The pharmacologic properties of individual local anesthetic agents become clinically meaningful only in the context of how and where they are administered. The route of delivery, whether topical, infiltration, peripheral nerve block, or neuraxial, determines the anatomic target, the volume and concentration required, the rate of systemic absorption, and the specific risks the clinician must anticipate and manage. Over the past two decades, the widespread adoption of ultrasound guidance for peripheral nerve blocks has transformed regional anesthesia from an anatomy-based practice relying on fascial planes and nerve stimulator endpoints into an image-guided discipline in which the needle, the nerve, and the spread of injectate are visualized in real time.1 This shift has not changed the pharmacology of local anesthetics, but it has changed the volume requirements, reduced the need for high-concentration solutions, and expanded the range of patients in whom regional techniques can be safely performed. This module surveys the principal clinical applications of local anesthetics from topical preparations through neuraxial blockade, with emphasis on agent selection, concentration and volume rationale, anatomic considerations, and the integration of regional techniques into contemporary perioperative analgesic care.
Topical local anesthetics act by diffusing across epithelial surfaces to reach superficial sensory nerve endings, producing anesthesia of the skin or mucous membrane without the need for injection. The depth and completeness of topical anesthesia depend on the concentration applied, the duration of contact, the integrity of the epithelial barrier, and the physicochemical properties of the agent, particularly its lipid solubility and the fraction present as the membrane-permeable free base.2 Intact keratinized skin is a formidable barrier to drug penetration; mucous membranes are far more permeable and allow rapid systemic absorption, which must be accounted for in maximum dose calculations for mucosal applications.
Eutectic Mixture of Local Anesthetics (EMLA) cream, a 1:1 mixture of lidocaine 2.5% and prilocaine 2.5%, remains the most extensively studied topical preparation for intact skin analgesia and is the standard agent for reducing pain from venipuncture, IV cannulation, lumbar puncture, and superficial dermatologic procedures in both pediatric and adult patients.1 2 The eutectic formulation reduces the melting point of both agents to below body temperature, creating an oil-phase system in which both drugs are present at concentrations far exceeding their individual aqueous solubilities (approximately 80 mg/g combined) and in predominantly free base form, enabling penetration through the stratum corneum. Effective analgesia requires application under occlusion for a minimum of 45–60 minutes for venipuncture sites and 60–90 minutes for deeper procedures; maximum depth of analgesia is approximately 3–5 mm after 60 minutes and up to 5 mm after 120 minutes of application.2
The primary safety concerns with EMLA are methemoglobinemia from prilocaine (relevant particularly in neonates and glucose-6-phosphate dehydrogenase (G6PD)-deficient patients, as discussed in CNS-02) and local vasoconstriction, a blanching effect mediated by the local anesthetic effect on superficial vasculature, which can make venipuncture more technically challenging by reducing visible vein caliber.2 Application over large areas, particularly in infants, requires attention to total prilocaine dose relative to body weight.
LMX-4 (lidocaine 4% liposomal cream) provides a useful alternative to EMLA that avoids the prilocaine methemoglobinemia risk entirely. The liposomal formulation enhances dermal penetration of lidocaine and achieves effective analgesia in 30 minutes without occlusion in many patients, making it more convenient for procedural settings where lead time is limited.2 Its analgesic depth and duration are comparable to EMLA for superficial procedures. Tetracaine 4% gel (Ametop) offers a third option with onset of 30–45 minutes and the advantage of producing vasodilatation rather than vasoconstriction at the application site, which facilitates venipuncture, a clinically relevant distinction in pediatric practice where vein visualization is already challenging.2
Mucous membranes, including the oropharynx, larynx, trachea, urethra, rectum, and nasal passages, lack the keratinized barrier of intact skin and allow rapid drug absorption, enabling onset of topical anesthesia within minutes but also creating meaningful risk of systemic absorption and toxicity if doses appropriate for mucosal application are not respected.2 Lidocaine is the dominant topical agent for airway anesthesia, available as viscous lidocaine 2% (for oropharyngeal application), lidocaine 4% solution (for nebulization, spray, or transtracheal injection), and lidocaine 10% pump spray (for oropharyngeal surface anesthesia prior to intubation or upper endoscopy). The maximum dose of topical lidocaine for airway anesthesia should not exceed 4–5 mg/kg, and this limit must be respected regardless of the perceived safety of the topical route; plasma lidocaine levels following mucosal application can approach or exceed those achieved by peripheral nerve block injection at equivalent doses.2 Cocaine 4–10% solution is used topically in rhinologic and otolaryngologic procedures for its unique combination of anesthesia and vasoconstriction, as discussed in CNS-02, with a practical ceiling of approximately 200 mg total dose in healthy adults.
