Local Anaesthesia in Dermatologic Surgery

• Local anesthetics are classified into two groups — amides and esters — depending on the linkage in their intermediate chain.
• “Anesthetic allergies” vary from palpitations secondary to epinephrine and vasovagal reactions, to urticaria and anaphylaxis from preservatives or the local anesthetic (especially esters).
• Additives to local anesthetic: epinephrine, sodium bicarbonate, and hyaluronidase.
• Nerve blocks are particularly helpful for procedures on the face, digits, and palmoplantar surfaces.

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• Effective anesthesia is essential to dermatologic surgery; almost all dermatologic surgical procedures can be performed under local anesthesia.
• Local anesthetics in use since the 1880s with cocaine hydrochloride, extracted from the leaves of the South American bush Erythroxylon coca.
• Procaine 1904; tetracaine 1930; lidocaine — the FIRST amide local anesthetic — 1943.
• Introduction of lidocaine was a major breakthrough: far less likely to cause an allergic reaction than the preceding ester-type anesthetics.
• Advantages of local over general anesthesia: reduced morbidity (especially in poor-risk patients), reduced cost, reduced procedure time, faster recovery.
• Disadvantages: some limitation on extent of a procedure; possibility of greater patient discomfort from the injections.
• Knowledge of physiology, dosage, side effects, and proper “painless” technique is essential for safety and satisfaction.

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• Local anesthetics act by blocking sodium channels in the axon cell membrane → prevents sodium entering the nerve cell → nerve cell is not depolarized → action potential is blocked.
• The cationic form binds to the inner pore of voltage-gated sodium channels, possibly causing both narrowing of the pore lumen (steric block) and creation of an electrostatic barrier to permeation.

• Smaller unmyelinated C-type fibers conducting pain are blocked most quickly and easily.
• Intermediate fibers carrying heat and cold sensation are blocked next.
• Myelinated A-type fibers carrying pressure sensation and motor fibers are blocked LAST.
• Clinical correlate: an area seems fully anesthetized for scalpel surgery, but the patient still feels the pressure of the surgeon's fingers.

• All local anesthetics have three parts:
• a secondary or tertiary amine end;
• an aromatic end;
• an intermediate connecting chain containing an ester or amide.
• Aromatic portion — hydrophobic and lipophilic; essential to allow diffusion through nerve cell membranes.
• Amine portion — hydrophilic; responsible for water solubility (important for preparing, storing, administering).

• Local anesthetics are weak organic bases; to be water-soluble and injectable they require the addition of a hydrochloride salt.
• In aqueous solution the salt equilibrates between ionized and non-ionized forms.
• Ionized form is water-soluble → allows injection into and diffusion through tissue.
• Non-ionized, lipid-soluble base is what can diffuse into the nerve cell membrane.
• Within the sodium channel's inner pore, it is the ionized cation that blocks nerve conduction.
• The dissociation constant (pKa) of each anesthetic determines the proportion of base to cation at a given pH.
• The pKa of ALL local anesthetics is HIGHER than physiologic pH.
• For most local anesthetics at pH 7.4, 80% or more is in the cationic ionized form.
• Alkalinization (adding sodium bicarbonate) speeds onset of action — more anesthetic in the non-ionized form.
• If pH is raised too much, the anesthetic may PRECIPITATE out of solution.
• pH sensitivity explains why infected tissue is difficult to anesthetize: inflammation acidifies the site (reduces pH) → reduces the proportion of anesthetic in the non-ionized, lipid-soluble form.

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• Two groups by intermediate-chain linkage: amide anesthetics (amide linkage) and ester anesthetics (ester linkage).
• They differ in how they are metabolized and in the risk of sensitization.

• Hydrolyzed by plasma pseudocholinesterase; metabolites excreted by the kidneys.
• Patients with deficiency of functional pseudocholinesterase — often diagnosed after prolonged paralysis following standard doses of succinylcholine — are at increased risk of ester anesthetic toxicity.
• The metabolite para-aminobenzoic acid (PABA) is responsible for allergic reactions with ester anesthetics.

• Metabolized by the hepatic microsomal cytochrome P450 enzyme system; metabolites excreted by the kidneys.
• Patients with severe liver disease may be at increased risk of amide anesthetic toxicity.

• LOW pKa → RAPID onset (more anesthetic in the non-ionized form).
• Greater lipid solubility → HIGHER potency (penetrates the nerve cell membrane more easily).
• Duration of action is determined by the strength of anesthetic binding to the sodium channel pore.

• Local anesthetic of choice in pregnancy = LIDOCAINE; historically FDA pregnancy category B (no teratogenic effects in animal studies).
• Studies in women receiving lidocaine in the first trimester show no increase in anatomic abnormalities in newborns.
• Still, use lidocaine (as with all pharmacologic agents) cautiously during the first 4 months of pregnancy, when maximum organogenesis takes place.
• Lidocaine crosses the placenta into the fetus.
• Lidocaine can be safely used in nursing mothers, recognizing some may be excreted in breast milk.
• Lidocaine can be safely used in children, but the maximum recommended dosage must be adjusted downward based on the child's weight and age.
• Care in premature infants due to cardiovascular effects.
• Parabens (preservatives) are bound to albumin; in a jaundiced newborn they could displace bilirubin from albumin, worsening hyperbilirubinemia → only PARABEN-FREE anesthetics should be used in newborns.

