ETT cuff residual volume?

[ketap]

hi i have been reading dorsch n dorsch's "practical approach to anesthesia equipment" and i have a problem to understand the ETT cuff..ok,here are the problems: the book
advices us to use " ETT with a cuff circumference at residual volume be at least equal to the tracheal diameter"..but the book didn't say any explanation about "residual volume" and honestly, i don't know anything about it...what is it? i am guessing that it is the volume within the cuff after we inflate the cuff,am i right?

and i have also heard about "resting cuff circumference"..what is it actually?

oh ya, another thing, about this statement: .."at least equal to..."

so,
if we don't have the equal size, should we choose bigger cuff or smaller one?
thx u, please help...
regards,Ketap

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[btbam]

hi i have been reading dorsch n dorsch's "practical approach to anesthesia equipment" and i have a problem to understand the ETT cuff..ok,here are the problems: the book
advices us to use " ETT with a cuff circumference at residual volume be at least equal to the tracheal diameter"..but the book didn't say any explanation about "residual volume" and honestly, i don't know anything about it...what is it? i am guessing that it is the volume within the cuff after we inflate the cuff,am i right?

and i have also heard about "resting cuff circumference"..what is it actually?

oh ya, another thing, about this statement: .."at least equal to..."

so,
if we don't have the equal size, should we choose bigger cuff or smaller one?
thx u, please help...
regards,Ketap

Hold pressure at 20, inflate cuff til leak goes away. End of story.

 

[twoliter]

hi i have been reading dorsch n dorsch's "practical approach to anesthesia equipment" and i have a problem to understand the ETT cuff..ok,here are the problems: the book
advices us to use " ETT with a cuff circumference at residual volume be at least equal to the tracheal diameter"..but the book didn't say any explanation about "residual volume" and honestly, i don't know anything about it...what is it? i am guessing that it is the volume within the cuff after we inflate the cuff,am i right?

and i have also heard about "resting cuff circumference"..what is it actually?

oh ya, another thing, about this statement: .."at least equal to..."

so,
if we don't have the equal size, should we choose bigger cuff or smaller one?
thx u, please help...
regards,Ketap

My guess as to what they mean is after intubation, inflate the cuff as your normally would (or maybe a little more) then let go with the syringe still attached. If the cuff pressure starts to push the plunger back, let it. Once it's stops, the cuff should be against the trachea, but without too much pressure.
That's actually the way one of my peds faculty taught me to do it, but never actually mentioned the phrase residual volume.

 

[deleted171991]

if we don't have the equal size, should we choose bigger cuff or smaller one?

The bigger tube is better than the smaller one, because you need to inflate the smaller tube's cuff much more (at a higher pressure) in order to avoid leaks.

 

[deleted162650]

The bigger tube is better than the smaller one, because you need to inflate the smaller tube's cuff much more (at a higher pressure) in order to avoid leaks.

More volume yes, but not necessarily more pressure.

 

[deleted171991]

More volume yes, but not necessarily more pressure.

Even if the two tubes have a similar size cuff, more volume equals more pressure in my mind, just by how the pilot balloon feels. Since the distance to the tracheal wall is greater in the case of the smaller tube, I would assume it needs more volume, hence pressure, to reach the wall. That's the pressure that will be transmitted to the airway mucosa, the lower the better.

Unfortunately, the same bigger size tube that decreases cuff pressure on the tracheal mucosa can also increase pressure and damage at the level of the vocal cords, and that's the reason why we don't just use 9.0 ETT in everybody.

 

[Noyac]

Even if the two tubes have a similar size cuff, more volume equals more pressure in my mind, just by how the pilot balloon fills. Since the distance to the tracheal wall is greater in the case of the smaller tube, I would assume it needs more volume, hence pressure, to reach the wall. That's the pressure that will be transmitted to the airway mucosa, the lower the better.

Unfortunately, the same bigger size tube that decreases cuff pressure on the tracheal mucosa can also increase pressure and damage at the level of the vocal cords, and that's the reason why we don't just use 9.0 ETT in everybody.