Benzocaine 20% spray, widely used for oropharyngeal anesthesia prior to endoscopy, carries a well-characterized risk of methemoglobinemia and should be applied in the minimum effective number of sprays, with each one-second spray delivering approximately 60–120 mg of benzocaine depending on the device; careful attention to the number of sprays delivered is essential.2
Topical urethral anesthesia with lidocaine 2% gel (Xylocaine gel) is standard practice prior to urethral catheterization, cystoscopy, and urodynamic studies. The gel provides both lubrication and local anesthesia; onset requires 2–5 minutes of contact time before instrumentation, and systemic absorption through urethral mucosa is clinically meaningful at doses used for cystoscopy preparation (typically 10–20 mL). In patients with urethral trauma or significant mucosal disruption, absorption may be accelerated, and the clinician should be alert to early signs of systemic lidocaine toxicity, including perioral numbness, tinnitus, and lightheadedness, particularly when the maximum recommended mucosal dose has been approached.2
Infiltration anesthesia involves direct injection of local anesthetic into the tissue surrounding the operative site, producing anesthesia by blocking the small terminal branches of sensory nerves within the injected field rather than targeting a named nerve trunk proximally.1 It is the most widely used form of local anesthesia across all clinical specialties, applicable to wound repair, skin biopsy, minor dermatologic and office-based surgical procedures, port placement, and diagnostic procedures, and the technical skills required are within the competence of any clinician who performs procedures.
The choice of agent for infiltration anesthesia is driven primarily by required duration. For procedures expected to last 30–60 minutes, lidocaine 1% or 0.5% with epinephrine 1:200,000 provides reliable onset in 2–5 minutes and duration of 60–90 minutes.1 For procedures requiring 2–4 hours of analgesia, bupivacaine 0.25% with epinephrine or ropivacaine 0.2–0.375% extends duration to 3–6 hours. Mixing lidocaine with bupivacaine to achieve faster onset than bupivacaine alone while extending duration beyond lidocaine alone is a widespread clinical practice; while the pharmacologic rationale is sound in principle, the clinical evidence that mixtures produce meaningfully better outcomes than either agent alone is modest, and the practice introduces the risk of calculation errors in maximum dose management.1
The volume of local anesthetic required for infiltration anesthesia is often the limiting factor rather than concentration, since dilute solutions (lidocaine 0.5%, bupivacaine 0.125%) are pharmacologically effective for infiltration into well-vascularized tissue and allow larger volumes to be used within safe dose limits. Buffering infiltration solutions with sodium bicarbonate (1 mEq per 10 mL of lidocaine) significantly reduces injection pain by raising pH toward physiologic, which both reduces the proportion of ionized (more irritant) drug and approaches the pKa equilibrium more favorably; the sting of subcutaneous local anesthetic injection is attributable primarily to the acidity of the commercial preparation (pH 4–5) rather than the drug itself.3 4 Warming the solution to body temperature provides additional reduction in injection discomfort. Slow injection through a fine-gauge needle, with gentle pressure applied as the needle advances, further minimizes procedural pain and is a simple courtesy to the patient that costs nothing.
Field block anesthesia extends the infiltration concept by targeting the sensory nerve supply to a region rather than the operative site itself, injecting local anesthetic in a perimeter or ring around the planned procedure to interrupt all sensory afferents entering the field.1 The ring block of the digit, which involves infiltrating local anesthetic circumferentially at the base of the digit to block the paired digital nerves, is one of the most commonly performed field blocks in emergency medicine and is distinguished from a true peripheral nerve block by the circumferential nature of the injection rather than targeting individual named nerve trunks. Field blocks of the scalp, anterior abdominal wall, and chest wall can be performed with surface landmark guidance and provide useful analgesia for minor procedures in anatomically defined territories.
