LOCAL ANAESTHETIC AGENTS Flashcards
Define local anaesthetics
=Local anaesthetics are agents that produce localized, reversible block to nerve conduction
=They act by inhibiting sodium channels on neuronal membranes
=They are administered locally by application to the skin or mucous membranes, infiltration in the immediate area of surgery, injection into or near the nerves that supply the surgical field, injection into a distal vein to anaesthetize the limb, and injection into the epidural or subarachnoid space
=Unlike general anaesthetics, they do not produce generalized depression of brain functions and full consciousness is maintained
What is the mechanism of action of local anaesthetics?
=Local anesthetics produce anesthesia by inhibiting excitation of nerve endings or by blocking conduction in peripheral nerves
=This is achieved by anesthetics reversibly binding to and inactivating sodium channels, the individual loses sensation in the area supplied by the nerve
Activity of local anesthetics is a function of their?
=Lipid solubility
=Diffusibility
=Affinity for protein binding
=Percent ionization at physiologic pH
=Vasodilating properties
How are local anaesthetic effects terminated?
=Local anaesthetic effects are terminated by uptake into the systemic circulation.
=The rate of systemic absorption is determined by:
*Pharmacokinetic properties of the drug
*Vascularity of the area
*Concentration of the solution
Why should you use vasoconstrictors when administering local anaesthetics?
=All local anesthetics, with the exception of cocaine, are vasodilators
=To counteract this vasodilatation, epinephrine (which induces vasoconstriction) is often included in local anesthetic solutions to:
*To delay systemic absorption hence prolonging the local block
*To limit toxicity (allows administration of lower doses)
❕Vasoconstrictors should be avoided in areas supplied by end arteries e.g. toes, fingers, nose, ears, penis (gangrene may occur)
What are the two classes of local anaesthetics？
Amides and Esters
Local anaesthetics: Esters
⊞x-caine
=cocaine, procaine, amethocaine, tetracaine and chloroprocaine
＝They are metabolized in plasma by esterases
Most likely to cause allergic reactions
Local anaesthetics: Amides
⊞x-i-x-caine
＝lignocaine, bupivacaine, prilocaine, cinchocaine, mepivacaine, etidocaine
=Metabolized in the liver by cytochrome P450 enzymes
List the adverse effects of Local anaesthetics
=Allergic reactions (ester-type local anaesthetics)
=Adverse effects on systemic absorption:
*Myocardial depression
*Vasodilatation (except cocaine)
*Hypotension (except cocaine)
*CNS excitation (restlessness, tremors, fits) followed by CNS depression
*Depress uterine contractility
*Can cross the placenta and cause neonatal bradycardia and CNS depression
Describe the techniques used in Local anesthetic administration
①Surface anaesthesia: skin or mucous membranes
❓Used to relieve pain and itching from various causes
❷Infiltration: injected directly into the immediate area of surgery
③Nerve block anaesthesia: injection is made into or near the nerves that supply the surgical field
④Intravenous regional anaesthesia: injected into a distal vein of an arm or leg to anaesthetize the limb
⑤Epidural anaesthesia: injected into the epidural space and it diffuses into the subarachnoid space producing anaesthesia of nerve roots and spinal cord
⑥Spinal anaesthesia: injected into the subarachnoid space to produce anaesthesia of the nerve roots and spinal cord
Which agents are Surface Anaesthesia
*lignocaine
*cocaine
*tetracaine
List the local anaesthetic agents administered by infiltration?
*procaine
*lignocaine
*bupivacaine
Which agents are used as nerve block anaesthesia
*lignocaine
*procaine
*prilocaine
*mepivacaine
Which agents are used as intravenous regional anaesthesia?
*prilocaine
*lignocaine
Which agents are used in epidural anaesthesia?
*lignocaine
*bupivacaine
