Infiltration and Nerve Block Anesthesia

Key Practice Points

  • A gentle and empathetic approach to patients is necessary when administering local anesthesia because of the near universal fear of injections and needles.

  • The onset of action of lidocaine is almost immediate when giving the anesthetic around the wound. For nerve blocks, onset of action is 5 to 10 minutes.

  • The addition of epinephrine reduces bleeding and extends the duration of local anesthesia.

  • Toxicity of local anesthetics can cause hypotension, bradycardia, and (rarely) seizures that are most often caused by inadvertent injection into a blood vessel. To avoid complications, aspirate before injecting.

  • Allergies to local anesthetics are uncommon and are often due to the preservative, methylparaben, in the solution.

  • Buffering local anesthetics with bicarbonate can reduce, in some patients, the pain of infiltration.

  • Moderate sedation with midazolam and fentanyl can effectively reduce pain in a procedure such as abscess drainage.

  • Topical anesthesia is most effective for small lacerations in pediatric patients.

  • Through-the-wound direct infiltration is the most common form of local anesthesia for lacerations repaired in emergency settings.

  • Nerve blocks create larger areas of anesthesia and do not cause tissue distortion with unwanted swelling of the wound.

Effective anesthesia is essential for successful patient intervention and wound repair. As with any procedure, success depends on a thorough understanding of the properties of anesthetic solutions and injection techniques. The choice of anesthetics and techniques must be individualized for every patient. The type, location, and extent of the wound and estimated length of time for repair are variables that make each patient unique. Besides technical considerations, patients have differing emotional characteristics and responses. Almost all patients often fear that injections and needles will cause excessive pain. A clear explanation of the procedure and gentle handling gain the confidence of the patient and ease any apprehension.

Local Anesthetics: Practical Points

  • Onset of action: Local wound infiltration of a laceration with lidocaine 1% brings on rapid anesthesia. If the anesthetic is delivered at the interface of the superficial fascia and dermis, nerve fibers are vulnerable to immediate blockade ( Fig. 6-1 ). Wound cleansing and suturing can begin almost immediately. A slightly shorter onset of action is yielded by lidocaine 2% solutions than by 1% solutions, but clinically speaking, this effect is negligible. The addition of epinephrine and the buffering of local anesthetics also can shorten the onset of action and are discussed later in this chapter. When blocking larger nerve trunks, such as digital nerves, onset of action is significantly slower. Technique of delivery is crucial, and knowledge of anatomy can mean the difference between a successful and an unsuccessful blockade. A bolus of local anesthetic delivered immediately adjacent to a digital nerve can lead to complete digital anesthesia within 1 to 2 minutes. Poor technique and delivery of that bolus even 2 or 3 mm from the nerve trunk can delay onset of action or lead to inadequate blockade and the need for repeat injection.

    Figure 6-1

    The plane of anesthesia for local skin infiltration is just below the dermis at the junction of the superficial fascia (subcutaneous tissue).

  • Duration of anesthesia: Duration of action is significantly affected by vasoactivity of the anesthetic, blood supply of the anesthetized region, addition of epinephrine to anesthetic solutions, and formulation (bupivacaine lasts longer than lidocaine). Of the commonly used anesthetics, lidocaine produces the most vasodilation. The duration of action can be significantly shortened in areas such as the face, which is highly vascular. In addition, vasodilation can cause excessive bleeding in a wound during repair. The addition of epinephrine to lidocaine eliminates unwanted bleeding and extends the action of lidocaine by 1 hour for facial lacerations and 5 hours for extremity injuries. Bupivacaine without epinephrine also extends the duration of action 2 to 4 hours compared with lidocaine alone.

  • Differential blockade: Myelin sheath coverings of nerve fibers within axons vary in diameter and thickness. Fibers that carry stimuli from pain receptors in the skin have no myelin sheath and have the smallest diameter. The sensations of pressure and touch and motor impulses are transmitted by larger, myelinated fibers. The thin pain fibers are blocked more rapidly and more easily by local anesthetic solutions. This fact is significant in wound care because a solution of 1% lidocaine might block pain stimuli only and not the sensation of touch and pressure. An overly anxious patient may react to touch and pressure as if in pain. A higher concentration of lidocaine (e.g., 2%) abolishes all awareness of stimuli and allows for unimpeded repair. Adding epinephrine to these solutions achieves the same effect.