Peripheral nerve blocks target named nerve trunks or plexuses at anatomically defined locations, producing regional anesthesia of the distribution supplied by the blocked nerve or nerves. They are the foundation of modern regional anesthesia practice and, when performed with ultrasound guidance, offer surgical anesthesia and postoperative analgesia that is superior to general anesthesia alone for many extremity and truncal procedures in terms of opioid-sparing, early mobilization, patient satisfaction, and facilitation of ambulatory surgery.1
The volume of local anesthetic injected at a peripheral nerve block site determines the spread of drug through the perineural and fascial space; the concentration determines the density of block (sensory block alone versus combined sensorimotor block) and, to a lesser extent, the onset speed. For ultrasound-guided blocks where drug can be deposited precisely adjacent to the target nerve, smaller volumes (10–15 mL) are effective for many blocks that historically required 30–40 mL using landmark-based techniques.5 This volume reduction translates directly into a reduction in peak plasma concentrations and systemic toxicity risk, a practical safety benefit of ultrasound guidance beyond its accuracy advantage. The total dose of local anesthetic across all blocks performed in a single patient must be tracked against the maximum recommended dose for the agent used, particularly when multiple blocks are planned simultaneously (e.g., femoral plus sciatic block for lower extremity surgery, or interscalene plus pectoral block for complex shoulder procedures).8
Long-acting agents (bupivacaine 0.25–0.5%, ropivacaine 0.375–0.5%, or levobupivacaine 0.25–0.5%) are the workhorses of peripheral nerve block analgesia, providing 8–16 hours of surgical anesthesia and postoperative analgesia, extended further with dexamethasone or other adjuvants as described in CNS-02. Intermediate-acting agents (lidocaine 1–1.5%, mepivacaine 1–1.5%) are used when shorter duration is clinically appropriate (e.g., for diagnostic blocks, outpatient procedures where prolonged motor block would delay discharge or ambulation, or when a patient-specific reason contraindicates long-acting agents).1
The brachial plexus arises from the ventral rami of C5–T1, passes between the anterior and middle scalene muscles (interscalene level), traverses the posterior triangle of the neck (supraclavicular level), crosses under the clavicle and over the first rib (infraclavicular level), and divides into its terminal branches within the axilla (axillary level). Each anatomic level provides anesthesia of a different distribution and carries a different risk profile, and agent selection must account for the site of injection in the context of the systemic absorption hierarchy described in CNS-01.6 The interscalene block targets the brachial plexus at the level of the nerve roots and trunks as they emerge between the scalene muscles, providing reliable anesthesia of the shoulder, proximal humerus, and lateral arm, making it the block of choice for shoulder arthroplasty, rotator cuff repair, acromioclavicular procedures, and proximal humeral fractures.5 The proximity of the phrenic nerve (C3–C5) to the injection site means that ipsilateral phrenic nerve block and hemidiaphragm paresis occur in virtually 100% of cases at standard volumes, reducing ipsilateral pulmonary function by approximately 25%.
This is clinically well-tolerated by patients with normal baseline pulmonary reserve but represents a relative contraindication in patients with contralateral phrenic nerve palsy, severe chronic obstructive pulmonary disease (COPD) with FEV1 less than 50% predicted, or other conditions reducing pulmonary reserve.5 Other consistent complications of interscalene block include recurrent laryngeal nerve block (producing transient hoarseness, a nuisance) and Horner syndrome (ptosis, miosis, anhidrosis from stellate ganglion involvement, benign and self-limiting). Vertebral artery injection is a catastrophic but rare complication that must be prevented by meticulous attention to needle tip position under ultrasound visualization and continuous aspiration before injection.
