Abstract
Providing continuous peripheral nerve blocks (CPNB)—also called “perineural local anesthetic infusion”—involves the percutaneous insertion of a catheter directly adjacent to the peripheral nerve(s) supplying the surgical site, as opposed to a “wound” catheter placed directly at a surgical site. Site-specific, potent analgesia may then be provided with few, if any, side effects. CPNB was first described in 1946 using a cork to stabilize a needle placed adjacent to the brachial plexus divisions to provide a “continuous” supraclavicular block. As with all procedures, CPNB is associated with inherent risks (see section on complications). Therefore CPNB is usually provided to patients expected to have at least moderate postoperative pain of a duration greater than 24 hours that is not easily managed with oral analgesics. The two main types of perineural catheters are stimulating and nonstimulating, and the two most common insertion methods utilize ultrasound guidance and electrical stimulation. There is a large and growing body of evidence that CPNBs provide a multitude of clinical benefits. However, because of the relatively recent evolution of modern techniques, illuminating data are often unavailable. Future prospective investigation is required to determine the optimal catheter design(s), insertion technique(s), insertion approach(es), infusate(s), delivery regimen, infusion duration, and true incidence of complications.
Keywords
continuous peripheral nerve blocks, perineural infusion, perineural local anesthetic infusion, postoperative analgesia
Introduction
Providing continuous peripheral nerve blocks (CPNB), also called “perineural local anesthetic infusion,” involves the percutaneous insertion of a catheter directly adjacent to the peripheral nerve(s) supplying the surgical site ( Fig. 16.1 ), as opposed to a “wound” catheter placed directly at a surgical site. Site-specific, potent analgesia may then be provided with few, if any, side effects. CPNB was first described in 1946 using a cork to stabilize a needle placed adjacent to the brachial plexus divisions to provide a “continuous” supraclavicular block.
Indications For Continuous Peripheral Nerve Blocks
As with all procedures, CPNB is associated with inherent risks (see section on “Potential Risks/Complications”). Therefore, CPNB is usually provided to patients expected to have at least moderate postoperative pain of a duration greater than 24 hours that is not easily managed with oral analgesics. However, opioid requirements and opioid-related side effects may be decreased with the use of CPNB following mildly painful procedures. Because not all patients desire, or are capable of accepting, the extra responsibility that comes with the catheter and pump system, appropriate patient selection is crucial for safe CPNB, particularly in the ambulatory environment. Although recommendations for the use of various catheter locations for specific surgical procedures exist, there is little published data specifically illuminating this issue. In general,
- •
Axillary, infraclavicular, or supraclavicular infusions are used for surgical procedures involving the hand, wrist, forearm, and elbow ;
- •
Interscalene catheters are used for surgical procedures involving the shoulder or proximal humerus ;
- •
Thoracic paravertebral catheters are used for breast or thorax procedures ;
- •
Psoas compartment catheters are used for hip surgery ;
- •
Fascia iliaca, femoral, and psoas compartment catheters are used for knee or thigh procedures ;
- •
Popliteal or subgluteal catheters are used for surgical procedures of the leg, ankle, and foot.
The authors recommend using an interscalene catheter for shoulder or proximal humerus procedures, infraclavicular catheter for more distal procedures of the upper extremity, a transversus abdominis plane catheter for inguinal or lower abdominal procedures, a femoral catheter for knee surgery, and a popliteal-sciatic catheter for foot/leg procedures.
Equipment and Techniques
Ultrasound-Guided Catheter Insertion
For ultrasound-guided procedures, the term “long axis” is used when the length of a nerve is within the ultrasound beam, compared with “short axis” when viewed in cross-section. A needle inserted with its length within a two-dimensional ultrasound beam is described as “in plane,” while a needle inserted across a two-dimensional ultrasound beam is “out of plane.”
