INTRODUCTION — Peripheral nerve blocks (PNB) are widely-used for surgical anesthesia as well as for both postoperative and nonsurgical analgesia. PNBs offer distinct benefits over general or neuraxial anesthesia in certain clinical situations [1]. In addition, PNBs provide analgesia that may be superior to other techniques for some patients.
This topic will discuss aspects of PNBs that are common to multiple blocks. Issues and techniques specific to particular blocks are discussed separately. (See 'Techniques for specific nerve blocks' below.)
USE OF NERVE BLOCKS
Indications — Indications for peripheral nerve blocks (PNBs) are diverse and vary widely. Blocks are often used to avoid the effects of alternative anesthetics or analgesics. The most common rationale for their use is to avoid side effects and complications of general anesthesia (GA), particularly respiratory-related effects, and to provide analgesia while minimizing opioid use.
Examples of circumstances in which PNBs might be preferable to GA as a sole anesthetic include:
●Patients at risk of respiratory depression related to GA (eg, obstructive sleep apnea, severe obesity, underlying pulmonary disease, advanced age)
●Patients with suspected difficult airway
●Patients at high risk of postoperative nausea and vomiting
●Patients who desire to remain conscious or avoid systemic medications (eg, fear of GA, pregnancy)
PNBs might be preferable to neuraxial anesthesia as a sole anesthetic in:
●Patients on antithrombotic medication or with a coagulopathy (only applies to PNBs in a compressible location)
●Patients in whom sympathetic blockade may cause hemodynamic problems (eg, aortic stenosis)
●Patients at high risk of urinary retention (eg, advanced age, male sex, benign prostatic hypertrophy, diabetes mellitus, hypertension, history of bladder or prostate surgery)
PNBs might provide the optimal means of analgesia in:
●Patients at risk of respiratory depression related to systemic or neuraxial opioids (eg, obstructive sleep apnea, severe obesity, underlying pulmonary disease, advanced age)
●Patients with another indication to minimize opioid use (eg, chronic opioid use, intolerance to opioids)
●Outpatients who will benefit from prolonged profound analgesia (using long-acting local anesthetics [LAs] or continuous PNB)
●Patients with acute, severe pain, poorly managed with systemic medication
Contraindications — There are few absolute contraindications to the use of PNBs; these include patient refusal or inability to cooperate and allergy to LAs. (See "Allergic reactions to local anesthetics".)
In some circumstances, risks from PNBs may be higher than usual, including:
●Active infection at the site of injection
●Patients on antithrombotic drugs or with coagulopathy, especially in noncompressible anatomic locations (eg, lumbar plexus, paravertebral, quadratus lumborum block, proximal sciatic nerve block)
●Preexisting neural deficits in the distribution of the block [2]
Patients on antithrombotic medication — Patients with an abnormal coagulation status have an increased risk of bleeding complications with invasive procedures, including PNBs. The risk is greatest with deep blocks (eg, paravertebral, lumbar plexus, infraclavicular, quadratus lumborum) in which compression of bleeding vessels is not possible, or in which an expanding hematoma would not be readily apparent. It may be reasonable to proceed with a PNB in a patient with abnormal coagulation status when the benefit of the block is felt to be greater than the risk of bleeding and any significant bleeding would be both apparent and manageable.
There is little literature to guide decisions to use or avoid PNBs in patients with abnormal coagulation, and existing guidelines are based primarily on expert opinion [3,4]. We follow the guidelines of the American Society of Regional Anesthesia and Pain Medicine (ASRA) for timing of blocks and antithrombotic medication [3] for patients having paravertebral, deep plexus, or peripheral nerve blocks not amenable to direct vascular compression. These guidelines are summarized in the table (table 1) (see "Neuraxial anesthesia/analgesia techniques in the patient receiving anticoagulant or antiplatelet medication"). Superficial blocks may be performed safely in anticoagulated patients in whom the benefits of the block are felt to be greater than the risk of bleeding.
Surgical patients on chronic antithrombotic medication usually have the medication discontinued or dosing modified to minimize surgical bleeding; if the medical condition of the patient requires continuation of antithrombotic medication, we do not perform "deep" nerve blocks. Management of antithrombotic medication in the perioperative period is discussed elsewhere. (See "Perioperative management of patients receiving anticoagulants".)
Bleeding from inadvertent vascular puncture during placement of a PNB may lead to nerve damage or significant blood loss. Nerve damage can result when a hematoma causes nerve compression within a closed space; this is of great concern with neuraxial blocks, but less common with PNBs. Significant blood loss is more common than neurologic damage in case reports of PNBs complicated by bleeding [3]. (See "Neuraxial anesthesia/analgesia techniques in the patient receiving anticoagulant or antiplatelet medication", section on 'Spinal epidural hematoma (SEH)'.)
TYPES OF NERVE BLOCKS
Single injection — Single-injection nerve block (sometimes called "single-shot" block) refers to a one-time injection of local anesthetic (LA) adjacent to the nerve or plexus for surgical anesthesia and/or analgesia. The duration and density of the block depends upon the dose, concentration, and pharmacology of the chosen LA; clinically effective duration may last from less than an hour to 24 hours or more.