The supraclavicular block targets the brachial plexus at the level of the trunks and divisions as they compact into the tightest anatomic arrangement above the clavicle (the "corner pocket" of regional anesthesia), providing reliable and rapid anesthesia of the entire upper extremity below the shoulder with a single injection.5 The proximity of the pleural apex (the lung apex extending above the clavicle) makes pneumothorax a recognized complication of supraclavicular block, occurring in approximately 0.5–1% of cases with landmark-based techniques and substantially less with ultrasound guidance due to real-time visualization of the pleural surface. The subclavian artery lies immediately medial and deep to the brachial plexus at this level; intravascular injection is prevented by careful ultrasound visualization and aspiration technique. Ropivacaine 0.5% or bupivacaine 0.375–0.5% in volumes of 20–25 mL provides excellent surgical anesthesia for forearm and hand surgery with onset of 15–25 minutes.
The infraclavicular block targets the brachial plexus at the level of the cords as they surround the axillary artery below the clavicle, providing reliable upper extremity anesthesia comparable to the supraclavicular approach with a reduced pneumothorax risk given the more inferior needle trajectory away from the pleural apex.5 It is technically demanding under ultrasound due to the depth of the plexus in this location and the need to visualize three cords surrounding the axillary artery, but produces excellent results in experienced hands and is preferred by many practitioners for elbow, forearm, and hand surgery when shoulder-level anesthesia is not required.
The axillary block targets the terminal branches of the brachial plexus, including the median, ulnar, radial, and musculocutaneous nerves, within the axilla, where they are superficial, compressible, and readily visualized with ultrasound.5 It is the safest brachial plexus block from a systemic complication standpoint, remote from the pleura and vertebral vasculature, and is an excellent choice for forearm and hand procedures. The musculocutaneous nerve, which has separated from the plexus sheath at this level and lies within the coracobrachialis muscle, must be blocked separately with a dedicated injection to ensure complete anesthesia of the lateral forearm, a step that is easily accomplished under ultrasound guidance and is one of the most common sources of incomplete axillary block when omitted.5
Lower extremity regional anesthesia is anatomically more complex than upper extremity blockade because the limb receives innervation from two distinct nerve plexuses, the lumbar plexus (L1–L4), which gives rise to the femoral, obturator, and lateral femoral cutaneous nerves, and the sacral plexus (L4–S3), which gives rise to the sciatic nerve and its tibial and common peroneal divisions.1 Comprehensive lower extremity surgical anesthesia therefore generally requires blockade of components from both plexuses, a consideration that significantly affects total local anesthetic dose calculations and procedural planning.
The femoral nerve block, targeting the femoral nerve immediately lateral to the femoral artery in the femoral triangle below the inguinal ligament, has been a cornerstone of lower extremity regional anesthesia for knee and thigh procedures for decades, providing analgesia to the anterior thigh, medial knee, and medial leg via the saphenous nerve branch.7 For total knee arthroplasty, femoral nerve block produces excellent quadriceps-involving analgesia but causes significant quadriceps weakness that impairs early ambulation and physical therapy participation, a recognized limitation in the context of enhanced recovery programs that prioritize early mobilization.
The adductor canal block has largely supplanted the femoral nerve block for knee arthroplasty analgesia in most centers precisely because it is a predominantly sensory block: the adductor canal at mid-thigh level contains the saphenous nerve and the nerve to the vastus medialis but not the main motor branches to the quadriceps, producing equivalent or near-equivalent knee analgesia with substantially less quadriceps weakness.7 This motor-sparing characteristic facilitates safer early ambulation and physiotherapy, and multiple randomized trials and meta-analyses have confirmed non-inferiority of adductor canal block compared to femoral nerve block for pain scores and opioid consumption in the early postoperative period after total knee arthroplasty, with superior ambulation outcomes. Ropivacaine 0.5% or bupivacaine 0.25–0.375% in volumes of 15–20 mL is standard for adductor canal block; continuous catheter techniques extending block duration over 48–72 hours are increasingly used for total knee arthroplasty and other procedures requiring prolonged lower extremity analgesia.