I agree with this statement. I'm a 8.0 male and 7.5 female tube guy. The younger population of anesthesiologists think I'm putting in tubes too large. But the sore throats that ensue do not agree. I routinely see cuff pressures <10cmh2o completely occlude the trachea and prevent leaking of air in my larger ETT scenario. I know this because we measure cuff pressure on cervicals (ACDF's) all the time. But if you put in a smaller tube, it requires a greater volume of air to inflate against the trachea and therefore, greater pressure.

 

[nimbus]

Maybe I'm missing something here. No matter what size tube we insert, the idea is to inflate the cuff just enough to prevent a cuff leak at a reasonable inspiratory pressure. We never fully inflate the cuff in a 7.0 or 8.0 tube. So why would you achieve seal at a lower cuff pressure with a larger tube? With hi volume, low pressure cuffs, I would think the cuff pressure would be the same at the same leak pressure whether the tube is a 7 or an 8.

A 7.0 tube will require more volume to achieve seal than an 8.0 tube but that doesn't mean cuff pressure is higher. Seal should be achieved at the same pressure. I don't think more volume equals more pressure.

 

[Noyac]

A 7.0 tube will require more volume to achieve seal than an 8.0 tube but that doesn't mean cuff pressure is higher. Seal should be achieved at the same pressure. I don't think more volume equals more pressure.

I think of it this way. The larger cuff will fill the space while doing it with less pressure. Maybe more volume but that volume is under less pressure. This is what matters. I am not good at describing this but that is how I see it.

 

[nimbus]

I think of it this way. The larger cuff will fill the space while doing it with less pressure. Maybe more volume but that volume is under less pressure. This is what matters. I am not good at describing this but that is how I see it.

The question is what is the source of cuff pressure?

A fully inflated cuff in free space has cuff pressure from elastic recoil of the cuff material, like a balloon at tension.

A deflated cuff or a partially inflated cuff in free space has zero pressure. It is not pressurized.

We use endotracheal tubes that are placed within the trachea with a partially inflated cuff that is abutting the tracheal lumen. The cuff pressure is generated by contact of the Tracheal lumen against the cuff material. So why would the cuff of a larger tube have less pressure than the cuff of a smaller tube if both are just partially inflated?

 

[nimbus]

Even if the two tubes have a similar size cuff, more volume equals more pressure in my mind, just by how the pilot balloon fills. Since the distance to the tracheal wall is greater in the case of the smaller tube, I would assume it needs more volume, hence pressure, to reach the wall. That's the pressure that will be transmitted to the airway mucosa, the lower the better.

With high volume low pressure cuffs, there is zero pressure within the cuff until the cuff abuts the tracheal lumen. A loose cuff containing 2ml or 4ml of air both have zero pressure until something external presses on it. Try it at work. Put 4ml of air into the cuff of a 7.0 tube and check the pilot balloon. There is zero pressure within that cuff until you squeeze the cuff. There is zero intrinsic pressure until the cuff is fully inflated. Cuff pressure in our clinical scenario is from the tracheal wall.

 

[deleted171991]

With high volume low pressure cuffs, there is zero pressure within the cuff until the cuff abuts the tracheal lumen. A loose cuff containing 2ml or 4ml of air both have zero pressure until something external presses on it. Try it at work. Put 4ml of air into the cuff of a 7.0 tube and check the pilot balloon. There is zero pressure within that cuff until you squeeze the cuff. There is zero intrinsic pressure until the cuff is fully inflated. Cuff pressure in our clinical scenario is from the tracheal wall.

Most people put much more than 4 ml of air in the cuff. It's typically more in the 5-10 ml range (I was trained with 10, but use 5). And the smaller the tube, the more air one will have to put in the cuff to avoid a leak. Of course there is barely any pressure in the cuff at low volumes; that's the whole idea, and that's why we can now use cuffed tubes even in kids.

Try the same 7.0 cuff with 5 ml of air inside and with 10, and feel the cuff (not the balloon, because it's the cuff that presses on the mucosa). Then try the 7.5 tube with 5 and 10. I would expect the 7.5 tube with 5 ml of air to have a much softer cuff than the 7.0 tube with 10 ml of air.

