Dibucaine of 20.

[sevoflurane]

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Possible board question with clinical implications.

55 y/o with Dibucaine of 20. with h/o burn 3 years ago comes in with SEM for shoulder repair. Echo shows AV area of 1.98 cm. Which statements are true?

1) If Dibucaine number was normal a reasonable anesthetic could include thiopental, sux and midaz.

2) Dose of NDMR should be increased

3) Compared with a perfectly healthy individual, Propofol/LMA plus regional technique with mepivicaine/tetracaine would show no difference

4) Vd would be increased

Please elaborate.

 

[sevoflurane]

Is this a K-type, with the standard K-type choices? (i.e., A is 1,2,3...etc.)

What is SEM?

I made up the question. So... just let me know what you think of the options.

SEM= systolic ejection murmur

 

[Jeff05]

strange question.
but the answer is #1.
3 years out you will not have sux hyperkalemia.
same with NDMB - the AAG content/receptors should be normal.
not sure who is doing regional with tetracaine, but i guess you are getting at ester metabolism, which would be impaired with a DN of 20.

 

[hoyden]

Since we are already on the path - I am doing the retired ABA exams questions and since there are no explanations to the answers, some answers are a bit confusing. Here are 2 K-type questions from the same exam:

Q1:
A patient with a dibucaine number of 20 would have

1 - increased risk of toxicity from intranasally administered cocaine
2 - increased risk of toxicity from subarachnoid administration of tetracaine
3 - prolonged paralysis after intravenous administration os sux
4 - decreased duration of local anesthesia with chlorprocaine
-------------------------------
Q2:
In a patient who takes pyridostigmine for MG, expected findings during delivery include

1 - prolonged sux-induced neuromascular block
2 - prolonged tetracaine-induced spinal anesthesia
3 - increased serum 2-chlorprocaine concentration during epidural anesthesia
4 - increased elimination half-life of atracurium


Your answers and thoughts, please.

 

[sevoflurane]

strange question.
but the answer is #1.
3 years out you will not have sux hyperkalemia.
same with NDMB - the AAG content/receptors should be normal.
not sure who is doing regional with tetracaine, but i guess you are getting at ester metabolism, which would be impaired with a DN of 20.

Hey now... don't be knocking magic mix. I used it for 1/2 of my residnecy. Doubt I'll ever see it again in PP.

Good pickup though. I wish I would have worded the question better. For single shot blocks your duration would have been the same as it is dependant on protein binding and concentration of LA. Single shot would have been safe as only the clearance is decreased. Continuous infusion would lead to toxicity. Certainly there would have been a difference in plasma levels in single shot... yet still safe as toxity levels would not be reached.

 

[sevoflurane]

Since we are already on the path - I am doing the retired ABA exams questions and since there are no explanations to the answers, some answers are a bit confusing. Here are 2 K-type questions from the same exam:

Q1:
A patient with a dibucaine number of 20 would have

1 - increased risk of toxicity from intranasally administered cocaine
2 - increased risk of toxicity from subarachnoid administration of tetracaine
3 - prolonged paralysis after intravenous administration os sux
4 - decreased duration of local anesthesia with chlorprocaine
-------------------------------
Q2:
In a patient who takes pyridostigmine for MG, expected findings during delivery include

1 - prolonged sux-induced neuromascular block
2 - prolonged tetracaine-induced spinal anesthesia
3 - increased serum 2-chlorprocaine concentration during epidural anesthesia
4 - increased elimination half-life of atracurium


Your answers and thoughts, please.

q1
1) Yes, with multiple doses
2) Minimal, but yes. Small doses used intrathecally.
3) Yes. homozygos for atypical psedu-ase
4) No... increased minimally.

q2
1) Yes as pseudochesterase is inhibited and decreased in pregnancy
2) No, there is no pseudocholinesterase in the spinal fluid to begin with
3) Yes,cause there is decreased metabolism/clearence although 1/2 life in serum is 21 seconds.
4) I think atracurium does have some plasma cholinesterase metabolism in addition to Hoffman. So yes.

 

[pgg]

Q1:
A patient with a dibucaine number of 20 would have

1 - increased risk of toxicity from intranasally administered cocaine
2 - increased risk of toxicity from subarachnoid administration of tetracaine
3 - prolonged paralysis after intravenous administration os sux
4 - decreased duration of local anesthesia with chlorprocaine

B (1 & 3).
Cocaine's an ester, 3 is obvious. 2 is wrong because tetracaine's intrathecal action ends with diffusion away from that space and metabolism elsewhere; besides, an intrathecal dose is far below the toxic dose. 4 is wrong for essentially the same reason, even though chloroprocaine will hang around a bit longer in the serum.

Q2:
In a patient who takes pyridostigmine for MG, expected findings during delivery include

1 - prolonged sux-induced neuromascular block
2 - prolonged tetracaine-induced spinal anesthesia
3 - increased serum 2-chlorprocaine concentration during epidural anesthesia
4 - increased elimination half-life of atracurium

Also B (1 & 3).
1 is obvious. Again tetracaine's intrathecal action ends because of diffusion, not metabolism. 3 is true although I wouldn't expect the epidural effects to last any longer. 4 is wrong because atracurium is metabolized by Hoffman elimination in addition to esterases.

 

[hoyden]

Thanks, pgg and sevoflurane.

The problem( with those questions) is that the same approach to the concept of Hoffman elimination and no valuable influence on atracurium metabolism by impairment of plasma cholinesterases is considered wrong in the different exam, from the different year.