CLINICAL

Overview

Background

Definitions

• Local anesthesia: refers to a temporary, reversible loss of sensation in a defined area of the body, often induced by the application of local anesthetics. 
• Local anesthetics: local anesthetics are medications that are warranted when a clinical procedure causes pain that could be eliminated by their use.[1]

Types of Local Anesthetic Agents

Tables 1 and 2 list local anesthetics commonly used in the office care setting or facility outside of ambulatory surgical centers and hospital settings.[2] Many local anesthetics fall into two general chemical classes, amino amides and amino esters.  

• Mechanism of action: local anesthetics block the conduction of nerve impulses by preventing sodium passage through the nerve sodium channels. Local anesthetic effects end when the substance is diffused away from the nerve membrane.[3]
• Factors that affect local anesthetics:
• Duration: the duration of action of local anesthetics depends on the concentration of local anesthetic and the blood flow to the nerve fiber. Also, the higher the lipid solubility of the local anesthetic, the longer the duration of action and greater potency. Local anesthetics can cause varying degrees of vasodilation, which also affects their duration of action and side effect profile.[3]
• Onset: dispersion of the local anesthetic through the tissue occurs more slowly with if the anesthetic solution has an increased acidity or if the target tissue is infected. 
•   Use of additives for local infiltrative anesthesia: 
• Sodium bicarbonate (buffering): evidence shows that the addition of sodium bicarbonate to local anesthetic in order to raise the pH (known as buffering) decreases patient pain by 20-40% during drug delivery via subcutaneous or intradermal infiltration compared to plain lidocaine with epinephrine.[2]
• Epinephrine (adrenaline):  epinephrine is the most common vasoconstrictor used in conjunction with local anesthetics.[2] Vasoconstrictors play an important role in providing optimal local anesthesia in cutaneous procedures by slowing mobilization of the anesthetic and thereby prolonging its effect, reducing peak blood levels, and providing hemostasis.[2] The most commonly used concentrations of epinephrine for office-based procedures are 1:100,000 and 1:200,000.[2] Patients with chronic wounds often present with multiple comorbidities that may pose a contraindication to the use of epinephrine mixed in anesthetic solutions. See section 'Contraindications' below.

Techniques for Local Anesthesia

This topic focuses on topical application and subcutaneous infiltration of local anesthetics but other techniques are also listed below for comparison purposes: 

• Topical application (topical anesthesia): certain anesthetic agents can be applied topically on the skin or on the wound (Table 1). These agents have been developed to replace, augment or reduce the pain of local infiltration, and thus reduce patient apprehension.[1]
• Subcutaneous infiltration (local infiltrative anesthesia): this method induces anesthesia through direct infiltration of anesthetics through the skin or wound (Table 2). Procedures including skin biopsy, wound debridement, excision, wound closure, tissue rearrangement, skin grafting, cauterization, may all be successfully performed under local infiltrative anesthesia.[2]
• Direct infiltration: this technique is better suited for intact, uninfected skin or uninfected wounds. It involves local injection of anesthetics directly through an open wound or through intact skin in the procedure field (e.g. skin that will be biopsied). See Figure 1.
• Field block: heavily contaminated, infected wounds, skin abscesses or wounds that require manipulation prior to closure should undergo a field block. In this technique, the anesthetic solution is infiltrated around the border of the surgical field, leaving the operative area undisturbed.[4] As a result, onset of the anesthetic agent is not delayed by the increased acidity of infected tissue. In addition, an advantage of this technique is that there is no tissue distortion in the operative field, allowing for more precise tissue manipulation and reconstruction.[1] See Figure 2.
• Peripheral nerve block: useful when refers larger areas must be anesthetized; in these cases, local infiltration would require large doses of anesthetic.[4] In a nerve block, anesthetic is injected into the extra-neural or paraneural spaces, providing complete anesthesia in the region supplied by that nerve, distal to the site of injection.[4]
• Tumescent anesthesia: tumescent anesthesia is a specialized form of local anesthesia in which large volumes of dilute anesthetic are injected subcutaneously to produce swelling and firmness of the targeted areas.[2] It is used for liposuction and other plastic, cosmetic, and dermatological surgical procedures involving large areas of skin. 

