Local anesthesia

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Local anesthesia refers to the reversible numbing of pain conduction by blocking nerve endings at and around the site of administration. It is commonly used in both adults and children for minor procedures and wound repair and is further subdivided into topical anesthesia and infiltration anesthesia, which is the loss of sensation in a localized superficial area via injection of a local anesthetic agent into subcutaneous or submucosal tissue. Contraindications include allergy to the class of anesthetic agent. The preparation consists of performing a baseline neurovascular examination and selecting the appropriate local anesthetic. Complications are rare.

See also “Regional anesthesia” and “Local anesthetic agents.”

Local anesthesia is used to decrease the pain associated with minor procedures. ^[2]

• Single point infiltration : localized painful procedures (e.g., lumbar puncture, incision and drainage)
• Local anesthesia for wound repair : larger lacerations (i.e., requiring more than one anesthetic injection)

Topical anesthesia may help reduce pain and anxiety in children before minor invasive procedures (e.g., IV placement, wound repair). ^[3]

• Absolute: medication allergy to an anesthetic class ^[4]
  • Ester anesthetics and amine anesthetics are chemically different and rarely cross-react.
  • Use a local anesthetic agent of the alternative class, if an allergy is present.
• Relative: injecting through inflamed tissue (e.g., cellulitis) at planned procedure site, if contraindicated by planned procedure ^[2]

We list the most important contraindications. The selection is not exhaustive.

Physical examination

• Perform a neurovascular examination prior to anesthetic infiltration to establish baseline function.

Medication selection

There are various combinations of local anesthetics; selection is based on the type of agent and potential benefit of additives.

• Commonly used agents: lidocaine, bupivacaine (see “Overview of local anesthetics” for additional agents)
• Common additives
  • Epinephrine: improves hemostasis, prolongs the anesthetic effect, and slows systemic absorption of the anesthetic agent
  • Sodium bicarbonate: reduces the pain of injection by buffering the anesthetic ^[2]
• Local anesthetic allergy: Consider using an agent of alternative class. ^[4]
• Dosage: varies depending on the area and sensitivity of the tissue requiring anesthesia and the individual's pain threshold
  • Choose syringe size according to the expected volume required (e.g., 5 mL or 10 mL).
  • Use sufficient anesthetic to blunt painful stimuli (pressure may still be felt).
  • Consider higher doses for inflamed tissue, e.g., abscesses.
  • Avoid exceeding the maximum local anesthetic dose.

Local anesthetic with epinephrine should be used with caution in areas supplied by end arteries (e.g., digits, penis) because of the risk of tissue ischemia. ^[6][7][8]

Calculate the maximum dose of local anesthetic, especially in pediatric patients, to avoid local anesthetic systemic toxicity.

This section describes common procedures for infiltration anesthesia in both adults and children.

Single-point local anesthesia infiltration ^[2]

1. Don PPE and prep skin.
2. Attach a 25–27 gauge needle of appropriate length to the syringe.
3. Insert the needle into the site and advance to the desired depth.
4. Aspirate to ensure the needle is not located intravascularly.
5. Inject the anesthetic slowly while withdrawing the needle.

If multiple injections are needed, minimize skin punctures by withdrawing the needle almost completely, then redirecting the needle along another path.

Local anesthesia for wound repair ^[2]

1. Don PPE and prep skin.
2. Attach a 25–27 gauge needle of a length comparable to that of the wound to the syringe.
3. Insert the needle into the subcutaneous tissue through the wound margin.
4. Advance the needle to the hub while following wound margins.
5. Aspirate to ensure the needle is not located intravascularly.
6. Inject the anesthetic slowly while withdrawing the needle.
7. Repeat as needed until wound margins are fully anesthetized.

In patients with a grossly contaminated wound, consider injecting the anesthetic agent through intact, clean skin. ^[2]

Administration of local anesthesia can be painful. The following are methods to reduce the pain associated with injection of local anesthetic. ^[9]

• Buffer the anesthetic agent using sodium bicarbonate (see “Medication selection” under “Preparation”)
• Warm the anesthetic agent
• Use the smallest diameter needle possible
• Replace used needles if multiple injections are required
• Distract the patient or ask them to look away
• Consider topical anesthesia or cooling the skin
• Insert the needle perpendicular to the skin
• Inject a subdermal wheal, allow the anesthetic agent to take effect, then continue injecting.

Complications are rare; see “Adverse effects of local anesthetic agents.”

We list the most important complications. The selection is not exhaustive.

• Definition: the loss of sensation to skin or mucosa by direct application of a local anesthetic agent (e.g., in the form of a gel, ointment, spray, or patch) ^[2]
• Indications: typically used for superficial and localized procedures, particularly in children
  • Good for anesthetizing small lacerations, intact skin, or mucus membranes
  • Common applications include minor wound repair, peripheral IV placement, and foley catheter placement
• Choice of agent is based on the intended location, e.g.: ^[2]
  • Skin: eutectic mixture of local anesthetic (EMLA) cream, lidocaine/epinephrine/tetracaine (LET) gel
  • Ophthalmic: tetracaine, proparacaine
  • Oropharyngeal: benzocaine spray, viscous lidocaine
  • Genitourinary: viscous lidocaine