Sterility is of great importance for the performance of CPNBs. Antiseptic hand washing, wearing of sterile gloves, surgical mask and hat, and the use of alcohol-based chlorhexidine antiseptic solution is recommended. If ultrasound guidance is used, the ultrasound probe should be covered by a sterile ultrasound cover. The patient is draped and during the procedure sterility of the “anesthetic” field should be maintained (Table 10.3 ) [29–34].

Regardless of which technique is used the classical “through-the-needle technique” or recently introduced “catheter -over-needle technique,” the shape of the needle tip is important in order to avoid neural damage and atraumatic needles should be used. Despite the use of atraumatic needles, intraneural injection and catheterization may still occur [35].

Pencil point needles are considered less traumatic compared to beveled and Tuohy needles. However, the magnitude of nerve injury after needle nerve perforation is not related to one of the applied needle types. In order to obtain tactile feedback (a “pop”) when fascias are pierced, blunt needles are recommended for the performance of continuous subfascial blocks such as fascia iliaca, transversus abdominis plane (TAP ), or pectoral nerve (PEC ) blocks [36, 37].

Mostly larger needles are used for the performance of CPNBs because a catheter needs to be threaded through the needle. Larger needles may make the procedure more painful; however, when the needle trajectory site is first anesthetized with local anesthetic then the procedure is only slightly painful.

Catheters are made of polyamide, polyurethane, and Teflon. There is no universally ideal catheter . The material, design, and diameter of the continuous block catheters are chosen according to the specific requirements associated with the needle and catheter design. Overall the catheter should be tension resistant and must not break or shear. Kinking should be prevented. Therefore, some manufacturers reinforce the catheter with an integrated metal wire in the catheter wall. Others use metal stylets in the catheter which are withdrawn after catheter insertion. The metal wires may also serve as electrical conduits when nerve stimulation is used [38].

The catheters should have an ascending length indication so that the depth of catheter insertion and its position can be followed during advancement and surveillance thereafter.

Catheter tips for CPNBs should be relatively stiff in order to allow catheter advancement. Metallic coiled tips may ease ultrasonic visualization but may contribute to formation of adhesions at the tip of the catheter when there is no active infusion of local anesthetic or saline [39].

Due to multiple orifices on the end of the catheter, stiffness of the catheter tip is lost and these nonstimulating catheters are more difficult to thread, but there is no difference in quality of pain relief between catheters with an end hole, triple hole, or six-hole catheter tip [40].

Luyet developed a catheter with soft tip which rolls up and remains at the point where the cannula is positioned, three orifices allow free flow of local anesthetic [41]. For safety reasons catheters should be labeled, colored, and equipped with unique connectors for tubing with the syringe and line in order to avoid tube misconnection and prevent medication errors [42, 43].

There are a number of different catheterization kits available. Catheterization equipment can be divided into: (1) catheter -through-needle devices, (2) cannula-over-needle-catheter-through-cannula devices, and more recently (3) catheter-over-needle devices, and finally, (4) preliminary suture/needle systems are available to anchor the catheters .

Needles with a specially designed tip, which facilitates placement along the nerve are now used. Facet tips ease catheter insertion parallel to the nerve; Tuohy tips are suitable for cases where it is necessary to introduce the catheter at an angle to the nerve. These needles are insulated and offer the possibility to be used with a peripheral nerve stimulator. The extension tube on the needle allows one to use an immobile needle technique.

The first CPNBs were performed using paresthesias or tactile feedback when the needle pierced the fascia and the fascial “pop” or “click” was felt [4, 5, 48, 49]. Decades ago Moore suggested that the most reliable way to guarantee successful blockade when performing peripheral nerve blockade was to first elicit a paresthesia. He used the term: “no paresthesia, no anesthesia” and it soon became doctrine [48]. Successful nerve blockade demanded proximity to the nerve as evidenced by the occurrence of mechanical paresthesias . Although the safety of this method has been questioned [50], and the sensitivity of eliciting paresthesias as an endpoint for needle to nerve contact, is only 38 % [51], no definitive evidence is available linking this technique (eliciting paresthesias ) with neurological damage [52]. This dictum first proposed by Moore more than 50 years ago is still being used as a nerve localization technique in daily practice [53]. The loss of resistance technique is simple, safe, and effective and can be applied with minimal resources; however, only limited indications for these exist when performing continuous peripheral nerve blocks (Table 10.4 ).

