Succinylcholine

Question 1

A T4:T1 ratio of 1 is characteristic of neuromuscular blockade, following a single dose of SCh (true or false).

Answer 1

True. The T4:T1 ratio remains 1 with a single dose of SCh.

Question 2

Post-synaptic antagonist at nicotinic receptors is characteristic of neuromuscular blockade, following a single dose of SCh (true or false).

Answer 2

False. SCh is an agonist at post-junctional nicotinic receptors.

Question 3

‘Fade’ with a tetanic stimulus is characteristic of neuromuscular blockade, following a single dose of SCh (true or false).

Answer 3

False. There is no fade of the tetanic response.

Question 4

Phase II block is characteristic of neuromuscular blockade, following a single dose of SCh (true or false).

Answer 4

False. Phase I block is characteristic of a single dose of SCh.

Question 5

Pre-junctional inhibition of nicotinic receptors is characteristic of neuromuscular blockade, following a single dose of SCh (true or false).

Answer 5

False. SCh does not inhibit pre-junctional nicotinic receptors after a single dose.

Question 6

A T4:T1 ratio of 1 is characteristic of neuromuscular blockade, following a single dose of vecuronium (true or false).

Answer 6

False. The T4:T1 ratio is less than 1 with non-depolarising relaxants.

Question 7

Post-synaptic antagonist at nicotinic receptors is characteristic of neuromuscular blockade, following a single dose of vecuronium (true or false).

Answer 7

True. There is competitive inhibition. Vecuronium acts as a post-synaptic antagonist at nicotinic receptors.

Question 8

‘Fade’ with a tetanic stimulus is characteristic of neuromuscular blockade, following a single dose of vecuronium (true or false).

Answer 8

True. ‘Fade’ with a tetanic stimulus is a characteristic of neuromuscular blockade following a single dose of vecuronium.

Question 9

Post-tetanic potentiation is characteristic of neuromuscular blockade, following a single dose of vecuronium (true or false).

Answer 9

True. Post-tetanic potentiation is a characteristic of neuromuscular blockade following a single dose of vecuronium.

Question 10

Pre-junctional inhibition of nicotinic receptors is characteristic of neuromuscular blockade, following a single dose of vecuronium (true or false).

Answer 10

True. Pre-junctional inhibition of nicotinic receptors can prevent fasciculations with SCh.

Question 11

What is the neonatal dose of succinylcholine?

Answer 11

2 mg/kg

Question 12

What is the infant and young child dose of succinylcholine?

Answer 12

1.5 mg/kg

Question 13

What is the older child and adult dose of succinylcholine?

Answer 13

1 mg/kg

Question 14

Which of the following muscles are blocked first by succinylcholine?

A. Adductor pollicis
B. Diaphragm
C. Glottic muscles

Answer 14

Glottic muscles before diaphragm, before adductor policis

Question 15

Which of the following muscles recovers first after a dose of succinylcholine?

A. Adductor pollicis
B. Diaphragm
C. Glottic muscles

Answer 15

Diaphragm, followed by glottic muscles, followed by adductor policis. Thus recovery of neuromuscular function at the end of any procedure is best reflected at the adductor pollicis muscle where neuromuscular transmission is last restored.

Question 16

Why is suxamethonium use associated with hyperkalaemia?

Answer 16

Opening of the cation channel at the NMJ allows the entry of sodium ions but potassium ions can also move out through the channel. After a normal intubating dose, a rise in plasma potassium concentration up to 0.5 mmol/L may occur. This rarely causes problems in adults, but arrhythmias can be seen more frequently in patients with renal failure. In those patients where extrajunctional receptors are present, hyperkalaemia can be much greater and cardiac arrest can occur.

Question 17

Hypernatraemia may be associated with SCh use (true or false).

Answer 17

False. No change seen in plasma sodium when SCh is used.

Question 18

Hyperkalaemia may be associated with SCh use (true or false).

Answer 18

True

Question 19

Reduced intragastric pressure may be associated with SCh use (true or false).

Answer 19

False. Intra-abdominal and hence intragastric pressure is raised by SCh.

Question 20

Hyperthermia may be associated with SCh use (true or false).

Answer 20

True

Question 21

Raised intracranial pressure may be associated with SCh use (true or false).

Answer 21

True

Question 22

SCh should be avoided in patients with (true or false):

Guillain-Barré syndrome

Answer 22

True. Sch should be avoided for a patient with Guillain-Barré syndrome.

Question 23

SCh should be avoided in patients with (true or false):

Alzheimer’s disease

Answer 23

False. There is no NMJ abnormality with Alzheimer’s disease.

Question 24

SCh should be avoided in patients with (true or false):

Acute spinal cord transection, day 1

Answer 24

False. Extra-junctional receptor proliferation is not significant so early.

Question 25

SCh should be avoided in patients with (true or false):

Day 10 of ICU admission in severe sepsis

Answer 25

True. Immobility is associated with significant extra-junctional receptors.

Question 26

SCh should be avoided in patients with (true or false):

Disseminated pancreatic carcinoma

Answer 26

False. Plasma cholinesterase activity may be reduced, but not significantly.

Question 27

The following drug is associated with plasma cholinesterase inhibition (true or false):

Neostigmine

Answer 27

True

Question 28

The following drug is associated with plasma cholinesterase inhibition (true or false):

Mivacurium

Answer 28

False. Mivacurum is a substrate for plasma cholinesterase.

Question 29

The following drug is associated with plasma cholinesterase inhibition (true or false):

Rivastigmine

Answer 29

True

Question 30

The following drug is associated with plasma cholinesterase inhibition (true or false):

Memantine

Answer 30

False. Memantine is used in the treament of Alzheimer’s disease, but is not a cholinesterase inhibitor.

