Subcutaneous infiltration of local anesthetics

INTRODUCTION — The subcutaneous infiltration of local anesthetics for minor skin procedures (eg, wound repair, lumbar puncture, or insertion of vascular catheters) will be reviewed here.

Topical anesthetics in children, peripheral nerve blocks, and regional anesthesia are discussed separately:

●(See "Clinical use of topical anesthetics in children".)

●(See "Clinical use of local anesthetics in anesthesia".)

●(See "Overview of peripheral nerve blocks" and "Overview of anesthesia", section on 'Peripheral nerve blocks' and "Digital nerve block".)

ANATOMY AND PHYSIOLOGY — The skin is made up of the epidermis and dermis. The subcutaneous layer lies beneath the dermis (figure 1). Direct infiltration of local anesthetic into the subcutaneous layer effectively blocks pain transmission from the free nerve endings located in the epidermal and dermal layers [1]. Intradermal injection is also effective but more painful than subcutaneous injection.

Local anesthetics reversibly block sodium channels within the nerve fibers, which prevents transmission of pain signals by disrupting depolarization of the nerve [2]. Pain fibers are relatively unmyelinated when compared with afferent fibers that transmit the sensation of touch or temperature or nerves that control muscle contraction. Thus, infiltration of dilute solutions of local anesthetics near the nerve fibers produces relief of pain with less interruption in the sense of touch or temperature and without muscle paralysis in most children and adults. Because myelin sheaths throughout the nervous system are not fully developed in neonates and young infants, even dilute solutions of local anesthetics have a higher potential for producing muscle paralysis and central toxicity in such patients [3].

Local anesthetics are weak organic bases that are composed of charged and uncharged forms when in solution [3-5]. Only the uncharged forms are thought to be capable of diffusion through interstitial tissues and transport across the nerve membrane [6]. Dispersion of the local anesthetic through the tissue occurs more rapidly as the percentage of uncharged form increases [4]. The pH of the solution and the surrounding tissues and the pKa of the specific agent determine the proportion of charged and uncharged anesthetic. Increased acidity of the solution or of the tissues (eg, infected skin) reduces the proportion of anesthetic in the uncharged form according to Henderson-Hasselbalch equation as follows [3,6]:

Most local anesthetic solutions are marketed in acidic forms with pH of 5.0 to 7.0. The anesthetic is more stable in this pH range and has a shelf life of three to four years at room temperature [4]. For some formulations, the pH of the anesthetic solution is increased to 7.2 to 7.4 (physiologic pH) by the addition of sodium bicarbonate. This results in a greater proportion of anesthetic being in the uncharged form, thereby enhancing the analgesic effect and decreasing the pain of injection [3,4,7]. (See 'Methods to decrease injection pain' below.)

However, once the pH is increased, the buffered lidocaine is more susceptible to photodegradation, aldehyde formation, and other denaturing reactions, leading to a shelf life of one to three weeks at room temperature [4,8]. This buffering approach cannot be used for some agents (eg, bupivacaine) because they will precipitate at physiologic pH [2].

CLASSIFICATION OF LOCAL ANESTHETICS — Most local anesthetics are classified as amides or esters (table 1) [9,10]. Local anesthetics in the amide class include lidocaine (the most commonly used agent), mepivacaine, bupivacaine, etidocaine, prilocaine, ropivacaine, and levobupivacaine [2,10]. Common ester agents include procaine (Novocaine), 2-chloroprocaine, tetracaine, cocaine, and benzocaine [2]. Because of toxicity and allergic reactions, the ester agents have limited indications for local infiltration, except in patients with allergy to amide agents [2,11]. (See "Clinical use of local anesthetics in anesthesia".)

CHOICE OF ANESTHETIC — Lidocaine, bupivacaine, mepivacaine, and procaine are the most commonly used agents for subcutaneous infiltration of local anesthesia [12,13]. The comparative properties of lidocaine, bupivacaine, procaine, and mepivacaine are provided in the table and can affect the choice of anesthetic in particular situations (table 2). A history of allergy to specific anesthetics or specific additives (eg, methylparaben, metabisulfite) contained in different formulations of the same anesthetic may also impact the choice of agent.

Lidocaine — Lidocaine is a local anesthetic in the amide class and is the most commonly used anesthetic for local infiltration.

