Local Skin Anesthesia

Aka: Local Skin Anesthesia, Local Anesthesia, Mepivacaine, Carbocaine, Bupivicaine, Marcaine, 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
2. 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. Infiltrate skin slowly
   3. Inject through wound edge if possible
   4. Warm Xylocaine to body temperature
   5. Be generous with local anesthetic
      1. However, may distort wound edges
   6. Use Buffered Lidocaine
      1. Bicarbonate 1 part to Xylocaine 9 part ratio
      2. Stable at room temp for one week
   7. Cool skin before injection
      1. Ice
      2. Quick spray of Liquid Nitrogen or frigiderm
      3. Avoid ethyl chloride when using electrocautery
   8. Have patient keep eyes open (analgous to Lamaze birth)
   9. Employ distraction techniques
      1. Patient lifts their own leg (Gate theory of pain)
      2. Vibrate skin or pinch skin as you inject
   10. Talk calmly to patient
   11. Consider topical anesthetic use before injection
       1. See topical pre-anesthetics below
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. 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. Local Anesthetics: Short acting Amide Anesthetics
   1. Local Lidocaine (Xylocaine) 1% or 2%
      1. Onset: 2 minutes
      2. Duration: 1.5 to 2 hours
      3. Max dose: 4 mg/kg to 280 mg (14 ml 2%, 28 ml 1%)
   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 (28 ml))
   3. Prilocaine (Citanest) 1%
      1. Onset: 2 minutes
      2. Duration: 1 hour
      3. Max dose: 7 mg/kg up to 500 mg (50 ml)
6. Local Anesthetics: Long acting Amide Anesthetics
   1. Lidocaine with Epinephrine 1:100,000 or 1:200,000
      1. Onset: 2 minutes
      2. Duration: 2 to 6 hours
      3. Max dose: 7 mg/kg to 500 mg (25 ml 2%, 50 ml 1%)
   2. Bupivacaine (Marcaine) 0.25%
      1. Onset: 5 minutes
      2. Duration: 2 to 4 hours
      3. Max dose: 2.5 mg/kg up to 175 mg (50 ml)
   3. Etidocaine (Duranest) 0.5% or 1%
      1. Max dose: 4 mg/kg to 280 mg (25 ml 1%, 50 ml 0.5%)
7. Other Local Anesthetics: Esters
   1. Procaine (Novocain)
   2. Chloroprocaine (Nesacaine)
   3. Tetracaine (Pontocaine)
8. Allergy to Local Anesthesia
   1. True amide anesthetic is rare
      1. Usually a reaction to preservative methylparaben
   2. Novocain 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. 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. References
   1. Pfenninger (1994) Procedures, Mosby, p. 135-155
   2. Mortiere (1996) Wound Management, p. 27-39
   3. Achar (2002) Am Fam Physician 66(1):91-4