Anesthesia

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3 Anesthesia

Local anesthesia is the reversible loss of sensation to a localized area achieved by the injection or topical application of anesthetic agents. Regional anesthesia involves larger areas and is achieved by nerve block and/or field blocks through the use of injectable anesthetic agents. Local anesthetics block the pain fibers of a nerve better than those fibers that carry sensations of pressure, touch, and temperature. Therefore, if the patient feels pressure or pulling but no pain, the patient should be reassured that this is not unusual. Many anesthetic agents can be injected or applied topically.

Topical Anesthetics

Common anesthetics include the following:

• EMLA (eutectic mixture of local anesthetics; 2.5% lidocaine and 2.5% prilocaine cream) (Rx) (Figure 3-1)

• LMX 4 and LMX 5 (4% liposome-encapsulated lidocaine and 5% cream) (OTC)

• Topical lidocaine (2% and 4% gel or viscous solution, 5% ointment, 10% spray)

• Tridocaine gel (20% benzocaine, 6% lidocaine, 4% tetracaine) (available from Canada).

FIGURE 3-1 (A) An assortment of topical anesthetics for skin surgery. (B) EMLA was applied to the lower eyelids prior to electrosurgery of syringomas.

Table 3-1 shows the onset of action for the most commonly used topical anesthetics in skin procedures. EMLA (eutectic mixture of local anesthetics) cream consists of 2.5% lidocaine and 2.5% prilocaine in an oil-in-water emulsion. This anesthetic cream works best if applied for 30 minutes under occlusion or 60 minutes without occlusion before anesthesia is needed. It can be useful in treating children or a patient of any age who is afraid of needles. EMLA cream is used for some laser procedures, superficial light electrodesiccation of benign growths, and curettage of molluscum contagiosum. In Figure 3-1B the EMLA has been applied to the lower eyelids before electrodesiccation of syringomas. EMLA is available in 5-g tubes with occlusive dressings or in 30-g tubes without dressings. EMLA should not be used in infants younger than 3 months because the metabolites of prilocaine form methemoglobin. In one randomized control trial, EMLA and LMX 4 provided comparable levels of anesthesia after a single 30-minute application under occlusion prior to electrodesiccation of dermatosis papulosa nigra.¹

TABLE 3-1 Topical Anesthetics

Topical lidocaine is available as a 2% and 4% gel or viscous solution, a 5% ointment, or a 10% spray. Regardless of the vehicle, topical lidocaine takes 15 to 30 minutes to produce anesthesia on mucosal surfaces. The degree of anesthesia is not comparable to injectable lidocaine, and unless it is combined with another agent such as phenylephrine, it has no vasoconstrictive action. Therefore, for mucosal surgery in the mouth, it is best to inject 1% lidocaine with epinephrine after the topical lidocaine has numbed the surface. For this purpose, it is easy to put topical lidocaine gel on a cotton swab and have the patient hold it against the mucous membrane before the subsequent injection. This technique might be used to anesthetize a mucocele or fibroma on the lip.

Tridocaine (20% benzocaine, 6% lidocaine, 4% tetracaine) is a local analgesic, anesthetic, and antipruritic. It is used to prevent pain associated with laser surgery, superficial skin surgery, needle insertion, and intravenous cannulation. It is indicated for intact skin only and anesthesia is obtained in 10 to 15 minutes. It can be purchased online from Canadian sources or be created by a compounding pharmacy.

EMLA Technique for Intact Skin

1. Use alcohol wipes to remove oil from the area of skin to be anesthetized.

2. Apply EMLA in a thick layer to skin then apply occlusive dressing (Tegaderm, OpSite, or plastic wrap) for 30 to 60 minutes. Thicker skin may take more than 1 hour to achieve anesthesia.

3. Remove EMLA with alcohol or with a tissue.

4. Perform the procedure or additional anesthesia without delay. Topical anesthesia will last only minutes after the EMLA is removed.