Since 1962 when Greenblatt and Denson constructed a neurostimulator [59], peripheral nerve stimulation has been used to localize nerves. Despite the advent of ultrasound-guided peripheral nerve blockade, nerve stimulation remains a popular technique used alone or in combination with ultrasound guidance [53].

The success of nerve stimulation-guided regional anesthesia relies on the reproducible observation that, as the needle moves closer to the nerve, less current is needed to evoke a motor response. When a motor response can be elicited by using less than a minimum current, the needle is sufficiently close to the nerve to predictably block the selected target with injection of local anesthetic [60].

An elicited motor response at or below 0.5 mA is considered a common end point for successful final needle placement adjacent to a peripheral nerve and this is usually followed by local anesthetic injection and catheter insertion. Because catheters are usually inserted blindly and some distance beyond the needle tip to avoid inadvertent dislocation, verifying a correct catheter tip position is not possible. There is no guarantee that the introduced catheter tip is close enough to the target nerve and that subsequent infusion through the catheter with diluted local anesthetic will provide analgesia. Therefore, most anesthesiologists choose to administer a loading dose through the needle before inserting the catheter . An incorrectly placed catheter only becomes apparent after the effect of the loading dose has worn off [61].

This secondary block failure occurs in up to 26 % of patients [62, 63].

In order to avoid secondary (continuous) block failure, the catheter may be directly inserted through the needle as soon as the optimal needle position is reached, followed by injection of local anesthetic through the catheter. Lack of anesthesia indicates an improperly positioned catheter and the needle insertion procedure and catheter insertion should be repeated. However, electrical nerve stimulation may no longer be used for nerve localization. Moreover, the first bolus injection precludes that an equal dose of local anesthetic is injected, which may influence the effectiveness of second attempt.

The introduction of real-time ultrasound guidance has been a major advancement in the practice of regional anesthesia. Compared with the previous described nerve localization techniques, US allows faster block performance, fewer needle passes, a reduced incidence of vascular puncture, faster block onset, and greater block success. For these outcomes, the recommendation that US guidance is superior to other nerve localization techniques can be made [88].

Unfortunately, this conclusion cannot be automatically inferred to perineural catheter placement, because in single-injection blocks it is always possible to reposition the needle in order to obtain optimal spread of local anesthetic around the nerve. This real-time positioning is not possible with a flexible catheter and the catheter insertion is therefore comparable to a single-point injection [89]. Moreover unlike needles, flexible perineural catheters rarely remain within the 2-dimensional 1 mm ultrasound (slice) view, making it difficult to observe catheter tip placement relative to the target nerve. Lastly, compared to single-injection blocks the angle between the long axis of the placement needle and target nerve is important if a catheter-through-needle technique is used for perineural catheter insertion. When a catheter is threaded through a needle with a position perpendicular to the nerve, then it may traverse the nerve [80].

For ultrasound-guided perineural catheter insertion, three approaches exist. The needle in plane, nerve in short-axis approach; the needle out of plane, nerve in short-axis approach; and the needle in-plane, nerve in long-axis approach [90].

Theoretically, ultrasound has the potential to confirm catheter tip location. However in practice, identifying the tip is often challenging because flexible catheters do not remain within the ultrasound plane of view. Therefore, additional means for tip identification are used such as observation of the location of fluid [92]. Injecting agitated microbubbles, which appear as a hyperechoic injectate within the anechoic local anesthetic fluid [103, 104], or the use of color Doppler in which the injectate appears as a mix of colors superimposed on the grayscale background, or simply inject air through the catheter [105]. The air test improves the assessment of catheter tip location compared to chance, but there is no difference compared to direct visualization of the catheter without air injection. The relationship of the hyperechoic artifact with the target nerve may aid in judging the catheter tip location and subsequent distribution of the local anesthetic injectate. The disadvantage of this air test is the introduction of an artifact near the target nerve that may blur the image and hinder catheter replacement. Therefore, it is recommended to keep the volume of injected air to a minimum (< 1 ml) to limit artifactual interference. Moreover, the detrimental effects caused by an accidental intravascular catheter placement with subsequent intravascular air injection are avoided when this minimal amount of air is used [106].

CPNB-specific complications during catheter insertion include inaccurate catheter tip placement. Catheter placement too far from the target nerve results in block failure. Secondary block (infusion) failure has an incidence varying between 10 % and 40 %.

A higher BMI and long indwelling time are likely to predispose to higher failure rates [109]. This is only a minor complication compared to epidural, intrathecal, intravascular, interpleural, and intraneural catheter placement all of which may result in poor outcomes [35, 110–118].