●Preparation – Lidocaine is usually given as a 1 percent solution (10 mg/mL). If large volumes are needed or a smaller dose is desired, the clinician may use a 0.5 percent solution. Higher concentrations of lidocaine beyond 1 percent do not promote improved onset or duration of analgesia and may increase the risk of toxicity [12]. Buffering of lidocaine with sodium bicarbonate (as described in the preceding section) decreases the pain of injection, especially when using lidocaine with epinephrine, and may shorten the time to anesthetic effect [12]. (See 'Methods to decrease injection pain' below.)

●Dose – The dose of lidocaine should not exceed the following [5,14,15]:

•Lidocaine without epinephrine (also called plain lidocaine) – 5 mg/kg (0.5 mL/kg of lidocaine 1 percent, maximum total dose: 300 mg [30 mL of lidocaine 1 percent])

•Lidocaine with epinephrine – 7 mg/kg (0.7 mL/kg of lidocaine 1 percent, maximum total dose: 500 mg [50 mL of lidocaine 1 percent with epinephrine]).

For an added margin of safety, 80 percent of the maximum allowable dose should be used in children under eight years of age [1]. In addition, because anesthetics in the amide class are metabolized by the liver and excreted by the kidneys, the total dose of lidocaine should be decreased by approximately 50 percent in older adults with severe liver or kidney disease [7,16].

●Onset of action and duration of anesthesia – The onset of anesthesia typically occurs within two to five minutes, and the duration of anesthesia varies from 30 minutes to two hours for plain lidocaine, which is long enough to complete most procedures [7,17,18]. The addition of epinephrine (available premixed at concentrations of 1:100,000 or 1:200,000) provides local vasoconstriction which prolongs the duration of action (table 2), decreases local bleeding during the procedure, and reduces systemic lidocaine absorption [17]. In addition, this combination may extend the duration of anesthesia up to three hours [7].

The concentration of epinephrine may be diluted to less than 1:200,000 by mixing plain lidocaine and lidocaine with epinephrine in patients who are sensitive to catecholamine injection [18]. Concentrations as low as 1:1,000,000 still maintain effective vasoconstriction. However, this dilution does decrease the duration of action, may allow for greater systemic absorption, and may increase the amount of local bleeding. (See 'Catecholamine sensitivity' below.)

Lidocaine with epinephrine may be used in the face (including the nose and ear), digit, or penis [18]. In the past, injection of epinephrine with local anesthetic was discouraged in these sites. However, there is no convincing evidence of harm with such use. As an example, comprehensive reviews of the medical literature and large observational studies have failed to find any reports of gangrene or major ischemic complications solely attributable to lidocaine with epinephrine. (See "Digital nerve block", section on 'Use of epinephrine'.)

Lidocaine with epinephrine should be avoided for digital anesthesia in patients with peripheral artery disease [18]. (See 'Contraindications' below.)

Bupivacaine — Bupivacaine is an amide anesthetic that is more potent and has a longer duration of action than lidocaine mepivacaine, or procaine [2,10]. The increases in potency and duration of action are related to prolonged binding of sodium channels. Thus, if systemically absorbed, bupivacaine has a higher risk of major toxicity (eg, seizures, intractable cardiac arrhythmias) than lidocaine and most other local anesthetics [3]. Bupivacaine is contraindicated for local infiltration in pregnant women [2,10], and should be infiltrated with caution in acutely ill, debilitated, or older adult patients.

Bupivacaine is a good choice for longer procedures, for patients who have contraindications to epinephrine injection, for situations where there will be a delay between infiltration of local anesthetic and the procedure, or for instances in which prolonged post-procedure pain control is preferred.

●Preparation – Bupivacaine is commercially available in concentrations of 0.25 percent (2.5 mg/mL) and 0.5 percent (5 mg/mL). The lower concentration should be used in awake patients because local infiltration with 0.5 percent bupivacaine is painful. Unlike lidocaine, buffering with sodium bicarbonate does not reduce the pain of injection and may lead to precipitation of the active drug [2]. (See 'Methods to decrease injection pain' below.)