Continuous nerve block — The continuous infusion of LA through a percutaneously-placed catheter adjacent to the peripheral nerve or plexus provides prolonged anesthesia/analgesia in the distribution of the nerve or plexus and may be managed as either an inpatient or an outpatient. Continuous blocks are useful in patients who are expected to have prolonged need for analgesia. This technique may increase patient satisfaction by decreasing pain, opioid use and side effects, and sleep disturbance [5]. (See 'Continuous catheter techniques' below.)
PATIENT PREPARATION — A directed medical history should include conditions that may impact the decision to perform a block, such as coagulopathy, respiratory compromise or pulmonary blebs (when a brachial plexus block is planned), or inability to use crutches (when a lower extremity block is planned). It is prudent to examine the patient for preexisting sensory or motor deficits in the distribution of the block; a patient with neurologic deficits may be more likely to develop new neurologic deficits following a block than a patient without preexisting deficits [2]. The patient should be made familiar with precautions and care needed during recovery of the block, as well as potential delayed complications.
Patients who receive a nerve block as a surgical anesthetic should follow normal fasting guidelines for surgery, whether or not general anesthesia is planned as deep sedation or general anesthesia may be necessary in cases of inadequate block.
Intravenous access should be obtained in all patients receiving a nerve block for a surgical procedure, due to the risk of complications such as vasovagal events, inadvertent IV injection, and local anesthetic (LA) toxicity, as well as the possible use of sedative medication(s). Lipid emulsion 20 percent and equipment for resuscitation should be available when any nerve block is placed. (See 'Local anesthetic systemic toxicity' below.)
Pre-procedure checklist — We perform a preprocedure time out prior to administering sedation for a peripheral nerve block (PNB). During this timeout, at the authors' institution a third party who is not involved in the block completes a checklist to verify the following, with patient confirmation:
●Patient name, date of birth, and medical record number, confirming that this information appears correctly on the patient’s wrist band
●Patient allergies and coagulation status
●Planned surgical procedure, including side of the body
●Surgical and anesthesia consents completed and signed
●Surgical site marked on the patient’s skin by the surgeon
●Block site marked on the patient’s skin by the anesthesiologists
Checklists have been shown to reduce medical errors, including in the operating room (see "Safety in the operating room", section on 'Checklists'). In a single institution retrospective review of blocks performed before and after implementation of a regional anesthesia specific preprocedure checklist, the use of a checklist was associated with a significantly lower incidence of wrong sided procedures (0 versus 4 per 10,000 blocks), though the absolute number of wrong sided blocks was small [6]. Risk reduction for wrong sided procedures is discussed separately. (See "Safety in the operating room", section on 'Wrong procedure or wrong site'.)
Sedation — PNBs in adult patients are administered with the patient awake to allow communication in order to minimize the potentially devastating sequelae of an intraneural injection. (See 'Nerve injury' below.)
Administration of an anxiolytic, possibly with an analgesic, improves patient comfort during the placement of most blocks; doses are titrated to patient comfort while maintaining a level of consciousness needed for communication and cooperation. Typical doses in healthy adults are intravenous (IV) midazolam 1 to 2 mg and fentanyl 25 to 100 mcg.
Monitoring — During the placement of peripheral nerve bocks, patients should be monitored with pulse oximetry, electrocardiography, and blood pressure monitoring, as described in the American Society of Anesthesiologists' Standards for Basic Anesthetic Monitoring (table 2) [7].
TECHNIQUES FOR SPECIFIC NERVE BLOCKS — Techniques for individual nerve blocks are discussed as follows:
●Upper extremity blocks
•Interscalene block – (See "Interscalene block procedure guide".)
•Suprascapular nerve block – (See "Upper extremity nerve blocks: Techniques", section on 'Suprascapular nerve block'.)
•Supraclavicular block – (See "Upper extremity nerve blocks: Techniques", section on 'Supraclavicular block'.)
•Infraclavicular block – (See "Infraclavicular brachial plexus block procedure guide".)
•Axillary block – (See "Axillary block procedure guide".)
•Intercostobrachial nerve block – (See "Upper extremity nerve blocks: Techniques", section on 'Intercostobrachial nerve block'.)
•Wrist blocks – (See "Upper extremity nerve blocks: Techniques", section on 'Wrist blocks'.)
•Digital nerve block – (See "Digital nerve block".)
●Lower extremity blocks
•Lumbar plexus (psoas compartment) block – (See "Lower extremity nerve blocks: Techniques", section on 'Lumbar plexus (psoas compartment) block'.)
•Femoral nerve block – (See "Lower extremity nerve blocks: Techniques", section on 'Femoral nerve block'.)
•Fascia iliaca (lateral femoral cutaneous) block – (See "Lower extremity nerve blocks: Techniques", section on 'Fascia iliaca (lateral femoral cutaneous) block'.)
•Obturator nerve block – (See "Lower extremity nerve blocks: Techniques", section on 'Obturator nerve block'.)