The sciatic nerve is the largest peripheral nerve in the body, arising from the sacral plexus (L4–S3) and providing motor and sensory innervation to the posterior thigh, the entire lower leg below the knee (with the exception of the medial aspect supplied by the saphenous nerve), and the foot. It can be blocked at several levels, including the subgluteal approach targeting the nerve as it exits the greater sciatic notch beneath the gluteus maximus, the popliteal approach targeting the nerve as it divides into the tibial and common peroneal branches in the popliteal fossa, and the anterior approach targeting the nerve in the proximal thigh, each offering distinct advantages for different surgical scenarios.1
The popliteal sciatic block is the most commonly performed lower extremity peripheral nerve block and is the analgesic foundation for foot and ankle surgery, providing complete anesthesia of the foot and ankle (combined with saphenous nerve block for medial ankle coverage) with an excellent safety profile and straightforward ultrasound visualization.5 Ropivacaine 0.5% or bupivacaine 0.375–0.5% in volumes of 20–25 mL provides 12–18 hours of analgesia for foot and ankle procedures, a duration that covers the most painful early postoperative period and substantially reduces opioid requirements.
The past fifteen years have seen an extraordinary expansion in the repertoire of fascial plane and truncal nerve blocks, driven by the recognition that effective analgesia for thoracic and abdominal surgery cannot rely on neuraxial techniques alone and that ultrasound-guided interfascial injections can target the nerve branches supplying specific regions of the trunk with a favorable safety profile compared to epidural or intrathecal approaches.5 The transversus abdominis plane (TAP) block targets the terminal branches of the thoracolumbar nerves (T10–L1) as they traverse the fascial plane between the internal oblique and transversus abdominis muscles, providing analgesia to the anterior abdominal wall from the umbilicus to the pubis.
It is applicable to a wide range of abdominal procedures, including appendectomy, inguinal hernia repair, cesarean delivery, hysterectomy, and laparoscopic abdominal surgery, and is well-established as a component of multimodal analgesic regimens in enhanced recovery protocols.1 The analgesic efficacy of TAP block is predominantly somatic: it does not block the visceral afferents from intraperitoneal structures, and should therefore be understood as a component of multimodal analgesia rather than a substitute for systemic or neuraxial analgesics for procedures with significant visceral pain components. Bupivacaine 0.25% or ropivacaine 0.2–0.375% in bilateral volumes of 20 mL per side provides 8–12 hours of abdominal wall analgesia, requiring careful attention to maximum dose in the context of the patient's weight and other local anesthetics administered.8
The erector spinae plane (ESP) block, in which local anesthetic is injected in the fascial plane deep to the erector spinae muscle at a thoracic or lumbar level, has gained rapid and widespread adoption for thoracic and abdominal wall analgesia despite a mechanistic understanding that remains incompletely characterized. The purported mechanism involves medial spread of injectate to reach the dorsal and ventral rami of thoracic spinal nerves, as well as possible epidural and paravertebral spread in some cases, producing multilevel dermatomal analgesia that extends both cephalad and caudad from the injection site.5 Clinical evidence supports its utility for rib fractures, thoracic surgery, breast surgery, and upper abdominal procedures, with a safety profile that is more favorable than thoracic epidural or paravertebral block due to the distance of the injection from the neuraxis and major vasculature. The PECS I and PECS II blocks (pectoral nerve blocks) and the serratus anterior plane block target the lateral chest wall and breast, providing analgesia for breast surgery, thoracoscopy, and lateral rib procedures with straightforward ultrasound-guided technique and an excellent safety profile.5
Neuraxial anesthesia, which encompasses the introduction of local anesthetic into the subarachnoid space (spinal anesthesia) or the epidural space (epidural anesthesia), is the most potent and comprehensive form of regional anesthesia, capable of producing complete surgical anesthesia of the lower half of the body from a single injection or a controllable band of analgesia through an indwelling catheter.9 The pharmacology of neuraxial local anesthesia differs in important ways from peripheral nerve block pharmacology: the subarachnoid and epidural spaces present unique anatomic compartments with distinct barriers to drug distribution, and the proximity of injection to the spinal cord and brainstem demands an understanding of how drug spreads within these spaces and what determines the level and density of block achieved.