  • Addition of epinephrine: Adding epinephrine to local anesthetic solutions increases the duration of action and the amount of drug that can be used. Epinephrine not only extends the duration of action of lidocaine, but it also increases the intensity of the block without an increase in concentration of the anesthetic in the neuron. The extended action lasts 1.3 times to 10 times longer than the action of lidocaine alone. The extension of time is shorter on the face than on other body locales. The most useful property of epinephrine is to decrease the amount of bleeding in a wound during laceration repair. There are potential but infrequent complications to its use. The most serious side effect, ischemia, can occur if epinephrine-containing anesthetics are improperly injected into fingers, toes, tip of the nose, pinna of the ear, or penis. Caution in the use of vasoconstrictors has been expressed because of the potential for tissue damage and increased rate of infection. However, lidocaine mixed with epinephrine continues to be used successfully for laceration repair.

Anesthetic Solutions

Three anesthetic solutions are commonly used for local infiltration and simple nerve block ( Table 6-1 ): lidocaine, mepivacaine, and bupivacaine. The amide derivatives have largely replaced the older ester compounds such as procaine.


Local Anesthetics for Wound Care

Agent Onset of Action
Concentration Infiltration Block (min) Duration of Action for Blocks (min) Maximal Allowable Single Dose
Lidocaine (Xylocaine) 1%, 2% Immediate 4-10 30-120 4.5 mg/kg of 1% (30 mL per average adult)
Lidocaine (with epinephrine) 1% Immediate 4-10 60-240 7 mg/kg of 1% (50 mL per average adult)
Mepivacaine (Carbocaine) 1%, 2% Immediate 6-10 90-180 5 mg/kg or 1% (40 mL per average adult)
Bupivacaine (Marcaine, Sensorcaine) 0.25%, 0.5% Slower 8-12 240-480 3 mg/kg of 0.25% (70 mL per average adult)
Articaine 4% 1-6 min 6-10 60 7 mg/kg of 4% (12.5 mL per average adult)
Topical anesthesia See text 5-15 min 20-30 2-5 mL of mixture


Lidocaine is the most commonly used anesthetic solution. The drug has a rapid onset of action that is almost immediate in local infiltration. Lidocaine’s tissue-spreading properties are good, and it readily penetrates nerve sheaths. Duration of action for nerve blocks is approximately 75 minutes (range 60 to 120 minutes). Although there is no clear information in the literature concerning the duration of action for direct wound infiltration, the anesthetic effect wears off in approximately 20 to 30minutes, which is much sooner than with a full nerve block. A small percentage of patients appear to metabolize lidocaine rapidly and require repeated local injections. Finally, it is important to note that the low pH environment of abscesses markedly reduces the anesthetic effect of lidocaine. Field blocks, sometimes supplemented by conscious sedation, might be necessary to achieve adequate pain control when draining abscesses.

Lidocaine with Epinephrine

With the addition of epinephrine 1:100,000, the duration of action is increased, and local hemostasis is better achieved. The maximal allowable doses of lidocaine and the other local anesthetics are summarized in Table 6-1 . The addition of epinephrine increases the duration of action and reduces bleeding. It is effective for most laceration repairs and foreign-body retrievals. I have found it the most useful anesthetic combination for common wound care problems requiring a local anesthetic. Anesthetics with epinephrine are contraindicated in anatomic areas with terminal circulation, such as the fingers, toes, ears, and nose. In a study comparing lidocaine 2% with and without epinephrine for digital blocks, there were no ill effects of vasoconstriction, and the anesthesia was more effective in the epinephrine group. Although one study should not lead to the elimination of a time-honored caution against the use of epinephrine in digital blocks, it does open the question to further investigation.


Mepivacaine is widely used as an emergency wound anesthetic but has some properties that are different from lidocaine. The drug has a slightly slower onset of action: 6 to 10minutes for a simple block. The duration of action is 30 to 60 minutes, which is longer than lidocaine. Mepivacaine has a less vasodilatory effect than lidocaine and usually does not require the use of epinephrine for local wound area hemostasis.


