Local Anaesthesia & Pain Management

43 Pages·2008·0.22 MB·English

Local Anaesthesia
&
Pain Management
RW Nieuwveld
Dept. of Anaesthesia
University of Cape Town
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Pre 1866 - Compression techniques
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1866 - “Freezing” with Ether
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1880 - Ethyl Chloride spray
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1880→84 - COCAINE used by Karl Köller
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1905 - PROCAINE developed
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1943 - LIGNOCAINE synthesised
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Unsaturated Intermediate 2 º or 3 º
Ring Chain Amine
(Lipophilic) (Ester or Amide) (Hydrophilic)
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Ionisation -
n
Must be Unionised (Lipophilic) to penetrate
tissues, but Ionised at the nerve
pKa -
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pH where Ionised = Unionised
Protein binding -
n
Affects the duration of action
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Numerous theories
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+ +
Main action is at the Na -K ionophore at
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the nodes of Ranvier
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ESTERS CLINICAL USUAL ONSET DURATION MAXIMUM COMMENTS
USES CONCEN DOSE
TRATION
a) *Infiltration 1% Fast 0,5 - 1 hr 10 mg kg-1 Procaine has marked vasodilator action
Procaine *Peripheral 1 - 2% Slow 0,5 - 1 hr ⊂ Adrenaline and is generally used with Adrenaline
*Spinal 10% Moderate 0,5 - 1 hr 1:200 000 to prolong its effects.
b) *Infiltration 1% Fast 0,5 - 1 hr 11 mg kg-1 Lowest systemic toxicity due to rapid
Chloro- *Peripheral 2% Fast 0,5 - 1 hr 14mg kg-1 hydrolysis by plasma cholinesterase.
procaine *Epidural 2 - 3% Fast 0,5 - 1 hr ⊂ Adrenaline May be neurotoxic intrathecally, due to
low pH or preservative.
c) *Topical 2% Slow 0,5 hr 1 mg kg-1 High potency, and high toxicity.
Ametho-/ *Spinal 0,5% Fast 2 - 4 hr
Tetra- caine
d) *Surface 4 - 10% Fast 20 - 30 min 3 mg kg-1 Potent vasoconstrictor.
Cocaine Sensitises adrenergic receptors to
endogenous & exogenous
sympathomimetic amines.
May cause addiction.
Addition of Adrenaline is redundant and
may be harmful.
AMIDES CLINICAL USUAL ONSET DURATION MAXIMUM COMMENTS
USES CONCEN DOSE
TRATION
a) *Topical 2 - 10% Fast 0,5 - 1 hr 3 mg kg-1 Remains the most versatile and widely
Lignocaine *Infiltration 0,5 - 1% Fast 1 - 2 hr 7 mg kg-1 used local anaesthetic.
*Peripheral 1 - 1,5% Fast 1 - 3 hr ⊂ Adrenaline Relatively low systemic toxicity.
*Epidural 1 - 2% Fast 1 - 2 hr Rapid onset, moderate potency and
*IV block 0,5% Fast Up to 2 hr moderate duration of action.
*Spinal 5% Fast 0,5 - 1,5 hr No vasoactive effects.
Addition of adrenaline decreases toxicity.
Antidysrrhythmic.
b) *Infiltration 1 - 2% Moderate 3 mg kg-1 Similar to Lignocaine but lasts longer.
Mepivacaine *Peripheral 1 - 1,5% Fast 2 - 3 hr 5 mg kg-1 Duration prolonged with Adrenaline.
*Epidural 1 - 2% Fast 1 - 2,5 hr ⊂ Adrenaline Marked accumulative potential and rapid
placental transfer.
c) *IV block 0,2- 0,5% Max 2 hr 6 mg kg-1 Least toxic amide.
Prilocaine *Peripheral 1,5 - 2% Fast 1,5 - 3 hr 9 mg kg-1 Methaemoglobinaemia possible if large
*Epidural 1 - 3% Fast 1 - 2,5 hr ⊂ Adrenaline doses used. ( > 600 mg)
d) *Peripheral 0,5 - 1% Fast 3 - 12 hr 5 mg kg-1 Profound motor block.
Etidocaine *Epidural 1 - 1,5% Fast 2 - 4 hr ⊂ Adrenaline
e) *Infiltration 0,2 - 0,5% Slow 4 - 12 hr 2 mg kg-1 Does not cause vasodilatation at site of
Bupivacaine *Peripheral 0,2 - 0,5% Moderate 4 - 12 hr injection, therefore only modest increase
*Epidural 0,2 - 0,5% Fast 2 - 4 hr in duration of action with Adrenaline.
*Spinal 0,5% Fast 2 - 4 hr Popular due to:-
Potency (3 - 4 x > than Lignocaine.)
Relatively low toxicity.
Long duration of action.
Relatively safe in obstetrics.
Exaggerated cardiotoxicity with intra-
venous injection.
Low concentrations produce a chiefly
sensory block.
Not used in Bier's (IV) block.
f) *Infiltration 0,2 - 1% Slow 4 - 12 hr 3 mg kg-1 New amide local anaesthetic prepared
Ropivacaine *Peripheral 0,2 - 1% Fast 2 - 4 hr as a pure S-isomer in contrast to others,
*Epidural 0,2 - 1% Fast 2 - 4 hr which are racemic mixtures
Recently released in RSA.
Not yet Similar to Bupivacaine in onset, potency
released for and duration, with less motor block.
*Spinal pKa = Bupivacaine. = 8,1.
Less cardiotoxic than Bupivacaine, but
still has dysrrhythmic potential.
TTooxxiicciittyy
May occur if a) Too much is given
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b) Rapidly absorbed
c) Inadvertently injected IV
Organ systems involved are the a) CNS
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and b) CVS
Hypersensitivity
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Rare with Amino-amides
but may occur with Amino-esters
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Determined by removal from the nerve
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Affected by a) - Perfusion
b) - Blood concentration
Perfusion modified by Vasoconstrictors
v
Concentration dependent on Metabolism
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Amides - Liver metabolism
Esters - Cholinesterase metabolism
in blood & liver