In spinal anesthesia, local anesthetic is injected into the cerebrospinal fluid (CSF) of the subarachnoid space, typically between L3–L4 or L4–L5 in adults (below the termination of the spinal cord at L1–L2), where it mixes with CSF and bathes the nerve roots of the cauda equina and, to a variable extent, the lower thoracic spinal cord.9 The primary determinants of block spread within the subarachnoid space are baricity of the solution relative to CSF, patient position at and after injection, and the total mass of drug (dose in milligrams); volume and concentration are relevant only insofar as they determine total mass. A hyperbaric solution (denser than CSF, achieved by mixing local anesthetic with 8% dextrose) sinks with gravity to the most dependent parts of the subarachnoid space, allowing the clinician to control block level by patient positioning: Trendelenburg position to encourage cephalad spread, sitting position to encourage sacral (saddle block) anesthesia. A hypobaric solution (less dense than CSF, achieved by dilution with sterile water) rises to the non-dependent compartment, enabling selective blockade of the ipsilateral side in a lateral decubitus patient. Isobaric solutions remain at the level of injection with minimal positional influence.9
Hyperbaric bupivacaine 0.5% (bupivacaine prepared in 8% dextrose) is the most widely used spinal anesthetic agent globally, producing dense and reliable surgical anesthesia with excellent sensorimotor block characteristics and a duration of 90–150 minutes depending on dose.9 Standard doses for lower abdominal, pelvic, and lower extremity surgery range from 10 to 15 mg (2–3 mL of 0.5%); for perineal and saddle block procedures, 5–7.5 mg (1–1.5 mL) in the sitting position suffices. Dose reduction is recommended in elderly patients (in whom CSF volume is relatively reduced and spread is more extensive for a given dose), pregnant patients at term (in whom engorged epidural veins reduce subarachnoid volume and spread is exaggerated), and very tall or obese patients (where dose adjustment is guided more by clinical experience than by pharmacokinetic formulae).9 Isobaric bupivacaine 0.5% is used when block spread independent of position is desired, as in hip fracture repair in elderly patients who cannot be positioned for hyperbaric injection, though its spread is less predictable than the hyperbaric preparation.
Intrathecal opioids, including fentanyl 10–25 μg or morphine 50–200 μg, are routinely added to spinal local anesthetic for major lower extremity, hip, and cesarean delivery procedures, providing synergistic analgesia through spinal μ-opioid receptor activation and extending postoperative analgesia beyond the duration of the local anesthetic block alone; intrathecal morphine specifically provides 12–24 hours of postoperative analgesia at doses of 100–200 μg, with the tradeoff of monitoring requirements for delayed respiratory depression.9
Chloroprocaine for spinal anesthesia (preservative-free formulation) offers a short-duration alternative to bupivacaine for procedures expected to last 30–60 minutes where rapid recovery and early ambulation are priorities: day-case inguinal hernia repair, knee arthroscopy, and outpatient gynecologic procedures.1 Its plasma half-life is negligible even when systemically absorbed, and its lack of the transient neurologic symptoms (TNS) association that limits intrathecal lidocaine makes it an attractive agent for ambulatory spinal anesthesia. Typical doses are 30–45 mg of preservative-free 1% or 2% chloroprocaine, with onset of dense block in 5–10 minutes and resolution typically complete by 60–90 minutes.
