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DA > Local Anaesthetics > Flashcards

Local Anaesthetics Flashcards

1
Q

Give your approach to postoperative weakness and hypoventilation

A

HHH - Declare situation | Get help
ABCDE - Resuscitate
- ? More FiO2 | ? Re-intubate IPPV | ? leave ETT in
Central causes
- Opioid | Volatile | Benzo | low/high CO2
Reverse potentiators of prolonged paralysis
- Electrolytes (Ca/K down | Mg up or given)
- Acidosis
- Hyperthermia (NDMR) | hypothermia (SUX)
- Drug interaction (Mg/aminoglycosides)
- Disease: Pre-existing renal dx / Myasthaenia gravis
Peripheral nerve stimulator
- TOF
- Post-tetanic facilitation

–> IF SUSPECT PERSISTENT NON DEPOLARIZING BLOCK - 1 further dose of reversal may be given. DO NOT EXCEED Neostigmine 5mg as more than this will cause weakness itself.

CONTINUE SUPPORTIVE MANAGEMENT

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2
Q

Give your approach to local anaesthetic toxicity

A

NB to mention is prevention

HHH - Declare | Help
ABCDE FGHIJKLMNOPQ

Specific measures for LA systemic toxicity
Goals
1. Limit LA exposure
2. Prolong normal resuscitation
3. Intralipid
4. Acidosis prevention (Hyperventilation | NaHCO3)

Specific measures

  1. Seizures (MIDAZ/DIAZ 0.1 mg/kg | THIO 2 mg/kg)
  2. Hyperventilate (Seizures/hypoxia/hypoxia/hypercarbia –> Acidosis–> traps ionized LA in cells)
  3. Intralipid 20% (Repeated boluses 1.5 ml/kg x 3 plus infusion 0.25 ml/kg/hr) Increase infusion to 0.5 ml/kg/hr if BP falling.
  4. Consider cardiopulmonary bypass
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3
Q

What is intralipid, what is its suggested mechanism of action and what is its uses?

A

20% Lipid emulsion

  • Soya oil
  • Egg phosphatide
  • Glycerol

Uses:

  • Lipid sink for highly lipid soluble drug toxicity
  • lipid substance in TPN
  • Solvent for propofol

Mechanism suggested
- “Circulating lipid sink” - draws bupivacaine out of the plasma and binding it so no more free fraction exists to bind the receptors.

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4
Q

Simplify the dosing of intralipid. Confirm maximum dosage.

A

For 70 kg

20 ml/hr —-> 40 ml/hr infusion (titrate to BP)

100 ml bolus
| 
| 3 mins
|
100 ml bolus
|
| 3mins
|
100 ml bolus

CPR to distribute
Continue infusion until haemodynamic stability restored
Max dose 10ml/kg = 700 mls

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5
Q

Summarize the goals in the treatment of local anaesthetic toxicity

A

Get the drug out of the cells alkalinize and bound to the intralipid

  1. Limit LA exposure
  2. Prolong CPR (consider cardiopulmonary bypass)
  3. Intralipid
  4. Prevent acidosis (hyperventilation | NaHCO3)
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6
Q

How can LA systemic toxicity be prevented? What is the mnemonic for this

A

mnemonic: MASSIVE

  1. Maximum doses (L 4.5 / 7) (B 2.5 / 3) (LB 2.5 / 3) (R 2.5 /2.5)
  2. ASPIRATE
  3. SLOW INJECTION with communication
  4. SITE (Consider vascularity)
  5. INCREMENTAL TEST DOSING
  6. VASOCONSTRICTORS
  7. ENSURE HOMEOSTASIS (Acidosis/hypoxia/hypercapnoea increase LA toxicity)
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7
Q

Which group of local anaesthetics are more likely to cause anaphylaxis?

A

Esters

  • metabolised by plasma cholinesterase
  • metabolite: p-aminobenzoic acid = PABA
  • PABA associated with hypersensitivity and anaphylaxis
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8
Q

Explain how the addition of vasoconstrictors enhance the efficacy of local anaesthetics

A
  1. Prolong duration of action
    Decrease the rate of systemic absorption of LA (through VC and decreased washout) –> enhances the amount of drug available for neuronal uptake.
    - more effective with lignocaine than bupivacaine
    - more effective with SC route than epidural
  2. Enhance quality of analgaesia
  3. Limit toxic side effects
  4. Decrease surgical bleeding
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9
Q

