supplied by end arteries, such as the digits, penis, or pinna of the ear, however recent studies have called this into question Lidocaine is advantageous because it provides excellent local anesthesia and takes effect quickly (within a few minutes) The effect lasts long enough to complete most procedures (about 1.5 to hours) It is generally a safe drug because few people have a true allergy to it Serious toxicity, such as seizures and cardiac arrest, can occur, but only when large amounts are injected inadvertently or when the drug is injected directly into a blood vessel The major disadvantage of using lidocaine as a local anesthetic is that a painful injection is required for administration This pain can be reduced, however, if a long, small (27- or 30-gauge) needle is used to produce a “fanning” effect of the anesthetic To avoid inadvertent injection into a vessel while injecting deep into tissue, a larger needle is needed to aspirate blood Otherwise, the small needle is recommended, and only a small amount of lidocaine should be injected to avoid tissue distortion Some physicians recommend using a syringe with a thumb ring during infiltration for better control It is best to inject lidocaine slowly, perhaps over 30 seconds This may cause less rapid distention of local tissue and activation of fewer nerve endings Warming the lidocaine by storing the medication and syringes in fluid warmed to 98.6°F seems to reduce the pain of infiltration It may also hurt less to inject the lidocaine into the damaged tissue inside the wound instead of into the intact skin The needle should be pulled out to the tip and the injection given again at 90-degree angles to minimize the number of punctures Subsequent injections to extend the area of anesthesia should be given through anesthetized tissue when possible It is helpful to rub the skin near the site of injection first because this reduces pain by stimulating other nerve endings Buffered lidocaine, prepared by mixing lidocaine and sodium bicarbonate in a 9:1 ratio, is more alkaline and subsequently less painful and has a faster onset Buffered lidocaine can be made as needed in the ED or in advance, and it will remain stable for approximately weeks In all cases, a few minutes should be allowed for the anesthesia to take effect Table 129.7 summarizes some hints to reduce the pain of lidocaine infiltration Bupivacaine 0.25% is similar to lidocaine but has a longer duration of action and may help reduce pain for to hours after a wound is repaired To avoid toxicity, inject no more than to 2.5 mg/kg of bupivacaine Diphenhydramine, 0.5% and 1%, has been used and studied as a local anesthetic in adult patients However, it seems to cause more pain on infiltration than lidocaine and has resulted in tissue necrosis Therefore, it is not recommended as an injectable anesthetic Benzyl alcohol has been shown as a reasonable alternative to lidocaine for SC anesthesia in the rare patient who has a history of allergy to amide anesthetics Multidose vials of physiologic saline solution that contain 0.9% benzyl alcohol can be mixed in a 1:100 dilution with epinephrine 1:1,000 strength to create a solution that has comparable effectiveness to 1% lidocaine for laceration repair and IV insertion Note that the duration of action of benzyl alcohol is shorter than that of lidocaine and thus may not be as effective for prolonged procedures Benzyl alcohol should never be used in infants because of the “gasping syndrome,” a syndrome of severe metabolic acidosis, neurologic deterioration, and gasping respirations seen in newborns TABLE 129.7 HINTS TO REDUCE PAIN OF LIDOCAINE INFILTRATION Do not allow child to see needles involved in preparing lidocaine Warm and buffer lidocaine with sodium bicarbonate Use a long, small needle for infiltration Rub skin around injection site before infiltration Infiltrate through devitalized tissue or anesthetized areas Inject slowly, only what is needed Wait for anesthetic effect Specific Uses of Local Agents Topical Anesthetics for Wound Repair LET is a solution of 4% lidocaine, 0.1% epinephrine, and 0.5% tetracaine It can be made in gel form with hydroxyethyl cellulose LET has been used successfully and safely for repair of uncomplicated facial and scalp lacerations in children The major advantage to using LET for suturing is that the anesthetic can be applied topically, without the use of a needle This reduces the fear and anxiety involved in wound repair and may help the suturing go more smoothly Even in the small number of children who have incomplete anesthesia from LET, the application of this topical anesthetic will reduce the pain of subsequent administration of lidocaine by injection The gel can be applied directly to the wound and allowed to remain for approximately 20 to 30 minutes, the solution can be “painted” onto the wound with a cotton-tipped swab, or a saturated