(Generic — Trade — Onset (min) — Duration plain (h) — Max dose plain (mg/70 kg) — Max dose with epinephrine (mg/70 kg))

Amides

• Articaine — Septocaine — 2–4 — 0.5–2 — 350 — 500
• Bupivacaine hydrochloride — Marcaine — 5–8 — 2–4 — 175 — 225
• Etidocaine — Duranest — 3–5 — 3–5 — 300 — 400
• Levobupivacaine hydrochloride — Chirocaine — 2–10 — 2–4 — 150 — Not available
• Lidocaine — Xylocaine — Rapid — 0.5–2 — 350 — 500 (3500 dilute)
• Mepivacaine — Carbocaine — 3–20 — 0.5–2 — 300 — 500
• Prilocaine hydrochloride — Citanest — 5–6 — 0.5–2 — 400 — 600
• Ropivacaine — Naropin — 1–15 — 2–6 — 200 — Not available; addition of epinephrine has NO effect on onset or duration of ropivacaine

Esters

• Chloroprocaine hydrochloride — Nesacaine — 5–6 — 0.5–2 — 800 — 1000
• Procaine — Novocaine — 5 — 1–1.5 — 500 — 600
• Tetracaine — Pontocaine — 7 — 2–3 — 100 — Not available

• Table notes: in clinical practice the duration of anesthesia appears to be LESS than stated, especially for head and neck areas. Addition of epinephrine prolongs anesthesia by a factor of two. 1% lidocaine solution = 10 mg/ml.

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• All local anesthetics EXCEPT cocaine hydrochloride relax vascular smooth muscle → vasodilation → increased bleeding at the operative site and reduced duration of anesthetic action (anesthetic rapidly removed via dilated vessels).
• Epinephrine (adrenaline) constricts blood vessels → prolongs duration of anesthesia by 100% to 200% by slowing removal of anesthetic from the site.
• Also reduces intraoperative bleeding via vasoconstriction.
• Provides more effective anesthesia by decreasing the volume of anesthetic needed; the reduced absorption rate decreases anesthetic toxicity and allows larger doses to be used safely.
• The vasoconstrictive effect (manifested by skin blanching) takes about 15 minutes to fully develop; while they usually coincide, blanching does NOT always denote the anesthetized area.

Concentrations

• Premixed with local anesthetics at 1 : 100 000 or 1 : 200 000.
• Concentrations as low as 1 : 1 000 000 achieve effective vasoconstriction.
• Concentrations >1 : 100 000 are associated with greater risk of side effects.
• Individualize: lower concentrations in patients with relative contraindications; higher concentrations in highly vascular areas such as the scalp.
• At 1 : 100 000, the maximum dose used is determined by the anesthetic with which epinephrine is premixed.
• Adding 0.5 ml epinephrine (1 : 1000) to 50 ml plain lidocaine gives a final concentration of 1 : 100 000.

Contraindications and cautions

• Epinephrine is a strong β- and α-agonist → use cautiously in patients with altered β- and α-receptors.
• ABSOLUTE contraindications: HYPERTHYROIDISM and PHEOCHROMOCYTOMA.
• Patients taking β-blockers, monoamine oxidase inhibitors, tricyclic antidepressants, and phenothiazines are more sensitive to epinephrine → use with caution, reduce dose and concentration.
• In patients on β-blockers, severe hypertension after injection of epinephrine-containing anesthetics has been reported — probably due to unopposed α-adrenergic activity with associated vasoconstriction; quite rare, mainly with higher doses.
• Patients with severe hypertension or severe cardiovascular disease (especially coronary artery disease) may have underlying disease exacerbated by large amounts of epinephrine.
• High doses of epinephrine can induce LABOR; however, the low doses used in cutaneous surgery can be safely used during pregnancy.
• Avoid epinephrine in the periorbital area in patients with NARROW ANGLE GLAUCOMA — may aggravate the glaucoma.

Epinephrine on digits

• Historically avoided for fear of vasoconstriction causing digital necrosis.
• More recent studies show no increased risk from epinephrine in digital anesthesia.
• Most cases of digital necrosis occurred due to: vessel compression from too much anesthetic volume (tamponade), constricting circumferential dressings, tourniquets, postoperative hot soaks (possibly heat-induced edema), infection, use of vasoconstrictive anesthetics such as cocaine hydrochloride, or non-standard mixing of lidocaine with epinephrine.
• No evidence of digital necrosis due SOLELY to commercially available lidocaine with epinephrine.
• Epinephrine IS contraindicated for digital anesthesia in patients with PERIPHERAL ARTERY DISEASE.
• Author's practice: lidocaine with dilute epinephrine (1 : 500 000) and small volumes provides safe digital anesthesia; ring blocks of the digit should be AVOIDED.

Epinephrine side effects

• Self-limited systemic: palpitations, anxiety, fear, diaphoresis, headache, tremor, weakness, tachycardia, elevated blood pressure.
• Can be seen even with normal doses used for skin surgery; usually resolve within a few minutes.
• More common when injecting highly vascular areas, especially the face and scalp.
• Skin necrosis from vasoconstriction — extremely rare; an issue only with severe vascular compromise at the injection site.
• Serious: cardiac arrhythmias (ventricular tachycardia, ventricular fibrillation), cardiac arrest, cerebral hemorrhage — none expected at doses used for skin surgery, but limit total dose in patients with severe cardiac disease.

pH and stability

• Epinephrine is stable ONLY in an acidic environment.
• Premixed anesthetic + epinephrine has the pH lowered into the 3.5 to 5.5 range with acidic preservatives such as sodium metabisulfite to stabilize epinephrine.
• This acidic solution is more painful on injection and slows onset of anesthetic action (less anesthetic in the non-ionized form).
• Preparing the mixture fresh daily and using it by the end of the day yields a higher pH and is less painful; alternatively, neutralize with sodium bicarbonate.