•Sciatic nerve block – (See "Sciatic blocks procedure guide".)
•Popliteal block – (See "Popliteal block procedure guide".)
•Adductor canal block – (See "Adductor canal block procedure guide".)
•Saphenous nerve block – (See "Lower extremity nerve blocks: Techniques", section on 'Saphenous nerve and adductor canal blocks'.)
•Ankle block – (See "Lower extremity nerve blocks: Techniques", section on 'Ankle block'.)
•Digital nerve block – (See "Digital nerve block".)
●Scalp block – (See "Scalp block and cervical plexus block techniques", section on 'Scalp block'.)
●Cervical plexus block – (See "Scalp block and cervical plexus block techniques", section on 'Cervical plexus blocks'.)
●Thoracic nerve blocks
•Intercostal nerve block – (See "Thoracic nerve block techniques", section on 'Intercostal nerve block'.)
•Thoracic paravertebral block – (See "Thoracic paravertebral block procedure guide".)
•Fascial plane blocks (Pecs I, Pecs II, serratus plane blocks, transversus thoracic muscle plane block, erector spinae plane(ESP) block) – (See "Thoracic nerve block techniques", section on 'Fascial plane blocks of the chest wall'.)
●Abdominal nerve blocks
•Transversus abdominis plane (TAP) block – (See "Transversus abdominis plane (TAP) blocks procedure guide".)
•Rectus sheath block – (See "Abdominal nerve block techniques", section on 'Rectus sheath block'.)
•Ilioinguinal and iliohypogastric nerve block – (See "Abdominal nerve block techniques", section on 'Ilioinguinal and iliohypogastric nerve block'.)
•Transversalis fascia plane block – (See "Abdominal nerve block techniques", section on 'Transversalis fascia plane block'.)
•Quadratus lumborum block – (See "Abdominal nerve block techniques", section on 'Quadratus lumborum block'.)
●Pudendal and paracervical blocks – (See "Pudendal and paracervical block" and "Vasectomy", section on 'Anesthesia'.)
BLOCK GUIDANCE TECHNIQUES — When performing a peripheral nerve block (PNB), the goal is to deposit the local anesthetic (LA) close to the nerve, avoiding intraneural injection that may cause direct trauma or toxicity to the nerve.
The nerve is located by anatomic landmarks in conjunction with one or more nerve identification techniques. Many experts feel that the use of these techniques decreases the risk of nerve trauma, but this has not been demonstrated, possibly due to the low baseline incidence of nerve injury.
We use ultrasound guidance rather than nerve stimulation for primary nerve localization for most peripheral nerve blocks. We suggest not using paresthesias to localize nerves for PNB, because of the risk of nerve injury. The technique of locating the nerve by deliberately eliciting paresthesias (described by the patient when the needle is in close proximity to the nerve) has generally been supplanted by techniques using ultrasound visualization, electrical nerve stimulation, or a combination of the two.
Ultrasound guidance — Ultrasound imaging permits direct visualization of needle location relative to target nerves, blood vessels, and related structures, as well as observation of the LA during and after the injection. Although results differ for different blocks, in general the use of ultrasound guidance (compared with nerve stimulator techniques):
●Improves the success rate of the block [8-10]
●Decreases placement time [10] and onset of block [8,9]
●Reduces the volume of LA required for successful block [11-14]
●Is associated with decreased vascular puncture and local anesthetic systemic toxicity (LAST) [10,15,16]
●Reduces incidence of pneumothorax and phrenic nerve block [17]
In a meta-analysis of 23 trials including over 2000 PNBs, compared with nerve stimulation alone, ultrasound guidance (with or without nerve stimulation) reduced the rate of vascular puncture (relative risk [RR] 0.23), pain during the procedure (RR 0.6), and the need for analgesic or anesthetic rescue (RR 0.4) [18]. There was no difference in the rate of postoperative neurologic complications. In a subsequent retrospective single institution study including approximately 23,800 nerve blocks, ultrasound guidance was associated with a lower incidence of short term nerve injuries (seven days to six months), compared with landmark based blocks (0.2 versus 0.5 percent), but no difference in long term injuries [19].
Patients in whom ultrasound guidance may be particularly advantageous include those with challenging anatomy (ie, scarring from previous surgeries, obese patients) and in those for whom improved visualization may improve safety, such as patients with abnormal coagulation status. Ultrasound may also be useful to "rescue" a block that is inadequate or incomplete, which may not be possible with a nerve stimulation technique. The nerve remains visible by ultrasound following LA injection, allowing the block to be repeated. In contrast, nerve stimulation is not possible once the nerve has been exposed to LA.
Disadvantages of ultrasound guidance include the need for specialized training, including use of ultrasound equipment and manipulation of needles under ultrasound guidance; these techniques can be more complex than nerve stimulator use in some situations. The equipment is also considerably more expensive than nerve stimulation equipment, including both ultrasound machines and sterile ultrasound probe covers.
An overview of the equipment and technique for ultrasound guidance for PNB is discussed here. These issues are discussed in detail separately. (See "Ultrasound for peripheral nerve blocks".)
