Local Skin Anesthesia

Aka: Local Skin Anesthesia, Local Anesthesia, Local Infiltrative Anesthesia, Infiltration Anesthesia, Mepivacaine, Carbocaine, Bupivacaine, Marcaine, Sensorcaine, Prilocaine, Citanest, Etidocaine, Duranest

1. See Also
   1. Digital Block
   2. Lidocaine Local Skin Anesthesia (Xylocaine)
   3. Lidocaine-Epinephrine-Tetracaine (LET Anesthesia)
   4. EMLA cream
   5. Field Block
   6. Local Anesthetic Systemic Toxicity (LAST Reaction)
2. Technique: Helpful hints to make local anesthetic more comfortable
   1. Use smaller gauge needles (higher numbers)
      1. Elective procedures: 27 to 30 gauge needle
      2. Avoid using anything larger than a 25 gauge needle
   2. Prepare the injection solution
      1. Warm Lidocaine (Xylocaine) to Body Temperature
      2. Use Buffered Lidocaine
         1. Bicarbonate 1 part to Xylocaine 9 part ratio
         2. Stable at room temp for one week
   3. Prepare the site
      1. Cool skin before injection
         1. Ice
         2. Quick spray of Liquid Nitrogen, ethyl chloride or frigiderm
         3. Avoid ethyl chloride when using electrocautery
      2. Consider topical anesthetic use before injection
         1. See topical pre-anesthetics below
   4. Employ a less painful injection technique
      1. Rapidly insert needle (do not allow to needle to linger on surface)
      2. Infiltrate skin slowly and steadily while withdrawing
      3. Inject through wound edge if possible
      4. Inject into subcutaneous tissue (equivalent efficacy to injecting into skin, and less painful)
      5. Be generous with local anesthetic
         1. However, may distort wound edges
   5. Employ distraction techniques
      1. Patient lifts their own leg (Gate theory of pain)
      2. Vibrate skin or pinch skin as you inject
      3. Have patient keep eyes open (analgous to Lamaze birth)
      4. Talk calmly to patient
   6. Mixing anesthetics offers no benefit
      1. Lidocaine (1 hour duration) and Bupivicaine (2-4 duration) have very similar onset of action (3 minutes)
      2. Select one agent for local anesthetic based on desired duration of anesthesia
      3. Ribotsky (1996) J Am Podiatr Med Assoc 86(10): 487-91 [PubMed]
      4. Alhelail (2009) Emerg Med J 26(5): 347-50 [PubMed]
3. Pharmacokinetics
   1. Amide and Ester anesthetic metabolism and excretion
      1. Metabolized by liver
      2. Excreted by Kidney
   2. Dose calculations
      1. Solution of 0.5%: 5 mg/ml
      2. Solution of 1%: 10 mg/ml
      3. Solution of 2%: 20 mg/ml
4. Preparations: Topical pre-anesthetics
   1. Ethyl Chloride Spray
      1. Do not use with electrocautery
      2. Site sprayed for 1-2 seconds
      3. Offers 1-2 seconds of anesthesia
   2. Lidocaine-Epinephrine-Tetracaine (LET)
      1. Replaces Tetracaine, Adrenaline, Cocaine (TAC)
      2. Indicated for open wound
      3. May be especially useful in children
   3. EMLA cream (Eutactic Mixture of Local Anesthetic)
      1. Indicated in closed wounds
      2. Apply ointment under Occlusion
      3. Use 90 minutes prior to injection
      4. ELA-Max (OTC) may offer similar effect (see below)
   4. Iontophoresis
      1. Lidocaine sponges applied to intact skin
      2. DC current applied to electrodes over anesthetic
      3. Onset within 10 minutes and duration of 15 minutes
      4. Penetration depth of 1-2 cm
      5. As effective as EMLA cream
   5. Other measures with unknown efficacy in procedures