cotton ball can be applied to the wound and held in place manually or with tape There may be a temporary stinging sensation when first applied Subsequently, the surrounding skin will be well blanched, indicating adequate local anesthesia Like lidocaine with epinephrine, the classic teaching advises that LET should not be applied to body parts where vasoconstriction is contraindicated, however some studies have questioned this One study found no cases of digit ischemia in patients with topical lidocaineadrenaline-tetracaine (LAT) applied to simple lacerations LET has essentially replaced tetracaine, adrenaline, cocaine (TAC) compound as the preferred topical anesthetic for wound repair because it is much less costly and has reduced toxicity TAC carries the risk of cocaine toxicity and can lead to seizures and death, especially if used near mucous membranes where rapid absorption can occur Topical Anesthetics for IV Placement and Venipuncture There are many products available for topical anesthesia through intact skin and these have been found helpful in relieving pain associated with IV catheter placement and venipuncture in children Decisions about IV line placement can often be made at triage, thus allowing topical agents time to take effect If preparing for IV line placement, one should prepare multiple sites in case the first attempt is unsuccessful, which occurs between 50% and 75% of the time, depending on whether or not the child is dehydrated These products are also useful for drainage of an abscess or paronychia, arthrocentesis, lumbar puncture, or to access implantable central venous catheters All topical anesthetics currently available contain lidocaine either alone or mixed with another anesthetic Mechanisms of delivery and onset times are variable The delivery mechanism must traverse the stratum corneum, which contains highly ordered lipid bilayers that block the entry or exit of water or water-soluble substances Products can traverse this barrier using needleless injection with pressurized gas, passive diffusion, or by interrupting or bypassing the barrier using heat, ultrasound, or electricity Multiple studies have demonstrated that intradermal injection of lidocaine, or saline with benzyl alcohol, can reduce IV insertion pain; although this technique requires an additional needle stick, most patients prefer it to no anesthesia at all Anesthesia is almost immediate, offering a distinct advantage over other modalities Products using pressurized helium or CO2 to achieve needleless SC infiltration of 1% or 2% powdered lidocaine achieve anesthesia within to minutes One pediatric study that showed good efficacy did not find that this method caused pain on administration, contrary to the adult studies using the same method Ethyl chloride vapocoolant spray applied to the puncture site has demonstrated variable effectiveness in multiple studies Perhaps because the needle stick needs to follow the topical application almost immediately, vapocoolants have been found more effective for IM injection than for IV insertion Passive diffusion can be time-consuming, and during the time required for onset of anesthesia, young children may become agitated, perspire, and have difficulty keeping the anesthetic in the correct skin location The oldest and most studied of these products, topical EMLA cream, is a eutectic mixture of lidocaine and prilocaine EMLA is applied with an occlusive dressing directly to the skin for 60 minutes before it is effective, so it is not practical for some situations in the ED Newer topical anesthetic creams that are a formulation of 4% lidocaine in a liposomal delivery medium (LMX-4, AneCream) are very effective An occlusive dressing is ideal but not required for application In contrast to EMLA cream, these products not contain prilocaine and therefore not increase the risk of methemoglobinemia in neonates The 20- to 30-minute onset of action makes this a better topical anesthetic choice for use in the ED Although there have been no safety studies in children younger than years of age, there have been no reports of lidocaine toxicity in any age group with this medication One manufacturer recommends not more than one 1-g application (one-fifth of a 5-g tube) in children younger than year of age This would represent a topical dose of lidocaine of only mg/kg for a 10-kg child or mg/kg for a 5-kg child Heat, ultrasound, laser, and iontophoresis have all been used to disrupt or more effectively bypass the lipid bilayers in the stratum corneum, thereby decreasing the anesthetic onset time for topical agents Many of these products have proven efficacy and work efficiently; however, most require ... needleless SC infiltration of 1% or 2% powdered lidocaine achieve anesthesia within to minutes One pediatric study that showed good efficacy did not find that this method caused pain on administration,