Equipment for ultrasound guidance — Portable ultrasound machines provide imaging of adequate quality for the placement of PNBs. A variety of ultrasound machines are available.
The high-frequency (10 to 15 MHz) probe is used to identify more superficial nerves (eg, upper extremity blocks), whereas low-frequency (5 to 7 MHz) probes provide greater tissue penetration for identification of deeper nerves (eg, sciatic nerve blocks).
Technique for ultrasound guidance — After aseptic skin preparation, anatomic structures at the block site are identified using an ultrasound probe in a sterile plastic sheath with sterile conductive gel. These structures include the target nerve and other nearby nerves, blood vessels, and bony and soft tissue structures (eg, lung). When the optimal ultrasound view is achieved (by rotating, tilting, or moving the probe), the probe is held immobile; the block needle is then advanced, with movement only when the needle tip is seen. If the tip disappears from view, it may be located using hydro-localization (injecting small increments of saline or LA).
Structures of interest can be imaged either in the short-axis (cross-section) or the long-axis. A short-axis view becomes a long-axis view when the transducer is turned 90° in either direction. In general, regional anesthesiologists prefer to image nerves and blood vessels in short-axis, with a simultaneous anterior-posterior and lateral-medial perspective and use of color Doppler imaging to recognize blood vessels. In the long-axis view, the lateral-medial perspective is lost.
Two techniques are used for needle insertion: "in-plane" and "out-of-plane" (picture 1 and picture 2).
●Using the in-plane approach, the needle is inserted parallel to the long side of the transducer and is visualized in long-axis so the full needle is visualized. This permits the tip of the needle to be visualized at all times.
●In the out-of-plane view of the needle, a cross-section of the needle appears as a small dot (which can be difficult to see). It can be very challenging to maintain a view of the needle throughout the entire procedure, and it is difficult to distinguish the tip from other portions of the needle; this may increase the potential for direct needle trauma to blood vessels and nerves. The needle is inserted perpendicular to the long axis of the transducer. Out of plane technique is often used for deeper blocks where it is more difficult to visualize the entire length of the needle to the target nerve.
In contrast to the nerve stimulation technique, in which the LA is placed in a single location, using ultrasound, LA may be injected in multiple locations under direct vision to improve blockade of all portions of the nerve.
Nerve stimulator guidance — The equipment used for nerve stimulator guidance is less expensive than the equipment required for ultrasound guidance. There is concern that nerve stimulation may cause a higher incidence of nerve trauma than ultrasound guidance, as it does not allow direct visualization of needle and nerve, but studies have not confirmed this.
Use of nerve stimulation relies on anatomic knowledge of the approximate location of the target nerve for the initial placement of the needle. The location of the needle tip is then "fine-tuned" with small electrical pulses delivered through the block needle. The current required to elicit a motor response serves as a surrogate for the distance between the needle tip and the nerve; that is, less current is required as the needle is guided closer to the nerve.
Equipment for nerve stimulator guidance — Many commercial peripheral nerve stimulators are available, which deliver an adjustable electrical current (0.0 to 2.0 mA for a duration of 0.3 seconds at a frequency of 2 Hz) to the tip of a hollow, insulated disposable needle (eg, Stimuplex, ProBloc). The needles have tubing that is attached to a syringe for aspiration and injection of LA; this allows the needle to be kept immobile while injecting or changing the syringe. A wire between the needle, the stimulator, and a grounding electrode on the patient, allows the electrical pulse to be transmitted to stimulate the nerve (picture 3).
Technique for nerve stimulator guidance — After aseptic preparation of the site the stimulator needle is placed in the approximate vicinity of the nerve using anatomic landmarks. When the tip of the needle is near a motor nerve, a muscular response (a "twitch") occurs in the distribution of the nerve. For most blocks, the initial electrical current is 1 mA. When a motor response occurs in the distribution of the desired nerve, the needle is shifted to maximize the motor response; this may involve advancing, withdrawing, or shifting the angle of the needle. When a maximal twitch response is found, the current is decreased by a small amount and the needle shifted as needed to again maximize the motor response; this procedure is repeated until there is a twitch at 0.5 mA, but the twitch is abolished if the current is reduced below 0.4 mA.
The LA is injected once the needle position has been optimized, a few milliliters at a time, aspirating to check for intravascular placement before administering the subsequent increment. Injection should be stopped immediately if the patient complains of severe pain (possible intraneural injection), or exhibits signs or symptoms of LA toxicity (possible intravascular injection). The needle should be repositioned (slight withdrawal may be sufficient) and symptoms resolved prior to resuming injection
Stimulus threshold — Most experts recommend obtaining a motor response with a current less than or equal to 0.5 mA prior to injection of LA [20]. This places the needle at an optimal distance; when currents greater than this are needed, the block may have a lower success rate when stimulation persists at currents below 0.4 mA, the needle may be too close to the nerve with increased risk of intraneural injection. However, many factors can affect the relationship between the current that elicits a motor response and the distance between the needle tip and the nerve. Both ultrasound imaging and laboratory studies have shown that intraneural needle placement can occur at threshold currents ≥0.5 mA, and the absence of a motor response does not exclude intraneural needle placement [21].
