Systemic absorption of LA is determined by site of injection, dosage and volume, addition of vasoconstricting additives, and pharmacologic profile of LA. Blood levels after injection of LA are highest for intercostal blocks > caudal> epidural> brachial plexus> sciatic/femoral> subcutaneous. (See table below.) The more vascular the region the higher the blood levels after injection. The addition of vasoconstrictors, like epinephrine, will lower the potential systemic toxicity of LA. Recommendations on maximal doses of LAs commonly found in pharmacology texts are not directly applicable to the practice of regional anesthesia. Any recommendation on the maximal doses can be valid only in reference to a specific nerve block procedure.
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