• Injecting standard lidocaine with epinephrine at pH 3.5 to 5.5 is quite painful, with significant stinging from the acidic pH.
• Buffering ratio: add ONE part 8.4% sodium bicarbonate to TEN parts lidocaine with epinephrine → brings pH into a more physiologic 7 to 8 range.
• This significantly reduces the pain of injection.
• Both components can be drawn up into the syringe immediately before injection.
• Alternatively, 5 ml sodium bicarbonate (8.4%) added to a 50 ml bottle of lidocaine with epinephrine.
• Epinephrine activity is lost at a rate of 25% per WEEK in an alkaline or neutral environment → label the mixture with the date prepared, keep refrigerated, and use within about 1 week.
• Evolving FDA and United States Pharmacopeia (USP) guidance (USP <797>) requires any buffered local anesthetic (in-office “compounding”) to be used within 4 HOURS of preparation.
• As state boards of pharmacy adopt this guidance, physicians in those states must comply.
• Several dermatology societies are developing a USP monograph to extend the usable time after preparation.

• Derived from bovine testicular hyaluronidase; depolymerizes hyaluronic acid, breaking up ground substance → allows anesthetics to diffuse further from the injection point.
• Results in less distortion of the injected structures.
• Greater diffusion may DECREASE the duration of action.
• Most useful for periorbital surgery and to increase the rate of successful nerve blocks.
• Preparation: 150 units (U) added to 30 ml of local anesthetic.
• Allergic reactions are rare but can occur; some surgeons recommend an intradermal skin test before use.
• The preparation may contain thimerosal preservative, which can cause contact dermatitis.

• Some surgeons combine two local anesthetics in one syringe — e.g. lidocaine (rapid onset) with bupivacaine hydrochloride (longer duration).
• A study found these mixtures do NOT live up to their promise — the mixture takes on the properties of one component to the exclusion of the other.
• Therefore most surgeons inject the rapid-onset anesthetic FIRST and the longer-acting anesthetic LATER — minimizing injection pain and maximizing duration.

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• BY FAR THE MOST COMMON side effect of local anesthetic injection.
• The vagus nerve discharges due to patient anxiety → increase in parasympathetic tone.
• Manifested by dizziness, diaphoresis, syncope, bradycardia, and hypotension.
• Trendelenburg position rapidly relieves symptoms; a cold towel on the forehead can also help.
• Oxygen, fluids, atropine, or epinephrine are usually NOT necessary.
• To avoid significant vasovagal reactions, infiltrate local anesthetic with the patient in the recumbent position.

• The most important side effect of local anesthetics.
• Usually a type I IgE-mediated reaction: urticaria, angioedema, bronchospasm, and rarely anaphylaxis with hypotension and tachycardia.
• Most true local anesthetic allergies are reported with ESTER anesthetics; AMIDE anesthetics are implicated only very rarely.
• Preservatives in multidose vials — especially methylparaben and sodium metabisulfite — have frequently been shown to be the cause of “local anesthetic” allergy.
• There is some cross-reactivity among the various esters and among the amides, but NO cross-reactivity BETWEEN the ester and amide classes.
• PABA (the metabolite of ester anesthetics) is thought responsible for ester anesthetic allergy.
• Esters can also cause type IV delayed hypersensitivity reactions and cross-react with several contact sensitizers: PABA, para-amino salicylic acid, and para-phenylenediamine (PPD).

Evaluating a reported anesthetic allergy

• Question in detail with review of relevant medical records whenever possible — often the “allergy” is a vasovagal reaction or epinephrine sensitivity.
• If a true allergic reaction and the offending anesthetic is known (usually an ester), use an anesthetic from the other class (usually an amide) in a preservative-free solution.
• Skin testing by an allergist may be warranted if the offending agent is uncertain — should include pinprick followed by intradermal tests of an ester anesthetic, an amide anesthetic, methylparaben, and sodium metabisulfite.
• Alternative for small procedures: intradermal injection of 1% diphenhydramine solution.
• Epinephrine may be added to counteract diphenhydramine-induced vasodilation, enhance the anesthetic effect, and reduce systemic antihistamine symptoms.
• Intradermal normal saline with benzyl alcohol preservative achieves very brief anesthesia through pressure effects on cutaneous nerve endings and the anesthetic properties of the benzyl alcohol; useful for very short procedures such as a shave biopsy.

Management of allergic reactions

• Limited reactions: oral antihistamines and prednisone.
• Bronchospasm, angioedema, or hemodynamic compromise require immediate emergency management: subcutaneous epinephrine, bronchodilators, parenteral antihistamines, corticosteroids, intravenous fluids, and oxygen.

• Bruising and edema are frequent after infiltration, especially in the periorbital area.
• Periorbital edema will often develop after surgery on the forehead and frontal scalp.
• Transient motor nerve paralysis is sometimes seen.
• May be delayed for some time after the sensory nerves are anesthetized, because of the large myelinated nerve fibers involved.
• May persist for several hours after sensory nerves have returned to normal.
• Inform the patient when a motor nerve has been affected — eliminates distressed telephone calls.
• Prolonged sensory nerve paresthesia may develop if a sensory nerve is injured by intraneural injection — most commonly after NERVE BLOCKS.
• Minimized by avoiding intraneural injections and using small-gauge needles.

• Clinical symptoms of overdose are unlikely if dosage is kept within recommended ranges.
• Maximum recommended lidocaine dosages:
• 5 mg/kg PLAIN (no epinephrine);
• 7 mg/kg WITH epinephrine at standard (1%–2%) concentrations;
• 35–50 mg/kg for TUMESCENT lidocaine anesthesia consisting of dilute 0.05%–0.1% lidocaine with 1 : 1 000 000 epinephrine.
• Symptoms are directly related to the serum blood level, with worsening CNS and cardiovascular signs as level rises.
• CNS sequence: circumoral and digital numbness and tingling → lightheadedness → tinnitus → visual disturbances → slurred speech → muscle twitching → seizures and coma.
• Cardiovascular and pulmonary symptoms develop at SIGNIFICANTLY HIGHER doses than early CNS symptoms: hypotension, arrhythmias, respiratory depression, cardiac arrest.

