How do local anaesthetics work?
Binds to voltage-gated sodium channels and blocks sodium influx into the nerve cells, preventing depolarisation
In what age group should bupivacaine be avoided?
< 12 years of age
Why does the patient’s temperature decrease during anaesthesia?
Because anaesthesia inhibits the protective reflexes that generate heat (shivering), depresses the thermoregulating centre in the hypothalamus and increases vasodilation, resulting in heat loss.
Why is low patient temperature so critical?
Because hypothermia increases the risk of surgical site infections
How does hypothermia increase the risk of surgical site infections?
Patients need to maintain their normal temperature at around 37ºC to ensure their organs function efficiently
List eight or nine signs and symptoms of LA toxicity
- Perioral (tongue) numbness/tingling - CNS 2. Restlessness - CNS 3. Dizziness -CNS 4. Blurred vision - CNS 5. Muscle twitching/tremors - CNS 6. Convulsions - CNS 7. Arrhythmia - CVS 8. Bradycardia - CVS 9. Hypotension - CVS
Why does LA toxicity require CPR?
Because continued inhibition of neuron depolarization (by Na+ channel blockade) from increased plasma concentrations of LA causes CNS toxicity and myocardial dysfunction (CVS toxicity). So CPR is crucial to prevent hypoxia and acidosis (metabolic or respiratory)
Besides CPR, what is the immediate management of LA toxicity?
20 % lipid emulsion (Intralipid) given IV at a bolus dose of 1.5 mL/kg over 1 minute
How does lipid emulsion (Intralipid) work?
Works by absorbing the circulating LA (lipophilic drug), thus reducing the free unbound amount able to bind to Na+ channels in any organ where these are found (e.g. myocardium).
What are the two existing formulations for Bupivacaine?
0.25 % and 0.5 % solution
What are the two existing formulations for Lignocaine?
1 % and 2 % solution
What is the toxic dose of Bupivacaine?
2 mg/kg
What is the toxic dose of Lignocaine?
3 mg/kg
What is the toxic dose of Levobupivacaine?
2 mg/kg
What is the toxic dose of Mepivacaine?
6 mg/kg
What is the marketed brand name of Bupivacaine?
Marcaine
What is the marketed brand name of Lignocaine?
Xylocaine
What is the marketed brand name of Levobupivacaine?
Chirocaine
What is the marketed brand name of Mepivacaine?
Scandonest
What are the two organ systems we’re worried about in term of LA toxicity?
The CNS and CVS
Which organ system gets affected first when you get LA toxicity?
The CNS
What’s the local anaesthetic formula?
mg = ml x % x 10
How is regional anaesthesia advantageous for wound healing?
Regional anaesthesia diminishes the stress response and increases the blood flow, which has benefits for wound healing
Describe the technique for blocking the tibial nerve during an ankle block
Inject 4-6 mL of anaesthetic 1 cm in depth 1 cm superior to this point.
With regional blocks, use a 27-gauge needle and either bupivacaine (0.25 %) or lidocaine (1 %)
Describe the technique for blocking the saphenous nerve during an ankle block
Inject 2-3 ml subcutaneously between the medial malleolus and the anterior tibial tendon.
With regional blocks, use a 27-gauge needle and either bupivacaine (0.25 %) or lidocaine (1 %)
Describe the technique for blocking the deep peroneal nerve during an ankle block
Have the patient dorsiflex their foot and insert the needle 1 cm above the medial malleolus, aiming underneath the extensor hallucis longus tendon and advance until you hit the tibia. Then inject 1-2 ml of anaesthetic.
It can also be blocked anterior to the ankle, using a ‘V’ pattern.
With regional blocks, use a 27-gauge needle and either bupivacaine (0.25 %) or lidocaine (1 %)
Describe the technique for blocking the superficial peroneal nerve during an ankle block
Start one finger breadth from the lateral malleolus. Raise a subcutaneous injection, advancing the needle medially as you inject.
Inject 6-10 ml (3-5 ml with two passes) of anaesthetic solution subcutaneously in a band between the lateral malleolus and the extensor hallucis longus tendon.
With regional blocks, use a 27-gauge needle and either bupivacaine (0.25 %) or lidocaine (1 %)
Describe the technique for blocking the sural nerve during an ankle block
With regional blocks, use a 27-gauge needle and either bupivacaine (0.25 %) or lidocaine (1 %)
Name the plantar nerves
