LA

Question 1

3 main roles of vasoconstrictors in LA

Answer 1

1) prolong length of action and increase depth of action of LA
2) reduce toxicity of LA
3) hemostatic effect

Question 2

absolute contraindications for LA

Answer 2

1) severe CVD
- <6 months after MI
- < 6 months after cerebrovascular accident
- < 6 months post coronary artery bypass surgery
- daily episodes of unstable angina
- cardiac dysrhythmias

2) untreated or uncontrolled severe HTN

3) thyrotoxicosis / uncontrolled hyperthyroidism

Question 3

what is the specific receptor theory for LA

Answer 3

the LA binds to specific receptor sites located at sodium channels of nervous tissues, blocking entry of Na+, resulting in

• threshold for excitation increasing
• impulse conduction slows
• rate of rise of AP declines
• generation and propagation of AP is inhibited

LA is a membrane stabilising drug so it will decrease rate of depol and prolong repol of excitable membranes

Question 4

contents of 2% Scandonest

Answer 4

1) mepivacaine hydrochloride
- 44mg (2.2ml cart)
- 36mg (1.8mL cart)

2) adrenaline
- 22 microgram (2.2ml cart)
- 18 microgram (1.8ml cart)

3) sodium chloride (helps to make solution isotonic with body tissues, ensure smoother injection)
4) HCL
5) disodium edetate (chelating agent which is a preservative)
6) potassium metabisulfite (prevents degradation of vasoconstrictor, prolongs shelf life)

Question 5

what is the risk of bupivacaine, how does it come about

Answer 5

it is cardiotoxic

other LAs block sodium channels rapdily during systole, but bupivacaine dissociates more slowly during diastole.
hence at the end of diastole, there will still be a large number of channels that are blocked -> accumulative cardiotoxic effect

Question 6

what are the possible ddx if after we give LA, the patient starts feeling cold, sweating, shivering

Answer 6

• la toxicity
• hypoglycemia
• vasovagal syncope