Drug interactions

• Over 150 potential drug–drug interactions with lidocaine; most minor or relevant only with large doses.
• Inhibitors of hepatic cytochrome P450 (e.g. erythromycin, ketoconazole, itraconazole; Ch. 131) inhibit lidocaine metabolism → signs of overdose at lower doses.
• With large lidocaine doses: patients on class I and III antiarrhythmics (e.g. amiodarone) are at increased risk of cardiac arrhythmias; those on CNS depressants (e.g. opiates) are at increased risk of CNS toxicity.

Agent-specific toxicities

• Bupivacaine hydrochloride has a GREATER risk of CARDIAC TOXICITY than lidocaine.
• Prilocaine hydrochloride metabolizes to ortho-toluidine, an oxidizing agent capable of converting hemoglobin to methemoglobin — significant with large doses of more than 500 mg.
• Benzocaine has also been implicated in methemoglobinemia when used on mucosal surfaces.
• Treatment of methemoglobinemia = METHYLENE BLUE infusion.

(Diagnosis — pulse — BP — signs/symptoms — emergency management)

• Vasovagal reaction — pulse LOW — BP LOW — excess parasympathetic tone; diaphoresis, hyperventilation, nausea — Trendelenburg position, cold compress, reassurance.
• Epinephrine reaction — pulse HIGH — BP HIGH — excess α- and β-adrenergic receptor stimulation; palpitations — reassurance (usually resolves within minutes), phentolamine, propranolol.
• Anaphylactic reaction — pulse HIGH — BP LOW — peripheral vasodilation with reactive tachycardia; stridor, bronchospasm, urticaria, angioedema — epinephrine 1 : 1000, 0.3 ml subcutaneous, antihistamines, corticosteroids, fluids, oxygen, airway maintenance.
• Lidocaine overdose, 1–6 mcg/ml — pulse normal, BP normal — circumoral and digital paresthesias, restlessness, drowsiness, euphoria, lightheadedness — observation.
• Lidocaine overdose, 6–9 mcg/ml — pulse normal, BP normal — nausea, vomiting, muscle twitching, tremors, blurred vision, tinnitus, dysgeusia (e.g. metallic taste), confusion, excitement, psychosis — diazepam, airway maintenance.
• Lidocaine overdose, 9–12 mcg/ml — pulse LOW, BP LOW — seizures, cardiopulmonary depression, arrhythmia — respiratory support.
• Lidocaine overdose, >12 mcg/ml — pulse severely low, BP severely low — coma, cardiopulmonary arrest — cardiopulmonary resuscitation and life support.
• Table note: in systemic reactions during/after local anesthetic injection, hemodynamic signs are helpful in determining the cause.

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• Historically the only anesthetic for topical anesthesia of keratinized skin was benzocaine (an ester).
• Generally effective only on traumatized skin; little if any anesthesia on intact normal skin.
• Of greater concern: high rate of allergic contact dermatitis with benzocaine.

EMLA®

• A eutectic mixture of 2.5% lidocaine and 2.5% prilocaine hydrochloride; available as a cream or a disc.
• Achieves superficial anesthesia; degree relates to the amount and duration of application before surgery.
• Cream applied as a thick layer under occlusion at least 1 hour before the procedure; the disc itself provides occlusion.
• Especially useful for reducing pain of non-ablative laser procedures and the pain of local anesthetic or other injections.
• Some dermatologists performing CO2 laser ablative resurfacing solely under EMLA®: prepare skin with vigorous degreasing, then two applications of EMLA® 1 hour apart under occlusion; additional EMLA® applied after the first laser pass has removed the epidermis.
• Safety: caution with large amounts on skin with a damaged skin barrier and in infants susceptible to methemoglobinemia from too much prilocaine absorption.
• Should NOT be used in patients with G6PD deficiency.
• Often blanches the skin after application, followed by vasodilation 30–60 minutes after removal; vasodilation is usually of no clinical significance, but petechiae and purpura at the application site have been reported.
• Other reported side effects: occasional burning and irritation, chemical injury to the eye, contact urticaria, and allergic contact dermatitis — the latter two most often due to the prilocaine component.

Other topical preparations

• LMX® — 4% or 5% lidocaine.
• Topicaine® — 4% lidocaine.
• 4% tetracaine gel.
• 30%–40% lidocaine in acid mantle cream.
• Various compounded mixtures of lidocaine, benzocaine, and tetracaine.
• Due to safety issues with compounded medications, the FDA has severely restricted access to compounded topical anesthetics.
• Comparison study ranking: EMLA® and LMX® 4% > tetracaine 4% gel > Betacaine LA® > control.
• Per the manufacturer, LMX® does NOT require occlusion to be effective.
• EMLA® under occlusion vs LMX® unoccluded: LMX® achieved equivalent anesthesia after LESS THAN ONE-THIRD of the application time.
• NONE of the topical anesthetics have any significant effectiveness for PALMAR or PLANTAR surfaces.
• Pliaglis® — 7% lidocaine / 7% tetracaine; a cream when cold, but on the skin exposed to air becomes a flexible membrane that can be peeled off once anesthesia is achieved (after about 30 minutes); useful for laser procedures; anesthetic level equivalent to other topical anesthetics.

Enhancing topical anesthesia

• Iontophoresis of 1%–4% lidocaine with epinephrine enhances depth and effectiveness; practical only for rather small areas; anesthesia within a few minutes with a 1 mA current; drawback is additional equipment and supplies.
• Ultrasound or warm steaming of the skin also enhances effect, probably by enhancing penetration.
• Fractionated ablative lasers and skin microneedling devices enhance penetration of topical anesthetics → improved local anesthesia.
• For multi-pass laser treatments of large areas, these techniques may reduce the need for injectable anesthetics.

