Equipment for Peripheral Nerve Blocks
Ali Nima Shariat, Patrick M. Horan, Kimberly Gratenstein, Colleen McCally, and Ashton P. Frulla
Over the past several decades, regional anesthesia equipment has undergone substantial technological advances. Historically, the development and consequent introduction of the portable nerve stimulator to clinical practice in the 1970s and 1980s was a critical advance in regional anesthesia, allowing the practitioner to better localize the targeted nerve. In recent years, however, the advent of ultrasound, better needles, catheter systems, and monitoring has entirely rejuvenated, if not revolutionized, the practice of regional anesthesia.
Induction and Block Room
Regional anesthesia is ideally performed in a designated area with access to all the appropriate equipment necessary to perform blocks. Whether this area is the operating room or a separate block room, there must be adequate space, proper lighting, and equipment to ensure successful, efficient, and safe performance of peripheral nerve blocks (PNBs). Provision for proper monitoring, oxygen, equipment for emergency airway management and positive-pressure ventilation, and access to emergency drugs is of paramount importance (Figure 1).
Cardiovascular and Respiratory Monitoring During Application of Regional Anesthesia
Figure 1: Typical block room setup. Shown are monitoring, oxygen source, suction apparatus, ultrasound machine, and nerve block cart with equipment.
Figure 2: Typical nerve block cart with labels for each drawer.
Patients receiving regional anesthesia should be monitored with the same degree of vigilance as patients receiving general anesthesia. Local anesthetic toxicity due to intravascular injection or rapid absorption into systemic circulation is a relatively uncommon but potentially life-threatening complication of regional anesthesia. Likewise, premedication, often necessary before many regional anesthesia procedures, may result in respiratory depression, hypoventilation, and hypoxia. For these reasons, patients receiving PNBs should have vascular access and be appropriately monitored. Routine cardiorespiratory monitoring should consist of pulse oximetry, noninvasive blood pressure, and electrocardiogram. Respiratory rate and mental status should also be monitored. The risk of the local anesthetic toxicity has a biphasic pattern and should be anticipated (1) during and immediately after the injection and (2) 10 to 30 minutes after the injection. Signs and symptoms of toxicity occurring during or shortly after the completion of the injection are due to an intravascular injection or channeling of local anesthetics to the systemic circulation (1-2 minutes). In the absence of an intravascular injection, the typical absorption rate of local anesthetics after injection peaks at approximately 10 to 30 minutes after performance of a PNB (1); therefore patients should be continuously and closely monitored for at least 30 minutes for signs of local anesthetic toxicity.
Regional Anesthesia Equipment Storage Cart
A regional anesthesia cart should have all drawers clearly labeled and be portable to enable transport to the patient's bedside. The anesthesia cart should also be well stocked with all equipment necessary to perform PNBs effectively, safely, and efficiently. Supplies such as needles and catheters of various sizes, local anesthetics, and emergency airway and resuscitation equipment should also be included (Figures 2,3, and 4). Different drawers are best organized in a logical manner to ensure quick and easy access. One drawer should be designated for emergency equipment and should include laryngoscopes with an assortment of commonly used blades, styletted endotracheal tubes and airways of various sizes (Figure 5). Emergency drugs that should be present include atropine, ephedrine, phenylephrine, propofol, succinylcholine, and intralipid 20%. The latter can alternatively be stored in a nearby drug cart or drug-dispensing system that is immediately available and in close proximity to the block room. This way, it can be prepared within minutes in case of emergency (Figures 6, 7, and 8).
Table 1: Suggested Emergency Drugs Required During Nerve Block Procedures
*A short-acting barbiturate (i.e., thiopental, Brevital) can be used instead of propofol; however, this requires dilution of the drug at the time when its prompt administration is of utmost importance. In addition, the hypnotic and sedative effects of a barbiturate may be longer lived than those of propofol. These drugs also require more intensive monitoring and airway management. The dosages recommended are for the purpose of abolishing the seizure activity.
Treatment of Severe Local Anesthetic Toxicity
Figure 9: An example of a custom nerve block tray, including lidocaine 1%, lidocaine 1% with epinephrine, sterile saline, syringes, connector, and marker, prep sponges and iodine solution, sterile occlusive dressing and drape, and extension tubing.