One common denominator in these reported complications is catheter threading. Most catheters are threaded more than 3 cm from the catheter tip. Therefore, in order to prevent complications do not thread the catheter more than 3 cm past the tip of the needle. Threading more than that is not necessary, it only increases the risk of complications and jeopardizes the success of the block.

These reports also prove that both single blocks and the first injection through the catheter (or the start of an infusion) should only be performed in an environment that allows the ready identification and prompt management of any resulting complications.

Catheter dislocation and leakage at the insertion site are complications arising during local anesthetic infusion. The diameter of the catheter is smaller than that of the needle used for skin puncture and creating space for local anesthetic to leak upon infusion when a catheter-through-the-needle catheter technique is used. The transparent dressing disconnects from the skin and the catheter gets dislocated. The incidence of catheter dislocation varies between 1 and 25 % [99, 119, 120]. Movement and time are considerable factors for perineural catheter tip displacement. For preventing accidental catheter removal, different strategies are used. Combining different methods of catheter fixation may reduce the incidence of accidental catheter removal to 1 % [120–122]. Other methods used are subcutaneous tunneling [123, 124]; however, tunneling and suturing are not without risks. The tunneling needle may inadvertently cut the catheter [125]. Catheter anchoring devices may be helpful in securing catheters for regional anesthesia [126–128].

Also sealing the insertion site with 2-Octyl cyanoacrylate (Dermabond® ) has been used to secure catheters [129]. Even shortly after application of the glue, catheter removal is still possible [130, 131]. The application of glue not only provides fixation but also a barrier to the entry of gram-positive skin flora along the catheter exit tract and this may prevent catheter-related infections [132]. Mostly transparent dressings, which allow inspection of the catheter insertion site are used, but chlorhexidine gluconate impregnated dressings may reduce bacterial colonization rates in regional anesthesia catheters [133].

Bacterial colonization of CPBNs occurs easily and the incidence varies between 27 % and 57 % depending on the location of the catheter and criteria used for the definition of colonization [134]. The highest microbial density is found in the axilla and groin region in men. This is not surprising when one considers the high density of sebaceous glands and humidity of these skin sites [135]. Skin disinfection is less efficient in areas with a high density of sebaceous glands [32]. So both factors contribute to the high incidence of colonization of femoral and axillary catheters. The most frequently identified organisms are Staphylococcus epidermidis (71 %), enterococcus (10 %), and klebsiella (4 %) [136]. Although colonization of the catheter may occur, this does not automatically lead to infection . Forty-four percent of the catheters are colonized if signs of local inflammation are present versus only 19 % when no evidence of inflammation exists. This suggests that catheters also become contaminated during removal despite aseptic conditions [119]. Tunneling of catheters seems to offer some protection against colonization [123, 137]. The incidence may decrease to 6 %, whether this will influence the infection rate should be examined [138].

In regional anesthesia, antimicrobial continuous peripheral nerve catheters have not yet been introduced, even though the effectiveness of antimicrobial central venous catheters has been confirmed [139]. CPNB infection is a rare event with an incidence between 0.02 % and 3 % [134, 136, 140, 141]. Serious case reports have been described such as psoas abscess complicating femoral nerve block [142], thigh abscess after continuous popliteal sciatic nerve block [143], acute neck cellulitis and mediastinitis complicating continuous interscalene block [144]. The German society for Anesthesia and Intensive Care has published clear definitions (Table 10.5) for an infectious complication after regional anesthesia [145].

Neuburger et al. examined 3491 CNPB catheters and used the definition (Table 10.5) in relation to infection occurring after CPNBs. A small infection occurred in 4.2 %, a mild in 2.4 %, and severe infection in 0.8 % of the patients who had a perineural infusion. The surgical intervention for severe infection consisted mostly of a simple superficial incision but in 58 % deep surgical drainage was necessary. All infections were successfully treated without sequela.

It is interesting to note that patients experienced pain upon pressure at the catheter insertion site, regardless of the severity of the infection . This sign seems to be an important predictor for a pending infection . So during follow-up in these cases the catheter insertion site should not only be visually inspected but also palpated. Pain upon palpation, redness, and pus on the catheter insertion site are reasons to remove the catheter [141].

