LOCAL ANAESTHETICS Flashcards
Local Anaesthetics 6
- causes reversible loss of sensory perception
- prevents transmission of nerve impulse in region applied to
- local area is numbed
- doesn’t affect conciousness
- no structural damage to nerves
Local Anaesthesia Chemical structure 4
- weak base
- lipophilic ring
- intermediate chain: amide / ester
- hydrophilic amine
LA - MOA
- pass through neuronal memb.
- block Na channels
- dec. Na influx
- prevent AP
- loss of sensation
LA - pka
low pKa } high % unionised } short onset } faster onset
high pKa } low % unionised } long onset } slower onset
infecected tissue - low pH } slow onset
- high BF } short DOA
LA - structure + protein binding
long chain } inc. lipophilic } inc. potency
high protein affinity } long DOA
LA - fibres
- small diameter + myelinated fibres } easily blocked by LA } LA more effective
- order of fibres blocked:
1. sympathetic + pain
2. Temp
3. Light, touch, proprioception
4. Motor - reversal of block in opp. order
LA + vasoconstrictors 5 + C/I 6
- vasoconstrictors: Epinephrine + Levonordefrin
1. localise anaesthetic @ desired site
2. inc. LA DOA
3. dec. LA absorbed into systemic circulation
4. dec. toxicity
5. dec. local haemorrhage
C/I:
1. low BP
2. severe heart disease
3. uncontrolled hyperthyroidism
4. pheochromocytoma
5. allergies - sulphite
6. asthma
vasoconstrictors + precautions 5
- tricyclic anti-depressants - inc. BP
- non-selective B blockers - inc BP + dec. HR
- cocaine - abuse + inc. hypertension + stroke + MI
- Digoxin - narrow TI + arrhythmias
- GA - halothane - dysrhythmic effects of vasoconstrictors
LA- Route of admin 5
- inc. alkalinity } faster onset
1. Topical - Benzocaine, Oxybuprocaine, Tetracaine (all esters) + Lignocaine, Prilocaine
2. Infiltration - Bupivacaine, Lignocaine, Mepivacaine, Ropivacaine (intradermal + SC) DENTISTRY
3. Peripheral nerve block - Bupivacaine, Lignocaine, Mepivacaine, Ropivacaine (nerve trunk - distal site)
4. Central nerve block - Bupivacaine, Lignocaine, Ropivacaine (spinal cord - above + below site) LABOUR - epidural
5. IV - Lignocaine (in limb w/ tourniquet) fractures + minor surgery
Injectable - all amides // Topical - all esters + lignocaine + prilocaine
LA- A/E 5 PTAMP
- Psychogenic - anxiety / hyperventilation / fainting / NV / BP change
- Toxicity - CNS / CVS - bupivacaine / resp.
- Allergy - PABA metabolite of ester / Metabisulfite from Epi/Levo vc
- Methaemoglobinaemia - blood disorders - Benzocaine, Articaine, Prilocaine
- Paraesthesia - dec. BF } pins + needles - Articaine
LA systemic toxicity symptoms + treatment
SAMS
- Speech - slurred { paraethesia lips + tongue
- Altered CNS - arrhythmias / confused / dizzy / drowsy / restless
- Muscle - twitching + tremors
- Seizures - convlusions / resp. depression / resp. + CVS arrest
unconscious - O2
seizure - benzodiazepines
hypotension - vasopressors
vent. fibrillation { bupivacaine - intralipid infusion (lipid binds to drug + dec. drug)
LA - prevention of toxicity 6
- use max. safe dose
- test doses
- monitor patients vitals
- stabilise needle carefully
- aspirate injection regularly
- adrenalin if appropriate
BUPIVACAINE
- Amide -
- PK: slow onset, long DOA
- V. Potent
- I : labour + long surgery + post - op
- Admin: epidural + infiltration + IV
- A/E : cardiotoxicity
LEVOBUPIVACAINE
- amide
- S - enantiomer of bupivacaine
- less cardiotoxic than bupivacaine
LIGNOCAINE
- amide
- PK: fast onset / medium DOA
- I: dental / eye blocks / epidural
- Admin: topical / infiltration / IV
- C/I: heart blocks
- D/I: NMB + B blockers + cimetidine