A 1998 study heralded the clinical utility of intralipid therapy in the treatment of local anesthetic toxicity. Administration of 20% intralipid solution to rats increased the lethal dose of bupivacaine by 48% when compared with untreated controls. The same study also showed increasing survival rates when used as part of a resuscitation protocol. The results were explained by the portioning of bupivacaine into the newly created lipid phase. (2) In follow-up studies, dogs that had bupivacaine-induced cardiovascular collapse were successfully resuscitated after receiving lipid infusion, demonstrating the utility of intralipid in a large animal model that more closely approximates human physiology. (3) In 2006, Rosenblatt et al published the first use of intralipids in a patient to reverse bupivacaine-induced cardiotoxicity. (4) Soon thereafter, additional case reports of successful resuscitation from local anesthetic-induced toxicity with intralipid were published (5-8) establishing intralipid infusion as an important emergency intervention in the practice of regional anesthesiology. Based on laboratory evidence and a growing body of anecdotal reports in clinical practice, it appears prudent to keep intralipid solution 20% in close proximity to locations where regional anesthesia is administered. (9)
Peripheral Nerve Block Trays
Commercially available, specialized nerve block trays are useful for time-efficient practice of PNBs. An all-purpose tray that can be adapted to a variety of blocks may be the most practical, given the wide array of needles and catheters that may be needed for specific procedures. Appropriate needles, catheters, and other specialized equipment are simply opened and added to the generic nerve block tray as needed (Figure 9).
Regional Nerve Block Trays
A wide array of needles is available for performing PNBs (Figure 10). Choice of needle depends on the block being performed, the size of the patient, and preference of the clinician. Needles are typically classified according to tip design, length, gauge, and the presence or absence of electrical insulation or other specialized treatment of the needles (e.g., etching for better ultrasound visualization).
Table 2: Block Technique and Recommended Needle Length
Needle Tip Design
Direct evidence for an association between needle tip design and the incidence of nerve injury is scarce. In a rabbit sciatic nerves model, Selander demonstrated that the risk of fascicle injury was lower when a short bevel needle penetrated a nerve as opposed to a long bevel needle. (10) However, another experiment by Rice and colleagues suggested that the reverse may be true. (11) This disparity might be explained by the fact that the study of Rice et al examined the effect of needle bevel design on the severity and consequences of intrafascicular should accidental fasicular penetration occur. Therefore, although it may be more difficult to enter a nerve fascicle with a short bevel needle as compared with a long bevel needle, the short bevel needle may cause a more severe lesion should a nerve be impaled by such a needle. (12) Needle design can also have a direct effect on the anesthesiologist's ability to perceive tissue planes. Tuohy and short bevel noncutting needles provide more resistance and thus enhance the feel of the needle traversing different tissues. Long bevel cutting needles, by contrast, do not provide as much tactile information while traversing different tissues. Pencil point needles may be associated with less tissue trauma than short bevel needles when bony contact occurs during spinal anesthesia, resulting in a lower incidence of postdural puncture headache. (13) It is unclear however, whether pencil point needles have any advantage over other needle designs in practice of PNBs.
The length of the needle should be selected according to the type of block being performed (Table 2). A short needle may not reach its target. Long needles have a greater risk of causing injury due to increased difficulty in their handling and possibility of being inserted too deeply. The needle lengths recommended in this text are based on the author's experience and are intended as a general guide. Note that the needle length is often longer by 2 to 3 cm for ultrasound-guided blocks because needles are inserted further from the target to visualize the course of the needle on the image. Needles should have depth markings on their shaft to allow monitoring for the depth of placement at all times.
The choice of the needle gauge depends on the depth of the block and whether a continuous catheter is placed. Steinfeldt et al recently demonstrated the correlation between larger needle gauge and increasing levels of nerve damage after intentional nerve perforation in a porcine model. (14) Thus, a small gauge needle may theoretically reduce the tissue trauma and discomfort to patients, whereas a long gauge needle bends more easily, making it more difficult to control. The needles of smaller caliber however, may also be more likely to penetrate the fascicles. In addition, needles of smaller gauges have more internal resistance, making it more difficult to gauge injection resistance and aspirate blood. Needles of very small size (25 and 26 gauge) are most commonly used for superficial and field blocks. Larger gauge needles (20-22 gauge) may be used in deeper blocks to avoid bending of the shaft and to maintain better control over the needle path. When placing a continuous catheter, the needle gauge must be large enough to allow passage of the catheter. Consequently, 17-19 gauge needles are most commonly used with an 18- gauge catheter for continuous catheters.