●Dose – The dose of bupivacaine should not exceed the following [12]:

•Bupivacaine without epinephrine – 2 mg/kg (0.8 mL/kg of bupivacaine 0.25 percent, maximum total dose: 175 mg [70 mL of bupivacaine 0.25 percent])

•Bupivacaine with epinephrine – 3 mg/kg (1.2 mL/kg of bupivacaine 0.25 percent, maximum total dose: 225 mg [90 mL of bupivacaine 0.25 percent with epinephrine])

●Onset of action and duration of anesthesia – The onset of action of bupivacaine is 5 to 10 minutes and the duration of effect is up to six hours (table 2) [12]. The addition of epinephrine does not increase the duration of anesthetic effect but may decrease systemic absorption, and use may be desirable for hemostatic purposes [2,3].

Mepivacaine — Mepivacaine, an amide local anesthetic, is an alternative to lidocaine, although it is less commonly used. Systemic toxicity is similar to that of lidocaine [2,10]. Pregnancy is a relative contraindication to the use of mepivacaine because of poor fetal metabolism related to hepatic immaturity [2].

●Preparation – Mepivacaine is usually administered as a 1 percent (10 mg/mL) solution. A 0.5 percent (5 mg/mL) solution is also commercially available.

●Dose – The dose of mepivacaine should not exceed the following [18]:

•Mepivacaine without epinephrine – 5 mg/kg (0.5 mL/kg of mepivacaine 1 percent, maximum total dose 300 mg [30 mL of mepivacaine 1 percent])

•Mepivacaine with epinephrine – 7 mg/kg (0.7 mL/kg of mepivacaine 1 percent, maximum total dose 500 mg [50 mL of mepivacaine 1 percent with epinephrine])

●Onset of action and duration of anesthesia – Similar to lidocaine, mepivacaine has an onset of action of two to five minutes and duration of anesthesia lasting up to two hours. [2,9]. Addition of epinephrine increases the duration of action up to three hours [10,18].

Procaine — Procaine (Novocaine) is an ester anesthetic. Its primary use is in patients undergoing dental procedures and those with allergy to amide anesthetics [12]. When compared with lidocaine, procaine has a longer time to onset of action, shorter duration of action, and poor penetrating ability [3]. However, it has very little systemic toxicity.

●Preparation – Procaine is typically administered as a 1 percent (10 mg/mL) solution. A 0.5 percent (5 mg/mL) solution is also commercially available.

●Dose – The dose of procaine should not exceed the following [12,18]:

•Procaine without epinephrine – 7 mg/kg (0.7 mL/kg of procaine 1 percent, maximum total dose 500 mg [50 mL of procaine 1 percent])

•Procaine with epinephrine – 9 mg/kg (0.9 mL/kg of procaine 1 percent, maximum total dose 600 mg [60 mL of procaine 1 percent with epinephrine])

●Onset of action and duration of anesthesia – Procaine has an onset of action of 5 to 10 minutes and duration of anesthesia of up to 1.5 hours.

INDICATIONS — Infiltration of local anesthesia is effective for pain control during a variety of procedures, including skin surgery (eg, skin biopsy, scar revision, small skin grafts), open wound repair, abscess drainage, foreign body removal from the skin, vascular access procedures, and lumbar puncture [12,18,19]. The choice of agent depends on several factors, including the duration of the procedure, need for hemostasis, patient sensitivity to catecholamines, and patient allergy to local anesthetics (table 2). (See 'Choice of anesthetic' above.)

In children, we suggest initial pain control with topical LET (lidocaine, epinephrine, tetracaine) rather than infiltrative anesthesia for uncomplicated facial or scalp lacerations. Children should also receive some form of topical analgesia prior to venipuncture, intravenous catheter placement, or Port-A-Cath access unless emergency testing or access is necessary. (See "Clinical use of topical anesthetics in children", section on 'Summary and recommendations' and "Clinical use of topical anesthetics in children", section on 'Lidocaine-epinephrine-tetracaine (LET)'.)

CONTRAINDICATIONS — True allergy to a local anesthetic is a contraindication for use of that anesthetic and other agents with the same chemical classification (ie, amide or ester) (table 1). In contrast, local administration of an anesthetic with a different chemical classification is safe in most instances, as long as prior administration was not associated with generalized urticaria or anaphylaxis. If the procedure is elective, it is optimal to have the patient evaluated by an allergist prior to the procedure to assist in distinguishing allergy to the local anesthetic from allergy to other chemical additives (eg, methylparaben) and to help differentiate an allergic reaction from other types of adverse reactions commonly associated with infiltration of local anesthetics. (See "Allergic reactions to local anesthetics", section on 'Evaluation' and "Allergic reactions to local anesthetics", section on 'Management algorithm for nonallergy clinicians'.)

