MedicalC ontinuingEducation CONTINUING MEDICAL EDUCATION Objectives After completing this CME, the reader should be able to: 1) Define the term local anesthesia 2) Know the pharmacokinet- ics and mode of action of local anesthetics. 3) Distinguish the different Local Anesthesia types of local anesthetics com- monly used in foot and ankle surgery. Techniques 4) Recognize the indication for different types of anesthesia These injections are commonly used technique 151 in podiatric surgery. 5) Perform local anesthesia techniques of the digits, hallux, BY KHURRAM H. KHAN, DPM medial column, lateral column, and ankle. Welcome to Podiatry Management’s CME Instructional program. Our journal has been approved as a sponsor of Con- tinuing Medical Education by the Council on Podiatric Medical Education. You may enroll: 1) on a per issue basis (at $26.00 per topic) or 2) per year, for the special rate of $210 (you save $50). You may submit the answer sheet, along with the other information requested, via mail, fax, or phone. You can also take this and other exams on the Internet at www.podiatrym.com/cme. If you correctly answer seventy (70%) of the questions correctly, you will receive a certificate attesting to your earned credits. You will also receive a record of any incorrectly answered questions. If you score less than 70%, you can retake the test at no additional cost. A list of states currently honoring CPME approved credits is listed on pg. 160. Other than those entities currently accepting CPME-approved credit, Podiatry Management cannot guarantee that these CME credits will be acceptable by any state licensing agency, hospital, managed care organization or other entity. PM will, however, use its best efforts to ensure the widest acceptance of this program possible. This instructional CME program is designed to supplement, NOT replace, existing CME seminars. The goal of this program is to advance the knowledge of practicing podiatrists. We will endeavor to publish high quality manuscripts by noted authors and researchers. If you have any questions or comments about this program, you can write or call us at: Podiatry Management, P.O. Box 490, East Islip, NY 11730, (631) 563-1604 or e-mail us at [email protected]. Following this article, an answer sheet and full set of instructions are provided (pg. 160).—Editor A Look at the Basics Local anesthesia is defined as any sia is that a relatively small dose of Local anesthesia history followed technique that renders part of the body local anesthetic can cover a large area. general anesthesia by approximately insensitive to pain without affecting The disadvantage is that placement 40 years. consciousness. The technique can be of a tourniquet may be limited by the 1860—Cocaine isolated from used for relief of non-surgical pain and area of the block and/or the block erythroxylum coca to enable diagnosis of the cause of may not work properly. 1884—Koller used cocaine for some chronic pain conditions. Local anesthetics medications topical anesthesia of the eye Peripheral nerve blocks occur produce a reversible loss of sensation 1885—Halsted used cocaine as when injecting local anesthetic near in a localized part of the body when peripheral nerve block the course of a named nerve. They are applied directly onto nerve tissues 1905—First synthetic local— used for surgical procedures involving or mucous membranes. This limits procaine the distribution of the blocked nerve. propagation of the action potential. 1943—Lidocaine synthesized The advantage over general anesthe- Continued on page 152 www.podiatrym.com MARCH 2017 | PODIATRY MANAGEMENT CME Continuing Medical EducationAnesthesia (from page 151) There are two categories of local anesthetics Some of the desirable character- Esters istics include rapid onset of action, Cocaine reversible block of nerve conduction, Chloroprocaine low degree of systemic toxicity, and Procaine effectiveness on all parts of the ner- Benzocaine vous system, all types of nerve and Tetracaine muscle fibers. The local anesthetic mechanism Amides of action occurs by binding to sodi- Bupivacaine um channels, which slows or pre- Lidocaine vents axonal conduction. These med- Ropivacaine Figure 1: Vapocoolant spray after a neuroma injection with ications have a lipophilic and hy- Etidocaine residual frostbite injury. drophilic end (they are ionizable). If Mepivacaine there is a low pH state, the anesthetic Prilocaine Bupivacaine (Marcaine) has no is in an ionized state and unable to topical effects so it is used as an infil- cross the membrane, so adding some Esters trate with a slower onset and is one sodium bicarbonate to the solution Cocaine, which is a Schedule II of the longer duration agents. It also creates a more non-ionized state. substance, has