Visualization of the needle tip is one of the more challenging aspects of performing an ultrasound-guided PNB. To facilitate the ease of needle visualization, specialized needle designs are being developed that allow greater visibility of the needle when performing ultrasound-guided PNBs. One example of such needle designs is coating with a biocompatible polymer that traps microbubbles of air, thus creating specular reflectors of air. (15) The design improves needle visibility and aids in the performance of sonographically guided biopsies. (16) Another echogenic needle design incorporates echogenic "dimples" at the tip to improve visibility. (17) Unique texturing on the needle tip also demonstrated improvement in visibility. (18) The design of echogenic needles is a continuously evolving field.
Ultrasound technology allows visualization of the anatomic structures, the approaching needle, and the spread of local anesthetic. (19) Ease of use, image quality, ergonomic design, portability, and cost are all important considerations when choosing an ultrasound machine. To curtail costs, some institutions or practices purchase a single ultrasound machine to use for several purposes such as obstetrics, regional anesthesia, abdominal scanning, or echocardiography. (20) Recently, a number of newer ultrasound machine models have evolved that are portable or can be mounted on the wall, which is beneficial in a setting where there is limited space to perform a block. The ultrasound technology is continually and rapidity evolving with an increasing focus on its application in regional anesthesia.
Strict adherence to sterile technique is of importance in the practice of regional anesthesia. Infections due to PNBs are uncommon, but potentially devastating, yet largely preventable complications. A report of a fatality due to an infectious complication of a PNB underscores the importance of sterile techniques. (21) One study found that 57% of femoral catheters demonstrated bacterial colonization, although only 3 of 208 showed signs suggestive of infection (shivering and fever) that subsided after catheter removal. (22) Another study documented 1 infectious complication of 405 axillary catheters placed, (23) reflecting the relative rarity of such events. However, several case reports reflect the severity of infections caused by indwelling catheters. One case of psoas abscess complicating a femoral catheter placement has been reported. (24) Capdevila and colleagues reported an occurrence of acute cellulitis and mediastinitis following placement of a continuous interscalene catheter that may have resulted from the refilling of local anesthetic into the elastomeric pump. (25) More recently, sepsis following interscalene catheter placement was complicated by hematoma. (26) These cases illustrate the importance of adherence to aseptic technique in all phases of needle puncture, catheter insertion and management, as well as administration of local anesthetics.
The hands of health care workers are the most common vehicles for the transfer of microorganisms from one patient to another. (27) Studies show that although soap and water may remove bacteria, only alcohol-based antiseptics provide superior disinfection, and solutions of povidone iodine and chlorhexidine possibly provide the most extended antimicrobial activity. (28) Sterile gloves should be used throughout in addition to all other measures discussed. (29) No evidence exists to prove that gowning decreases the incidence of nosocomial infection. (30) One study showed no difference between infection or colonization rates between gowning and not gowning in the pediatric intensive care unit (ICU). (31) Another study showed that use of gowns and gloves was no better than use of gloves alone in preventing rectal colonization of vancomycin-resistant enterococci in the medical ICU. (32) Therefore, although gowning during the performance of PNBs is recommended by some, there is not sufficient evidence that such practice is beneficial in decreasing the incidence of infection. (30)
Surgical masks have become commonplace when performing invasive procedures. In an experiment where volunteers were asked to speak with and without surgical masks in close proximity to agar plates, it was found that wearing a mask significantly reduced the contamination of the plates. (33) However, there is considerable debate whether their use is effective at decreasing nosocomial infection with some arguing that they represent an essential component of sterile practice (34,35) and others maintaining there is no scientific evidence to support the practice. A postal survey of 801 anesthesiologists in Great Britain found that only 41.3% routinely wore face masks while performing spinal and epidural anesthesia, whereas 50.6% did not. (36) The work of Schweizer indicates that masks may increase contamination of a sterile field possibly due to the increase in shedding skin scales. (37) These results were supported by the work of Orr et al that found a significant ( 0.05) decrease in the amount of infections when masks were not worn during surgical procedures. (38) However, one case series reported four cases of meningitis due to viridans streptococci following spinal anesthesia performed by the same anesthesiologist. (39) The same causative bacteria were later cultured from the anesthesiologist's nasopharyngeal mucosa, and the anesthesiologist was noted not to wear surgical masks when performing spinal anesthesia. Another case report described two cases of bacterial meningitis following diagnostic lumbar puncture due to Streptococcus salivarius. The same bacteria were cultured from the oropharyngeal mucosa of the neurologist who performed the lumbar puncture. (40)At this time there is no evidence that wearing a mask can prevent infectious complications of PNBs, although some clinicians suggest this practice. (41-43)
Transducer Covers and Gel
Sterile clear dressings or sterile ultrasound transducer covers constitute sound clinical practice and are routinely used by most clinicians. A variety of sterile ultrasound transducer covers are available. Some come in sets with sterile ultrasound gel and rubber bands to pull the transducer covers tightly over the transducers to facilitate imaging.