Infiltration of local anesthetics is not recommended for the management of large or multiple lacerations where the total dose needed for adequate effect is expected to be close to the maximum allowable anesthetic dose (table 2) [12]. In such situations, a regional block or Bier (IV regional) block may be performed instead.

A regional block may be preferable to infiltration of local anesthetic for repair of wounds that require precise anatomic alignment (eg, lacerations through the vermillion border of the lip) because local infiltration might distort important skin landmarks [12]. (See "Overview of peripheral nerve blocks".)

The clinician should not use epinephrine with local anesthetic infiltration in the following settings [18]:

●Large wounds in patients with underlying conditions (eg, hyperthyroidism, pheochromocytoma, severe hypertension, coronary artery disease) that may be exacerbated by systemic epinephrine effects.

●Digital anesthesia in patients with compromised digital circulation

●Periorbital infiltration in patients with narrow angle glaucoma

●Patients with catecholamine sensitivity (see 'Catecholamine sensitivity' below)

●Patients taking lurasidone (may cause hypotension, category X drug interaction [avoid combination])

●Patients taking ergot alkaloids, such as ergotamine (enhanced hypertensive and vasoconstrictive effect, category X drug interaction [avoid combination])

Epinephrine infiltration with local anesthetics has the potential for enhancing hypertensive effects when combined with the following medications which may warrant lower dosing of epinephrine (eg, mixing lidocaine with epinephrine 1:1 with plain lidocaine) [18]:

●Beta blockers (less risk with cardioselective medications, category D drug interaction, consider therapy modification)

●Monoamine oxidase inhibitors (category C drug interaction, monitor therapy)

●Phenothiazines (category D drug interaction, consider therapy modification)

●Tricyclic antidepressants (category D drug interaction, consider therapy modification)

PREPARATION — The clinician should determine the patient’s prior experience with local anesthesia and if allergies or adverse reactions have occurred. The patient and family/caregiver(s) should receive an explanation of the planned approach. A child life specialist or other personnel are often helpful in reducing the anxiety of children undergoing painful procedures. Procedural sedation may be necessary in addition to infiltration of local anesthesia for certain patients (eg, young children or anxious older patients) who are undergoing cosmetic laceration repairs or other procedures (eg, central venous access, lumbar puncture) that require complete patient cooperation. (See "Procedural sedation in children: Approach" and "Procedural sedation in adults in the emergency department: General considerations, preparation, monitoring, and mitigating complications".)

History of adverse reaction — Clinical situations may arise in which local anesthesia is required for a patient with a history of a prior adverse reaction to a specific local anesthetic. True IgE-mediated allergic reactions to local anesthetic agents are rare, but convincing case reports do exist. The approach to patients with a history of prior adverse reactions to local anesthetics depends upon the specific history and is provided in the algorithm (algorithm 1) (see "Allergic reactions to local anesthetics"):

●Nonallergic reaction – If a local anesthetic is needed in a patient with a past adverse reaction, the patient's past signs and symptoms should be reviewed along with any procedures that were performed with local anesthesia since the adverse reaction (eg, dental procedures). If the reaction can be specifically identified as something other than allergy (eg, catecholamine sensitivity, systemic toxicity, vasovagal syncope), then the clinician should focus on strategies that specifically limit anxiety, pain, total dose of anesthetic administered, or catecholamine exposure. (See 'Methods to decrease injection pain' below and 'Lidocaine' above and "Allergic reactions to local anesthetics", section on 'Patients with past nonallergic reactions'.)

●Contact dermatitis – If the reaction consists of contact dermatitis or delayed local swelling, it is reasonable to proceed with the use of a local anesthetic from the other group (ester or amide) (table 1). In most cases, patients with type IV allergic reactions are tolerant of a local anesthetic chosen from the group of agents to which they did not react. As an example, a patient with past possible allergy to procaine (group I) would be predicted to tolerate lidocaine (group II) in most cases. In addition, it is prudent to use a preservative-free formulation that does not contain metabisulfites or methylparaben in patients with type IV allergic reactions to local anesthetics. Patch testing prior to the procedure is ideal. (See "Allergic reactions to local anesthetics", section on 'Management'.)