Topical Refrigerants/Cryoanesthesia

• Ethyl chloride spray

• Medi-Frig (tetrafluoroethane) (Ellman International, Inc.)

• Liquid nitrogen.

Topical refrigerants make the skin cold and provide some anesthesia for the removal of small superficial skin lesions such as skin tags and molluscum. These agents provide some cryoanesthesia before snip excisions of skin tags or curettage of molluscum. Cryoanesthesia does not provide adequate anesthesia for the removal of larger lesions. These agents are sprayed on the skin until a white frost develops. The numbing effect is partial at best and disappears in seconds. Refrigerant sprays may be used before injecting local anesthesia with a needle in a needle-phobic patient. While these sprays are probably less effective than EMLA, they work faster and are therefore more convenient if the patient can tolerate the subsequent procedure.

Ethyl chloride is the only one of the refrigerants listed that is flammable, so it must not be used before electrosurgery. Medi-Frig can be safely used before electrosurgery for small skin tags and molluscum contagiosum. The manufacturers of Medi-Frig claim that it is nontoxic and ozone safe, whereas the label on ethyl chloride warns against inhaling too much of the product.

Liquid nitrogen can freeze the skin to cause a numbing effect; however, its use causes immediate pain and little real anesthesia. Rather than using liquid nitrogen for local anesthesia for skin tag excision, it is easier and less painful to use the liquid nitrogen with a Cryo Tweezer to treat the skin tags directly (see Chapter 15, Cryosurgery). Also, liquid nitrogen can be sprayed or directly applied to skin tags or molluscum rather than using it as anesthesia. This also avoids the need to deal with blood and hemostasis issues.

Contact cooling devices and assistive external devices are frequently used in laser treatments and are covered in Chapter 20, Anesthesia for Cosmetic Procedures.

Local Anesthesia by Injection

Lidocaine is the most widely used local anesthetic for injection in skin surgery. Bupivacaine (Marcaine) is used occasionally when long-lasting anesthesia is desired. Lidocaine has the advantage of having a more rapid onset (within 1 minute) and shorter duration of anesthesia than bupivacaine. This shorter duration is sufficient and preferable for most skin surgery. When lidocaine is mixed with epinephrine, it lasts almost as long as bupivacaine and hurts less.² See Table 3-2 for a comparison of amide local anesthetics.

TABLE 3-2 Local Anesthetics for Injection

Epinephrine

Epinephrine is a vasoconstrictor, whereas lidocaine alone is a vasodilator. Epinephrine with lidocaine decreases bleeding during surgery. Also, the vasoconstriction of epinephrine keeps the lidocaine in the area where it was injected, thereby decreasing immediate systemic absorption and toxicity while increasing the duration of anesthesia. This allows greater amounts of lidocaine to be used safely for local anesthesia by reducing systemic absorption and increasing the local action of the lidocaine.

1% Lidocaine with Epinephrine

For most skin surgery procedures, the recommended anesthetic is 1% lidocaine with epinephrine. Its advantages include almost immediate anesthesia, adequate duration of anesthesia, and decreased bleeding because of the epinephrine. The incidence of true allergies is negligible. Lidocaine without epinephrine has a duration of 1.5 to 2 hours, whereas lidocaine with epinephrine has a duration of 2 to 6 hours.³ The most common commercial preparation contains 1% lidocaine (10 mg/mL) with 1 : 100,000 of epinephrine. In a study that measured the effect of subdermal injection of lidocaine combined with epinephrine on cutaneous blood flow, laser Doppler imaging demonstrated an immediate decrease in cutaneous blood flow, which was maximal at 10 minutes in the forearm and 8 minutes in the face.⁴

Note that the initial skin blanching with injection is due to hydrostatic pressure along with the effect of epinephrine. When hemostasis is critical to the procedure, it is best to wait 8 to 10 minutes for the epinephrine to produce maximal vasoconstriction. Waiting is less important for shave biopsies of lesions that are not very vascular in patients who are not anticoagulated (Figure 3-2). Injecting enough anesthetic so that the skin is firm can limit the amount of bleeding because small blood vessels become compressed by the anesthetic fluid (Figure 3-3).