Bupivacaine is an amide that is widely used in emergency wound care. It is an effective anesthetic, but its chief drawback is that it has slow onset of action, approximately 8 to 12 minutes for simple blocks of small nerves. The main advantage of bupivacaine is its duration of action, which is considerably longer than lidocaine and mepivacaine. In a study comparing lidocaine with bupivacaine, no significant difference was noted in the pain of local infiltration, onset of action, and level of satisfactory anesthesia. Because the anesthetic effects of bupivacaine lasted four times longer than those of lidocaine, and significantly extended the period of pain relief, bupivacaine was recommended by Fariss et al to be considered for anesthesia of lacerations sutured in the emergency department.


Articaine hydrochloride 4% (Septocaine) is an amide local anesthetic that has been used in Europe and other parts of the world for years and has now been approved for use in the United States. The only preparation available contains 1:100,000 epinephrine. Articaine is particularly effective in dental procedures because of its ability to penetrate hard tissues such as bone. It has yet to be studied for nondental procedures but can be used for facial and oral blocks. Onset of action is 1 to 6 minutes, and the duration of action is approximately 1 hour. Its safety profile is similar to other local “caine” anesthetics.

Toxicity of Local Anesthetics

The injection of local anesthetics can cause three toxic, but uncommon, reactions. Cardiovascular reactions include hypotension and bradycardia and are caused by a myocardial inhibitory effect of the anesthetic. Local anesthetic solutions can cause excitatory phenomena in the central nervous system that ultimately can culminate in seizure activity. The cardiovascular and central nervous system effects commonly are caused by an inadvertent injection of a solution directly into a vessel, causing a bolus effect on the heart or brain. A key principle in the use of local anesthetics is always aspiration of the syringe before injection to check for blood return. If blood is aspirated, the needle has to be moved to avoid injecting the solution into a vein or artery.

The most common reaction to local anesthetics is vasovagal syncope (fainting). The anxiety and pain of injection can cause dizziness, pallor, bradycardia, and hypotension. This reaction can largely be avoided with gentle handling of the patient, proper counseling, and slow and careful injection technique. No anesthetic infiltration is ever performed on a patient who is not in the supine position. Preferably the patient should be placed so that he or she cannot see the injection being administered.

Treatment of toxic reactions is largely supportive. The airway is appropriately protected, and ventilations are maintained. Hypotension and bradycardia usually are self-limited and can be reversed by placing the patient in the Trendelenburg position. An intravenous line is started with normal saline, and a bolus of 250 to 500 mL is infused to counteract hypotension in any patient who does not respond to that maneuver. Cardiac monitoring with frequent vital signs is instituted. Seizures also are self-limited but may need to be controlled by intravenous lorezapam (Ativan) or diazepam (Valium).

Allergy to Local Anesthetics

Allergic reactions are uncommon with the newer amide local anesthetics, such as lidocaine, mepivacaine, and bupivacaine. Reactions were more frequent with the older ester solutions, procaine (Novocain) and tetracaine. Multiple-dose vials still contain the preservative methylparaben, which has been implicated as a possible mediator of allergic responses. Allergic reactions are characterized by either delayed appearances of skin rashes or the acute onset of localized or general urticaria. Rarely, outright anaphylactic shock can occur. True allergic responses occur in fewer than 1% of patients receiving local anesthetics. This observation was confirmed in a study of 59 patients who reported previous reactions to local anesthetic agents. None responded adversely to skin testing and provocative drug challenge.

Management of Allergic Responses

Allergic responses are managed in the standard manner with airway control; establishment of intravenous access; and administration of epinephrine, diphenhydramine, and steroids as needed.

Alternatives for Allergic Patients

Because patients cannot always describe accurately a prior adverse reaction to a local anesthetic, and it is usually impossible to perform skin testing in an emergency department setting, the clinician may be faced with a patient who is truly allergic to local anesthetics. The following strategies are suggested:

  • For calm patients who have small lacerations, no anesthetic should be used. Often the pain of injection exceeds the pain of placing two or three sutures.

