Local anesthetics

Local anesthetics

1. Drug used in Mechanical Ventilation Dr. S. Parasuraman Associate Professor, Faculty of Pharmacy, AIMST University, Malaysia.

2. Content Part II - Medications used for local and general anaesthesia

3. Local anesthetics

4. Local anesthetics Local anesthetics provide a reversible regional loss of sensation. They reduce pain and thereby facilitate surgical procedures. Local anesthetics block nerve conduction of sensory impulses and in higher concentrations block motor impulses from the periphery to the CNS . Sodium ion is required for an action potential that are blocked to prevent the transient increase in permeability of the nerve membrane to Na + .

5. Comparative features of general and local anaesthesia

6. Classification of local anesthetics

7. Mechanism of local anesthetic action

8. Mechanism of local anesthetic action The local anesthetics block nerve conduction by decreasing the entry of Na+ ions during upstroke of action potential. As the concentration of the local anesthetics is increased, the rate of rise of action potential and maximum depolarization decreases causing slowing of conduction.

9. Delivery techniques of local anesthetics The techniques include topical administration, infiltration , perineural , and neuraxial (spinal, epidural, or caudal) blocks . Regional anesthesia Surface anesthesia Infiltration anesthesia Field block Nerve block Spinal anesthesia Epidural anesthesia

10. Pharmacological properties of local anesthetics

11. Local anesthetics – actions All local anesthetics cause vasodilation, which leads to a rapid diffusion away from the site of action and short duration when these drugs are administered alone . By adding the vasoconstrictor epinephrine , the rate of local anesthetic absorption and diffusion is decreased . This minimizes systemic toxicity and increases the duration of action . However, epinephrine should not be coadministered for nerve block in extremities such as fingers and toes as vasoconstriction of end arteries may lead to ischemia and necrosis. It should be used with caution in patients with thyrotoxicosis or cardiovascular disease and in labor. Hepatic function does not affect the duration of action of local anesthesia.

12. Local anesthetics – systemic actions Central nervous system: All local anesthetics are capable of producing a sequence of stimulation followed by depression. Cocaine is a powerful CNS stimulant causing in sequence euphoria—excitement—mental confusion—restlessness — tremor and twitching of muscles—convulsions—unconsciousness—respiratory depression— death , in a dose-dependent manner.

13. Local anesthetics – systemic actions Cardiovascular system : Local anesthetics are cardiac depressants, but no Significant effects are observed at conventional doses . At high doses (2–3 times the doses producing CNS effects) or on inadvertent i.v . injection , they decrease automaticity, excitability , contractility , conductivity and prolong effective refractory period (ERP).

14. Local anesthetics – systemic actions Blood vessels: Local anesthetics tend to produce fall in BP. This is primarily due to sympathetic blockade , but high concentrations, as obtained locally at the site of injection, do cause direct relaxation of arteriolar smooth muscle.

15. Local anesthetics Onset , potency, and duration of action The onset of action of local anesthetics is influenced by several factors including tissue pH, nerve morphology, concentration, pKa , and lipid solubility of the drug . Local anesthetics with a lower pKa have a quicker onset.

16. Local anesthetics Onset , potency, and duration of action

17. Local anesthetics – Allergic reactions (topical) Patient reports of allergic reactions to local anesthetics are fairly common , but often times reported “allergies” are actually side effects from the coadministered epinephrine . Systemic toxic effect: Toxic blood levels of a local anesthetic may be due to repeated injections or could result from a single inadvertent IV injection.

18. Sites and uses of surface anaesthesia

19. Local anaesthetics used for spinal and epidural anaesthesia and continuous epidural analgesia

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