FIGURE 3-2 Local anesthetic injected under and around a seborrheic keratosis prior to shave biopsy to confirm that this highly pigmented lesion is benign. The elevation of the tissue makes the shave easier to perform.

FIGURE 3-3 Local anesthesia before excising a basal cell carcinoma on the forehead. Note how the tissue distends in this location to improve hemostasis as well as ensure adequate anesthesia.

Maximal Doses

Maximal safe doses of 1% lidocaine with or without epinephrine are found in Table 3-3. Above these doses the risk of neurotoxicity and seizures is increased. In most adults (over 50 kg) up to 35 mL of 1% lidocaine with epinephrine is safe. Use of 1% lidocaine is preferable to 2% in most cases because a larger volume of anesthesia produces greater hemostasis and makes most cutaneous surgery easier to perform. Two percent lidocaine without epinephrine is useful in various nerve blocks including digital blocks when less volume is needed. Some clinicians prefer 2% lidocaine with epinephrine when they want to avoid tissue distortion from too much anesthetic volume. In this case, toxicity is not an issue because less than 5 mL of anesthesia are being used.

TABLE 3-3 Maximum Doses of 1% Lidocaine (10 mg/mL)

Decreasing the Pain of Local Anesthesia

Techniques to decrease the pain caused by injection of local anesthesia include the following:

• Inject very slowly because tissue distention hurts.

• Use a small-gauge needle (27 or 30 gauge).

• Pinch or vibrate the skin as the needle enters (based on the gate theory of pain).

• Distract the patient in conversation or with music.

• Add sodium bicarbonate to the lidocaine.

• Warm anesthesia to 40°C.

• Use only one injection site if possible and place subsequent injections into areas already anesthetized.

The main technique for decreasing the pain of injection is to inject the local anesthetic very slowly using a small-gauge needle (27 or 30 gauge). The larger the gauge number, the smaller the needle diameter and the less painful the injection. Use 30-gauge needles on the most sensitive areas including the face, the ears, the fingers, and the genitals. When injecting anesthesia for a laceration repair, injecting from within a laceration is less painful than injecting into intact skin.⁵

It may be helpful to pinch or vibrate the skin as the needle enters and distract the patient with conversation. Although the needle should be inserted quickly, the injection will be less painful if the volume of anesthesia is injected slowly. The more superficial the injection, the more painful it is. For example, an injection bleb similar to that of a tuberculin skin test is more painful than a deeper subcutaneous injection. It is usually less painful if the injection is done slowly and deeply at first, followed by redirecting the needle for a more superficial, dermal, blanching type of injection. In this manner, a volume of 5 mL or more can be given slowly through one injection site. Skin blanching and visible tissue distention help determine the area that has been anesthetized. Also, tissue induration can be palpated to determine the distribution of the anesthesia. If need be, this area can be extended by reinjecting through another site that has already been anesthetized.

Adding sodium bicarbonate (8.4% for injection) in a 1 : 10 dilution to the lidocaine and epinephrine anesthetic solution markedly decreases the pain caused by injection (e.g., 1 mL of sodium bicarbonate can be added to 9 mL of lidocaine). The addition of sodium bicarbonate neutralizes the commercially available lidocaine-epinephrine solutions that have a pH of 4 to 6. Although this takes more time, your patients will appreciate that the injection is less painful. The lidocaine-bicarbonate syringes need to be made at the time of use or may be kept for 1 week at room temperature and up to 2 weeks with refrigeration.⁶ In our office we make the following syringes each morning:

• 3-mL syringes with 2.25 mL of lidocaine and 0.25 mL bicarbonate.

• 5- or 6-mL syringes with 4.5 mL of lidocaine and 0.5 mL bicarbonate.

• 10- or 12-mL syringes with 9 mL of lidocaine and 1 mL bicarbonate.