      1. Lidocaine 4% in liposomal matrix (ELA-Max)
         1. Similar application as with EMLA cream
      2. Anesthetic Patch (Lidoderm)
5. Preparations: Local Anesthetics - Short acting Amide Anesthetics
   1. Local Lidocaine (Xylocaine) 0.5%, 1% or 2%
      1. Onset: 2-5 minutes
      2. Duration: 1 hour (up to 1.5 to 3 hours in some cases)
      3. Max dose: 4 mg/kg to 300 mg/dose (15 ml 2%, 30 ml 1% or 60 ml 0.5%)
         1. Epinephrine increases Lidocaine duration or activity and maximal safe dose to 7 mg/kg (see below)
   2. Mepivacaine (Carbocaine) 1%
      1. Onset: 3 to 5 minutes
      2. Duration: 1.5 to 2 hours
      3. Max dose: 4 mg/kg up to 280 mg/dose (28 ml))
   3. Prilocaine (Citanest) 1%
      1. Onset: 2 minutes
      2. Duration: 1 hour
      3. Max dose: 7 mg/kg up to 500 mg/dose (50 ml)
6. Preparations: Local Anesthetics - Long acting Amide Anesthetics
   1. Lidocaine with Epinephrine 1:100,000 or 1:200,000
      1. Onset: 2 minutes
      2. Duration: 1 to 4 hours (up to 6 hours in some cases)
      3. Max dose: 7 mg/kg to 500 mg/dose (25 ml 2%, 50 ml 1%)
   2. Bupivacaine (Marcaine) 0.25% or 0.5%
      1. Onset: 5 minutes
      2. Duration: 2 to 4 hours (up to 6 hours, esp. when combined with Epinephrine)
      3. Max dose: 1.25 mg/kg up to 175 mg/dose (35 ml 0.5%, 70 ml 0.25%)
      4. Avoid in pregnancy (increased bioavailability, crosses placenta)
      5. Always confirm not intravascular (withdraw first) as risk of lethal arrhythmias (Ventricular Fibrillation)
         1. See LAST Reaction
         2. Less risk of systemic absorption when combined with Epinephrine
   3. Etidocaine (Duranest) 0.5% or 1%
      1. Max dose: 4 mg/kg to 280 mg/dose (25 ml 1%, 50 ml 0.5%)
7. Preparations: Local Anesthetics - Esters
   1. Background: Mnemonic to distinguish the Ester Anesthetics from the Amide Anesthetics
      1. Amides have two "i"
      2. Esters have one "i"
   2. Chloroprocaine (Nesacaine)
   3. Procaine (Novocain) 1%, 2%
      1. Onset: 2-5 minutes
      2. Duration: 15 to 60 minutes
      3. Max Dose: 7 mg/kg up to 600 mg/dose (30 ml 2%, 60 ml 1%)
   4. Tetracaine (Pontocaine) 0.5%
      1. Onset: 5-10 minutes
      2. Duration: 2-3 hours
      3. Max Dose: 1.4 mg/kg up to 120 mg/dose (24 ml 0.5%)
8. Adverse Effects: Allergy to Local Anesthesia
   1. True amide anesthetic is rare
      1. Usually a reaction to preservative methylparaben
   2. Novocaine allergy does not predict Lidocaine allergy
      1. Lidocaine is an amide and novocaine an ester
      2. Lidocaine may be used if novocain allergy
   3. Options if history of Lidocaine allergy
      1. Preservative-free Lidocaine (single use bottles)
      2. Select an ester anesthetic (e.g. Nesacaine, Procaine, Tetracaine)
      3. Diphenhydramine Hydrochloride 1%
         1. Dilute 50 mg (1 ml) in 4 ml Normal Saline
         2. Equivalent to Lidocaine 1% activity
         3. Avoid use in peripheral Nerve Block
9. Resources
   1. Local Anesthetics: Clinical Pharmacology and Rational Selection
      1. http://www.nysora.com/regional-anesthesia/foundations-of-ra/3492-local-anesthetics-clinical-pharmacology-and-rational-selection.html
10. References
    1. Acker, Koval and Leeper (2017) Crit Dec Emerg Med 31(4): 3-13
    2. Pfenninger (1994) Procedures, Mosby, p. 135-155
    3. Mortiere (1996) Wound Management, p. 27-39
    4. Achar (2002) Am Fam Physician 66(1):91-4 [PubMed]
    5. Latham (2014) Am Fam Physician 89(12): 956-62 [PubMed]