Diabetes mellitus and diabetic neuropathy may increase stimulation thresholds [22,23]. In one study of popliteal sciatic nerve blocks in patients with and without diabetic neuropathy, stimulus thresholds for common peroneal nerve response were higher in patients with neuropathy, and 15 of 55 patients with neuropathy required a current >0.5 mA to evoke a response despite ultrasound confirmed intraneural needle placement or needle-nerve contact [22]. (See 'Complications' below.)
CONTINUOUS CATHETER TECHNIQUES — The placement of a catheter adjacent to a nerve or plexus allows the nerve block to be prolonged by intermittent injection or continuous infusion. Following location of the nerve by nerve stimulation or ultrasound guidance, a flexible catheter is placed alongside the nerve or plexus.
Continuous blockade can be used in either the hospital or ambulatory setting. A protocol to manage outpatient continuous nerve catheters should include: extensive preoperative oral and written instructions, contact with the patient on the first postoperative day, 24-hour anesthesiologist availability to manage questions or complications, and examination by a clinician (often the operating surgeon) within the first week following discharge. Under these conditions, the majority of patients are able to manage and remove their catheters at home [24,25]. Catheters are placed in a sterile fashion and generally may be left in place for up to seven days, but more typically, duration of use is limited by the volume of local anesthetic (LA) in the pump that is used after hospital discharge.
Equipment — There are numerous kits available to place catheters. They usually contain a needle and catheter and may also have equipment to secure the catheter in place. Most kits use a catheter-through-needle technique, but catheter-over-needle products are also available. It is possible to use a standard epidural tray for continuous catheter techniques, when longer needles are needed and nerve stimulation is not planned. A sterile ultrasound probe cover is also necessary. Many choose to use a medical glue to affix catheters, as it may decrease leakage when catheter-through-needle techniques are employed.
Technique — Continuous catheters may be placed using nerve stimulation and/or ultrasound techniques [26-30]. Use of ultrasound guidance compared with nerve stimulation may decrease the time from needle insertion to catheter placement, pain from the placement procedure [31], and the risk of accidental vascular puncture [16].
More meticulous sterile technique and draping are employed when continuous catheters are placed. A sterile ultrasound probe cover is used to keep the probe from directly touching the sterile block area, and a sterile drape or towels are used to drape out the procedural area. Antibiotics used for a surgical procedure may be helpful to minimize catheter infection, but are not generally indicated when continuous nerve catheters are placed for nonsurgical pain control.
The nerve is located in the same manner as for a single-shot peripheral nerve block (PNB; using nerve stimulation and/or ultrasound guidance), followed by advancement of a flexible catheter (through or over the needle) adjacent to the nerve, and fixation of the catheter to the skin at the site of insertion. Use of a medical glue (rather than suture or tape) to affix catheters may decrease leakage when catheter-through-needle techniques are employed.
DRUGS
Local anesthetics — Local anesthetics (LAs) are chosen according to onset of action, duration of action, degree of motor blockade, and toxicity; these are also influenced by the dose, concentration, and volume injected (table 3). The desired characteristics depend upon the circumstance: for example, motor blockade is desirable when a nerve block is used as the sole surgical anesthetic, but not when an outpatient is sent home with a block for analgesia; a long-acting LA is desirable for prolonged postoperative analgesia, but not when sensory examination is needed after the end of surgery. LAs with shorter duration of action (and generally quicker onset) include lidocaine and mepivacaine; longer-acting LAs include bupivacaine, levobupivacaine, and ropivacaine.
The concentration of LA determines the rate of diffusion into the nerve, with higher concentrations providing more rapid onset of nerve block.
More than one LA can be combined to decrease onset time while providing a longer duration of analgesia. However, mixing LAs can lead to unpredictable block characteristics and generally results in an onset and duration that is intermediate between the two LAs used [32].
Use of liposomal bupivacaine for peripheral nerve block (PNB) is discussed separately. (See "Clinical use of local anesthetics in anesthesia", section on 'Sustained release bupivacaine'.)
Adjuvants — A number of drugs have been added to LAs with the aim of decreasing onset time, increasing duration, increasing block density, or decreasing toxicity. Practice varies, and some of our contributors do not add any adjuvants, while others do.
There is limited available evidence regarding potential adjuvants for PNBs.
●Vasoconstrictors – Epinephrine is the most common vasoconstrictor added to PNBs, typically at a concentration of 1:200,000 to 1:400,000. It is used both to indicate rapid vascular uptake (eg, during inadvertent intravascular injection) and to decrease the absorption of the LA from tissues. Slower absorption may decrease potential toxicity (in vascular areas) and prolong the duration of the block. Side effects include tachycardia and a potential for ischemia to nerves and other tissues from decreased blood flow seen in animal models; based on these effects it is reasonable to use the lower concentration (1:400,000) in patients at risk of cardiac ischemia or those with possibly decreased perineural blood flow (eg, post-chemotherapy, with diabetes or vascular disease) [33].