A warm (40°C) and neutral (pH 7.35) anesthetic preparation has been found to be less painful on injection than room-temperature nonneutral preparations.⁷^–⁹ One study suggests that warming and buffering have a synergistic effect.⁸ Skin infiltration with warm buffered lidocaine was significantly less painful than infiltration with room-temperature unbuffered lidocaine, warm lidocaine, or buffered lidocaine.⁸ In another study, the mean pain scores for the four solutions were 44.2 for plain lidocaine, 42.2 for warmed lidocaine, 36.7 for buffered lidocaine, and 29.2 for warmed buffered lidocaine (lower numbers equal less pain).⁹ In one study, to reduce the pain of lidocaine infiltration, buffering was more effective than warming (warming was only to 38.9°C).¹⁰

Injection Technique

The skin surface can be cleaned adequately with an alcohol wipe. Gloves should be clean, but need not be sterile for the injections. When performing a biopsy or excision, it is helpful to mark the planned lines of incision with a surgical marker before doing the injection. This prevents losing sight of a nonpigmented lesion when the swelling and blanching occur from the anesthesia. The lines and circles drawn provide a guide to the biopsy or excision. Start anesthesia by inserting the needle into one site of the circumference of the circle of anesthesia needed around the lesion—typically 5 mm back for a shave or punch biopsy. Most anesthesia for a shave or punch biopsy can be done with one injection.

For shave and punch biopsies, the tip of the needle should reach the deep dermis so that an elevation and blanching of the tissue occurs (Figures 3-2 and 3-3). If the anesthetic is injected too deep into the subcutaneous tissue, no elevation will occur. When an injection is superficial in the dermis, you may see an accentuation of the follicles called peau d’orange. This skin distention is more painful than the pain that occurs with a deeper dermis injection. However, if you intend to do a shave biopsy, you can start with a deeper dermis injection and finish with a more superficial injection to raise the lesion for biopsy. Starting deeper and adjusting the needle to a more superficial level is an effective technique (this can be done without removing the needle from the original injection site).

If the lesion to be removed is large, a second insertion site may be needed. When injecting subcutaneously, it is important to pull back on the plunger before injecting at any one site to avoid injecting into a vessel. Advancing the needle and injecting simultaneously can be done in the dermis but should be avoided in the subcutaneous tissue because of the presence of larger blood vessels.

Preloading a number of syringes at the start of each day can save time if several procedures are to be done that day. A smaller syringe requires less force for injections. Three-milliliter and 5-mL (or 6-mL) syringes are a good compromise between cost and comfort. These hold enough anesthetic for most small procedures and will be comfortable for the injector.

Adverse Reactions

Adverse reactions to lidocaine and epinephrine and the needle used for injections include the following:

Lidocaine

• Allergy to lidocaine

• Central nervous system (CNS) effects from too much lidocaine (light-headedness, tinnitus, perioral tingling, metallic taste, tremors, slurred speech, and seizures)¹

• Cardiovascular effects from too much lidocaine (myocardial depression, arrhythmias).

Epinephrine

• Tachycardia

• Anxiety

• Tremulousness

• Decreased peripheral circulation.

Needle

• Laceration of nerve (rare but more likely during a nerve block)

• Infection or abscess from lack of sterile technique.

For patients with normal circulation, it is safe to use epinephrine for local anesthesia in areas such as the tip of the nose, the fingers and toes, the ears, or the penis despite old dogma that epinephrine should not be used in these areas (Figure 3-4). However, epinephrine is generally not recommended for digital ring blocks, full ring blocks around the ear, penile nerve blocks, and other regional or field blocks in these areas. Furthermore, epinephrine should not be used in the very distal extremities of a patient with poor circulation such as patients with peripheral vascular disease or Raynaud’s phenomenon.

FIGURE 3-4 Local anesthetic with epinephrine is safe to use on the digits, nose, ears, and penis in a patient with normal circulation about to undergo a local excision. In this case, a squamous cell carcinoma was about to be excised from the finger using Mohs surgery. While a digital block without epinephrine is another option, local anesthetic used at the site of surgery with epinephrine allows for better hemostasis during the excision.

