Local Anaesthesia WK1 Flashcards
If you do not hold an endorsement for scheduled medicine which local anaesthetic drugs are you permitted to access and administer in
i) NSW
ii) Vic
NSW - synthetic cocaine substitutes that are required by the clinical practice
VIC - lignocaine 2% prilocaine 2% or less
What dose 1% mean in terms of the dose of LA
Concentration of the drug
%= 1g/100ml
Why is the topical product ELMA appropriate to anaesthesia the skin and not a lignocaine prep?
Deeper penetration, higher concentration for topical application
Lignocaine combines to make anti septic
What are nociceptors?
What are the two main principle types of nociceptor neurones?
Pain receptors, free nerve endings
A Delta - fast sharp pain myelinated
C Fibres - slow aching pain unmyelinated
How does a local anaesthetic drug prevent a person from feeling pain ?
Reversibly block membrane depolarisation in excitable tissues
Inhibits action potential
How can a LA molecule be both water soluble and lipid soluble
Hydrochloride solution can change across equilibrium
Weak base injected into body rises in ph
Depending on the pH
Increase in pH favours lipid soluble
decrease in pH favours water soluble
Which chemical and or biological factor determines if a LA drug is more water or lipid soluble
pH determines which solute
Increase in pH lipid soluble
Decrease in pH water soluble
What is mode of action for all LA drugs
5 steps
Administered via Injection
- Unionised LA moles diffuse into nerve axon
- LA Moles reionise
- Ionised LA Moles bind to Calcium in NaK channels
- Axon depolarisation prevented
- Nerve conduction temperoliary Inhibited
Why is it a contradiction to inject into inflamed or infected tissue
3
Blood flow is increased
pH has decreased due to inflammation which slows onset of action
Increased vascular re absorption reduces potency of drug
What is potency
Why are bupivacaine levobipivacaine and ropivacaine the most potent drugs ?
Potency is the drug ability to produce biological change
Drugs with higher lipid solubility have greater potency !
Which factor determines the duration of action for LA drug
3
Adrenaline acts as vasoconstrictor and reduces systemic re absorption prolonging action
Increase in pH increase duration
High degree of protein binding to sites increases duration
How are the pharmacokinetics of
ADME relevant to clinical use of LA
A can be influenced by blood flow LA solution (adrenaline presence)
D depends on site of injection, blood flow, plasma protein binding (high bind low distribution
M esters metabolised quicker. Amides metabolised much slower
E renal excretion
Why are drugs such as roxithromycin and itraconazole considered to be a relative contraindication of LA use
Inhibit cytochrome P450 Liver enzymes which may impair the metabolism of LA drugs
Why are beta blockers such as metoprolol to be a relative contraindication for the use of LA drugs
Cause bradycardia which reduces hepatic perfusion
Which is the most common vasoconstrictor substance added to LA solution?
Rationale for LA+ Vasoconstrictor?
Contraindications ?
Adrenaline - felypressin
Once tournquet removed reflex vasodilation to surgery area. Vasoconstrictor will reduce blood flow prolonging duration and reduce rate of absorption increasing the safety margin
Contraindication includes monoamine oxidse inhibitor antidepressant as this inhibits adrenaline metabolism
Which two system drug reactions could potentially result from the administration of LA drugs?
Systematic toxicity - LA binds to cns and cardiac tissue
Hypersensitivity reaction (allergy) Anaphylaxis - systemic/dermal reaction to allergn
Signs and symptoms of Systemic Toxicity
Cns excitation 3
CNS depression 3
CVS depression 2
CNS excitation - dizzy, perioral paraesthesia, tongue numbness
CNS depression - confusion, sedation, seizures
CVS depression - (cns effects evident) hypotension arrthymia
Symptoms of anaphylaxis clinical presentation 5
Restless from puritis and hives Anxiety and tremor Air hunger - STRIDOR Tachycardia GI disturbances
Patho physiology of acute anaphylaxis reaction
1 broad term
5 physiological reaction
Mediators (histamine, prostaglandin D2) cause symptoms:
Tissue swelling
Increased bronchial smooth muscular tone
Decreased vascular smooth muscle tone
Increased vascular capillary permeability
Rapid increase in secretion from mucous membrane
What is the child dose and adult dose in Adrenaline auto injector such as Epipen ?
Adult - 0.3mg
Child - 0.15mg
Absolute Contraindications of LA
Know How to Say No
Known Allergy
Haemorragic disorder
Sepsis in area of Injection
No pt consent
Relative contraindications for LA use
Happy Rowdy Pods Are Excellent Company
Hepatic impairment Renal impairment Prenancy (1st 3rd trimester) Anti coagulant drug therapy Epilepsy Concurrent Drug therapy