Risk factors for infection include male sex, absence of perioperative prophylaxis, admission to an intensive care unit, the experience of the anesthesiologist, and the duration of catheterization [119]. Diabetic patients have a 2.4 times higher risk for catheter -associated infections compared with nondiabetic patients [146]. It is unknown whether the site of catheter insertion increases the risk of infection . Some report a higher incidence of infection with axillary and femoral catheter s [119, 147], while others report the highest incidence of infection with the interscalene catheter insertion site [141].

No guidelines exist regarding whether regional anesthesia can be safely performed in immune compromised patients or in patients with systemic infections . On an individual basis the risks and benefits of regional anesthesia should be considered. The general consensus suggests not to perform regional anesthesia if an active infection exists at the presumed needle insertion point. If an active infection exists and the decision is made to perform a CPNB, then the distance between the active infection site and needle and catheter insertion site should be as far away as possible. Ideally, catheter insertion should not be performed if there is any evidence of active infection and only if active antibiotic treatment has already been started. The use of immunosuppressive drugs is not associated with a higher risk of infectious complications after regional anesthesia. The opposite is true of patients with diabetes mellitus and malignant diseases. Prophylactic use of antibiotics may be considered in these patients [134].

Strict adherence to aseptic technique is a cornerstone of preventing infectious complications in regional anesthesia. It is recommend to wear a hat, surgical mask, and sterile gloves. Skin preparation should be performed with an alcohol-based chlorhexidine solution [32].

It is interesting to note that EMLA cream (an eutectic mixture of lidocaine 2.5 % and prilocaine 2.5 %) has a similar bactericidal effect to Skinsept Pur (alcohol-based preoperative skin disinfectant) and has a longer bacteriostatic effect. This difference was significant after 4 h and lasted 12 h. Whether this finding has clinical relevance in terms of reducing nosocomial infection needs further studies [148].

Close surveillance of bacterial infections of CPNBs makes a veritable detection of adverse events possible and the effects of changes in clinical procedures can be followed. Reisig et al. revised an existing hygiene regime for CPNBs based on the results of a close surveillance system. A major change occurred when the skin disinfection (spray-and-scrub) combined procedure, lasted 10 min. The effect was a decrease in infection rate by almost 75 % [33]. For further discussion on this topic, please refer to Chap. 6.

Serious permanent complications after continuous peripheral nerve blockade are uncommon. The origin of neurologic symptoms and signs in the perioperative period are most likely unrelated to the blocks. New, all-cause neurological symptoms were reported in 8.2 % at day 10, 3.7 % at 1 month, and 1.3 % at 6 months, but after careful examination of these patients it was shown that few complications were block related [140, 165].

For peripheral regional anesthesia, in general, the incidence of transient adverse neurologic symptoms purely associated with CPNBs is 0 % to 0.2 % [119, 141, 166–169]. Introducing a catheter in the close vicinity of a nerve does not increase the risk of neurological complications. This suggests that if neurological damage occurs after CPNBs, it is most likely caused by the needle during the initial block insertion.

Based on the estimated rate of occurrence of nerve injury after single-injection peripheral nerve block , almost twice as many nerve injuries are seen in proximal brachial plexus (interscalene) blocks compared with distal brachial plexus (axillary blocks) [170].

The observed differences in risk of nerve injury between proximal and distal parts of the brachial and lumbosacral plexus may be explained by the observed differences in the ratio of neural to nonneural tissue [171].

Unintended catheterization of nerves might be much more common than usually thought and may be influenced by the needle and catheter tip, but this does not invariably lead to neural injury [35].

It is suggested that stiff catheter tips more easily penetrate the outer epineurium and become embedded in the loose epineurium. Intrafascicular penetration is prevented by the strong sheath of the perineurium which is different from the loose tissue framework of the interfascicular epineurium. Intraepineural injection through the catheter will separate the fascicles upon injection [172, 173]. High injection pressures during injection should be prevented and might indicate intrafascicular injection [174].

When the catheter is placed under ultrasound guidance it is common to inject a small amount of fluid to confirm correct placement of the needle tip. Subepineural, parafascicular injections are characterized by low injection pressures and when ultrasound is used, expansion of the cross-sectional surface area with a change in echogenicity during injection is noted [175]. Discrimination of subepineural and extraneural tip position based on an injection of 0.5 ml is possible. The first injection of local anesthetic through the catheter should preferentially be performed under ultrasound guidance.