Table 1. Anesthetics for topical application 

Table 2. Anesthetics for local infiltration

Relevance

• Use of local anesthesia increases patient comfort and facilitates patient cooperation during procedures.[1]
• In wound management, procedures such as wound debridement, biopsy or abscess drainage often inflict pain and discomfort and thus the use of local anesthetics should be considered. A common misconception is to assume that patients with diabetic  peripheral neuropathy or with spinal cord injury would not benefit from the use of local anesthetics prior to such procedures:
• Neuropathic symptoms can be both positive or negative, that is, patients with positive symptoms usually report  burning or shooting pain, electrical or sharp sensations, or an  exaggerated response to painful stimuli.[5]    
• Patients with spinal cord injury may present with autonomic dysreflexia, an abnormal, overreaction of the involuntary (autonomic) nervous system to stimulation, such as pain. This reaction may include change in heart rate, excessive sweating, increase in blood pressure and muscle spasms.[6]

Care Setting

• Topical anesthetic application or subcutaneous infiltration of local anesthetic may be performed in several care settings, including inpatient hospital, outpatient hospital, home health, skilled nursing facilities and others, according to each facility's policies and procedures.[2]
  

Scope of Practice

Local anesthetic agents infiltration

• For registered nurses (RNs) and licensed practical nurses (LPNs) in the United States, guidance on scope of practice is provided by each state's Board of Nursing. Infiltration of local anesthetic agents (intradermal, subcutaneous, and submucosal) for the  purposes of analgesia and/or anesthesia prior to potentially painful procedures falls within the scope of practice of RNs and LPNs in several states. Clinicians should consult their respective Boards.
• For nurse practitioners, physician assistants and physicians practicing in the United States, infiltration of local anesthetic agents falls within respective scopes of practice.[7] 

Understanding Relevant Anatomy 

The 3 layers of the skin are: epidermis, dermis, and subcutaneous fat layer or subcutis (Figure 3). For details, see section 'Skin Appendages and Nerves' in topic "The Skin". 

• Input from free nerve endings (nociceptors) present in the epidermal and dermal layers are perceived as pain. Infiltration of local anesthetic into the subcutaneous layer prevents transmission of pain.
• Because nerve endings are concentrated in the dermis, intradermal injections are more painful than sub-dermal injections.[8]
• Because of their orientation and concentration in the dermis, there is a lower probability that free nerve endings may be pierced causing pain if the needle is inserted perpendicularly to the skin (i.e. at 90 degrees perpendicular to the skin) as opposed to obliquely (e.g. at 45 degrees from the skin surface).[8]

Fig. 3. Schematic of histological cut of the skin showing neural fibers. Aδ fibers: myelinated, respond to nociceptive stimuli such as cold and pressure (provide fast/first pain information). C fibers: unmyelinated, slowest neural impulse conduction, respond to temperature and pain stimuli (nociceptive). 

General Indications and Contraindications

Indications

Topical anesthesia

• 2CFor minor skin procedures (e.g. skin biopsy, small excisions, minor debridements), clinical guidelines suggest the use of topical anesthesia prior to the procedure to minimize pain (Grade 2C).[2]
• 2CFor larger procedures (e.g. debridements), clinical guidelines suggest the use of topical anesthetic agents to  lessen the pain of injection and reduce the dose of infiltration anesthesia (Grade 2C).[2] 
• For pregnant or nursing women, a limited amount of topical lidocaine is safe for use, but there is insufficient evidence to recommend use of other topical anesthetics.[2]
• 1B2CFor children, guidelines recommend topical anesthesia as the first-line method for repair of dermal lacerations (Grade 1B) and other minor procedures (Grade 2C). [2]

 Local infiltrative anesthesia

• Infiltrative anesthesia is safe and recommended for potentially painful procedures, such as obtaining a biopsy specimen, wound debridement, excision, wound closure, tissue rearrangement, skin grafting, cauterization, abscess drainage and foreign body removal from the skin.[2]

Contraindications

• Known allergies or sensitivities to a local anesthetic is a contraindication for use of that anesthetic or other agents with the same chemical classification (i.e. amide or ester; see Table 2). 
• Allergy to lidocaine is rare, with a genuine immunologic reaction representing only 1% of all adverse reactions to these medications.[2]
• For multiple wounds or large wounds that require large amounts of local anesthetics such that the total dose needed for adequate effect is expected to reach the maximum allowable anesthetic dose, infiltration of local anesthetics is not recommended. 
  

Addition of epinephrine

• Patients with chronic wounds often present with multiple comorbidities that may pose a contraindication to the use of epinephrine mixed in anesthetic solutions. Addition of epinephrine is not recommended in the following cases [9]:
• For patients with underlying comorbidities that may be exacerbated by systemic epinephrine effects (e.g., hyperthyroidism, pheochromocytoma, severe hypertension, coronary artery disease)
• Local anesthesia of wounds on limbs if patients have compromised peripheral circulation (e.g. peripheral artery disease)
• Patients taking lurasidone (may cause hypotension), ergot alkaloids (enhanced hypertensive and vasoconstrictive effect)
• For patients taking the medications below, consider avoiding epinephrine or modifying therapy due to potential drug interaction:
• Beta blockers 
  
