صفحه محصول - پاورپوینت بی حس کننده های موضعی

پاورپوینت بی حس کننده های موضعی (pptx) 26 اسلاید

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تعداد اسلاید: 26 اسلاید

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Local Anesthetics Case study A 67-year-old woman is scheduled for elective total knee arthroplasty. What local anesthetic agents would be most appropriate if surgical anesthesia were to be administered using a spinal or an epidural technique, and what potential complications might arise from their use? What anesthetics would be most appropriate for providing postoperative analgesia via an indwelling epidural or peripheral nerve catheter? Local anesthesia Local anesthesia results when sensory transmission from a local area of the body to the CNS is blocked. The local anesthetics: chemically similar agents (esters and amides) that block the sodium channels of excitable membranes. As administered by injection in the target area, or by topical application >>> anesthetic effect can be restricted to a localized area (eg, the cornea or an arm) CHEMISTRY Most local anesthetics are esters or amides of simple benzene derivatives. Subgroups within the local anesthetics are based on this chemical characteristic and on duration of action. The commonly used local anesthetics are weak bases with at least 1 ionizable amine function that can become charged through the gain of a proton (H+). The degree of ionization is a function of the pKa of the drug and the pH of the medium. Representative structures of ester and amide anesthetics As pH of tissue may differ from the physiologic 7.4 (eg, it may be as low as 6.4 in infected tissue), the degree of ionization of the drug will vary. Because the pKa of most local anesthetics is between 8.0 and 9.0 (benzocaine is an exception), variations in pH associated with infection can have significant effects on the proportion of ionized to nonionized drug. Structure and properties of some ester and amide local anesthetics PHARMACOKINETICS Shorter-acting local anesthetics >>> readily absorbed into the blood from the injection site The duration of local action is limited unless blood flow to the area is reduced This can be accomplished by a vasoconstrictor (usually an α-agonist sympathomimetic) with the local anesthetic agent Cocaine is an important exception because it has intrinsic sympathomimetic action (inhibition of norepinephrine reuptake into nerve terminals) Surface activity (ability to reach superficial nerves when applied to the surface of mucous membranes) is a property of certain local anesthetics, especially cocaine, benzocaine, lidocaine, and tetracaine. Metabolism: Ester local anesthetics: is carried out by plasma cholinesterases (pseudocholinesterases) and is very rapid for procaine (halflife, 1–2 min), slower for cocaine, and very slow for tetracaine Amides: are metabolized in the liver by cytochrome P450 isozymes. The halflives of lidocaine and prilocaine are approximately 1.5 h. Bupivacaine and Ropivacaine are the longest-acting amide local anesthetics with half-lives of 3.5 and 4.2 h, respectively. Liver dysfunction may increase the elimination half-life of amide local anesthetics (and increase the risk of toxicity). Acidification of the urine promotes ionization of local anesthetics; the charged forms of such drugs are more rapidly excreted than nonionized forms.