Epidural anesthesia differs from spinal anesthesia in that local anesthetic is deposited in the epidural space, the potential space between the dura mater and the ligamentum flavum / vertebral periosteum, rather than in the CSF.9 Drug diffuses across the dura to reach the CSF and nerve roots, enters the nerve root sleeves (dural cuffs) where the barrier is thinnest, and is partially absorbed into the epidural vasculature and adjacent fat. Because drug must cross the dural barrier and distribute through a larger, less confined space, epidural anesthesia requires substantially larger volumes and higher doses than spinal anesthesia to achieve equivalent block levels (typically 15–25 mL of local anesthetic solution for a lumbar epidural versus 2–3 mL for a spinal), and onset is correspondingly slower (10–20 minutes versus 3–5 minutes for spinal).9
The epidural technique offers the decisive advantage of catheter placement, allowing continuous or repeated bolus dosing to extend analgesia or anesthesia over hours to days, a capability that has made epidural catheters the foundation of labor analgesia, major thoracic and abdominal surgical anesthesia, and postoperative analgesia for high-risk patients. Agent selection for epidural use reflects the clinical goal: for labor analgesia, low-concentration bupivacaine (0.0625–0.125%) or ropivacaine (0.1–0.2%) combined with fentanyl 1–2 μg/mL achieves excellent differential sensory block with minimal motor impairment; for surgical anesthesia, higher concentrations (bupivacaine 0.5%, lidocaine 2%, ropivacaine 0.5–0.75%) produce the dense sensorimotor block required for intraoperative use.9 Thoracic epidural analgesia, placing the catheter between T4 and T8 for thoracic, upper abdominal, or cardiac surgery, provides unmatched segmental analgesia for the most painful procedures and is associated with reduced postoperative pulmonary complications and preserved bowel function compared to systemic opioid analgesia alone; benefits that have sustained thoracic epidural as the analgesic gold standard for open thoracotomy, esophagectomy, and open aortic surgery despite the growth of alternative regional techniques.10
The epidural test dose, a standard practice before administering the full epidural dose, consists of 3 mL of lidocaine 1.5% with epinephrine 1:200,000 (containing 45 mg lidocaine and 15 μg epinephrine). Intravascular injection produces tachycardia ≥20 bpm within 45–60 seconds (epinephrine marker), while intrathecal injection of 45 mg lidocaine produces a rapidly ascending dense motor block within 2–3 minutes (spinal marker), enabling identification of catheter misplacement before the full epidural dose is administered. In parturients receiving β-blockers, tachycardia may be blunted and the epinephrine marker unreliable; alternative signs of intravascular injection including hypertension and palpitations should be sought, and the test dose should be accompanied by real-time heart rate monitoring.9
Beyond the basic pharmacology of the local anesthetic agent, several factors modify block characteristics in the neuraxial setting. The addition of epinephrine to epidural local anesthetic solutions prolongs block duration and reduces systemic absorption, and provides the intravascular injection marker in the test dose. The addition of intrathecal or epidural clonidine (50–150 μg) prolongs both sensory and motor block duration by 1–2 hours through spinal α2 receptor activation and may reduce the local anesthetic dose required for surgical anesthesia, at the cost of dose-dependent sedation and hypotension. Intrathecal neostigmine (10–50 μg) augments spinal analgesia through inhibition of acetylcholinesterase in the dorsal horn, increasing acetylcholine at spinal muscarinic receptors, but its clinical use is limited by a high incidence of nausea. The addition of bicarbonate to epidural lidocaine or chloroprocaine solutions (as discussed in CNS-02) reduces onset time modestly and is used by many practitioners for urgent epidural activation.9
Liposomal bupivacaine (EXPAREL) is a formulation in which bupivacaine is encapsulated within multivesicular lipid particles (DepoFoam technology), producing a sustained-release depot that releases drug over approximately 72–96 hours following a single injection.11 This extended release profile was developed to address the primary limitation of conventional long-acting local anesthetics, namely the 8–16 hour duration of bupivacaine or ropivacaine peripheral nerve blocks, and to provide prolonged analgesia without the need for perineural catheter placement. Liposomal bupivacaine is FDA-approved for wound infiltration (surgical field infiltration at the conclusion of the procedure) and, more recently, for interscalene brachial plexus block. Its use has expanded considerably off-label to include a wide range of infiltration and regional applications.11
The clinical evidence for liposomal bupivacaine is nuanced and has been the subject of considerable debate. For wound infiltration applications, particularly in total knee and hip arthroplasty where it is extensively used, randomized trials and meta-analyses have produced mixed results: some studies demonstrate modest reductions in opioid consumption and pain scores in the first 24–72 hours compared to plain bupivacaine infiltration, while others show no significant difference.11 The most consistent benefit is observed when liposomal bupivacaine is compared to no local anesthetic infiltration rather than to conventional bupivacaine wound infiltration, which suggests that the benefit may reflect the analgesic effect of any long-acting local anesthetic at the wound site rather than a specific advantage of the sustained-release formulation per se.
For perineural applications (interscalene block), a phase III trial demonstrated significantly prolonged analgesia compared to bupivacaine HCl. The cost of liposomal bupivacaine, which is substantially higher than conventional bupivacaine, must be weighed against the clinical benefit in any institutional formulary decision.11 The maximum total dose of liposomal bupivacaine for wound infiltration is 266 mg (20 mL of the 1.3% formulation); if admixed with plain bupivacaine HCl, the total bupivacaine dose from both sources must be considered.