• Monoamine oxidase inhibitors 
• Phenothiazines
• Tricyclic antidepressants 
• 2BFor local anesthesia on the ear, nose, and digits in healthy individuals, clinical guidelines suggest the addition of epinephrine to local infiltration anesthesia to minimize use of anesthetics and decrease bleeding (Grade 2B).[2]
• Rationale : although clinicians historically maintained the idea that using vasoconstrictors in areas of skin served by terminal vessels would lead to necrosis, multiple systematic reviews and randomized controlled trials have found the addition of epinephrine to local infiltrative anesthesia at a concentration of 1:100,000 and 1:200,00 to be safe for use in the digits, hands, and feet of healthy individuals.[2] However as stated above, patients with chronic wounds often present with comorbidities that may pose a contraindication to the use of epinephrine in anesthetic solutions (e.g. peripheral artery disease).Therefore as a rule, it is suggested that clinicians do not keep anesthetics with epinephrine within reach when managing patients with nonhealing wounds, to avoid accidental infiltrations of solutions containing epinephrine and potential complications.

Complications

Topical application or local infiltrative anesthesia

• Adverse reaction to the anesthetic or to preservatives (e.g. methylparaben) [10]

Local infiltrative anesthesia

• Toxicity due to anesthetic overdose (eg, seizure, cardiac arrhythmias) or sympathomimetic effects due to epinephrine  [10]
• Intravascular injection of anesthetic/epinephrine
• Hematoma
• Spread of infection, by passing the needle through an infected area

Selection of Local Anesthesia for Wound Care

Several medications and techniques for local anesthesia are available. Selection of local anesthesia is primarily based on the experience and comfort level of each clinician, but is also influenced by patient factors including contraindications to any of the local anesthetic components, duration of the procedure, need for hemostasis, and others.[2]

Choice of technique for local anesthesia in wound care

• Prior to procedures that may cause pain and are commonly performed in wound management (e.g. wound debridement, biopsies, etc), clinicians might opt to start by applying topical anesthetics, and then provide further anesthesia by infiltrating anesthetics if the patient continues to feel pain or discomfort. Exceptions include:
• Wounds with extensive tunneling, in which application of topical anesthetic may fill up the tunneling. In those cases, removal of the topical anesthetic prior to the procedure may be challenging.   
• If muscle, fascia or bone are visible on the wound bed, application of topical anesthetic on those tissues may not be necessary. However, application of topical anesthetic on the wound margin and periwound skin would help prevent/minimize pain, as free nerve endings (nociceptors) are present in the epidermal and dermal layers. 
• For patients with spinal cord injury, clinicians might opt for local infiltrative anesthesia prior to a potentially painful procedure (e.g. pressure ulcer/injury debridement) in order to avoid autonomic dysreflexia. 

Choice of local anesthetic agent in wound care

• Choice of topical anesthetics: clinical guidelines recommend use of noncocaine formulations over cocaine formulations as the latter is associated with higher costs and increased potential for side effects.[2]
• For chronic wounds, 2-5% lidocaine gel, viscous or cream applied topically have been shown to be safe and effective in reducing pain prior to debridement. Onset is typically within 3-5 minutes.[11][12][13]  
• Choice of anesthetic for local infiltration:
• For most patients with chronic wounds, clinicians might opt for buffered 1-2% lidocaine without epinephrine as the local anesthetic of choice for local infiltrative anesthesia. 
• Many patients with chronic wounds present with comorbidities (e.g. peripheral artery disease) that may pose a contraindication to the use of epinephrine in anesthetic solutions for local infiltrative anesthesia.
• For patients with true allergy to lidocaine, clinical guidelines suggest use of either ester-type local anesthetics as an alternate form of local infiltration anesthesia.[2]

HOW TO ADMINISTER LOCAL ANESTHESIA FOR WOUND CARE PROCEDURES

Assessment

• Prior to administering local anesthesia for wound care procedures, it is important that a comprehensive patient and wound assessment be performed. See topic "How to Assess a Patient with Chronic Wounds" and "How to Determine Healability of a Chronic Wound". 
• Specifically, it is important to investigate whether the patient has any history of allergies or adverse reactions to local anesthesia. Patients with history of severe reactions suggestive of anaphylaxis should not receive any local anesthetics until they undergo an evaluation by an allergy specialist. 

Procedure: application of topical anesthetic

Table 3. Procedure

Procedure: subcutaneous infiltration of local anesthetic (local infiltrative anesthesia)

Table 4. Procedure

Videos: How to Administer Local Anesthesia for Wound Care Procedures 

Video 1. Use of topical anesthetic prior to conservative sharp wound debridement. By Scott Robinson, MD

Video 2. Use of local infiltrative anesthesia prior to wound biopsy. By Scott Robinson, MD

Documentation

Documentation should include:

• History of any allergies or adverse reactions to local anesthetic(s)
• Previously existing nerve damage distal to the anesthetized area
• Type and dose of local anesthetic(s) used
• Techniques used for local anesthesia
• Document procedure and patient tolerance
  
• Patient confirmation that the area was anesthetized prior to initiating the intervention
• Any adverse reactions or complications from local anesthesia