Sevo vaporizer

[dhb]

You pull the tube at any time and don't really worry much about laryngospasm or tube biting?

There's no laryngospasm when you know how to jaw thrust. Typically don't worry about tube bitting when i've pulled it.

Do you do this often?

All the time

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[coffeebythelake]

Well let me say from the get go, I don’t fully comprehend the difference you point out but I think it has something to do with the idea about 3 half-life’s described for propofol (1 min, 16 min, 300 min), and that the graph I posted is a computer sim, and the graph you posted is more clinically relevant.

the reason I like the graph is it just shows what I have experienced, and not what my staff always told me, and what my colleagues believe - and that is that if I run propofol for a very long time, it doesn’t matter much...it still goes away very quickly.

Eh... I think your conclusion is close but not quite. The plasma concentration does drop quickly when u stop infusion, but you see that the plasma concentration at several half lives does stay elevated a bit higher when infusion is going on a long time. Question is how high a dose of propofol you are running and at what point that plasma concentration after stopping infusion goes from a hypnotic to a subhypnotic concentration. Bottom line running propofol over long periods does linger longer (i think of it as similar functionally although not mechanistically to the PK/PD of gas anesthetics, you can easily drop it from 1 MAC of gas to 0.2 MAC, but that last little bit lingers with long cases)

 

[propadope]

Well let me say from the get go, I don’t fully comprehend the difference you point out but I think it has something to do with the idea about 3 half-life’s described for propofol (1 min, 16 min, 300 min), and that the graph I posted is a computer sim, and the graph you posted is more clinically relevant.

the reason I like the graph is it just shows what I have experienced, and not what my staff always told me, and what my colleagues believe - and that is that if I run propofol for a very long time, it doesn’t matter much...it still goes away very quickly.

That graph doesn’t seem to simulate clinical conditions. It shows the plasma concentration peaking at 480min for example. In reality you would give a bolus to reach a peak concentration quickly and then an infusion to maintain stable plasma levels.

I think long propofol infusions can be unpredictable and in my experience it does accumulate and can prolong recovery. Of course like anything if you turn it off judiciously you might be able to speed things up but it might be wise to have BIS if using muscle relaxant

 

[propadope]

Eh... I think your conclusion is close but not quite. The plasma concentration does drop quickly when u stop infusion, but you see that the plasma concentration at several half lives does stay elevated a bit higher when infusion is going on a long time. Question is how high a dose of propofol you are running and at what point that plasma concentration after stopping infusion goes from a hypnotic to a subhypnotic concentration. Bottom line running propofol over long periods does linger longer (i think of it as similar functionally although not mechanistically to the PK/PD of gas anesthetics, you can easily drop it from 1 MAC of gas to 0.2 MAC, but that last little bit lingers with long cases)

Exactly. Say you are trying to maintain a plasma concentration of 4ug/ml of propofol. Even at 50% or 2ug/ml that is still a potentially hypnotic dose. So the question is how long it will take to get down to 1ug/ml or lower for example. After a 10 hour infusion you will be waiting a long time as the muscles and fat will have plenty of time to accumulate.

 

[coffeebythelake]

There's no laryngospasm when you know how to jaw thrust.

What does this even mean

 

[GassYous]

There's no laryngospasm when you know how to jaw thrust. Typically don't worry about tube bitting when i've pulled it.

All the time

I also don't worry about tube biting and haven't placed a bite block since residency. Zero problems with that. But laryngospasm is definitely a problem if you mistime the extubation. I always pull before stage 2 when the iso or sevo is around 0.2 and 99% of the time there's no issue. I pulled a tube recently with end tidal 0.3-0.4, pulling good tv and the patient spasmed. They had stridor thirty minutes into their pacu stay.

 

[epidural man]

Honestly, the length of a propofol infusion hasn’t changed wake up times for me.
When I worked at the plasticS ASC, we would run it 8,9,10 hours - and the patients woke up very quickly regardless. Maybe we are talking about 5 vs 8 min. That I would buy.

the issue is people do polypharmacy WITH PROPOFOL, and that totally can last forever - and people tend to blame it on the propofol.

as far as I know, no one has studied the multi compartment model with multiple drugs.

