Uses and Actions of Local Anaesthetics Flashcards
Define Local Anaesthetics
Reversibly block nerve conduction when applied to restricted area of body to enable procedure to be carried out without loss of consciousness
How does the chemical nature of LA affect function
Aromatic ring gives lipid solubility
Basic amine group can have additional H+ so can be charged
Time of action determined by strength of linkage as this is metabolised
Why are LA weak bases
Ionisation state determined by pH
How does pH of environment determine proportion of LA ionised/unionised?
Alkaline = more unionised Acidic = more ionised
At physiological pH, what are the proportions of ionised/unionised
Ionised > unionised
How does LA work
Unionised form diffuses through membrane.
Ionised form blocks ion channel
What is a use dependent block
Increase pain = increase block
Why would inflammation infection affect LA effectiveness
Create acidic environment so more ionised LA which doesnt cross the membrane
Why do you lose sensation with LA but not motor capability?
Motor neurones are not as sensitive to LA as sensory axons
What are some routes of admin for LA
Epidural = injected into epidural space Topical = applied to surface Infiltration = all neurones in a periph. nerve eg. whole Jaw Spinal = injected into subarachnoid space
What are some unwanted effects of LA
Hypersensitive reactions Cardiac muscle = decrease contractility BV dilate BP decrease Bupivocaine most cardiotoxic Tremor, convulsion
What drugs are injected with LA and why
Vasoconstrictors eg. Ad to localise LA
Increase duration of action
Decrease unwanted effects
What is the precaution of injecting Ad with LA
Vasoconstriction of extremities