  • Ice placed directly over the wound can provide a short period of decreased pain sensation.

  • Because the preservative methylparaben has been implicated in allergic reactions, local anesthetic preparations for spinal, epidural, and intravenous anesthesia should be used. They are preservative-free. They can be obtained from the operating room of the hospital.

  • If the allergy-causing drug can be identified as an ester (tetracaine, benzocaine, chloroprocaine, cocaine, procaine), it can be substituted with an amide (lidocaine, mepivacaine, bupivacaine, diphenhydramine [Benadryl]).

  • Diphenhydramine has properties similar to standard local anesthetics. Compared with lidocaine, it provides adequate anesthesia for laceration repair for at least 30minutes. Compared with lidocaine, it is not as effective for procedures lasting longer than 30 minutes. A 50-mg (1-mL) vial is diluted in a syringe with 4 mL of normal saline to produce a 1% solution. Local infiltration is carried out in the usual manner. Diphenhydramine is more painful to inject than lidocaine, and this pain is not reduced by buffering.

Reducing the Pain of Local Anesthesia

Anesthetic Buffering

It has been demonstrated that buffering of lidocaine can reduce the pain of injection. In addition, buffering can reduce the time to onset of anesthesia and increases the intensity of the blockade. However, more recent studies, although showing a positive effect of buffering, do not reach significance when compared with nonbuffered solutions. In addition, buffering can reduce the shelf life of local anesthetics. It seems that lidocaine alone, when buffered with bicarbonate, has a shelf life of at least 7 days. Buffering also has been shown to degrade epinephrine, up to 20% of the total, within 24 hours in open containers exposed to light. Buffered solutions containing epinephrine do not show any significant epinephrine degradation in a 72-hour period if kept in a closed container that is stored in the dark. Shelf life studies of buffered mepivacaine and bupivacaine have not been performed.

Because they have shown some positive effect, the following techniques are included for the buffering of local anesthetics:

  • Lidocaine: 1 mL of bicarbonate per 9 mL of 1% lidocaine; buffering of 2% solutions may cause precipitates; shelf life 7 days

  • Mepivacaine: 0.5 to 1 mL of bicarbonate per 9 mL of mepivacaine; shelf life unknown after 24 hours

  • Bupivacaine: 0.1 mL of bicarbonate per 20 mL of bupivacaine; shelf life unknown after 24 hours

When mixing a 20-mL lidocaine or mepivacaine vial, 2 mL of anesthetic is removed and is replaced with 2 mL of bicarbonate. This technique not only ensures the correct buffering mixture, but also maintains the original volume of solution in the vial. Because shelf life is shortened, the vial should be marked or labeled with the date of preparation. Bicarbonate is available in solutions of 8.4% sodium bicarbonate stored as 50 mEq/50 mL (1 mEq/mL).

Choice of Needles

Experienced operators caring for wounds often limit themselves to 27-G or 30-G needles. Not only is a small gauge likely to reduce the pain of needle insertion, but also it reduces the rate of injection. Rapid injection and tissue expansion are significantly more painful than slow injection.

Considerable experience is necessary in handling small-diameter needles. They bend easily, and it can be difficult to judge the amount of anesthetic injected without observing plunger movement past the syringe hatch marks. It is recommended that inexperienced operators become familiar with the properties of a 25-G needle before proceeding to smaller 27-G and 30-G needles. A 25-G, 1½-inch needle can be used for most local infiltration procedures and for facial and digital blocks.

Adult Patient Sedation

Patient sedation for emergency wound care (see Chapter 5 for pediatric sedation) has become a common procedure, most commonly used for abscess drainage. Wound care can cause significant anxiety and discomfort, and patients can benefit by the administration of anxiolytics or pain relievers that supplement local anesthesia. Opiates, such as fentanyl, morphine, and meperidine (Demerol), and the benzodiazepines, midazolam and diazepam, can be delivered orally or parenterally for this purpose. Other sedative agents used for painful procedures are ketamine and nitrous oxide. Commonly used sedative and pain-reducing agents are summarized in Table 6-2 .