Clinical use and cautions

• Useful primarily for non-invasive laser, intense pulsed light, and other energy-based therapies (Ch. 137).
• Helpful in reducing pain of needle insertion and some pain of injection when injecting local anesthetics, botulinum toxin, or filler materials such as hyaluronic acid–based fillers that sting on injection due to their acidity.
• Filler materials are now frequently premixed with lidocaine to reduce injection pain.
• Anesthesia is too unpredictable to use topical skin anesthetics even for minor surgical procedures such as skin biopsies, curettage, or electrodesiccation.
• Preparations differ in recommended application times and occlusion needs; for maximal effectiveness apply a THICK layer UNDER OCCLUSION for at least 1 hour.
• CAUTION with large areas, especially compounded mixtures with high lidocaine concentrations — several DEATHS have been reported in patients applying compounded topical anesthetics under occlusion to their entire lower extremities.

• Topical anesthetics for mucous membranes are far more effective than skin anesthetics — the stratum corneum barrier is absent.
• One to two drops of 0.5% tetracaine into each eye achieves complete conjunctival anesthesia after a few seconds of stinging — allows insertion of eye shields or painless injection through the conjunctiva.
• Proparacaine (proxymetacaine) hydrochloride — equally effective alternative conjunctival anesthetic with less stinging.
• A 2%–10% solution of cocaine hydrochloride is the topical anesthetic of CHOICE for INTRANASAL anesthesia, because of its excellent vasoconstrictive and hemostatic properties.
• Onerous record-keeping requirements make it relatively impractical for in-office use.
• Due to significant cardiac stimulatory effects, use with caution in patients with significant heart disease.
• Oral and anal mucosa — effectively anesthetized within a couple of minutes with 2%–4% lidocaine jelly or viscous lidocaine, as well as various benzocaine-containing preparations.
• Topical intraoral anesthesia is especially helpful in reducing the pain of nerve block injections done via the intraoral route.

(Generic — Trade — Concentration % — Type — Primary use)

• Benzocaine — Americaine otic — 20 — Ester — tympanic membrane.
• Benzocaine gel, liquid, spray — HurriCaine — 20 — Ester — mucous membranes.
• Benzocaine/tetracaine/butamben (butyl aminobenzoate) gel, liquid, spray — Cetacaine, Exactacain — Esters — mucous membranes.
• Benzocaine/lidocaine/tetracaine compounded — Various — Ester/amide/ester — intact skin.
• Cocaine hydrochloride nasal solution — Goprelto, Numbrino — 2–10 — Ester — nasal mucosa.
• Dibucaine (cinchocaine) — Nupercainal — 1 — Amide — mucous membranes.
• Lidocaine cream — LMX — 4–5 — Amide — intact skin (4%); anorectal (5%).
• Lidocaine gel — Topicaine 4 — 4 — Amide — intact skin.
• Lidocaine solution — Xylocaine — 2–5 — Amide — mucous membranes.
• Lidocaine in acid mantle cream — compounded — 30–40 — Amide — intact skin.
• Lidocaine/prilocaine eutectic mix [cream or disc] — EMLA — 2.5/2.5 — Amides — intact skin.
• Lidocaine/prilocaine cream — Lidopril — 2.5/2.5 — Amides — intact skin.
• Lidocaine/tetracaine peel — Pliaglis — 7/7 — Amide/ester — intact skin.
• Lidocaine/tetracaine patch — Synera — 7/7 — Amide/ester — intact skin.
• Proparacaine (proxymetacaine) ophthalmic solution — Alcaine — 0.5 — Ester — conjunctiva.
• Tetracaine gel — Tetracaine gel — 4 — Ester — intact skin.
• Tetracaine ophthalmic solution — Pontocaine — 0.5 — Ester — conjunctiva.
• Table notes: anesthetics for topical skin anesthesia require application 0.5–2 hours prior to surgery under occlusion for maximal effect. Benzocaine is a potent topical sensitizer.

(Age — weight (kg) — max total dose of cream (g) — max area (cm²) — max time (hours))

• <3 months — <5 kg — 1 g — 10 cm² — 1 hour
• 3–12 months — 5–10 kg — 2 g — 20 cm² — 4 hours
• 1–6 years — 10–20 kg — 10 g — 100 cm² — 4 hours
• 7–12 years — >20 kg — 20 g — 200 cm² — 4 hours
• Because of the prilocaine, EMLA® should NOT be used in:
• premature neonates with gestational age <37 weeks — increased risk of methemoglobinemia due to immature reductase pathways;
• young children (especially <1 year of age) receiving medications that may increase risk of methemoglobinemia — e.g. acetaminophen, antimalarials, dapsone, nitrofurantoin, nitroglycerin, phenobarbital, phenytoin, sulfonamides.

(Age — weight — max area — max time)

• <12 months — <10 kg — 100 cm² (4 × 4 in) — 1 hour
• 1–6 years — 10–20 kg — 200 cm² (5.5 × 5.5 in) — 2 hours
• 7–12 years — >20 kg — 600 cm² (9 × 9 in) — 2 hours
• Calculation: 0.072 mg 4% lidocaine absorption/cm²/h × 600 cm² × 2 h = 86 mg (≤4 mg/kg).
• Cream should be applied to intact skin, with or without occlusion.
• Currently NOT FDA approved for children <2 years of age — application in that age group is off-label.

