to protect the skin under the skin bridge. Various adhesive materials and methods have been used with success (eg, medical adhesive spray, Steri-Strips, and transparent occlusive dressings).25

The development of the stimulating catheter technique has significantly improved the precision with which catheters are placed near the peripheral nerves and plexuses. More research is needed to clarify optimal surgical indications and infusion strategies for continuous nerve block techniques.