Agents for Adult Sedation in Wound Care Procedures

Agent(s) Initial Dose * Route
Midazolam 0.02-0.1 mg/kg IV
0.3-0.5 mg/kg Oral
Diazepam 0.05-0.10 mg/kg IV
Fentanyl 1-2 mg/kg IV
Meperidine 0.5-1 mg/kg IV, IM
Morphine 0.05-0.2 mg/kg IV, IM

* Often two doses are needed to obtain adequate sedation in many patients. The use of additional doses should be based on individual responses. In the elderly, smaller doses should be used in an incremental fashion.

Midazolam and Fentanyl are commonly used in combination for moderate sedation.

Midazolam is an effective anxiolytic that comes in oral, intranasal, parenteral, and rectal forms but is most commonly administered parenterally in adults. Intravenously, it achieves sedation in 3 to 5 minutes and has an elimination half-life of 1 hour. Alone or in combination with fentanyl, it has become commonly used for moderate sedation ( Box6-1 ). Hypoxia and oversedation are the most significant, but uncommon, side effects of midazolam. Administration must be in a controlled setting with readily available airway and resuscitation equipment. The reversal agent, flumazenil, is effective if needed to reverse the actions of this benzodiazepine. Caution must be used, however, in patients on chronic benzodiazepines, because reversal might cause seizures.

BOX 6-1

  • 1.

    Establish an intravenous infusion of normal saline (18-G catheter preferred in adults) in the supine patient with the bed rails in the up position.

  • 2.

    Pulse, respiratory rate, blood pressure, and level of consciousness should be recorded initially, after every dose of each agent, and every 5 to 10minutes throughout the procedure.

  • 3.

    Continous monitoring of oxygen saturation with a pulse oximeter probe (to maintain at >95% or no less than 3% to 5% less than the initial value) must be performed. Supplemental oxygen via nasal prongs can be administered based on need. ECG monitoring is optional but suggested in the elderly or in patients with a cardiac history.

  • 4.

    A resuscitation cart with a bag-valve mask, oral and nasal airways, endotracheal tubes, and a functioning laryngoscope must be nearby. Suction equipment and naloxone should be at the bedside.

  • 5.

    Administer 1 mg of midazolam over 30 to 60 seconds; if after 3 to 5 minutes there is no evidence of mild sedation (subjective relaxation by the patient with mild drowsiness and normal or minimally altered speech), additional 1-mg doses can be administered in a similar fashion, up to a maximum of 0.1 mg/kg. The goal is mild sedation and anxiolysis, achievable in most patients with 1 to 2 mg of midazolam.

  • 6.

    Reassess clinical status (see Step 2).

  • 7.

    Administer fentanyl

    Sublimaze, 50 μg/mL.

    100 μg (2 mL) over 60 seconds; this may be repeated in 0.5- to 1-μg/kg (50 to 100 μg) increments every 3 to 5 minutes until adequate analgesia and sedation have been obtained (slurred speech, ptosis, drowsy, but responsive to painful and verbal stimuli, and good analgesia with initial stages of procedure). The maximal total dose recommended is 5 to 6 μg/kg.

    For children, fentanyl alone is suggested in 0.5-μg/kg increments up to a maximal total dose of 2 to 3 μg/kg.

  • 8.

    Administer local anesthesia if indicated (this often helps gauge effectiveness of systemic analgesia).

  • 9.

    Perform the procedure. Additional doses of fentanyl may be required based on the response and length of the procedure.

  • 10.

    If hypoxemia, deep sedation, or slowed respirations unresponsive to external stimuli are seen during or after procedure, ventilation should be assisted with a bag-valve mask, and naloxone (0.4- to 0.8-mg increments) should be administered. Naloxone should not be given routinely at the termination of procedures because it abruptly reverses all analgesia.

  • 11.

    Continue close observation until the patient is awake and alert, and discharge the patient only after a minimum 1 hour of further observation. Instruct the patient not to drive or operate dangerous machinery for at least 6 hours.

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May 12, 2019 | Posted by in ANESTHESIA | Comments Off on Infiltration and Nerve Block Anesthesia
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