(Copyright Richard P. Usatine, MD.)

A number of studies have even provided evidence to dispute the dogma that using epinephrine in a digital block produces digital necrosis.¹¹^–¹³ Proper injection technique and adequate selection of patients (absence of thrombotic, vasospastic conditions, or uncontrolled hypertension) are mandatory to minimize complications. The addition of epinephrine, in fact, reduced the need for the use of tourniquets and large volumes of anesthetic and provided better and longer pain control during digital procedures.¹¹^–¹³ We still choose to use 2% lidocaine without epinephrine for digital blocks but do use epinephrine in wing blocks when a matrix biopsy is planned (see Chapter 18, Nail Procedures).

Some patients ask that no epinephrine be used because it makes them anxious. It is true that some patients may get tachycardia for a few minutes along with a feeling of anxiousness shortly after the injection. This can usually be handled by warning the patient about this and reassuring him or her that the feeling will pass in a few minutes. For most patients, this may have occurred in the past during a dental procedure (reason enough for anxiety in many people).

Rare adverse effects associated with too large a systemic dose of injectable anesthetics (injection into a vein or too large a dose of the anesthetic) include myocardial depression and CNS effects such as light-headedness, tinnitus, perioral tingling, metallic taste, tremors, slurred speech, and seizures.¹

Lidocaine Allergies

Lidocaine allergies are extremely rare. Almost all patients who report an allergy actually have had a vasovagal reaction with lidocaine injections or sensitivity to the epinephrine effects. Other patients are actually allergic to the paraben preservative in the multidose vials of lidocaine or they had an allergic reaction to a local anesthetic ester such as Novocain (procaine, novocaine). Because the paraben is not added to the single-use vials, it may be helpful to try these vials when the patient reports an allergy.

The ester forms of local anesthetics, such as novocaine, produce more allergic reactions. Fortunately, there is no cross-reactivity between novocaine and lidocaine. Therefore, lidocaine use is safe in a patient with a true novocaine allergy. Most dentists currently use lidocaine. Patients may think they are receiving novocaine in the dentist’s office, but they are most likely receiving lidocaine or articaine, which has increased perfusion in bone.

The approach to a patient who reports a specific allergy to lidocaine is to take a careful history to determine if a vasovagal or epinephrine reaction may be the actual cause of the patient’s adverse experience. Referral to an allergist is rarely indicated, except for someone with a history consistent with a life-threatening type of allergic reaction. It is reasonable to try a test injection of a small amount of lidocaine (from a single-use vial), because true systemic lidocaine reactions are so rare.

An alternative to lidocaine is injectable diphenhydramine (Benadryl) or normal saline. Diphenhydramine provides adequate short-term anesthesia, but it may cause the patient to become drowsy. When normal saline is injected to induce a firm wheal, it provides a few minutes of anesthesia as well.

Nerve Blocks

Digital blocks and regional blocks are examples of nerve blocks (see Boxes 3-1 to 3-5). The advantages of a nerve block are that it provides a longer duration of anesthesia and does not distort the anatomic landmarks.

BOX 3-1

Nerve Blocks

Advantages

• Anesthetizes the nerve before it reaches the operative site.

• Affects a large area with small amount of anesthetic.

• No distortion of operative site.

Disadvantages

• No vasoconstriction.

• Longer onset.

• Shorter duration.

• Risk of nerve laceration.

Source: Adapted from Vidimos A, Ammirati C, Pobleti-Lopez C. Dermatologic Surgery. Philadelphia: Elsevier; 2009.

BOX 3-2

Supraorbital/Supratrochlear Nerve Block (V1)

Provides sensation to forehead.

Indications

• Laser resurfacing.

• Large surgical defects.

Location

• Supraorbital nerve—midpupillary line along superior bony orbit.

• Supratrochlear nerve—superior/medial corner of bony orbit.

Technique: General Principles

• Inject about 1 mL lidocaine (±epinephrine) in subcutaneous fat overlying supraorbital foramen.