●Sodium bicarbonate – Sodium bicarbonate is used to decrease onset time of the local anesthetic effect. Because local anesthetic molecules must be in the uncharged, basic form to cross the nerve membrane, the addition of sodium bicarbonate increases the proportion of active molecules. The quicker onset is most apparent in local anesthetics with commercially added epinephrine – which are formulated at a lower pH – but is often not of clinical significance [33].
The addition of sodium bicarbonate to local anesthetic for PNBs has increased speed of onset and quality of blocks in some trials, but not others [34-36].
●Opioids – The addition of fentanyl or morphine to PNBs does not clearly provide clinical benefit [37-39].
●Dexamethasone – Dexamethasone has been reported to prolong the duration of block when added to a variety of LAs for brachial plexus blocks [40-42], sciatic nerve block [43], and saphenous nerve block [44]. A meta-analysis of randomized trials reported that dexamethasone added to LA solutions prolonged PNBs (weighted mean difference 351 minutes), compared with LA solutions alone [45]. The optimal dose of dexamethasone added to LA solutions has not been established, but there appears to be no benefit to adding more than 4 to 5 mg to the LA solution [45-49].
Systemic administration of dexamethasone may also prolong analgesia after PNB, at doses commonly used to prevent postoperative nausea and vomiting. In one study, analgesia after interscalene block for shoulder surgery was prolonged in patients randomly assigned to receive dexamethasone IV (4 or 10 mg), compared with saline (block duration approximately 19.5 hours versus 12 hours) [50]. In contrast, in a small study of median nerve block in volunteers, time to recovery of sensory and motor function was similar in patients who received dexamethasone 2, 4, or 8 mg IV, or saline [51].
Trials comparing perineural with intravenous administration of dexamethasone have reported conflicting results, with some reporting no difference in duration of analgesia [43,52-57], and others reporting more prolonged analgesia with perineural administration [48,49,58-60]. One meta-analysis of 11 randomized controlled trials including approximately 900 patients compared analgesic efficacy of adjunctive perineural versus systemic dexamethasone for PNB [61]. Perineural dexamethasone modestly prolonged analgesia, compared with intravenous administration, when injected with bupivacaine (27 versus 22 hours), but not with ropivacaine. In another meta-analysis that included many of the same trials, perineural dexamethasone prolonged PNB by 3.77 hours (95% CI, 1.87 to 5.68 hours) compared with intravenous administration [62].
To date, multiple human studies have reported no neurologic complications after the use of perineural dexamethasone [46,61-64]. However, clinicians should realize that perineural administration of dexamethasone is an off label use, and should be aware of potential side effects of dexamethasone, including hyperglycemia, infection, and hypertension.
●Alpha2 agonists – In trials of the addition of clonidine to local anesthetic for PNB, the duration of sensory and motor blockade was prolonged, but with an increase in hypotension, bradycardia, and sedation [65]. The addition of dexmedetomidine may improve the onset and quality of PNBs [66], but is accompanied by prolonged motor block, and transient bradycardia and hypotension [67,68].
RECOVERY — The time to resolution of peripheral nerve blocks (PNBs) is extremely variable for different blocks, and between patients, even when all block-related factors are equal. Typical ranges for duration are presented in the table (table 3). When patients are discharged from the operating area or from the hospital prior to complete resolution of the block precautions should be taken to avoid injury to an insensate limb, and to avoid falls. Equipment such as slings, protective padding, and crutches may be needed.
Rebound pain — The term rebound pain (RP) refers to a substantial and rapid increase in pain once a PNB wears off. The reported incidence of rebound pain is as high as approximately 80 percent [69-71]. We do the following to minimize the risk of rebound pain:
●Educate patients – Inform patients about the risk of RP and advise them to take prescribed oral nonopioid analgesics (eg, acetaminophen, nonsteroidal antiinflammatory drugs) before the block is likely to wear off. We do not advise taking opioids before the block wears off, as this may increase the risk of respiratory depression, particularly in vulnerable patients.
●Time the block resolution – Choose local anesthetics to try to avoid having blocks wear off in the middle of the night, based on the time the block is placed (table 3).
Whether RP represents an actual hyperalgesic effect of the block or unmasking of the expected response in the absence of adequate systemic analgesics remains to be determined, and literature is limited. The latter mechanism is supported by some evidence that prolonging the effect of PNBs beyond the most painful immediate postoperative period may reduce the incidence of RP. Some studies have found reduced incidence of RP after the use of dexamethasone (IV or perineural) [69,70] or the use of continuous nerve block [72].
●In retrospective cohort study of over 900 patients who had PNBs for ambulatory surgery, approximately 50 percent experienced rebound pain [69]. RP was defined as an increase in numerical rating scale (NRS) pain scores from ≤3 (on a scale of 0 to 10) while the block was in effect to a score ≥7 within 24 hours of surgery. Risk factors for RP included younger age, female sex, and bone surgery. Administration of IV dexamethasone was associated with lower risk of RP. Conclusions from this study are limited by widely variable prescribed postoperative analgesics and lack of data on patient use.