medical use limited provides sensory and motor dissocia- The question asked by many is to surface or topical anesthesia (cor- tion, which means it provides sensory if buffering reduces pain. This issue neal or nasopharyngeal). Benzocaine analgesia with a minimal motor block. was addressed in a 1997 paper in (americaine) is available in many Ropivacaine is an enantiomer of 152 JAMA by HE Friedman, KT Jules, OTC preps for relief of pain and ir- bupivacaine and clinically equivalent. K Springer, and M Jennings titled ritation for surface anesthesia (topi- It has similar sensory versus motor “Buffered Lidocaine Decreases the cal), only ointments, sprays, etc. selectivity as bupivacaine with signifi- cantly less cardiovascular toxicity. Prilocaine has a similar clinical Vasoconstrictors such as epinephrine decrease the rate profile to that of lidocaine but causes significantly less vasodilation than of systemic absorption and decrease systemic toxicity. lidocaine, so less vasoconstrictor needs to be added. Its most popular clinical application is for topical an- Pain of Digital Anesthesia in the Procaine (Novocaine) is topically esthesia as in combo with lidocaine Foot”. A randomized, double-blind ineffective and is used for infiltration in a eutectic mixture combination study demonstrated that 24 out of 30 because of low potency and short product such as EMLA (eutectic mix- participants indicated on a visual an- duration. It produces significant va- ture of local analgesics). alogue scale that buffered lidocaine is sodilation so epinephrine is used to EMLA is a mixture of local an- less painful than plain lidocaine. The prolong its effect. esthetics, the most common form pain decreased by 50% or more for Tetracaine (Pentocaine) is used for of which is lidocaine and prilocaine almost half of the participants. infiltration and spinal anesthesia as (this becomes an oily mixture). The well as being frequently used for top- lidocaine/prilocaine combination is Absorption Factors ical ophthalmological anesthesia be- indicated for dermal anesthesia. Spe- Factors that affect local anes- cause of its slow onset and more pro- cifically, it is applied to prevent pain thetic absorption factors influencing longed effect than procaine. Tetracaine associated with intravenous catheter peak plasma concentration include has the longest duration of the esters. insertion, blood sampling, superficial the site of injection (vascularity), surgical procedures, and topical an- total dose, specific drug character- Amides aesthesia of leg ulcers for cleansing istics, and the presence of vasocon- Lidocaine (Xylocaine) is the most or debridement. strictors (e.g., epinephrine, phenyl- widely used local anesthetic and is ephrine). Vasoconstrictors decrease effective by all routes. It has a fast- Dosages—Local Anesthetic the rate of systemic absorption and er onset, is more intense, and lon- Toxicity decrease systemic toxicity. They in- ger-lasting than procaine. It’s one of • Cardiovascular myocardial de- crease the local drug concentration the most widely used local anesthet- pression and vasodilation can cause and increase neuronal uptake of the ics in podiatry. hypotension and circulatory collapse. local anesthetics, which increases Mepivacaine (Carbocaine) has a • Allergic reactions are rare (less the local duration of action (e.g. similar onset and duration as lidocaine, than 1%) and usually are due to pre- lidocaine’s duration may increase but is toxic to neonates so it is not servatives or metabolites of esters: two-fold with the addition of epi- used in obstetrical anesthesia (the fetus rash, bronchospasm. nepherine). poorly metabolizes mepivacaine). Continued on page 153 MARCH 2017 | PODIATRY MANAGEMENT www.podiatrym.com MedicalC ontinuingEducation CME Anesthesia (from page 152) Always palpate for landmarks, and local blockade, when using prepare the site with an antiseptic solu- a 50/50 mixture of plain lido- Toxicity occurs primarily from tion. While maintaining sterile tech- caine and plain bupivacaine in intravascular injection or an exces- nique, place a wheal of local anesthetic place of their independent use. Oka, sive dose. There are ways to prevent using a 25 gauge needle or smaller. et al.,in Anesth Prog 1997, ststed that and treat toxicity which include as- Decrease the perceived pain of no difference was found in the time pirating, often with slow injection. injections by using a vapocoolant until onset of anesthetic; however, Always ask about previous CNS tox- spray, distracting the patient, pinch- the duration of anesthetic effect was icity and have monitoring available, including resuscitative equipment, CNS-depressant drugs, and cardio- vascular drugs. Procaine (Novocaine) is topically ineffective Before you begin the