 

[Drwine]

How long have you been practicing. You know there were other halogenated volatile anesthetics before iso.. u talk as if you've never heard of halothane

I am very close to retirement so not only have I heard of halothane it and ethrane were the only choices when I was a 3rd and 4th year medical student doing anesthesia rotations. I remember when isoflurane was approved and was introduced into clinical practice. Because of surgeons throwing us under the bus for every case of hepatitis which was mainly from their liberal use of blood components we completely moved away from halothane except for pediatrics while I was a resident. After we transitioned to isoflurane our intraoperative use of narcotics increased exponentially and muscle relaxants use also increased. Sevoflurane kinetics allow it to be titrated much easier to varying levels of surgical stimulus. I still stand by my statement that sevo and des have made isoflurane obsolete.

 

[drmwvr]

What does this even mean

Larson's maneuver? Pretty well described.

 

[MirrorTodd]

Larson's maneuver? Pretty well described.

That's probably what he was referencing, but those are pretty two different and distinct maneuvers. One can't just say "jaw thrust" and expect people to believe it fixes laryngospasm.

 

[drmwvr]

That's probably what he was referencing, but those are pretty two different and distinct maneuvers. One can't just say "jaw thrust" and expect people to believe it fixes laryngospasm.

if you do a lot of peds, you know exactly what he meant.

 

[coffeebythelake]

Larson's maneuver? Pretty well described.

It is a maneuver to break laryngospasm and it doesn't work 100% of the time. It also isn't a preventive measure. Not exactly equivalent to saying no laryngospasm by jaw thrusting.

 

[woopedazz]

Re Propofol: Both graphs are correct. We need to remember that context sensitive half time for propofol remains short for nearly all durations of surgery given its short T1/2a and high clearance ... However... There is virtually no clinical relevance to CSHT, instead we mainly rely on context-sensitive decremement times (specifically 80% decrement time) as it is more relevant to clinical effect. And more in line with wake-up. Sometimes these terms are (incorrectly) used interchangeably.

For propofol the CSHT remains short for most operations (The 8 hour 40min number gets quoted a bit... but I think it's actually much less when you look at other studies), but the 80% decrement time can extend anaesthesia for hours when you think about re-distribution and T1/2b. Good graphs.

 

[dhb]

What does this even mean

It's hard to spell it out more clearly...

 

[coffeebythelake]

It's hard to spell it out more clearly...

Refer to subsequent posts. You also ask your colleagues for "cricoid pressure" when you don't have a good view on laryngoscopy?

 

[propadope]

Re Propofol: Both graphs are correct. We need to remember that context sensitive half time for propofol remains short for nearly all durations of surgery given its short T1/2a and high clearance ... However... There is virtually no clinical relevance to CSHT, instead we mainly rely on context-sensitive decremement times (specifically 80% decrement time) as it is more relevant to clinical effect. And more in line with wake-up. Sometimes these terms are (incorrectly) used interchangeably.

For propofol the CSHT remains short for most operations (The 8 hour 40min number gets quoted a bit... but I think it's actually much less when you look at other studies), but the 80% decrement time can extend anaesthesia for hours when you think about re-distribution and T1/2b. Good graphs.

This talks about the 80% decrement time of propofol and also compares the pharmacokinetic modelling of iso vs sevo. Propofol has an even slower offset than even iso on a 4 hour case. This is all assuming that the modelling is accurate of course and actually reflects what is happening clinically

Context Sensitive Decrement Time Abstract

 

[dhb]

Refer to subsequent posts. You also ask your colleagues for "cricoid pressure" when you don't have a good view on laryngoscopy?

No i can intubate a gravid fire ant with a Miller 4

 

[deleted162650]

No i can intubate a gravid fire ant with a Miller 4

Gravid fire ants aren’t actually difficult airways - common misconception.

Try a micrognathic gnat and get back to me.

 

[propadope]

Honestly, the length of a propofol infusion hasn’t changed wake up times for me.
When I worked at the plasticS ASC, we would run it 8,9,10 hours - and the patients woke up very quickly regardless. Maybe we are talking about 5 vs 8 min. That I would buy.

the issue is people do polypharmacy WITH PROPOFOL, and that totally can last forever - and people tend to blame it on the propofol.

as far as I know, no one has studied the multi compartment model with multiple drugs.

“The context-sensitive decrement time [34] for propofol is thus generally favourable compared with other hypnotics. For a short infusion (< 3 h), the 80% decrement time is < 50 min, whereas for longer infusions (> 12 h) it increases up to 3.5 h
[35].”