Maybe I am wrong. Still, anybody who uses a larger tube with less air in the cuff won't cause more sore throat. That's the principle with LMAs, too, by the way: keep them as minimally inflated as possible.

 

[deleted162650]

@nimbus is right. Boyle's Law doesn't apply to modern HVLP ETT cuffs. They are designed to occlude the trach with minimal pressure. The pressure volume curve is not linear but rather hockey stick shaped. You don't see pressure increases until you really distend the cuff. But even still, if you are inflating the cuff to some endpoint like "no leak @ 30cm/H20" then the pressure exerted on the tracheal wall is gonna be the same regardless of the tube/cuff size. To blindly put in a set volume of air into the cuff is to practice bad anesthesia.

But just to illustrate a point, lets take things to the extreme. Let's put a veeeery tiny tube into a trachea - like a 4.0 into an adult. You will have to really overinflate/distend the cuff to eliminate the leak. Thus the pressure in the cuff will be very high. However, the cuff may be just kissing the walls of the trachea enough to occlude it. The trachea is seeing minimal pressure despite the high intra-cuff pressure. Hope I explained that well.

Phew, that was some intense mental masturbation. I need a cigarette. Was it good for you??

But the sore throats that ensue do not agree.

I think tube size is a relatively minor factor when it comes to sore throat. That being said, I don't think sore throats are caused by the cuff but more so by the shaft of the tube sitting on the cords. So in my my feeble mind, a smaller tube will cause less sore throat than a bigger one. I believe the biggest factors in sore throat are rough DL's, and especially coughing/bucking on the tube where the cords and trachea are forcibly being contracted and rubbed against the tube. Noy's pts don't get sore thoats because they never cough and buck.

 

[pgg]

Most sore throats are caused by the laryngoscope, not the piece of warm/soft PVC tube that rests against the tissue, regardless of size, position, or cuff pressure.

The "sore throat" pain patients complain about postop is dysphagia and oropharyngeal pain, and there's obviously no connection at all between that and endotracheal tube cuff pressure.

I think Miller blades, used as designed (get under the epiglottis and lift it) cause more sore throats than Mac blades, used as designed (or better yet, keeping the tip out of the deeper recess of the vallecula).

I think deliberately using less force and routinely intubating with a grade 3 or 4 view instead of the grade 1 you could get if you lifted harder, will result in fewer sore throats. It's good practice for trainees to do this too, so that when they get airways where the absolute best view they can get is an almost-4, they can still easily slip the tube in the top hole.


I use the smallest tube I think I can get away with because they're easier to place and because a big tube propping the cords open probably causes more inflammation and maybe more postop discomfort/hoarseness. The exception is patients who are going to remain intubated postop. I put big tubes in them because bigger tubes make pulmonary toilet and bronchoscopy easier for the ICU.

Cuff pressure is the wrong metric to be measuring anyway. Inflate to the minimum pressure you need to prevent a leak, given the inspiratory pressure you need to ventilate the patient.

There just isn't enough difference in the cuff size of a 7.0 and 8.0 tube to meaningfully alter the transmucosal pressure needed to occlude the airway at normal inspiratory pressures.

 

[deleted171991]

Throat = pharynx + larynx + trachea. Damaging the soft tissue at any level, even just by vigorous suction = sore throat.

 

[pgg]

Throat = pharynx + larynx + trachea. Damaging the soft tissue at any level, even just by vigorous suction = sore throat.

I don't entirely disagree, but I disagree a little with including tracheal irritation with the classic postop sore throat presentation.

Irritation at the tracheal level primarily causes coughing. The postop patients with sore throats mainly complain about pain and dysphagia. They'll sit there swallowing repeatedly but they rarely cough. I don't think tracheal irritation is a big part of the typical postop sore throat.

I'm splitting hairs though.



While we're on the topic, one more bit of bad intubating style common in newbies: leaving an endotracheal tube stylet in the tube as you advance it to its final position. Using that big rigid stick with a sharp bend near the end helps get anterior airways, sure, but stop advancing when you see the tip of the tube get past the vocal cords, take out the stylet, and then advance the tube the rest of the way. Otherwise you're just roughly scraping the tip of the tube along the whole anterior surface of the trachea. I'll readily concede that that probably causes postop discomfort, regardless of whether we label it a sore throat or not.