However, the incidence of contact dermatitis due to ultrasound gel is rare considering the frequency of its worldwide use, several case reports have emerged that have been attributed to the bacteriostatic preservatives propylene glycol and parabens. (44,45) Regardless, contact dermatitis from ultrasound gel has also been attributed to the imidazolidinyl urea. (46) Drugs such as diazepam that have propylene glycol in their solvent solutions are known to cause myotoxicity when injected intramuscularly. In the 1950s, a preparation of procaine called Efocaine was introduced for its long duration of action. However, reports surfaced of neuritis and local irritation after perineural injection of Efocaine. The mechanism of action of the drug was attributed to coagulation necrosis, and it is noteworthy that the preparation of Efocaine contained 78% propylene glycol. (48) Likewise, safety of inadvertent injection of ultrasound gel during ultrasound-guided nerve blocks has been questioned. A recent study has demonstrated that the lumen of PNB needles can carry and deposit ultrasound gel in close proximity to nerves, suggesting that further studies are needed to ascertain whether the amounts of gel under consideration are enough to cause toxicity.
Injection Pressure Monitoring
Figure 11: Monitoring injection pressure at the interscalene brachial plexus using an in-line injection pressure monitor (BSmart, Concert Medical USA). A color-coded piston moves during the block performance to indicate pressure during injection.
Intrafascicular injections during the performance of PNBs are associated with high injection pressures during injection of the local anesthetic. (50) Such injections lead to neural damage and neurologic deficits in animal models. (51) Assessment of resistance to injection is routinely done in clinical practice to reduce a risk of an intraneural injection and constitutes a suggested routine documentation of PNB procedure. (71) Traditionally, however, anesthesiologists have relied on a subjective “syringe feel,” that is, the feeling of increased resistance on injection. Recent studies have cast doubt on the ability of anesthesiologists to detect intraneural injections using this method. In fact, studies show that anesthesiologists may often inject local anesthetic at injection pressures capable of rupturing a fascicle. (52) An inline injection pressure manometer can be placed between the syringe and the injection tubing with the needle to objectively quantify and monitor the injection pressure (Figure 11). Injection pressures greater than 20 psi are associated with intraneural intrafascicular injection. Alternatively, an air-compression test in the syringe is used to avoid injection using pressure greater than 20 psi. (72,73) In actual clinical practice, injection with pressures
Continuous Nerve Catheters
Sutherland was first to introduce the stimulating catheter to improve the success rates over blindly inserted catheters. (53) This was followed closely by further reports of similar techniques. (54,55) For the performance of continuous peripheral nerve catheters, a wide range of needle and catheter types are available. Two main types of catheters are the stimulating catheters, which can provide stimulation through the catheter itself, and the nonstimulating catheters, which do not allow this option. Stimulation is typically accomplished through a metal stylet or coil that conducts electricity through or around the catheter lumen. Several designs are available on the market. Although it would appear logical that the confirmation of the catheter placement using electrolocalization should result in a greater consistency of catheter placement and higher success rate, the data on any advantages of the stimulating catheters over nonstimulating catheter remain conflicting. One study in volunteers found that although there was no statistically significant difference in block success rate between stimulating and nonstimulating catheters, the stimulating catheters did provide an increase in depth of both sensory and motor block. (56) Another study found that using a stimulating catheter as opposed to a nonstimulating catheter resulted in a significant lowering of the local anesthetic volume required to block the sciatic nerve. (57)
Stimulating may also result in shorter onset time for sensory and motor block, a lower consumption of local anesthetics postoperatively, and less need for rescue pain medication. (58) Several other studies, however, have found no significant differences in local anesthetic required, speed of onset for motor and sensory block, visual analog scores, or opioid consumed postoperatively when comparing stimulating with nonstimulating catheters. (59-62) The most recent meta-analysis investigating 649 patients comparing stimulating and non-stimulating catheters from 11 trials showed a statistically significant benefit in analgesic effect from stimulating catheters. (63) Significantly, these studies did not use ultrasound guidance and only used nerve stimulation for localization of the nerve and confirmation of the catheter position. The position of a nonstimulating catheter can be confirmed by bolusing local anesthetic or saline through the catheter and visualizing the spread under ultrasound. If normal saline or local anesthetic is bolused through the catheter, it must be noted that should replacement of the catheter be necessary, electrical nerve stimulation will no longer be possible. (64) A nonconducting solution, such as dextrose 5% in water, may be used to ascertain the catheter tip location and preserve the ability to stimulate. (65) Any advantage of stimulating over nonstimulating catheters placed with ultrasound guidance may be even further diminished because the spread of the local anesthetic solutions injected through the catheter (as evidenced by ultrasound) is the gold standard of documenting proper catheter placement, rather than a specific motor response to nerve stimulation (Figures 12 and 13).