• Inject about 1 mL at root of nose/medial border of orbit.

Source: Adapted from Vidimos A, Ammirati C, Pobleti-Lopez C. Dermatologic Surgery. Philadelphia: Elsevier; 2009.

BOX 3-3

Infraorbital Block (V2)

Provides sensation to lower eyelid, medial cheek, nose, and upper lip.

Indications

• Fillers.

• Laser resurfacing.

• Large surgical defects.

Location

• Foramen is 1 cm inferior to the infraorbital ridge along the midpupillary line.

Technique: General Principles

• Approach through the oral cavity.

• The nerve is 0.5 to 1 cm above superior labial sulcus.

• Anesthetize oral mucosa with topical benzocaine first.

• Enter at apex of first bicuspid and direct needle toward estimated location of foramen.

• Inject 1 to 2 mL with a

-inch needle (27 or 30 gauge).

Source: Adapted from Vidimos A, Ammirati C, Pobleti-Lopez C. Dermatologic Surgery. Philadelphia: Elsevier; 2009.

BOX 3-4

Mental Nerve Block (V3)

Sensation to lower lip, chin, and mucous membranes.

Indications

• Fillers.

• Laser resurfacing.

• Large surgical defects.

Location

• Midway between upper and lower edge of mandible below second bicuspid (midpupillary line).

Technique: General Principles

• Approach through the oral cavity.

• Anesthetize oral mucosa with topical benzocaine first.

• 27- or 30-gauge

-inch needle.

• Enter inferior labial sulcus between first and second bicuspids.

• Inject 1 to 2 mL around mental foramen.

Source: Adapted from Vidimos A, Ammirati C, Pobleti-Lopez C. Dermatologic Surgery. Philadelphia: Elsevier; 2009.

BOX 3-5

Digital Block

Paired dorsal and medial digital nerves.

Indications

• Nail plate avulsion.

• Nail unit biopsy.

• Distal digit surgery.

• Periungual warts.

Technique: General Principles

• Use plain lidocaine 1% or 2%.

• Use a 5-mL syringe.

• Use a 27- or 30-gauge needle.

• Apply topical anesthesia or ice prior to injecting.

• Use no more than 5 mL total volume.

Source: Adapted from Vidimos A, Ammirati C, Pobleti-Lopez C. Dermatologic Surgery. Philadelphia: Elsevier; 2009.

The digital block can be more effective than a local injection on the digit especially for surgery around the nail. Anesthetizing the digital nerves with lidocaine will almost always provide good anesthesia. Injection on each side of the digit with lidocaine will anesthetize both dorsal and ventral nerves on either side of the digit (Figure 3-5). A 3- to 5-mL syringe may be used with 1% or 2% lidocaine, delivering 1.0 to 1.5 mL on each side of the digit and 1.0 mL on the top (Figure 3-6).

FIGURE 3-5 Digital innervation and nerve block. (A) Dorsal and palmar digital arteries and nerves run together. (B) A dorsal approach for administration of a digital nerve block allows anesthesia of dorsal and palmar bundles with one puncture.

(From Robinson J, Hanke CW, Siegel D, Fratila A. Surgery of the Skin. London: Mosby; 2010.)

FIGURE 3-6 Three steps of a digital block prior to nail matrix biopsy for longitudinal melanonychia. (A) Injection into the affected side. (B) Injection into the other side of the digit. (C) Anesthetizing the nerves that run on the dorsum of the toe.

A wing block is an alterative for surgery on any part of the nail unit (Figure 3-7). The main advantage over a digital block is that it provides better hemostasis at the site of surgery regardless of whether or not epinephrine is used. Some clinicians will use half-strength epinephrine by mixing 2% lidocaine with 1% lidocaine with epinephrine in a 1 : 1 solution. Wing blocks work faster than a digital block, but the injection usually hurts more at first. A wing block can be performed after a digital block to help with hemostasis and to ensure excellent anesthesia (see Chapter 18, Nail Procedures).