Pre-op Anaesthesia

Question 1

How do local anaesthetics work?

Answer 1

Binds to voltage-gated sodium channels and blocks sodium influx into the nerve cells, preventing depolarisation

Question 2

In what age group should bupivacaine be avoided?

Answer 2

< 12 years of age

Question 3

Why does the patient’s temperature decrease during anaesthesia?

Answer 3

Because anaesthesia inhibits the protective reflexes that generate heat (shivering), depresses the thermoregulating centre in the hypothalamus and increases vasodilation, resulting in heat loss.

Question 4

Why is low patient temperature so critical?

Answer 4

Because hypothermia increases the risk of surgical site infections

Question 5

How does hypothermia increase the risk of surgical site infections?

Answer 5

Patients need to maintain their normal temperature at around 37ºC to ensure their organs function efficiently

Question 6

List eight or nine signs and symptoms of LA toxicity

Answer 6

1. 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

Question 7

Why does LA toxicity require CPR?

Answer 7

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)

Question 8

Besides CPR, what is the immediate management of LA toxicity?

Answer 8

20 % lipid emulsion (Intralipid) given IV at a bolus dose of 1.5 mL/kg over 1 minute

Question 9

How does lipid emulsion (Intralipid) work?

Answer 9

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).

Question 10

What are the two existing formulations for Bupivacaine?

Answer 10

0.25 % and 0.5 % solution

Question 11

What are the two existing formulations for Lignocaine?

Answer 11

1 % and 2 % solution

Question 12

What is the toxic dose of Bupivacaine?

Answer 12

2 mg/kg

Question 13

What is the toxic dose of Lignocaine?

Answer 13

3 mg/kg

Question 14

What is the toxic dose of Levobupivacaine?

Answer 14

2 mg/kg

Question 15

What is the toxic dose of Mepivacaine?

Answer 15

6 mg/kg

Question 16

What is the marketed brand name of Bupivacaine?

Answer 16

Marcaine

Question 17

What is the marketed brand name of Lignocaine?

Answer 17

Xylocaine

Question 18

What is the marketed brand name of Levobupivacaine?

Answer 18

Chirocaine

Question 19

What is the marketed brand name of Mepivacaine?

Answer 19

Scandonest

Question 20

What are the two organ systems we’re worried about in term of LA toxicity?

Answer 20

The CNS and CVS

Question 21

Which organ system gets affected first when you get LA toxicity?

Answer 21

The CNS

Question 22

What’s the local anaesthetic formula?

Answer 22

mg = ml x % x 10

Question 23

How is regional anaesthesia advantageous for wound healing?

Answer 23

Regional anaesthesia diminishes the stress response and increases the blood flow, which has benefits for wound healing

Question 24

Describe the technique for blocking the tibial nerve during an ankle block

Answer 24

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 %)

Question 25

Describe the technique for blocking the saphenous nerve during an ankle block

Answer 25

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 %)

Question 26

Describe the technique for blocking the deep peroneal nerve during an ankle block

Answer 26

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 %)

Question 27

Describe the technique for blocking the superficial peroneal nerve during an ankle block

Answer 27

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 %)

Question 28

Describe the technique for blocking the sural nerve during an ankle block

Answer 28

With regional blocks, use a 27-gauge needle and either bupivacaine (0.25 %) or lidocaine (1 %)

Question 29

Name the plantar nerves

Answer 29