 

[deleted162650]

While we're on the topic, one more bit of bad intubating style common in newbies: leaving an endotracheal tube stylet in the tube as you advance it to its final position.

Or better yet, just skip the stylet all together.

 

[Noyac]

With high volume low pressure cuffs, there is zero pressure within the cuff until the cuff abuts the tracheal lumen. A loose cuff containing 2ml or 4ml of air both have zero pressure until something external presses on it. Try it at work. Put 4ml of air into the cuff of a 7.0 tube and check the pilot balloon. There is zero pressure within that cuff until you squeeze the cuff. There is zero intrinsic pressure until the cuff is fully inflated. Cuff pressure in our clinical scenario is from the tracheal wall.

I tried to take photos to show my point. But the files are too large. I'm too dumb to fix it.
But the point is that the size of cuff btw an 8.0 and a 7.0 is pretty significant. When I inflated the cuff outside the pt in open air just enough to remove all wrinkles the volume of air was about half of the 8.0 in the 7.0 ETT. Then I connected our manometer to it and the pressures were pretty close. Both about 10cmH2O. But the point again is that the 8.0 will require much less volume to achieve the seal and in my opinion less pressure. Therefore, less mucosal ischemia.

 

[Noyac]

Who uses stylets these days?


Wait, the nurses still do.

 

[Noyac]

Most people put much more than 4 ml of air in the cuff. It's typically more in the 5-10 ml range (I was trained with 10, but use 5). And the smaller the tube, the more air one will have to put in the cuff to avoid a leak. Of course there is barely any pressure in the cuff at low volumes; that's the whole idea, and that's why we can now use cuffed tubes even in kids.

Try the same 7.0 cuff with 5 ml of air inside and with 10, and feel the cuff (not the balloon, because it's the cuff that presses on the mucosa). Then try the 7.5 tube with 5 and 10. I would expect the 7.5 tube with 5 ml of air to have a much softer cuff than the 7.0 tube with 10 ml of air.

Maybe I am wrong. Still, anybody who uses a larger tube with less air in the cuff won't cause more sore throat. That's the principle with LMAs, too, by the way: keep them as minimally inflated as possible.

Exactly what I'm saying. The difference is huge.

 

[Noyac]

@nimbus Noy's pts don't get sore thoats because they never cough and buck.

You have a witness to my care. Ask Patti. Lots of truth to that tho.

 

[deleted171991]

Who uses stylets these days?


Wait, the nurses still do.

I do.

I just remove it ASAP.

 

[nimbus]

I tried to take photos to show my point. But the files are too large. I'm too dumb to fix it.
But the point is that the size of cuff btw an 8.0 and a 7.0 is pretty significant. When I inflated the cuff outside the pt in open air just enough to remove all wrinkles the volume of air was about half of the 8.0 in the 7.0 ETT. Then I connected our manometer to it and the pressures were pretty close. Both about 10cmH2O. But the point again is that the 8.0 will require much less volume to achieve the seal and in my opinion less pressure. Therefore, less mucosal ischemia.

That's funny I tried to upload photos too but the files were too large. At least for the mallinkrodt hilo tubes we use, both 7.0 and 8.0 tubes will take about 10ml air in the cuff. I usually get cuff seal With 4-7 ml air. If you look at the cuffs after you put in 7 ml air, they are both floppy loose whether the tube is a 7 or 8.

And I stylette if I think the intubation will be hard. I'm a wuss that way. But I do a one-handed maneuver where I advance the tube into the trachea without the stylette.

 

[deleted162650]

You have a witness to my care. Ask Patti. Lots of truth to that tho.

I believe you as the overwhelming majority of my pts don't cough/buck/gag either (after all, I learned a lot from you on this forum over the years ), and I do believe that's why you see a low incidence of sore throat.

I'm not quite at the point where none of my pts cough/buck/gag but you've go a few years of experience on me.

This thread may mark the first time I've ever disagreed with you. The pressure needed to prevent a leak is the same regardless of the volume in the cuff.