List 5 situations when vasoconstrictors are contraindicated with LA

A
  1. Sites that lack collateral supply: digits, penis, eyes
  2. IV local anaesthesia (Bier’s)
  3. High CVS risk
  4. Utero-placental insufficiency
  5. Drug interactions: TCAs and MAOIs –> HPT/dysrhythmia
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10
Q

What two effects does alkalinisation of LA have and how is this done for lignocaine and bupivacaine

A
  1. Faster onset (more unionized)
  2. Less burning on injxn

Lignocaine: 1 ml NaHCO3 8.5% added to 10ml ligno
Bupivacaine: 0.1 ml NaHCO3 8.5% added to 10 ml bup.
(bupivacaine precipitates if too alkaline)

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11
Q

How does the addition of glucose to the LA affect its effect

A

LA are hypobaric compared to CSF meaning the tend to rise when added to CSA

Addition of glucose makes the LA solution hyperbaric which allows the anaesthetist to manipulate the distribution of the LA with knowledge of spinal curvatures and strategic positioning of the patient.

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12
Q

Which drugs can be added to LA during neuraxial anaesthesia? What is their effect with regard to LA efficacy

A

PRESERVATIVE FREE:

  1. Opioids (RSA!)
  2. Ketamine
  3. Clonidine
  4. Midazolam
  5. Neostigmine
  6. Adrenalin

Addition of opioids to the neuraxial anaesthetic injection have a synergistic effect with the local anaesthetic enhancing both the quality and duration of the analgaesia.

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13
Q

Compare the clinical uses of lignocaine and bupivacaine

A

Lignocaine

  • Topical
  • Biers block

Lignocaine and bupivacaine

  • Infiltration
  • Peripheral
  • Epidural
  • Spinal
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14
Q

Why can’t bupivacaine be used for Bier’s block?

A

Contra-indicated in Bier’s block due to high risk of severe cardiotoxicity if given IV.

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15
Q

Describe the steps and drugs for doing a Bier’s block

A
  1. Emergency equipment & monitoring available
  2. IV line
  3. Elevate arm for 3 minutes then inflate proximal cuff to 250 mmHg
  4. Lidocaine 3mg/kg 0.5% (mini-Bier’s 1.5 mg/kg) - slow
  5. Blotchy erythema = working
  6. Paraesthesia/warmth in 3 - 5 mins from fingertips to proximal
  7. Single cuff deflation ok after minimum 30 minutes
  8. Sensation returns when cuff is deflated - to baseline function in 5 - 10 mins
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16
Q

Describe the usual % concentration and duration of action for the following routes of administration for lignocaine

Topical
Infiltration
Peripheral
Epidural
Spinal
Bier's Block
A 
Topical: 2 - 10% --- 30 min
Infiltration: 0.5 -1% --- 1 - 2 hr
Peripheral: 1 -1.5% --- 1 - 3 hr
Epidural: 1 - 2 % --- 1 - 2
Spinal: 1 - 2 hr
Bier's Block: < 2 hr
17
Q

Describe the usual % concentration and duration of action for the following routes of administration for Bupivacaine

Peripheral
Epidural
Spinal
Bier’s Block

A

Infiltration 0.2 - 0.5% 4 - 12 hr
Peripheral 0.2 - 0.5% 4 - 12 hr
Epidural 0.2 - 0.5% 2 - 4 hr
Spinal 0.5% 2 - 4 hr

18
Q

Why is bupivacaine a popular choice of agent

A
  1. Potency 3 -4 x ligno
  2. Safe in obstetrics
  3. Long duration of action
  4. Relatively low toxicity
19
Q

What are the benefits of lignocaine

A
  1. Widely available
  2. Relatively low systemic toxicity
  3. Used as an antiarrhythmic drug
  4. Rapid onset
20
Q

What is levo-bupivacaine

A

The s-enantiomer of bupivacaine: lower CVS toxicity potential

21
Q

What is ropivacaine

A

Similar to bupivacaine - lower risk of CVS toxicity

22
Q

What is amethocaine

A

Ametop cream 0.5 - 2% for venepuncture in kids
lasts 30 mins
Max dose: 1 mg/kg

23
Q

What is tetracaine

A

Topical eye drops 0.5 - 2%
Lasts 30 mins
Max dose 1 mg/kg

24
Q

Describe the use of cocaine in anaesthesia

A 
4 - 10%
ENT surgery
Potent vasoconstrictor
Lasts 30 mins
Rapid onset

Side effects:
Sensitizes adrenergic receptors to CATS: elev BP+HR
Myocardial ischaemia

DA (50 decks)

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