●Anaphylaxis or other life-threatening reaction – Patients who report a history of symptoms that are suggestive of anaphylaxis (ie, diffuse hives, wheezing, throat closure) or any other life-threatening reaction should not receive local anesthetics until they undergo a complete evaluation by an allergy specialist. If the procedure is elective, it should be deferred until this evaluation has occurred. If the procedure is urgent, then the patient should receive an alternative to local anesthesia (eg, procedural sedation). (See "Procedural sedation in children: Approach" and "Procedural sedation in adults in the emergency department: General considerations, preparation, monitoring, and mitigating complications".)

The evaluation of possible allergy to local anesthetics is reviewed separately. (See "Allergic reactions to local anesthetics".)

Materials — The clinician should assemble the following items:

●Povidone-iodine or chlorhexidine solution

●Sterile gauze

●Sterile gloves

●25-, 27-, or 30-gauge long (1.5 inch) hypodermic needle

●Syringe (1 ,3, 5, 6, or 10 mL)

●Local anesthetic agent (see 'Choice of anesthetic' above)

PROCEDURE

Methods to decrease injection pain — When lidocaine injection is used for local anesthesia during urgent or routine procedures, we suggest buffering with sodium bicarbonate and warming the anesthetic agent to approximately body temperature (37°C) prior to injection. In a systematic review and meta-analysis of randomized trials that assessed pain of local buffered lidocaine injection in children and adults (7 parallel-group studies, n = 635 patients; 10 crossover studies, n = 432 patients), buffered lidocaine decreased the pain of injection compared with unbuffered lidocaine, although the effect was modest (pooled pain reduction 2 out of 10 pain units in crossover studies [95% CI -2.6 to -1.3 units] and 1 out of 10 pain units in parallel trials [95% CI -1.4 to -0.5]) [20].

In a meta-analysis of 18 randomized or pseudo-randomized trials (over 830 patients), warming of lidocaine to body temperature prior to injection significantly decreased pain (mean difference -11 mm on a 100-mm scale) [21]. .

The standard solutions of plain lidocaine or commercially prepared lidocaine with epinephrine have pH values of 5.0 to 7.0 and 3.0 to 5.0 [2,22]. These preparations can be buffered by adding one part of 1 mEq/mL of sodium bicarbonate to 9 or 10 parts of 1 percent lidocaine or lidocaine with epinephrine. The shelf life of buffered plain lidocaine is approximately one week [8]. However, the addition of bicarbonate to lidocaine with epinephrine inactivates epinephrine within 24 hours. Thus, when using multidose vials of lidocaine, it is best to buffer it by drawing the appropriate volumes of sodium bicarbonate and lidocaine into the syringe rather than injecting sodium bicarbonate into the vial.

Several other techniques may decrease the pain associated with injection. They include [1,12,18]:

●Patient distraction (eg, television, mental imagery, and in children, books or toys [eg, pinwheel, blowing bubbles])

●Gentle pinching or vibration adjacent to the site of injection

●Use of small needles (25-, 27-, or 30-gauge)

●Slow rate of injection

●Subcutaneous instead of intradermal injection

●Reducing pressure of injection by using small volume syringes (eg, 1 or 3 mL)

●Injecting with a needle angle of 90 rather than 45 degrees when penetrating intact skin for elective procedures (eg, skin biopsy) [23]

Technique — Intact, uninfected skin and clean lacerations may undergo direct infiltration. Heavily contaminated lacerations or skin abscesses should undergo a field block.

Direct infiltration — The steps for direct infiltration of local anesthetic are as follows [1]:

●For lacerations, ensure that the areas distal to the wound show no neurovascular compromise.

●Explain the procedure to the patient and, in children, the caregiver.

●Provide sedation and restraint, as needed (eg, children or other potentially uncooperative patients). (See "Procedural sedation in children: Approach" and "Procedural sedation in adults in the emergency department: General considerations, preparation, monitoring, and mitigating complications".)

●Cleanse the site of infiltration with povidone-iodine or chlorhexidine solution or other similar antiseptic preparation and allow to air dry or dry with sterile gauze.

●Hide the needle from view prior to and during injection, especially in children.

●For open wounds, put a few drops of anesthetic into the wound and then immediately place the needle into the subcutaneous layer (figure 1) by inserting it through the wound margin rather than intact skin.

●For intact skin, rapidly insert the needle through the skin into the subcutaneous layer (figure 1).