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• Rapid cooling of the skin surface is routine for many non-ablative laser procedures.
• Methods:
• a short burst of cryogen sprayed onto the skin surface (Dynamic Cooling Device™);
• a cold glass window placed directly onto the treated site (contact cooling);
• an iced gel placed on the treated surface (passive cooling);
• −5°C refrigerated air blown onto the skin surface with a coupling gel in place (Cryo 5™).
• All methods cool the skin to reduce the pain of laser treatment and protect the epidermis from laser-induced heat injury.
• Dermabrasion can be done entirely under cryoanesthesia by freezing the skin with a cryogen spray before dermabrading.
• The most effective and safe cryogen sprays (Frigiderm®, Fluro-Ethyl®) contain chlorofluorocarbons harmful to the ozone layer — manufacture has been DISCONTINUED.
• Ethyl chloride spray achieves brief anesthesia via evaporative cooling to reduce the pain of needle insertion.
• An ice cube or −5°C forced air cooling will likewise numb the skin just long enough to reduce needle-insertion pain.
• Forced air cooling is helpful in reducing pain of palmar and finger injections of botulinum toxin A for hyperhidrosis.
• PITFALL: if cold air is aimed directly onto the needle, the liquid within the needle may freeze momentarily, making the needle seem clogged — move the cold air blower away for 5 to 10 seconds to let the contents thaw and continue injecting.

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• The great majority of dermatologic surgical procedures are done under local infiltration.
• Reducing the pain of NEEDLE INSERTION:
• Reassurance, verbal distraction, and mechanical distraction such as a pinch at the injection site.
• Mechanical distraction works via the gate theory of pain — pinching stimulates cutaneous nerves, making them somewhat refractory to the immediately following pinprick.
• Vibration at or immediately proximal to the injection site — also gate theory; very useful in very anxious or young patients; has made it feasible to eliminate the need for nerve block anesthesia when injecting botulinum toxin A into palms and soles in many patients.
• Caution: with a vibrator at the site the needle may move unpredictably across the skin surface before insertion.
• Small 30-gauge needles inserted QUICKLY further reduce pain — slow, timid needle insertion is felt MORE than quick insertion.
• Topical anesthesia can almost completely eliminate the pain of needle insertion.
• Reducing the pain of INJECTION (the stinging sensation, usually far more painful than needle insertion):
• Buffering the anesthetic to physiologic pH and warming the anesthetic to body temperature.
• Injecting as slowly as practical reduces pain from tissue distention and allows additional anesthetic to be injected through an already numb area.
• Additional sticks should be made through an already numb area.
• Injection should start on the side the sensory innervation is coming FROM and proceed distally.
• Use the smallest practical syringe size — usually 1 or 3 ml — for low injection pressures, which are less painful.
• SUBCUTANEOUS injection is LESS PAINFUL than intradermal, but has SLOWER onset and SHORTER duration.
• Author's sequence: start with a small intradermal wheal → subcutaneous injection → finish with intradermal injection at the incision line to enhance anesthesia and hemostasis.
• Compressed air delivery systems deliver lidocaine into the dermis and may be useful in children.

• Lidocaine HCl monohydrate powder — delivery: pressurized helium — Zingo — 0.5 mg (pre-filled) — Amide — intact skin.
• Lidocaine buffered powder — delivery: compressed carbon dioxide — J-tip — 1% or 2% — Amide — intact skin.
• Lidocaine is delivered into the DERMIS.

• Involves injecting a ring of anesthetic around the proposed surgical site.
• Useful for anesthetizing large areas while conserving anesthetic and minimizing distortion of the surgical site.
• Injecting a ring around a cyst avoids puncturing the cyst.
• Ring block anesthesia is practical ONLY where innervation arrives HORIZONTALLY through the skin (e.g. scalp), rather than VERTICALLY from deeper tissues (e.g. eyelid).
• A ring block may achieve anesthesia but there will be NO hemostasis at the incision site → add intradermal anesthetic with epinephrine at the proposed incision site.
• Most frequent uses: scalp, nose (for rhinophyma repair), ear pinna, trunk and extremities (started as a ring block but often finished with infiltration inside the ring).

• Subcutaneous infiltration of large amounts of dilute 0.05%–0.1% lidocaine with 1 : 1 000 000 epinephrine.
• Used most extensively for liposuction under local anesthesia (Ch. 156), ambulatory phlebectomy, hair transplantation, and dermabrasion.
• Infiltrated with the help of a pump, via long 18- to 20-gauge 3.5 inch (8.9 cm) spinal needles or specially designed multiport cannulas.
• Infiltration is started slowly with small needles, then gradually sped up using spinal needles and finally infiltration cannulas.
• Deep subcutaneous plane infiltrated FIRST, followed by the superficial fat compartment; injected until firm tumescence of the tissue is achieved.
• Anesthesia and epinephrine-induced hemostasis develop within about 20 minutes and last for SEVERAL HOURS — significantly longer than with conventional concentrations of lidocaine with epinephrine.
• In the subcutaneous fat, dilute lidocaine is absorbed at a MUCH SLOWER rate than standard concentrations.
• Doses as high as 35–50 mg/kg lidocaine have been found to be safe in tumescent anesthesia.

• Lidocaine 1% — 50–100 ml
• Epinephrine (1 : 1000) — 1 ml
• Sodium bicarbonate 8.4% — 10 ml
• Hyaluronidase 150 U/ml — 6 ml (optional)
• Triamcinolone acetonide 40 mg/ml — 0.25 ml (optional)
• Normal saline 0.9% — 900–950 ml
• Final concentration: 0.05% to 0.1% lidocaine with 1 : 1 000 000 epinephrine.
• Hyaluronidase may be added to enhance diffusion; corticosteroids may be added to reduce inflammation, edema, and possibly fibrosis.