Needle In-Plane, Nerve in Short-Axis Approach
This is the most frequently published single -injection peripheral nerve block orientation because this view allows for easier identification and differentiation from surrounding structures. When the long axis of the needle is inserted within the ultrasound plane, the needle tip location can be more easily identified relative to the target nerve. Local anesthetic spread may be observed if the initial local anesthetic bolus is placed through the needle, and adjustment of the needle tip made when necessary. However, when the perineural catheter is inserted past the needle tip, it has the tendency to bypass the nerve given the perpendicular orientation of the block needle and target nerve, although there are certain anatomic locations that often allow a catheter to be passed and remain perineural. Some practitioners have advocated either passing the catheter a minimal distance past the needle tip, or advancing the catheter further initially and then, after needle removal, retracting the catheter such that its orifice(s) lie a minimal distance (<2 cm) past the original needle tip position (although others have suggested this may result in a dislodged catheter tip as the needle is withdrawn over the catheter, especially by trainees). Some advocate using an extremely flexible perineural catheter in an attempt to keep the catheter tip in close proximity to the target nerve if the catheter is inserted more than a minimal distance. Nonetheless, others describe reorienting the needle from an in-plane to a more parallel trajectory and inserting a stimulating catheter to better monitor catheter tip location.
There are multiple benefits of the needle in-plane, nerve in short-axis approach. First, practitioners may learn only one technique since it may be used for both single-injection and catheter insertion procedures. Furthermore, it may be used for nearly all anatomic catheter locations, even for deeper target nerves. If a 17- or 18-gauge needle is used, the needle tip may be more easily identified and remains within the ultrasound plane due to its rigidity compared with smaller gauge needles. While some have speculated that the use of a large needle is more painful, seven prospective studies reported a median catheter-insertion pain score of 0–2 on a 0–10 numeric rating scale (10 = most pain imaginable) when the needle track was first anesthetized with lidocaine via a 25–27-gauge needle. In addition, the potential benefits of using a larger needle gauge (fewer needle passes given the relative ease of keeping a rigid, larger-gauge needle in plane; less risk of undesired tissue contact due to misinterpretation of the needle shaft for the needle tip) must be weighed against the potential risks (increased patient discomfort; increased tissue trauma; increased injury if a vessel is punctured).
There are disadvantages of this approach as well. They include new needle entry sites relative to the nerve compared with more traditional nerve stimulation modalities which typically use a parallel needle-to-nerve insertion; challenges keeping the needle shaft in-plane ; difficult needle tip visualization for relatively deep nerves ; and, as noted above, the catheter tip may bypass the target nerve given the perpendicular orientation of the needle and nerve. If an extremely flexible catheter is used in an attempt to minimize this issue, it is sometimes difficult to thread past the tip of the placement needle.
Needle Out-of-Plane, Nerve in Short-Axis Approach
There are potential benefits of this approach. They include a generally familiar parallel needle-to-nerve trajectory used with traditional nerve stimulation techniques (and also vascular access); and because the needle is parallel to the target nerve, the catheter theoretically may remain in closer proximity to the nerve, even when threaded more than a centimeter past the needle tip. However, a disadvantage of this technique is the relative inability to visualize the advancing needle tip, which some speculate increases the likelihood of unwanted contact with nerves, vessels, peritoneum, pleura, or even meninges. Practitioners often use a combination of tissue movement and “hydro-location” in which fluid is injected and the resulting expansion infers the needle tip location (either with or without color Doppler flow). It has been suggested that for superficial catheters (e.g., interscalene and femoral), the consequent “longitudinal” orientation of needle with nerve makes precise visualization of needle tip less critical, as the needle tip tends to remain relatively close to the nerve if the needle tip is advanced beyond the ultrasound beam. However, for deeper nerves, this technique is not as straightforward as guiding the needle tip to a target nerve as in the in-plane technique described above and may be more difficult to master (and nearly impossible at times).
Needle In-Plane and Nerve in Long-Axis Approach
Superficially, this technique appears to have the benefits of both previously described approaches, with few limitations. The nerve can be viewed along with the needle shaft/tip, and the catheter monitored as it exits the needle parallel to the target nerve. The difficulty lies in keeping three structures, the needle, nerve, and catheter, in the ultrasound plane. In addition, to view the nerve in long axis, the nerve itself must be relatively straight; and there can be only one target nerve as opposed to multiple trunks or cords as found within the brachial plexus. Evidence of this technique’s difficulties may be found in the scarcity of published reports.