Question 31

The following drug is associated with plasma cholinesterase inhibition (true or false):

Cocaine

Answer 31

False. Cocaine is a substrate for plasma cholinesterase.

Question 32

You have diagnosed SCh apnoea in a 6-year-old child. He required ventilation on the paediatric intensive care unit for 10 hours. TOF monitoring of neuromuscular function showed return of T1 8 hours after administration of SCh.

Which of these is his most likely genotype?

A. Ea Ea
B. Ea Ef
C. Es Es
D. Eu Ea
E. Eu Ef

Answer 32

C. Es Es

These are all abnormal genotypes, but given the very long duration of paralysis, 8-10 hours, the most likely is Es Es.

Eu Ea and Eu Ef do not give significantly prolonged SCh action because there is one normal allele.

Question 33

Which of these are recognised unwanted effects of SCh?

A. Central nervous system excitation
B. Bradycardia
C. Malignant neurolept syndrome
D. Hypokalaemia
E. Myalgia

Answer 33

B. Bradycardia and E. Myalgia.

SCh does not cross the blood-brain barrier. Malignant hyperthermia (not malignant neuroleptic syndrome) is triggered by SCh and hyperkalaemia (not hypo) is associated with use of SCh in certain conditions.

Question 34

A 19-year-old female student presents for emergency appendicectomy. She is otherwise well but tells you that her mother had an abnormal reaction under anaesthesia 8 years ago during a Caesarean section and was told to avoid drugs that cause her muscles to relax. None of the rest of the family has had an anaesthetic and your patient did not have any tests following this event. Unfortunately, her mother is not available on the telephone to discuss this and her surgery was in a different hospital.

Which of these is the most likely cause of the abnormal reaction under anaesthesia?

A. A drug interaction between SCh and neostigmine
B. Allergy to vecuronium
C. Malignant hyperthermia
D. SCh anaphylaxis
E. SCh apnoea

Answer 34

D. Anaphylaxis is the most likely cause here.

A. Incorrect. The drug interaction is predictable and would not require avoidance of any drug.

B. Incorrect. Anaphylaxis is more common with SCh than with vecuronium and is the most likely cause here.

C. Incorrect. If malignant hyperthermia were suspected, more than one group of drugs should be avoided.

E. Incorrect. If SCh apnoea were the cause, the family would have been tested. There is a small chance your patient may not recall the actual testing. However, she knows her mother had a major problem and recalls her mother was told to avoid one class of drugs. It is therefore unlikely she has simply forgotten she had a blood test. There is cross-reactivity among muscle relaxants, so the whole group of muscle relaxants should be considered possible triggers for anaphylaxis.

Question 35

A 75 kg, 16-year-old boy presents for elective lower limb surgery. There are no medical conditions of note, no particular family history and neither parent has had problems with anaesthetics. You have chosen to induce with propofol (180 mg) and fentanyl (100 μg), intubate on SCh (100 mg) and plan to let the patient breathe spontaneously through an appropriately-sized endotracheal tube. Twenty minutes after administering SCh, spontaneous respiration has not resumed.

Which of these is the most appropriate action to establish the reason for non-return of spontaneous respiration?

A. Take an arterial blood gas
B. Send blood for tryptase and IgE levels
C. Measure serum potassium
D. Give 4 mg of naloxone intravenously
E. Identify the response to a TOF

Answer 35

E. Identify the response to a TOF

The opioids may cause delayed return of spontaneous respiration, but the TOF should be back to normal with four equal twitches.

None of the others identify SCh apnoea.

Question 36

Regarding suxamethonium apnoea (true or false):

About 80% of the population carry the normal genotype

Answer 36

False. About 96% of the population is homozygous for the normal gene with normal duration of action of suxamethonium.

Question 37

Regarding suxamethonium apnoea (true or false):

Dibucaine number of 70 reliably excludes suxamethonium apnoea

Answer 37

False. Dibucaine is a local anaesthetic agent that inhibits plasma cholinesterase. Dibucaine inhibits normal variant of the enzyme by 80% but other variant forms of plasma cholinesterases are inhibited less effectively. Therefore a patient homozygous for the normal variant will have a dibucaine number of 80 or above.
A DN of 30–79 and normal to decreased PChE enzyme activity indicate a variable risk. A patient homozygous for the fluoride-resistant genotype (as opposed to the more common atypical or ‘dibucaine-resistant’ type) may still have a dibucaine number of 70 but with reduced plasma cholinesterase activity.

Question 38

Regarding suxamethonium apnoea (true or false):

Pregnancy may cause prolonged effect by suxamethonium

Answer 38

Reduced plasma cholinesterase activity may be acquired and is associated with pregnancy, renal failure, hepatic disease, malignancy and concomitant drug use. In renal failure plasma cholinestrase levels are reduced by haemodilution and reduced liver production.

Question 39

Regarding suxamethonium apnoea (true or false):

The alleles for plasma cholinesterase level are carried on chromosome 19

Answer 39

Plasma cholinesterase activity may be reduced due to genetic variability. The alleles are found on chromosome 3. The alleles are usual (normal), atypical (dibucaine-resistant), silent (absent) and fluoride-resistant. About 96% of the population is homozygous for the normal gene with normal duration of action of suxamethonium.

Question 40

Regarding suxamethonium apnoea (true or false):

Renal failure is associated with reduced plasma cholinesterase levels

Answer 40

Reduced plasma cholinesterase activity may be acquired and is associated with pregnancy, renal failure, hepatic disease, malignancy and concomitant drug use. In renal failure plasma cholinestrase levels are reduced by haemodilution and reduced liver production.