●In a randomized trial of 70 patients who underwent arthroscopic shoulder surgery and had interscalene blocks, addition of perineural dexamethasone to the block solution reduced the incidence of RP from 83 to 37 percent, and increased the time until rebound pain occurred from 12 to 18 hours after performance of the block [70].
COMPLICATIONS
Nerve injury — Peripheral nerve injury is rare following regional anesthesia, making the incidence difficult to assess with confidence. Although the definition of injury varies between studies, the incidence of persistent symptoms of nerve dysfunction may be as high as 8 to 10 percent in the days following the block [73,74]. The majority are transient, lasting days to months. Major complications resulting in permanent (greater than six months) nerve damage ranged between 0.015 and 0.09 percent in three registry studies [75-77]. The reported incidence of nerve injury associated with continuous catheters is reported up to 0.21 percent [78,79].
Most nerve injuries are believed to occur secondary to intraneural injection, which can be categorized as extra fascicular or intrafascicular. Intrafascicular injections, particularly at high pressure, are felt to result in greater risk of nerve damage [80-85]. However, ultrasound images of intraneural injections without neurologic sequelae have refuted the previous belief that nerve damage is inevitable when local anesthetic (LA) is injected through the epineurium [86,87]. To minimize the incidence of intrafascicular injection, injection of anesthetic should be halted if the patient feels a paresthesia (shooting pain), or if the pressure required for injection is greater than usual; appropriate spread of the anesthetic should be observed when US guidance is used.
Additional risk factors for nerve injury remain uncertain, but may include [88]:
●Preexisting nerve pathology (including diabetes) may make a nerve more susceptible to injury [2,89,90].
●Use of standard longer-beveled needles may increase likelihood of intrafascicular injection with clinical nerve injury compared with short-beveled "block needles" [91,92].
●Continuous visualization of the block needle using ultrasound is presumed to decrease the risk of intrafascicular injection, but a reduced risk of nerve injury has not been demonstrated [93].
Nerve injury can also occur as a direct effect of LA drugs. All LAs have been shown to cause neurotoxicity in vitro at clinically relevant concentrations, but the relevance of these findings to clinical practice is unclear [94]. This issue is discussed separately. (See "Clinical use of local anesthetics in anesthesia", section on 'Neurotoxicity of local anesthetics'.)
Symptoms of nerve injury are primarily sensory (pain, tingling, or paresthesias), but can include any combination of motor or sensory deficits depending on the nerve involved and severity of the injury. It is not always clear whether a nerve block is the cause of a patient's symptoms [95]. For example, in a prospective study of 1010 peripheral nerve blocks (PNBs), 0.6 percent of patients reported neurologic symptoms at six months, of which at least two-thirds were judged by a neurologist to be due to causes unrelated to the block [74].
Most symptoms resolve within six months; if symptoms are either severe or persistent, the patient should be referred to a specialist.
Hematoma — Inadvertent puncture of nearby vascular structures can lead to perineural hematoma. It is prudent to avoid performing PNBs in patients with an abnormal coagulation status in anatomic locations in which application of pressure to the puncture site is not possible. The vast majority of hematomas may be controlled with direct pressure to the needle puncture site; rarely, surgical decompression may be required. (See 'Patients on antithrombotic medication' above.)
Local anesthetic systemic toxicity — Local anesthetic systemic toxicity (LAST) can occur whenever LAs are administered, and can occur with all LAs and any route of administration. Severe LAST can result in central nervous system toxicity, including seizures, and/or cardiovascular toxicity, including arrhythmias and cardiac arrest. The signs, symptoms, and treatment of LAST are shown in a table (table 4). The pathopharmacology, risk factors, prevention, and management of LAST are discussed separately. (See "Local anesthetic systemic toxicity".)
Allergic reaction — Most adverse reactions to LAs are nonallergic. However, two different types of allergic reactions to LAs have been described:
●Allergic contact dermatitis and delayed swelling at the site of administration – Affected patients develop a localized eczematous and pruritic rash within 72 hours at the site of LA administration. (See "Allergic reactions to local anesthetics", section on 'Rare: Delayed reactions (contact dermatitis or local swelling)'.)
●Urticaria and anaphylaxis – These types of reaction are rare and the data implicating LAs are limited to case reports. (See "Anaphylaxis: Emergency treatment" and "Allergic reactions to local anesthetics", section on 'Rare: Immediate reactions (urticaria and anaphylaxis)'.)
An algorithm for preprocedural evaluation of patients who report history of allergic reactions to LAs is provided (algorithm 1).
Infection — Infection risk for single-shot PNB is negligible.
Bacterial colonization of peripheral nerve catheters ranges from 7.5 to 57 percent [96,97], but risk of infection is low (0 to 3.2 percent) [98]; risk of infection is increased in patients with critical care unit admission, trauma, immune compromise, male sex, and the absence of antibiotics, and may be minimized by removing the catheter within 48 to 72 hours of placement [78,79,96,98-100].
