Pharmacology





Regional anesthesia is a fast-growing field with application in a wide range of surgical procedures. Better technique with the help of ultrasound, better and safer local anesthetics, and better drug delivery systems for continuous anesthesia all helped in gaining the current status. Far too often, those unfamiliar with regional anesthesia regard it as complex because of the long list of local anesthetics available and the varied techniques described. The goal throughout this book is to simplify regional anesthesia by providing specific information about various elements involved in decision making.


One of the first steps in simplifying regional anesthesia is to understand the two principal decisions necessary in prescribing a regional technique. First, the appropriate technique needs to be chosen for the patient, the surgical procedure, and the physicians involved. Second, the appropriate local anesthetic and potential additives must be matched to patient, procedure, regional technique, and physician. This book will detail how to integrate these concepts into your practice.


Drugs


Numerous local anesthetic drugs are used in varied concentrations and with different additives. The decision to choose one particular local anesthetic is influenced by patient factors, surgical factors, and the available resources (cost factors). Not all procedures are created equal in terms of the amount of time needed to complete an operation, and the severity or nature of pain will be different. If anesthesiologists are to use regional techniques effectively, they must be able to choose a local anesthetic that lasts the right amount of time and provides effective anesthesia and analgesia. To do this, they need to understand the local anesthetic timeline from the shorter-acting to the longer-acting agents ( Fig. 1.1 ) and the effect of additives. Also, they need to understand the factors associated with successful continuous nerve block management.




Fig. 1.1


Local anesthetic timeline (length in minutes of surgical anesthesia). Epi, epinephrine.


All local anesthetics share the basic structure of aromatic end, intermediate chain, and amine end ( Fig. 1.2 ). This basic structure is subdivided clinically into two classes of drugs: the amino esters and the amino amides. The amino esters possess an ester linkage between the aromatic end and the intermediate chain. These drugs include cocaine, procaine, 2-chloroprocaine, and tetracaine ( Figs. 1.3 and 1.4 ). The amino amides contain an amide link between the aromatic end and the intermediate chain. These drugs include lidocaine, prilocaine, etidocaine, mepivacaine, bupivacaine, and ropivacaine (see Figs. 1.3 and 1.4 ).




Fig. 1.2


Basic local anesthetic structure.



Fig. 1.3


Local anesthetics commonly used in the United States. (A) Amides. (B) Esters.





Fig. 1.4


Chemical structure of commonly used amino ester and amino amide local anesthetics.


Amino esters







Cocaine was the first local anesthetic used clinically, and it is used today primarily for topical airway anesthesia. It is unique among the local anesthetics in that it is a vasoconstrictor rather than a vasodilator. Some anesthesia departments have limited the availability of cocaine because of fears of its abuse potential. In those institutions, mixtures of lidocaine and phenylephrine rather than cocaine are used to anesthetize the airway mucosa and shrink the mucous membranes.



Jun 15, 2021 | Posted by in ANESTHESIA | Comments Off on Pharmacology
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