●Slowly inject small volumes of anesthetic. During anesthetic infiltration, either slowly advance the needle or initially insert it to the hub and infiltrate as the needle is withdrawn. Aspiration is not necessary prior to each infiltration unless the area undergoing local anesthesia is close to major blood vessels.

●Anesthetize adjacent areas by inserting the needle through the previously injected skin or wound until the entire region requiring anesthesia is infiltrated. This is ordinarily accomplished in a linear laceration, for example, by entering the proximal portion of the wound and administering lidocaine as one proceeds forward or by moving the needle forward to the distal end of the wound and withdrawing back to the original point while injecting lidocaine. The clinician should know where the last portion of anesthesia was delivered and insert the needle in that area if additional injections are required to avoid subjecting patients to additional pain from repeated insertion of the needle into unanesthetized areas.

●After a few minutes, lightly test the skin or wound margins for adequate anesthesia using the injection needle or other sharp object (suture needle, Adson forceps). Timing of complete and optimal anesthesia will depend upon the local anesthetic that is used (table 2).

Field block — For heavily contaminated wounds or when anesthetizing for incision and drainage of a skin abscess, prepare the patient and wound in the same way as for direct infiltration [1]. (See 'Direct infiltration' above.)

Procedural sedation may also be necessary to ensure proper wound decontamination in a relatively painless manner. Alternatively, a regional block may be performed. (See "Overview of peripheral nerve blocks".)

Proceed with the field block as follows:

●Insert the needle into the subcutaneous layer through intact, clean skin along the margin of the contaminated wound or through uninfected skin immediately adjacent to the abscess.

●Slowly inject small volumes of anesthetic taking care to monitor the total dose administered. During anesthetic infiltration, either slowly advance the needle or initially insert it to the hub, and infiltrate as the needle is withdrawn. Aspiration is not necessary prior to each infiltration, unless the area undergoing local anesthesia is close to major blood vessels.

●Reinsert the needle through the area just anesthetized, redirecting it along the margins of the wound or circumferentially around the abscess and infiltrate additional anesthetic.

●Continue infiltration through previously injected skin until the entire region requiring anesthesia is infiltrated.

●After a few minutes, lightly test the skin or wound margins for adequate anesthesia using the injection needle or other sharp object (suture needle, Adson forceps). Timing of complete and optimal anesthesia will depend upon the local anesthetic that is used (table 2).

FOLLOW-UP CARE — The patient, and in children, the caretaker, should be advised that full recovery of sensation in the anesthetized region is expected soon after the procedure. The exact timing of recovery will depend upon the anesthetic used (table 2). Until full sensation has returned, the patient should be told that the region is prone to inadvertent injury, including thermal injury from excessive heat or cold exposure.

COMPLICATIONS — Complications during infiltration of local anesthetics are rare. Avoidance of intravascular injection into major vessels and care not to exceed the maximum total dose of anesthetic helps to avoid complications in most patients.

Systemic toxicity — Systemic toxicity following subcutaneous local anesthetic infiltration may manifest as (see "Local anesthetic systemic toxicity", section on 'Differences in toxicity among local anesthetics'):

●Central nervous system effects including:

•Metallic taste

•Tinnitus

•Tingling of the lips

•Dizziness

•Anxiety

•Agitation

•Confusion

•Lethargy

•Loss of consciousness

•Seizures

and/or

●Cardiovascular effects including:

•Bradycardia

•Decreased myocardial contractility

•Atrioventricular block

•Vasodilation

•Ventricular arrhythmias

•Cardiac arrest

Although an usual event, systemic toxicity can occur if the recommended local anesthetic dose is exceeded (table 2), if a major vessel is inadvertently injected with a large amount of anesthetic, or as an idiosyncratic response. Among the local anesthetics commonly infiltrated, bupivacaine has the greatest potential for systemic toxicity.

Treatment — The management of local anesthetic systemic toxicity is provided in the rapid overview (table 3) and is discussed in detail separately. (See "Local anesthetic systemic toxicity", section on 'Management of LAST'.)

Catecholamine sensitivity — Tachycardia, hypertension, palpitations, and anxiety (eg, a sense of doom) may accompany subcutaneous injection of epinephrine in sensitive patients or inadvertent intravascular injection in normal patients [18].