It is important to avoid late secondary neurological damage due to an insensate limb. Theoretically, patients with blocked extremities are more predisposed to limb injury and pressure neuropathy because of the lack of protective pain reflexes and reduced proprioception. Some anesthesiologists consider discharge of patients with a motor block controversial, but withholding the analgesic benefits of long-acting local anesthetics and CPNBs in ambulatory patients is unjustified. Klein et al. found an infrequent incidence of neurologic complications and injuries despite discharge with an insensate extremity [63]. When patients are discharged, they should be provided with instructions, to wear a sling, not to bear weight and to protect the anesthetized limb in order to avoid damage.

In conclusion, neurologic injury after peripheral nerve blocks is multifactorial and involves anatomy, site of needle and catheter insertion, bevel and catheter tip type, nerve–needle tip interaction, pressure of the needle tip, and underlying patient factors.

During CPNB placement, the incidence of vascular puncture is 5.7 % and 6.6 % for femoral and sciatic nerve catheters , respectively [176]. Ultrasound-guided PNB is associated with a reduced incidence of inadvertent vascular puncture [166, 177]. Serious hemorrhagic complications have been rarely described in CPNBs. Significant blood loss is more worrisome than neural damage. Hematoma formation may lead to nerve injury due to pressure ischemia, either as perineural hematoma or by occupying and pressurizing an anatomic compartment [169, 178]. Moreover, hematoma formation may be a risk factor for bacterial infection .

Bleeding complications of peripheral nerve blocks are less serious than those caused by central neuraxial blocks and the risks remain undefined. Information regarding the safety of CPNBs in patients treated with low-molecular-weight heparin (LMWH) or oral anticoagulants is scarce. A few studies have been performed involving the risk of hemorrhagic complications. Chelly et al. removed lumbar plexus catheters in patients with an INR between 1.5 and 3.9 and no serious complications occurred [179]. In another study, they demonstrated that continuous and single peripheral nerve blocks can be safely performed before the initiation of thromboprophylaxis and aspirin on the day of surgery and that perineural catheters can be safely removed when the patient is receiving thromboprophylaxis using low-molecular-weight heparin, warfarin, and aspirin [180]. Buckenmaier applied CPNB catheters for the management of pain in combat wounded patients who are anticoagulated with LMWHs. They used a liberal policy regarding LMWH and CPNBs and demonstrated that no catheter -related bleeding complications occurred [181]. Idestrup et al. showed that the concurrent administration of a continuous femoral nerve block and once-daily administration of the anticoagulant rivaroxaban (orally administered Xa inhibitor) and the timed removal (20 h) of the femoral catheter were not associated with severe hematoma formation. Ecchymoses were observed in 12 % of patients following total knee arthroplasty. No patients required removal of hematoma or decompression at the femoral catheter site [182]. Visoiu and Yang placed bilateral continuous nerve blocks in a child with coagulopathy undergoing laparotomy. The final decision to perform this technique was based on normal thromboelastogram (TEG) but abnormal PT and PTT. They suggested to evaluate the validity of TEG in the prediction of bleeding risk and the safety of regional anesthesia in coagulopathic patients [28].

Recommendations from the American Society of Regional Anesthesia differ from the European Society of Anesthesiology and state that for patients undergoing deep plexus or peripheral nerve block the same recommendations suggested for neuraxial techniques, should be followed. This conflicts with the European recommendation which state that single-injection axillary, femoral, or distal sciatic nerve block may be performed in the presence of aspirin or anticoagulants use. However, these should be stopped when deep blocks, where access is difficult and arterial trauma is a risk, are performed such as interscalene, supraclavicular, infraclavicular, and lumbar plexus blocks. Whenever lumbar plexus, paravertebral blocks with or without catheters , are inserted or withdrawn, the same guidelines that apply to neuraxial blocks should be followed [183].

The Dutch Society of Anesthesia states that a simple difference between superficial and deep blocks does not exist and proposed an alternative strategy. A block classification based on the negative consequence of bleeding complication was made (Table 10.6). Blocks in the category “limited consequences in case of bleeding ” can be performed without stopping the use of anticoagulants. When blocks in the category “ intermediate negative consequences of bleeding complication” are performed, then low-molecular-weight heparins prophylaxis, aspirin, NSAIDs, clopidogrel, prasugrel, ticagrelor, dabigatran, rivaroxaban may be continued. In these cases the INR should be lower than 2. If LMWHs or dabigatran or rivaroxaban is prescribed for therapeutic use then they should be stopped for at least 24 h. When continuous lumbar plexus or cervical paravertebral blocks are performed then the recommendations that apply for neuraxial blocks should be followed. For some additional discussion on this topic, please refer to Chap. 7.