Enhanced recovery after surgery (ERAS) protocols represent the systematic application of evidence-based perioperative care elements to optimize patient outcomes, with particular emphasis on reducing opioid dependence, facilitating early nutrition and mobilization, and shortening length of hospital stay.10 Regional anesthesia is a cornerstone of ERAS for virtually all major surgical procedures, and the pharmacology of local anesthetics intersects directly with ERAS goals in several ways.
Effective neural blockade replaces or significantly reduces systemic opioid requirements, eliminating opioid-related adverse effects including nausea, vomiting, ileus, sedation, respiratory depression, and urinary retention, that are the primary drivers of delayed recovery and prolonged hospital stay.10 The motor-sparing characteristics of low-concentration local anesthetic techniques (dilute epidural solutions, adductor canal block instead of femoral nerve block, fascial plane blocks) align with the ERAS goal of early ambulation by preserving lower extremity strength and balance. Continuous perineural catheter techniques extend local anesthetic analgesia over the 48–72 hour window when postoperative pain is most intense and opioid rescue is most likely to be required. The integration of dexamethasone as a block adjuvant, which extends block duration by 6–8 hours for a single dose, provides a pharmacologically rational, evidence-based strategy for bridging the gap between single-injection block duration and the period of peak postoperative pain, reducing the need for catheter placement in some surgical contexts.10
Hadzic A, ed. Hadzic's Peripheral Nerve Blocks and Anatomy for Ultrasound-Guided Regional Anesthesia. 2nd ed. New York: McGraw-Hill; 2011.
Taddio A, Ohlsson A, Einarson TR, Stevens B, Koren G. A systematic review of lidocaine-prilocaine cream (EMLA) in the treatment of acute pain in neonates. Pediatrics. 1998;101(2):E1
doi:10.1542/peds.101.2.e1Stoelting RK, Hillier SC. Pharmacology and Physiology in Anesthetic Practice. 4th ed. Philadelphia: Lippincott Williams & Wilkins; 2006:179–207.
Becker DE, Reed KL. Local anesthetics: review of pharmacological considerations. Anesth Prog. 2012;59(2):90–102
doi:10.2344/0003-3006-59.2.90Neal JM, Brull R, Horn JL, et al. The second ASRA practice advisory on neurologic complications associated with regional anesthesia and pain medicine. Reg Anesth Pain Med. 2015;40(5):401–430
doi:10.1097/AAP.0000000000000286Urmey WF, Talts KH, Sharrock NE. One hundred percent incidence of hemidiaphragmatic paresis associated with interscalene brachial plexus anesthesia as diagnosed by ultrasonography. Anesth Analg. 1991;72(4):498–503
doi:10.1213/00000539-199104000-00014Jaeger P, Nielsen ZJ, Henningsen MH, Hilsted KL, Mathiesen O, Dahl JB. Adductor canal block versus femoral nerve block and quadriceps strength: a randomized, double-blind, placebo-controlled, crossover study in healthy volunteers. Anesthesiology. 2013;118(2):409–415
doi:10.1097/ALN.0b013e318279dc54Rosenberg PH, Veering BT, Urmey WF. Maximum recommended doses of local anesthetics: a multifactorial concept. Reg Anesth Pain Med. 2004;29(6):564–575
doi:10.1016/j.rapm.2004.08.003Butterworth JF, Mackey DC, Wasnick JD, eds. Morgan and Mikhail's Clinical Anesthesiology. 6th ed. New York: McGraw-Hill; 2018:937–992.
Guay J, Nishimori M, Kopp S. Epidural local anaesthetics versus opioid-based analgesic regimens for postoperative gastrointestinal paralysis, vomiting and pain after abdominal surgery. Cochrane Database Syst Rev. 2016;7:CD001893
doi:10.1002/14651858.CD001893.pub2Haas E, Onel E, Miller H, Ragupathi M, White PF. A double-blind, randomized, active-controlled study for post-hemorrhoidectomy pain management with liposome bupivacaine, a novel local anesthetic formulation. Am Surg. 2012;78(5):574–581.