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• Nerve blocks anesthetize large areas using the LEAST amount of anesthetic, minimizing both patient discomfort and distortion of the operative site.
• Care must be taken NOT to inject the accompanying blood vessels.
• Use larger, 25- to 27-gauge needles so one can draw back to confirm the needle is not intravascular.
• To reduce injection pain, place an intradermal wheal with a 30-gauge needle first.
• Aim: deposit anesthetic NEAR, but NOT INTO, the nerve — intraneural injection may cause nerve injury and subsequent dysesthesia.
• Insertion into a nerve is usually felt as a SHARP PAIN RADIATING ALONG THE NERVE → pull the needle back and reposition slightly.
• Intra-foramina injections should also be avoided to minimize nerve injury risk.
• With proper placement, most nerves can be blocked with a 1–2 ml injection.
• Hyaluronidase enhances diffusion and increases the rate of nerve block “take”.
• Standard mix for most nerve blocks: 1% lidocaine with epinephrine and sodium bicarbonate.
• If prolonged anesthesia is desired, add 0.25% bupivacaine hydrochloride with epinephrine.
• Because sensory nerves are large and myelinated, anesthetic effect may take 10 to 20 minutes to develop.
• Using 2% lidocaine may increase success of the nerve block.
• Articaine 4% with or without epinephrine supplied in dental carpules seems especially effective for relatively painless facial nerve blocks, with very small volumes (often <0.2 ml/injection site) needed — apparently due to more effective diffusion from the site of injection compared to lidocaine.
• Some surgeons omit epinephrine from nerve block anesthetic since vasoconstriction is not needed at the site of the nerve; the author uses it to prolong the duration of the block.
• Once a nerve is effectively blocked, local infiltration of lidocaine with epinephrine along the proposed incision line achieves local vasoconstriction and reduces bleeding.

(Sensory innervation of the central face — Fig. 143.2; skull exit points — Fig. 143.3; needle insertion sites — Fig. 143.4. Nerves: SO supraorbital (V1), ST supratrochlear (V1), IT infratrochlear (V1), AE external nasal branch of the anterior ethmoidal nerve (V1), IO infraorbital (V2), M mental (V3).)

Supraorbital nerve

• Innervates the forehead and frontal scalp above the eyebrows.
• Exits the skull through the supraorbital foramen at or immediately above the orbital rim in the MIDPUPILLARY LINE; the notch can often be palpated.
• Technique: ~1 ml of anesthetic infiltrated through a 0.5 inch (1.3 cm) needle inserted PERPENDICULARLY into the skin immediately superficial to the periosteum at the orbital rim in the midpupillary line.

Supratrochlear nerve

• Innervates the midforehead, glabella, and frontal scalp.
• Exits the skull at the upper medial portion of the orbit.
• Technique: inject 1 ml immediately superficial to the periosteum at the superomedial orbital rim, at the junction of the glabella and eyebrow.

Completing forehead/frontal scalp anesthesia

• Extend a line of anesthetic injected into the SUBCUTANEOUS plane laterally from the supraorbital nerve to the region immediately superior and posterior to the attachment of the ear pinna.
• This blocks the auriculotemporal nerve and greater auricular nerve branches innervating the forehead, temple, and frontal scalp (see Ch. 142).

Infraorbital nerve

• Exits through the infraorbital foramen; innervates the medial cheek, upper lip, and nasal ala.
• Percutaneous: a 1 inch (2.5 cm) needle inserted perpendicularly to the skin; 2 ml of anesthetic injected approximately 1 cm inferior to the orbital rim in the midpupillary line, immediately superficial to the maxillary bone periosteum.
• Intraoral approach (LESS PAINFUL and MORE RELIABLE): needle inserted between the first and second premolars (bicuspids), moving cephalad parallel to the periosteum until the horizontal portion of the maxillary bone is reached; pull back slightly and inject.
• Pain of needle insertion can be lessened by applying topical anesthetic to the mucosa a couple of minutes prior.

Infratrochlear nerve

• Innervates the lateral and dorsal nose.
• Blocked by injecting anesthetic superficial to the periosteum at the INFEROMEDIAL orbital rim at the superior end of the nose–cheek concavity.

External nasal branch of the anterior ethmoidal nerve

• Innervates the nasal tip; emerges at the nasal cartilage and bone junction, slightly lateral from the midline.
• Perichondrial infiltration of anesthetic at this spot anesthetizes the nasal tip.
• To complete nasal anesthesia, a few drops of anesthetic at the base of the columella may also be needed.

Mental nerve

• Innervates the lower lip and portions of the chin; exits the mandible through the mental foramen in the midpupillary line.
• Percutaneous: a 0.5 inch (1.3 cm) needle inserted perpendicular to the skin to the level of the periosteum in the midpupillary line HALFWAY CEPHALAD along the mandible; inject 1 ml.
• Intraoral route is less painful and more reliable: needle inserted between the first and second premolars (bicuspids), caudally along the periosteum to a halfway point down the mandible.

• Techniques for fingers and toes are technically very similar; two options.
• Option 1 (most commonly used by dermatologists) — blocks the sensory nerves coursing laterally along the digit:
• A 0.5 inch (1.3 cm) needle inserted perpendicular to the digit near its base in the horizontal plane until the BONE is touched.
• Withdraw the needle slightly, position DORSALLY and inject; then position VENTRALLY and inject additional anesthetic.
• Repeat on the other side of the digit.
• Can be done without epinephrine or with dilute 1 : 500 000 epinephrine; inject small volumes (usually <1.5 ml) to minimize the risk of ischemic injury from mechanical circumferential compression of the digit's blood supply.
• There is no documented risk of ischemic injury from standard 1 : 100 000 epinephrine concentrations for digital anesthesia in patients without significant peripheral vascular compromise (as long as injected volume is limited).
• Option 2 — block at the level of the metacarpal or metatarsal bone:
• A 1.5 inch (3.8 cm) needle inserted dorsally BETWEEN the metacarpal/metatarsal bones; anesthetic infiltrated as the needle is advanced ventrally, with most of the anesthetic injected just dorsal to the palmar/plantar skin.
• Blocks the metacarpal/metatarsal nerve, which travels immediately superficial to the flexor retinaculum.
• Repeat on the other side of the metacarpal/metatarsal bone of the digit being anesthetized.
• Advantage: LESS risk of compression injury than the more commonly performed digital block.

