anaesthetics

Question 1

how should metformin be changed on day of surgery

Answer 1

Surgery / metformin on day of surgery:
OD or BD: take as normal
TDS: miss lunchtime dose
assumes only one meal will be missed during surgery, eGFR > 60 and no contrast during procedure

Question 2

inhaled anaeshetics x2

Answer 2

1. volatile liquid anaeshetics - isoflurane, desflurane, sevoflurane
2. nitrous oxide

Question 3

volatile liquid anaesthetics use, MoA , adverse effects

Answer 3

I+maintenance of anaesthesia

• exact MoA unknown, may act via GABAa, Glycine + NMDA receptors
• SE: Myocardial depression, Malignant hyperthermia, Halothane (not commonly used now) is hepatotoxic

Question 4

nitrous oxide use, MoA, adverse effects

Answer 4

Used for maintenance of anaesthesia and analgesia (e.g. during labour)

• -exact MoA unknown, may act via NDMA, nACH, 5-HT3, GABAa + glycine receptors
• SE: May diffuse into GAS-FILLED body compartments → INCR in pressure. Should therefore be avoided in certain conditions e.g. PNEUMOTHORAX

Question 5

OD insulin + surgery adjustments

Answer 5

Surgery / diabetes: once-daily insulin dose should generally be reduced by 20% on the day before and the day of surgery

Question 6

Gliclazide = SU + surgery adjustements

Answer 6

Surgery / sulfonylureas on day of surgery:

• omit on the day of surgery
• exception is morning surgery in patients who take BD - they can have the afternoon dose

Question 7

Myasthenia gravis pts at risk with which anaesthetic agents

Answer 7

Patients with myasthenia gravis are very sensitive to non-depolarising agents

• eg rocuronium
• work by antagonoising nACh receptors in motor end plate –> paralysis by their blockade
• This is in contrast with suxamethonium, which produces paralysis by acting on these receptors. The myasthenic patient has fewer available nicotinic receptors due to autoimmune-mediated destruction, meaning that they are more sensitive to non-depolarising blockade

Question 8

Etomidate - MoA + SE

Answer 8

-potentiates GABAa
SE: PRIMARY ADRENAL SUPRESSION + MYOCLONUS
-NB. Causes less hypotension than propofol and thiopental during induction and is therefore often used in cases of haemodynamic instability

Question 9

malignant hyperpyrexia

Answer 9

• caused by an inherited mutation in the ranitidine receptor which interferes with calcium regulation in skeletal muscle
• Anaesthetic agents known to trigger an episode of malignant hyperpyrexia include all potent INHALED general anaesthetic agents (e.g. halothane, thiopental) and all depolarising muscle relaxants (e.g. suxamethonium)

Question 10

how many mg of lidocaine in 20ml of 2% lidocaine

Answer 10

-2% strength liquid = 2g of drug dissolved in 100ml
-so in 20ml = 2000mg/5 = 400mg
400mg lidocaine

Question 11

suxamethonium apnoea

Answer 11

ADom mutation –> lack of specific AChE in plasma which acts to break down suxamethonium, terminating its muscle relaxant effect
- so effects of sux are prolonged + pt needs to be mech ventilated + observed in ITU until effects of sux wear off