Limitations on the length of this chapter precludes a discussion of multiple additional ultrasound-related issues, such as transducer selection, the concomitant use of nerve stimulation (an important tool in a subset of patients), and various methods for catheter tip localization. Overall, little clinical data exists comparing aspects of any one placement technique with another.
Stimulating Versus Nonstimulating Catheters
Up to 40% of catheters have been reported misplaced upon insertion. There are multiple techniques and equipment available for catheter insertion. One common technique involves locating the target nerve using nerve stimulation via an insulated needle, and then injecting a bolus of local anesthetic via a needle to provide a surgical block, followed by the introduction of a “nonstimulating” catheter. However, when using this technique, it is possible to provide a successful surgical block but inaccurate catheter placement. With the use of ultrasound guidance, the catheter tip may be directly viewed if inserted 1 cm past the needle tip, and then the needle can be withdrawn over the catheter with the operator continuously visualizing the catheter tip location to be certain that it is not dislodged. If ultrasound is not used, some investigators first insert the catheter and then administer a bolus of local anesthetic via the catheter in an effort to avoid catheter tip misplacement, with a reported failure rate of 1%–8%. Alternatively, catheters that deliver current to their tips have been developed in an attempt to improve initial placement success rates. These catheters provide feedback on the positional relationship of the catheter tip to the target nerve prior to local anesthetic dosing. While there is evidence that passing current via the catheter may improve the accuracy of catheter placement with minor benefits in the lower extremity, the nonstimulating catheters of these three studies were advanced 4–10 cm past the needle tip, which greatly increases the risk of the catheter tip-to-nerve distance and decreasing the effectiveness of the local anesthetic infusion. Further study is required to identify the optimal equipment for perineural infusion.
Infusion Management
Currently, there is insufficient information to determine if there is an optimal local anesthetic for CPNB. The majority of perineural infusion publications have involved bupivacaine (0.1%–0.25%) or ropivacaine (0.1%–0.4%), although levobupivacaine and shorter acting agents have been reported. The main determinant of CPNB effects, local anesthetic concentration and volume or simply total drug dose, remains unknown, although there is evidence that for continuous femoral and posterior lumbar plexus blocks, local anesthetic concentration and volume do not influence nerve block characteristics, suggesting that local anesthetic dose (mass) is the primary determinant of perineural infusion effects. There are no adjuncts added to local anesthetics that have been demonstrated to provide benefits during CPNB. Additionally, epinephrine and opioids have been added to local anesthetic infusions, but there are currently insufficient published data to draw any definitive conclusions regarding the safety of the former or the efficacy of the latter.
Many variables probably affect the optimal regimen, including the surgical procedure, catheter location, physical therapy regimen, and the specific local anesthetic infused. For procedures resulting in at least moderate postoperative pain, a basal infusion optimizes benefits such as analgesia and sleep quality. Providing patients with the ability to self-administer local anesthetic doses increases perioperative benefits such as improving analgesia, minimizing supplemental opioids, and allowing a decreased basal infusion rate, which minimizes the risk of limb weakness and maximizes the infusion duration for ambulatory patients with a finite local anesthetic infusion pump reservoir volume. Unfortunately, insufficient information is available to base recommendations on the optimal basal rate, bolus volume, or lockout period accounting for the many variables that may affect these values (e.g., catheter type, location, surgical procedure). Until recommendations based on prospectively collected data are published, practitioners should be aware that investigators have reported successful analgesia using the following with long-acting local anesthetics: basal rate of 4–8 mL/h, bolus volume of 2–5 mL, and lockout duration of 20–60 minutes.
One relatively new technique is now possible due to the advent of new infusion pumps that can repeatedly administer automated bolus doses. Initial reports suggested improved analgesia using this technique ; however, subsequent volunteer-based trials do not appear to support using this modality. Additional research is required, especially involving adductor canal, supraclavicular, and transversus abdominis plane catheters for which a bolus dose might improve local anesthetic spread with beneficial effects.