Myotoxicity — Myotoxicity is a known rare complication of injection of LAs. The true incidence of myotoxicity after PNBs is unknown; it is usually associated with prolonged administration or high concentration of LA [101]. Symptoms usually appear within several days and can take up to a year to resolve.
Secondary injury — The use of more dilute LA, lower volume injections, and perineural catheters may minimize dense sensory and motor blocks and prevent injury.
●Patients with reduced sensation after nerve block are at risk of tissue or nerve injury in the blocked extremity; clear instructions to protect the extremity for the duration of the block should be given to nursing staff and patients.
●Motor block associated with lower extremity blocks may cause falls. Patients should be assisted with ambulation until resolution of the motor block has been confirmed.
Complications related to specific blocks are discussed separately. (See "Upper extremity nerve blocks: Techniques" and "Lower extremity nerve blocks: Techniques" and "Thoracic nerve block techniques".)
PATIENTS WITH SUSPECTED OR CONFIRMED COVID-19 — Understanding of coronavirus disease 2019 (COVID-19) is evolving. UpToDate has added information on many aspects of COVID-19, including infection control, airway and other aspects of anesthetic management, and general and intensive care in topic reviews linked here, and others. Regional anesthesia is not contraindicated in patients with COVID-19. Regional anesthesia may avoid the need for general anesthesia (GA) and airway management, with associated aerosolization of airway secretions and viral spread. The American Society of Regional Anesthesia and Pain Medicine and the European Society of Regional Anesthesia and Pain Therapy have published practice recommendations for neuraxial anesthesia and peripheral nerve blocks (PNBs) for patients with COVID-19. Important considerations specific to PNBs, based on expert opinion and what is known about the virus, include the following:
●The decision to perform surgery with regional anesthesia alone should be considered carefully, including the likelihood that conversion to GA might be required. Unplanned conversion to GA should be avoided if at all possible.
●If supplemental oxygen is required during regional anesthesia, the lowest flows possible to maintain oxygenation should be used. Sedation should be titrated to effect, and doses may need to be reduced to minimize respiratory depression and the need for supplemental oxygen.
●Patients should wear a surgical mask at all times, including throughout the procedure.
●If possible, choose blocks that are least likely to cause respiratory compromise (eg, perform phrenic nerve sparing upper extremity blocks).
●Cover ultrasound equipment with plastic drapes.
●Consider the benefits and risks of adjuvant drugs for PNBs (eg, immunosuppression with dexamethasone, and hypotension, bradycardia, or sedation with clonidine or dexmedetomidine). (See 'Adjuvants' above.)
UpToDate topic reviews of COVID-19 related issues include the following:
●(See "COVID-19: Management in hospitalized adults".)
●(See "COVID-19: Infection prevention for persons with SARS-CoV-2 infection".)
SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Local and regional anesthesia" and "Society guideline links: Local anesthetic systemic toxicity".)
INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5th to 6th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10th to 12th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.
Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)
●Basics topic (see "Patient education: Anesthesia (The Basics)")
SUMMARY AND RECOMMENDATIONS
●Uses – Peripheral nerve blocks (PNBs) are widely used for surgical anesthesia as well as for both postoperative and nonsurgical analgesia. Although there are no specific indications, they are often used to avoid general anesthesia and to minimize the use of opioids. (See 'Use of nerve blocks' above.)
●Patients with coagulopathy – Nerve blocks in deep anatomic locations (eg, plexus blocks, paravertebral blocks) and blocks near major blood vessels that are not easily compressed are generally avoided in patients with abnormal coagulation status (table 1). (See 'Patients on antithrombotic medication' above.)
●Block guidance techniques – Peripheral nerves are located by direct visualization with ultrasound, by using motor responses to an electrical nerve stimulator, or both. We use ultrasound guidance rather than nerve stimulation for primary nerve localization for most PNBs. The use of ultrasound guidance generally improves the quality of the block, decreases placement time and time to onset, decreases the volume of LA required, and decreases incidence of some complications; there is insufficient evidence to demonstrate any difference in neurologic complications with either technique. We suggest not deliberately eliciting paresthesias to localize nerves for PNB because of the risk of nerve injury (Grade 2C). (See 'Block guidance techniques' above.)
●Single injection versus perineural catheter – PNB may be performed as a one-time administration of local anesthetic (LA; single-injection) or an infusion of LA through a perineural catheter (continuous nerve block). (See 'Types of nerve blocks' above.)
Continuous catheter techniques allow nerve blocks to be prolonged by intermittent injection, or continuous infusion. Continuous blockade can be used in either the in-patient or ambulatory setting. (See 'Continuous catheter techniques' above.)
●Drugs for nerve block – PNBs are performed with injection of local anesthetics, with or without adjunctive medications. (table 3) (See 'Drugs' above.)
●Complications – Complications that may occur with PNBs include nerve injury, hematoma, local anesthetic systemic toxicity (LAST), and secondary tissue injury. Infection and LA allergy are rare. Other complications may occur with specific blocks. (See 'Complications' above.)
LAST can occur whenever local anesthetic is injected by any route. A rapid overview of risk factors, signs and symptoms, and management of LAST is shown in a table. (table 4)
