Esters

Procaine (Novocain) Tetracaine (Pontocaine) Chloroprocaine (Nesacaine) Cocaine

Benzocaine (Lanocaine, Americaine) Proparacaine (Alcaine, Ophthetic, Paracaine)

Expanded from Archar S, Kundar S. Principles of office anesthesia. Part I. Infiltrative anesthesia. Am Fam Physician 2002;6:91-94.

total (10 mL per side). Lidocaine has an elimination half-life of 1.5 to 2.5 hours in most patients, and average infiltrative anesthesia lasts 2 to 6 hours. Bupivacaine has a longer onset and length of action and an elimination half-life of 2.7 hours in adults and 8 hours in neonates. Data on mixing lidocaine and bupivacaine are limited.

Some local anesthetics have epinephrine as an additive to help with hemostasis in very vascular locations. Buffering any local anesthetic containing epinephrine with a 1:10 ratio of sodium bicarbonate to anesthetic before injection helps reduce discomfort during the injection by neutralizing the acidic properties of the fluid. The current dogma is to avoid the use of epinephrine on end-artery areas, including fingers, ears, nose, lips, penis, and toes. However, a recent review on the use of local anesthesia with epinephrine in a digital block challenges this dogma (Mohan and Cherian, 2007). To be safe, epinephrine should not be used in distal-end vascular beds until the data are more conclusive. (See Tuggy Video: Local Anesthesia.)

Local Ring Anesthesia Block

For anesthesia around a superficial skin lesion, a ring block can be placed with good results. Use a larger needle to draw up the anesthetic and a 25- to 30-gauge needle to infiltrate the tissues. Insert the needle into the subcutaneous skin a few millimeters outside the planned incision line, and advance along that circular line around the lesion. Aspirate intermittently to ensure no flashback of blood, to avoid direct instillation of anesthetic into a vein or artery. Infiltrate the local anesthetic as the needle is advanced. Use anesthetized areas to puncture the skin, and inject more distal areas as needed around the planned surgical field until the lesion is fully circumscribed. Slow instillation with the anesthetic solution and warming the syringe by holding in the hand can make the infiltration more comfortable for the patient. Local anesthesia may be instilled through the subcutaneous tissue through a laceration side wall and may be less painful than going through intact skin.

Digital Block

A digital block can be an effective method for providing anesthesia for fingers and toes. A dorsal or interdigital approach is used to provide anesthesia to the digit. The digital nerves are 3 to 5 mm under the skin at the 2, 4, 8, and 10 o'clock positions around the digit. Each location can be infiltrated with 1 to 2 cc (mL) of 1% lidocaine without epinephrine. It may take 5 to 30 minutes for distal anesthesia to develop after injection. Occasionally, local anesthesia is needed at the base of the digit circumferentially if achieving complete anesthesia becomes difficult (Fig. 28-2). Patients may continue to feel pressure and motion but should not feel sharp pain when the anesthesia is effective. (See Tuggy Video: Digital Block.)

Complications with Local Anesthesia

Recognizing the various side effects and reactions to local anesthesia is critical to prevent serious complications. The most common complication with the use of local infiltrative anesthesia is a vasovagal episode. The patient may look pale, begin to sweat, and then feel faint or even fall unconscious.

Although accompanied by one or two tonic-clonic beats in some cases, this is not considered a seizure. Lying the patient down in reverse Trendelenburg positioning with both legs elevated can increase blood return to the heart and improve vagally depressed cardiac output. Atropine can reverse vagal bradycardia but is rarely needed. Recovery occurs spontaneously within minutes, but the queasiness may persist for 30 to 60 minutes.

Inadvertent instillation of an anesthetic into a blood vessel may cause seizures, jitteriness, or palpitations and may be avoided by always aspirating before infiltrating the local anesthetic. If a flash of blood is obtained on aspiration, pull the needle back partially, aspirate again, and instill only if no blood return occurs. Other reactions to local anesthesia are discomfort, bruising, and edema of the injection site. True anaphylaxis to lidocaine is estimated to occur in less than 1% of injections (Haugen and Brown, 2007). Administer diphenhydramine (Benadryl), 25 to 50 mg orally, intravenously, or intramuscularly in adults and 1 mg/kg in children, and epinephrine 1:1000 subcutaneously every 5 minutes as needed. The adult dose of epinephrine 1:1000 is 0.3 to 0.5 mL/kg and the pediatric dose 0.01 mL/kg at the same intervals. Emergency response personnel should be notified, and prolonged observation may be warranted.

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