The dosing issue has particular importance for lower extremity CPNB. Although inhibition of pain fibers is the primary goal for postoperative CPNB, currently available local anesthetics approved for clinical use decrease other afferent (e.g., nonpain-related sensory and proprioception) and efferent (e.g., motor) nerve fibers as well, resulting in undesirable side effects such as muscular weakness. There is growing evidence that lower extremity CPNB may increase the risk of patient falls, although to what degree the perineural local anesthetic infusion was a contributing factor in these cases remains unknown, because the studies were neither designed nor powered to detect such (presumably) rare complications. Nonetheless, patient falls during perineural infusion are now being highlighted in the surgical and anesthesiology literature. Until additional data are available, practitioners may want to consider steps that may minimize the risk of falls, including minimizing the dose/mass of local anesthetic; providing limited-volume patient-controlled bolus doses that allow for a decreased basal dose without compromising analgesia in some cases, although not all ; using a knee immobilizer and walker/crutches during ambulation, and educating physical therapists, nurses, and surgeons of possible CPNB-induced muscle weakness and necessary fall precautions.
In addition, a perineural infusion into the adductor canal, an aponeurotic tunnel in the midthird of the thigh deep to the sartorius muscle, dramatically reduces quadriceps weakness relative to a catheter inserted adjacent to the femoral nerve. This is most likely due to the fact that there is only one nerve within this canal that serves the quadriceps, as opposed to the femoral that innervates the entire quadriceps muscle. Unfortunately, there is also data that suggests adductor catheters provide somewhat inferior analgesia compared with femoral infusions ; but considering that a weakened quadriceps muscle probably increases the risk of falling, the risk-benefit ratio might be favorable towards the adductor location.
Potential Risks/Complications
Two of the largest prospective investigations to date involving over 2100 patients combined suggest that the incidence of CPNB-related complications is very low—at least as low as, if not lower than, single-injection techniques. Other prospective studies suggest a similar incidence of complications.
The most commonly reported complication is “secondary block failure” with a range of 0%–50%. The incidence of this complication is presumably dependent upon many factors, including the experience of the practitioner, equipment and technique, and patient factors such as body habitus. Although definitive data is lacking, it is probable that the use of ultrasound improves catheter insertion success rates. Ultrasound also decreases other risks, such as vascular puncture (reported between 0 and 11% with nerve stimulation), peri-neuraxis catheter placement, and intravascular and intraneural catheter insertion. Prolonged Horner syndrome due to neck hematoma is a rare complication, but it has been reported. While a hematoma may require weeks for resolution (months for a Horner syndrome), practitioners and patients should be reassured with the multiple case reports of complete neural recovery following hematoma resolution.
Nerve injury is a recognized complication following placement of both single injection and CPNB, presumably related to needle trauma and/or subsequent local anesthetic/adjuvant neurotoxicity. The prospective clinical evidence from human subjects suggests that the incidence of neural injury from a perineural catheter and ropivacaine (0.2%) infusion is no higher than following single-injection regional blocks. There is also evidence that for patients with diabetes, the risk of local anesthetic-induced nerve injury is increased.
The most common complication during perineural infusion is simply inadvertent catheter dislodgement (0%–50%). Every effort to optimally secure the catheter must be made to maximize patient benefits ( Fig. 16.2 ). Measures have included the use of sterile liquid adhesive (e.g., benzoin), sterile tape (e.g., Steri-Strips), securing of the catheter-hub connection with either tape or specifically designed devices (e.g., Statlock), subcutaneous tunneling of the catheter ( Fig. 16.3 ), and the use of 2-octyl cyanoacrylate glue. Using a combination of these maneuvers, investigators have reported a catheter retention rate of 95%–100% for over 5 days of infusion. Other complications occurring during infusion include phrenic nerve block and ipsilateral diaphragm dysfunction during interscalene CPNB, local anesthetic toxicity (incredibly rare), and infection. While the reported rate of inflammation (3%–4%) and catheter bacterial colonization (6%–57%) are seemingly high, clinically relevant infection is relatively rare (incidence 0%–3% ; but most reports <1%). In all but a few cases, infections completely resolve within 10 days; even in the worst-case scenarios, there has never been a permanent injury due to infection. There are additional potential CPNB complications, such as catheter knotting (do not pass the catheter >5 cm past the needle tip), retention (on with the Arrow Stimucath), and shearing (do not withdraw the catheter back into the needle unless the design is approved for this maneuver).
