Flashcards in Week 9 - Chapter 26 Local Anesthetics Deck (20):
amide-type agents, represented by lidocaine [Xylocaine], contain an amide linkage. Very low incidence of allergic reactions. Hepatic enzymes as the method of metabolism
achieved by injecting a local anesthetic into the epidural space (ie, within the spinal column but outside the dura mater). A catheter placed in the epidural space allows administration by bolus or by continuous infusion. Following administration, diffusion of anesthetic across the dura into the subarachnoid space blocks conduction in nerve roots and in the spinal cord itself. Diffusion through intervertebral foramina blocks nerves located in the paravertebral region. With epidural administration, anesthetic can reach the systemic circulation in significant amounts. As a result, when the technique is used during delivery, neonatal depression may result. Lidocaine and bupivacaine are popular drugs for epidural anesthesia. Because of the risk of death from cardiac arrest, the concentrated (0.75%) solution of bupivacaine must not be used in obstetric patients.
ester-type anesthetics, represented by procaine [Novocain], contain an ester linkage in their structure. Low incidence of allergic reactions. Plasma esterases as the method of metabolism.
achieved by injecting a local anesthetic directly into the immediate area of surgery or manipulation. Anesthesia can be prolonged by combining the anesthetic with epinephrine. The agents employed most frequently for infiltration anesthesia are lidocaine and bupivacaine.
Intravenous Regional Anesthesia
employed to anesthetize the extremities—hands, feet, arms, and lower legs, but not the entire leg (because too much anesthetic would be needed). Anesthesia is produced by injection into a distal vein of an arm or leg. Before giving the anesthetic, blood is removed from the limb (by gravity or by application of an Esmarch bandage), and a tourniquet is applied to the limb (proximal to the site of anesthetic injection) to prevent anesthetic from entering the systemic circulation. To ensure complete blockade of arterial flow throughout the procedure, a double tourniquet is used. Following injection, the anesthetic diffuses out of the vasculature and becomes evenly distributed to all areas of the occluded limb. When the tourniquet is loosened at the end of surgery, about 15% to 30% of administered anesthetic is released into the systemic circulation. Lidocaine—without epinephrine—is the preferred agent for this type of anesthesia.
Local anesthetics stop axonal conduction by blocking sodium channels in the axonal membrane. Recall that propagation of an action potential requires movement of sodium ions from outside the axon to the inside. This influx takes place through specialized sodium channels. By blocking axonal sodium channels, local anesthetics prevent sodium entry, and thereby block conduction.
Nerve Block Anesthesia
Nerve block anesthesia is achieved by injecting a local anesthetic into or near nerves that supply the surgical field, but at a site distant from the field itself. This technique has the advantage of producing anesthesia with doses that are 249smaller than those needed for infiltration anesthesia. Drug selection is based on required duration of anesthesia. For shorter procedures, lidocaine or mepivacaine might be used. For longer procedures, bupivacaine would be appropriate.
Spinal (Subarachnoid) Anesthesia
Spinal anesthesia is produced by injecting local anesthetic into the subarachnoid space. Injection is made in the lumbar region below the termination of the cord. Spread of anesthetic within the subarachnoid space determines the level of anesthesia achieved. Movement of anesthetic within the subarachnoid space is determined by two factors: (1) the density of the anesthetic solution and (2) the position of the patient. Anesthetics employed most commonly are bupivacaine, lidocaine, and tetracaine. All must be free of preservatives.
Procaine - Mechanism of Action
The drug is not effective topically, and must be given by injection. Administration in combination with epinephrine delays absorption.
Procaine - Category
ester-type local anesthetics
Procaine - Uses
Procaine - Adverse Effects
Although procaine is readily absorbed, systemic toxicity is rare because plasma esterases rapidly convert the drug to inactive, nontoxic products. Being an ester-type anesthetic, procaine poses a greater risk of allergic reactions than do the amide-type anesthetics. Individuals 247allergic to procaine should be considered allergic to all other ester-type anesthetics, but not to the amides.
Lidocaine - Mechanism of Action
local anesthetics, lidocaine can be administered topically and by injection.
Lidocaine - Category
prototype of the amide-type agents
Lidocaine - Uses
analgesic. treat dysrhythmias.
Lidocaine - Adverse Effects
Anesthesia with lidocaine is more rapid, more intense, and more prolonged than an equal dose of procaine. Effects can be extended by coadministration of epinephrine. Allergic reactions are rare, and individuals allergic to ester-type anesthetics are not cross-allergic to lidocaine. If plasma levels of lidocaine climb too high, CNS and cardiovascular toxicity can result. Inactivation is by hepatic metabolism.
Cocaine - Mechanism of Action
Despite its ability to constrict blood vessels, cocaine is readily absorbed following application to mucous membranes. The drug is inactivated by plasma esterases and liver enzymes.
Cocaine - Uses
local anesthesia, cocaine has pronounced effects on the sympathetic and central nervous systems.
Cocaine - Category
first local anesthetic. It is an ester-type anesthetic