regional.ppt

LOCAL ANESTHETICS AND REGIONAL ANESTHESIA UNIFORMED SERVICES UNIVERSITY OF THE HEALTH SCIENCES Local Anesthetics- History 1860 - cocaine isolated from erythroxylum coca Koller - 1884 uses cocaine for topical anesthesia Halsted - 1885 performs peripheral nerve block with local Bier - 1899 first spinal anesthetic Local Anesthetics - Definition A substance which reversibly inhibits nerve conduction when applied directly to tissues at non-toxic concentrations Local Anesthetics - Classes Local anesthetics - Classes (Rule of “i’s”) Esters Cocaine Chloroprocaine Procaine Tetracaine Am”i”des Bupivacaine Lidocaine Ropivacaine Etidocaine Mepivacaine Local anesthetics - Formulation Biologically active substances are frequently administered as very dilute solutions which can be expressed as parts of active drug per 100 parts of solution (grams percent) Ex.: 2% solution = _2 grams__ = _2000 mg_ = __20 mg__ 100 cc’s 100 cc’s 1 cc Local Anesthetics - Allergy True allergy is very rare Most reactions are from ester class - ester hydrolysis (normal metabolism) leads to formation of PABA - like compounds Patient reports of “allergy” are frequently due to previous intravascular injections Local Anesthetics - Toxicity Tissue toxicity - Rare Can occur if administered in high enough concentrations (greater than those used clinically) Usually related to preservatives added to solution Systemic toxicity - Rare Related to blood level of drug secondary to absorption from site of injection. Range from lightheadedness, tinnitus to seizures and CNS/cardiovascular collapse Local anesthetics - Duration Determined by rate of elimination of agent from site injected Factors include lipid solubility, dose given, blood flow at site, addition of vasoconstrictors (does not reliably prolong all agents) Some techniques allow multiple injections over time to