• The dorsal nerve of the penis is a branch of the PUDENDAL nerve.
• It divides into major anterior (dorsal) and minor posterior (ventral) branches at the base of the penis.
• Technique: inject a ring of anesthesia WITHOUT epinephrine or with 1 : 500 000 epinephrine in the subcutaneous plane around the base of the penis → most of the penis is anesthetized.
• Areas that may require additional infiltration: the periurethral region of the glans and sometimes the ventral glans and frenulum.

• Needed with the popularity of botulinum toxin A for palmar and plantar hyperhidrosis.
• Topical anesthetics are ineffective on palmoplantar skin, and local anesthetic injections into palms and soles are very painful.
• Median nerve block anesthetizes the palmar surface of the first three and a half fingers plus two-thirds of the palmar surface.
• Ulnar nerve block anesthetizes the rest of the fingers and palm.
• Sensory innervation of the hand: M median, R radial, U ulnar nerves (palmar and dorsal surfaces).

Median nerve technique

• The median nerve lies in the carpal tunnel, DEEP to the palmaris longus tendon and BETWEEN the flexor digitorum superficialis and flexor carpi radialis tendons.
• Apposing the thumb and fifth finger with the wrist slightly flexed makes the palmaris longus tendon apparent.
• A 0.5–1 inch (1.3–2.5 cm) needle is inserted at the first (proximal) wrist crease, immediately MEDIAL (ULNAR) to the palmaris longus tendon, then advanced deep into the carpal tunnel; inject a few milliliters.
• A slight “popping” or reduction in resistance can be felt as the needle enters the carpal tunnel.

Ulnar nerve technique

• Most easily blocked at the ELBOW, where it travels between the olecranon process and the epicondyle of the humerus — the “funny bone”.
• The patient's arm is flexed and the needle is inserted between the bones; several milliliters injected.

Bier block (alternative, by an anesthesiologist)

• Blood is pushed out of the arm with a compressive bandage, a tourniquet applied, and dilute lidocaine injected intravenously.
• Anesthesia of the hand develops in 5 to 10 minutes and lasts about 1 hour.
• Once complete, the tourniquet is gradually released and the anesthetic enters the general circulation → the dose administered should be monitored to keep it at a safe level.

• Anesthesia of the plantar surface requires blocks of five nerves:
• Posterior tibial nerve (PT) — innervates the heel and middle of the sole.
• Sural nerve (SU) — innervates the fifth toe and the lateral side of the sole.
• Superficial peroneal nerve (SP) — innervates the skin of the toes.
• Saphenous nerve (SA) — innervates the instep.
• Deep peroneal nerve (DP) — innervates the skin between the first and second toes.
• Before starting injections around the ankle, thoroughly prep the area with antiseptic to minimize infection risk.

Posterior tibial nerve

• Patient placed PRONE.
• The posterior tibial artery is palpated or located with a Doppler ultrasound probe.
• A 1.5 inch (3.8 cm) needle is directed anteriorly and laterally, immediately LATERAL to the arterial pulse, until the BONE is touched; pull back slightly and inject several milliliters in the groove between the medial malleolus and the Achilles tendon.

Sural nerve

• Blocked by injecting anesthetic in the groove between the LATERAL malleolus and the Achilles tendon — identical fashion to the tibial nerve injection.

Saphenous and superficial peroneal nerves

• Patient SUPINE; blocked by infiltrating anesthetic SUBCUTANEOUSLY from MALLEOLUS TO MALLEOLUS along the dorsum of the foot.

Deep peroneal nerve

• A 1.5 inch (3.8 cm) needle inserted LATERAL to the extensor hallucis longus tendon (toward the middle of the foot) down to the bone; pull back slightly and inject several milliliters.
• The tendon is identified by having the patient DORSIFLEX the great toe against resistance.
• Alternative: local anesthetic infiltrated between the first and second toes for easier, more expeditious anesthesia.

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• For anxious patients or when relatively large areas are to be anesthetized, oral or sublingual anxiolytics reduce anxiety and may generate a degree of amnesia:
• Triazolam (Halcion®) 0.25–0.5 mg
• Zolpidem tartrate (Ambien®) 5–10 mg
• Diazepam (Valium®) 5–10 mg — useful for longer procedures due to longer duration of action, but does NOT produce amnesia.
• Adding a narcotic analgesic acts synergistically with anxiolytics for greater sedation and reduces the pain of local anesthetic infiltration:
• Oxycodone (10 mg)/acetaminophen (325 mg) orally (Percocet®)
• Meperidine hydrochloride (Demerol®) 50 mg intramuscularly
• Useful for longer procedures done under tumescent anesthesia.
• Consent for the procedure must be obtained BEFORE taking any of these medications, and patients must have someone else take them home afterwards.
• Credentialing for higher levels of anesthesia may be regulated by state or national medical licensure authorities and hospitals — the physician must be in full compliance.
• Most regulations require procedures under general anesthesia or intravenous sedation to be done in an ambulatory surgery center or hospital with a supervising anesthesiologist.
• Higher levels involving IV medications such as midazolam hydrochloride (Versed®) and fentanyl should be done in a monitored environment with appropriate resuscitative equipment readily available.

• A useful form of moderate analgesia, with degree depending on concentration administered.
• At 20% concentration, analgesia is equivalent to giving a narcotic analgesic.
• At 80% concentration, most patients become UNCONSCIOUS.
• Advantage: rapid reversal of anesthetic effect as soon as the gas is turned off.
• With proper training, can be safely administered in the office (as done for many years in dental offices).
• Pro-Nox™ (Clarion Medical Technologies) — an easier version delivering a fixed ratio of 50% nitrous oxide and 50% oxygen; the patient holds the mouthpiece and controls how much they inhale, remaining conscious throughout.
• General inhalation anesthesia or deep intravenous sedation with propofol should generally be performed by ANESTHESIOLOGISTS.