Question regarding propofol and thiopental

[LuckiestOne]

Hey everyone, I have been getting some mixed answer from the medical students so I've decided to ask this question to be answered by the appropriate specialist!

http://img841.imageshack.us/img841/3091/89840903.png

Some say A, some say E.. I think I'd go with E just because both thiopental and propofol are highly lipophillic....

Also, if both are lipophillic, then why do durations of recovery differ by so much?

Thank you in advance.

P.S. if the picture is too small, please hold down Ctrl + scroll mouse wheel up to enlarge the picture

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[Bertelman]

Hey everyone, I have been getting some mixed answer from the medical students so I've decided to ask this question to be answered by the appropriate specialist!

http://img841.imageshack.us/img841/3091/89840903.png

Some say A, some say E.. I think I'd go with E just because both thiopental and propofol are highly lipophillic....

Also, if both are lipophillic, then why do durations of recovery differ by so much?

Thank you in advance.

P.S. if the picture is too small, please hold down Ctrl + scroll mouse wheel up to enlarge the picture

Had to break out Miller for this one. I'm just gonna start out by saying this would probably end up as a keyword for us, as maybe 40% of anesthesia residents would get this right on our training exams. I bet maybe one of my friends would get it right, but that says something for the company I keep. Of course, in true NBME style, thiopental is not even available for use anymore. But I am guessing that's why you are seeing it in their released questions pool. Or because too many people missed it.

It's E. With a standard, one-time induction dose, thiopent follows 1st-order kinetics. Subsequent doses/infusions follow zero-order. Renal clearance is not relevant, and propofol "tolerance" is not significant enough to produce that profound of an effect.

 

[ketap]

i am not the expert and i am not an anesthesiologist but IMHO, it is because of they are using three compartment model (biophase concept)..and the different liphophilic characteristic and their compartment rate that can determine the duration ..btw, of course you should differentiate the duration if they are on continuous infusion (context sensitive time) and bolus doses..

btw, i can't open the link you posted...

 

[LuckiestOne]

Had to break out Miller for this one. I'm just gonna start out by saying this would probably end up as a keyword for us, as maybe 40% of anesthesia residents would get this right on our training exams. I bet maybe one of my friends would get it right, but that says something for the company I keep. Of course, in true NBME style, thiopental is not even available for use anymore. But I am guessing that's why you are seeing it in their released questions pool. Or because too many people missed it.

It's E. With a standard, one-time induction dose, thiopent follows 1st-order kinetics. Subsequent doses/infusions follow zero-order. Renal clearance is not relevant, and propofol "tolerance" is not significant enough to produce that profound of an effect.

Thank you so much for taking time of your busy schedule to entertain my question.

A follow up question: what contributes to quick recovery in propofol anesthesia? I would think that since it has such high lipophillicity, it would get distributed into the tissues quickly and linger around... How does it get eliminated from the body?

 

[LuckiestOne]

i am not the expert and i am not an anesthesiologist but IMHO, it is because of they are using three compartment model (biophase concept)..and the different liphophilic characteristic and their compartment rate that can determine the duration ..btw, of course you should differentiate the duration if they are on continuous infusion (context sensitive time) and bolus doses..

btw, i can't open the link you posted...

It still works when I click on it.. Perhaps try manually copying and pasting the link?

 

[ketap]

hi,Luckiestone: propofol is not always fast in recovery..sometime if the patient is fat and he /she had a long time continuous infusion..it will take quiet long time because of the redistribution from the 3rd compartment..but, yes,..if they given as bolus, i think they are quickly distributed to 2nd compartment and then to fat tissues after they reach the brain blood equilibrium..just a begginer opinion actually.

 

[Bertelman]

Thank you so much for taking time of your busy schedule to entertain my question.

A follow up question: what contributes to quick recovery in propofol anesthesia? I would think that since it has such high lipophillicity, it would get distributed into the tissues quickly and linger around... How does it get eliminated from the body?

Compensation aside, I'd rather answer ten questions like that than endure another total knee revision until midnight, which is what I was doing last night before I answered your post.

As for recovery from propofol, Miller again tells us a few points as compared to thiopental.
1) Propofol clearance is about 10 times that of thiopental
2) volume of ditribution is about double v. thiopental
3) Propofol only requires about a 50% decrease in plasma drug levels for return of consciousness

 

[Idiopathic]

Thank you so much for taking time of your busy schedule to entertain my question.

A follow up question: what contributes to quick recovery in propofol anesthesia? I would think that since it has such high lipophillicity, it would get distributed into the tissues quickly and linger around... How does it get eliminated from the body?

the redistribution into the peripheral tissues is what determines the quick reocovery for propofol - it doesnt mean the drug is gone, just that it is no longer as active when redistributed (i.e. stored in a sink, over time it will seep back out, and this may contribute to prolonged sedation, but not dramatically so)

that graph of thiopental defines zero-order elimination

 

[mymembernames]

So is the answer E for this?