Figure 12: Continuous nerve block set with stimulating catheter, including lidocaine 1%, lidocaine 1% with epinephrine, needles, syringes, and gauze, sterile sponges with iodine solution, stimulating needle, securement device, stimulating catheter, sterile drape and swabstick pack, and adaptor.
Securing Perinerual Catheters
Dislodgement of a catheter is relatively common and leads to ineffective analgesia and requires reinsertion of the catheter. There are a variety of methods and devices for securing indwelling continuous catheters, most of which incorporate some means of fixing the device and/or catheter to the skin via adhesive tape on one side of the device.
Some practitioners tunnel the indwelling catheters to better secure them, although there is no data documenting that tunneling a catheter decreases the incidence of dislodgement. The benefits of tunneling should be weighed against the potential for dislodging the catheter in the process of needle insertion. If the decision is made to tunnel the catheter, then applicvation of a topical skin adhesive to the puncture site that the catheter passes through can help secure the catheter and prevent leakage of local anesthetic. This is due to the fact that the puncture sites produced by catheters have larger diameter than the catheters themselves. The catheter should be covered with a transparent, sterile occlusive dressing to allow daily inspection of the catheter exit site. This allows for monitoring catheter migration and early signs of infection. (66)
Figure 13: Nonstimulating catheter set, including nonstimulating catheter, extension tubing, clamp-style catheter connector, 2-inch stimulating Tuohy needle, 4-inch stimulating Tuohy needle, and label.
Patients are increasingly being sent home with peripheral nerve catheters attached to portable infusion pumps that ensure the accurate and reliable delivery of local anesthetic. The pumps can be either elastomeric or electronic. The elastomeric pumps use a nonmechanical balloon mechanism to infuse local anesthetics and consist of an elastomeric membrane within a protective shell. The pressure generated on the fluid when the balloon is stretched is determined by the material of the elastomer (e.g., latex, silicon, or isoprene rubber) and its shape. (67) These pump sets typically contain an elastomeric pump with a fill port, a clamp, an air-eliminating filter, a variable controller, a flow rate dial, a rate-changing key, and a lockable cover. Most electronic pumps can hold 400 mL of local anesthetic, and the anesthesiologist can easily program the concentration, rate, and volume. These pumps are lightweight, typically come with carrying cases, and do not impose any limitations on mobility for the patient. One study found that the elastomeric pumps were as effective as electronic pumps in providing analgesia following ambulatory orthopedic surgery; however, the elastomeric pumps led to higher patient satisfaction scores due to fewer technical problems. (68) However, underfilling the elastomeric pump results in a faster flow rate, whereas overfilling results in a slower rate. The elastomeric pump flow rate is also affected by changes in temperature that affect the solution viscosity. Recently, the elastomeric pump was shown to have technical difficulties with 20.5% not deflating correctly after being attached to the catheter resulting in insufficient analgesia. (69) The patient should be given emergency contact information and be informed of the signs and symptoms of excessive local anesthetic absorption. Typically the catheter remains in place for 2 to 3 days postoperatively, and an anesthesiologist or another health care worker guides the patient through the removal of the catheter over the phone.
The advent of nerve stimulation has been a great advance in the performance of regional anesthesia. Because the electrical properties of a nerve stimulator contribute to the performance of a successful PNB, practitioners should be familiar with the model used in their institution. Past models of electrical nerve stimulators have used a constant voltage system. However, the current, not the voltage, stimulates a nerve. Therefore, the amplitude of those nerve stimulators required constant adjustment to maintain a desirable current output. Ideally, the current output of a nerve stimulator should not change as the needle is being advanced through various resistances encountered from the tissue, needle, and connectors. Resistance is a measure of the resistance to flow of alternating current through tissue, and there is an inverse relationship between resistance and current thresholds necessary to elicit a motor response. (70) Most modern models deliver a constant current output in the presence of varied resistance. Settings that can be altered on these models include frequency, pulsewidth, and current milliamperes.
|01/19/2017 (+ 2017 Dates)|
|06/20/2017(+ 2017 Date)|
|02/18/2017(+ 2017 Dates)|