Clinical Pharmacokinetics and Pharmacodynamics of Propofol

Propofol is an intravenous hypnotic drug that is used for induction and maintenance of sedation and general anaesthesia. It exerts its effects through potentiation of the inhibitory neurotransmitter γ-aminobutyric acid (GABA) at the GABA[A] receptor, ...

www.ncbi.nlm.nih.gov

 

[epidural man]

“The context-sensitive decrement time [34] for propofol is thus generally favourable compared with other hypnotics. For a short infusion (< 3 h), the 80% decrement time is < 50 min, whereas for longer infusions (> 12 h) it increases up to 3.5 h
[35].”

Clinical Pharmacokinetics and Pharmacodynamics of Propofol

Propofol is an intravenous hypnotic drug that is used for induction and maintenance of sedation and general anaesthesia. It exerts its effects through potentiation of the inhibitory neurotransmitter γ-aminobutyric acid (GABA) at the GABA[A] receptor, ...

www.ncbi.nlm.nih.gov

This hasn't been my experience at all. I have lots of patient (all of them recently) to prove it.

 

[propadope]

This hasn't been my experience at all. I have lots of patient (all of them recently) to prove it.

Not doubting you. Probably due to synergism of alfentanil allowing you to keep your infusion rate low? Or possibly the patient population?

 

[epidural man]

Not doubting you. Probably due to synergism of alfentanil allowing you to keep your infusion rate low? Or possibly the patient population?

I think it maybe has more to do with all those models being computer generated.

 

[epidural man]

This was on an ACE question earlier this year.

 

[Airway]

Can you please tell me which issue to find this question? I've found (nearly) no clinical relevance for CSHT w fentanyl in patients in the ICU (both MICU and SICU). Perhaps rapid upregulation of receptors make it unimportant?

Thanks

 

[jwk]

How long have you been practicing. You know there were other halogenated volatile anesthetics before iso.. u talk as if you've never heard of halothane

LOL - halothane & enflurane were the standards in the early 80's. Isoflurane was still being studied while I was in anesthesia school 79-81 and had not been released. I had occasion to use Penthrane a number of times. Grady in Atlanta still had and used copper kettles on their anesthesia machines when I was there as a student, and "sidearm vernitrol" vaporizers were in use well into the 90s. Ah, the good old days. If halothane was as bad on the liver as some people thought it was, I should be dead. Open mask inhalation techniques with high flows and little or no scavenging.....yikes.

 

[deleted875186]

Can you please tell me which issue to find this question? I've found (nearly) no clinical relevance for CSHT w fentanyl in patients in the ICU (both MICU and SICU). Perhaps rapid upregulation of receptors make it unimportant?

Thanks

Good point. Even for hydromorphone infusions in the ICU the offset time is much much faster than expected in these patients.

 

[DrOwnage]

I mix 2000mcg alfentanil in the 100ml bottle of propofol. Sometimes, I need to put 3000mcg in a bottle, I've even gone up to 4000mcg in a 100ml bottle.

Sounds like an interesting prospect... You've probably used it a lot and it sounds like it works for you. However is that really enough alfentanil to keep patients still for very stimulating parts of a procedure? I don't know if I would trust that to my spines. If you calculate that for a 70kg person at a rate of 150mcg/kg/min its around 1 cc a minute. With the 2000mcg of alfentanil in the 100ccs that means its only 20mcg/cc or 20mcg a minute. That's really not a lot of opioid compared to normal remi dosed TIVAs. In my limited experience with alfentanil it takes a good amount to have any observable effects in bolus doses usually like 200-300mcgs.

 

[propadope]

Sounds like an interesting prospect... You've probably used it a lot and it sounds like it works for you. However is that really enough alfentanil to keep patients still for very stimulating parts of a procedure? I don't know if I would trust that to my spines. If you calculate that for a 70kg person at a rate of 150mcg/kg/min its around 1 cc a minute. With the 2000mcg of alfentanil in the 100ccs that means its only 20mcg/cc or 20mcg a minute. That's really not a lot of opioid compared to normal remi dosed TIVAs. In my limited experience with alfentanil it takes a good amount to have any observable effects in bolus doses usually like 200-300mcgs.

He said he uses that mix for plastics