Answer
The 2 main classes of local anesthetics currently in use are amino esters and amino amides. Both inhibit ionic fluxes required for the initiation and conduction of nerve impulses. [13]
Lidocaine, the most commonly used anesthetic, has a fast onset of action and a duration of action of 30-120 minutes, which is increased to 60-400 minutes with the addition of epinephrine. [12, 13] The total cumulative dose of lidocaine to be infiltrated is 5 mg/kg (not to exceed 300 mg) if lidocaine without epinephrine is used, and 7 mg/kg (not to exceed 500 mg) if lidocaine with epinephrine is used.
Anesthetic preparations that contain epinephrine are commonly used in the emergency department. Epinephrine induces vasoconstriction, decreasing the amount of local bleeding at the site of injection. In addition, it increases the duration of action of the anesthetic with which it is combined. Despite these advantages, the vasoconstrictive properties of epinephrine may contribute to tissue hypoxia, and its use should be avoided in areas of poor perfusion (ie, fingers, toes, penis, ears, nose).
In children or noncompliant adults, consider using topical anesthetic mixtures, such as lidocaine, epinephrine, and tetracaine or a eutectic mixture of lidocaine and prilocaine.
Pediatric or elderly patients may require additional sedation for compliance.
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The posterior tibial nerve courses down the posterior calf.
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Medial and lateral plantar nerves after branching from the posterior tibial nerve.
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Cutaneous innervation by the medial and lateral branches of the posterior tibial nerve.
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Cutaneous innervation of the calcaneal region by the medial plantar nerve.
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The tibialis posterior tendon, flexor digitorum tendon, posterior tibial artery, posterior tibial nerve, and flexor hallucis longus tendon at the ankle level.
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Areas of anesthetization to complete an ankle block. This block requires anesthetization of 5 nerves for complete sensory block below the ankle. The areas to anesthetize include a line along the anterior ankle for the superficial peroneal nerve (blue line), the deep peroneal nerve (red star), the saphenous nerve (pink star), the sural nerve (green arrow), and the posterior tibial nerve (orange arrow).
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Equipment needed for the regional block.
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Posterior tibial nerve block landmarks. Medial malleolus (MM) is at the left and Achilles tendon is at right. Posterior tibial artery (A) is approximately 1 cm inferior to the site marked for needle insertion (arrow).
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Palpation of the posterior tibial artery.
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Marking the injection site, which is 0.5-1 cm superior to the posterior tibial artery.
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Location of injection site when unable to palpate the posterior tibial artery.
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Using povidone iodine solution (Betadine) to clean the injection site.
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Placing a skin wheal.
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Injection posterior and superior to the posterior tibial artery.