Vasovagal syncope — Vasovagal (also called neurocardiogenic) syncope is usually associated with bradycardia (rather than tachycardia) and pallor (rather than flushing). These differences can be helpful in distinguishing it from anaphylaxis. (See "Reflex syncope in adults and adolescents: Clinical presentation and diagnostic evaluation".)

Allergic reaction — Two different types of allergic reactions to local anesthetics 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 local anesthetic administration. Vesiculation, blistering, and/or weeping can occur. The affected area is limited to tissue that was in direct contact with the anesthetic. Treatment is as for other types of contact dermatitis. (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 local anesthetics are limited to case reports. Patients who display signs of acute anaphylaxis (eg, hives, facial or intraoral swelling, stridor, wheezing, hypotension) (table 4) should receive emergent treatment (table 5 and table 6). (See "Anaphylaxis: Emergency treatment" and "Allergic reactions to local anesthetics", section on 'Rare: Immediate reactions (urticaria and anaphylaxis)'.)

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 5^th to 6^th 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 10^th to 12^th 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

●Indications and choice of local anesthetic – Infiltration of local anesthesia is effective for pain control during a variety of procedures, including (see 'Indications' above):

•Open wound repair

•Skin surgery (eg, skin biopsy, scar revision, small skin grafts)

•Abscess drainage

•Foreign body removal from the skin

•Vascular access procedures

•Lumbar puncture

Characteristics of agents commonly used for local anesthetic infiltration are summarized in the table (table 2). The choice of local anesthetic for infiltration depends on several factors, including duration of the procedure, need for hemostasis, patient sensitivity to catecholamines, and patient allergy to local anesthetics. (See 'Choice of anesthetic' above.)

For most procedures and for most patients, lidocaine is a good choice. (See 'Lidocaine' above.)

●Contraindications – Local anesthetic infiltration is contraindicated in the following instances (see 'Contraindications' above):

•The amount of anesthetic needed to provide adequate analgesia exceeds the maximal safe total dose.

•The patient has had generalized urticaria or anaphylaxis in association with administration of local anesthesia and has not undergone evaluation by an allergy subspecialist.

●Patients with prior adverse reactions – Prior to infiltration, the clinician should determine if the patient has any history of allergy or adverse reaction associated with receiving local anesthesia. The approach to patients with a history of prior adverse reactions to local anesthetics depends upon the specific history; an approach is provided in the algorithm (algorithm 1). (See 'History of adverse reaction' above and "Allergic reactions to local anesthetics", section on 'Common: Nonallergic reactions'.)

●Preparation – When lidocaine is used for local anesthesia during urgent or elective procedures, we suggest buffering with sodium bicarbonate and warming the anesthetic agent to approximately body temperature (37°C) prior to injection (Grade 2B). Buffering of lidocaine may be of particular benefit for children or when injecting lidocaine with epinephrine. (See 'Methods to decrease injection pain' above.)

Other techniques to reduce the pain of injection may also be successful (see 'Methods to decrease injection pain' above):

•Patient distraction (eg, television, mental imagery, and in children, books or toys [eg, pinwheel, blowing bubbles])

•Gentle pinching or vibration adjacent to the site of injection

•Use of small needles (25-, 27-, or 30-gauge)

•Slow rate of injection

•Subcutaneous instead of intradermal injection

•Reducing pressure of injection by using small-volume syringes (eg, 1 or 3 mL)

•Injecting with a needle angle of 90 rather than 45 degrees when penetrating intact skin for elective procedures (eg, skin biopsy)

●Procedure – The techniques for direct infiltration of local anesthetics (infiltration through uninfected skin and clean lacerations) and field block (heavily contaminated lacerations or skin abscesses) are described above. (See 'Direct infiltration' above and 'Field block' above.)

●Systemic toxicity – Systemic toxicity, such as central nervous system effects (eg, metallic taste, paresthesia, confusion, lethargy, seizures) and cardiovascular effects (eg, bradycardia, atrioventricular block, ventricular arrhythmias, shock, or cardiac arrest), is unusual following subcutaneous local anesthetic infiltration but can occur if the recommended dose is exceeded, if a major vessel is inadvertently injected with a large amount of anesthetic, or as an idiosyncratic response. (See 'Complications' above.)

The management of local anesthetic systemic toxicity is provided in the rapid overview (table 3) and is discussed in detail separately. (See "Local anesthetic systemic toxicity", section on 'Management of LAST'.)