I sadly don't work with Patti anymore. I miss the nurses, staff, and surgeons at my old shop - but my partners and payer mix where I'm at now more than make up for it.

 

[pgg]

I still prepare most of my tubes with stylets. I don't see a down side. They cost pennies. They hurt nothing.

I always been a little puzzled by some persons' aversion to stylets. Often heard from the same people who call desflurane a "nurse gas" ...

It's just a tool. I don't really get the pride in choosing not to use simple tools.

 

[deleted162650]

I still prepare most of my tubes with stylets.

That's funny, I always though you were a doc not a CRNA.

 

[Noyac]

I still prepare most of my tubes with stylets. I don't see a down side. They cost pennies. They hurt nothing.

I always been a little puzzled by some persons' aversion to stylets. Often heard from the same people who call desflurane a "nurse gas" ...

It's just a tool. I don't really get the pride in choosing not to use simple tools.

Hey, I'm just messing around and trying to keep things lite here. I have nothing against a stylet. I just don't use them any longer. It's just a style, not a criticism.

When I find out that I need a stylet the I just grab the boogie. I find the stylet just doesn't add that much to my approach usually.

 

[Noyac]

I believe you as the overwhelming majority of my pts don't cough/buck/gag either (after all, I learned a lot from you on this forum over the years ), and I do believe that's why you see a low incidence of sore throat.

I'm not quite at the point where none of my pts cough/buck/gag but you've go a few years of experience on me.

This thread may mark the first time I've ever disagreed with you. The pressure needed to prevent a leak is the same regardless of the volume in the cuff.

I sadly don't work with Patti anymore. I miss the nurses, staff, and surgeons at my old shop - but my partners and payer mix where I'm at now more than make up for it.

I actually like it when people disagree with me. This is the first time you have and therefore, maybe I can learn to like you one day.

 

[Urzuz]

I still prepare most of my tubes with stylets. I don't see a down side. They cost pennies. They hurt nothing.

I always been a little puzzled by some persons' aversion to stylets. Often heard from the same people who call desflurane a "nurse gas" ...

It's just a tool. I don't really get the pride in choosing not to use simple tools.

I use stylets AND desflurane. I guess I am a CRNA

 

[Noyac]

I use stylets AND desflurane. I guess I am a CRNA

Whoa, when did DES become a nurse tool?

 

[Arch Guillotti]

Whoa, when did DES become a nurse tool?

Because it's easy.

So is the BIS.

 

[deleted171991]

Whoa, when did DES become a nurse tool?

When real MEN started using ISO.

 

[Noyac]

See, I knew I was a nurse all along.

 

[deleted162650]

See, I knew I was a nurse all along.

We'll give you a free pass since nitrous doesn't work at elevation.

 

[Noyac]

We'll give you a free pass since nitrous doesn't work at elevation.

No wonder my pts keep moving.

 

[epidural man]

I was just telling my student today - "I have no idea why anyone would use anything other than Des (except when not a good idea clinically)..."

Fast on - Fast off...the wish for every anesthesiologist for every anesthesia drug...I'm not sure why it would be any different for a gas.

I love it when someone says "I can wake up just as fast with ISO as anyone can with DES." Yes...true - but this isn't about YOU. It is about how the patient feels in 6 hours.

Noyac, how do you keep someone from coughing?

Again -telling my student today (after a patient...for whatever reason...was coughing non-stop for 15 minutes after the tube was pulled) "think about when you get just a teeny tiny bit of spit in your trachea - you cough up a storm for a very long time...and we are sticking a huge piece of foreign material down there likely irritating the crap out of all that cilia."

Anyway, I'd love to hear how you prevent it. It's a mystery to me - other than lots of opioids, or propofol from the OR to the PACU.

 

[ketap]

hi,guys thank you so much for all the replies and discussions..i really appreciate it..however i need to ask again:
1. i found the definition from another dorsch's book:
"residual volume is the amount of air that can be withdrawn from the cuff after it has been allowed to assume its shape with the inflation tube exposed to atmospheric pressure"
i don't really get it.. what does this complicated sentence mean?




2. @nimbus and saltydog : i understand that with low pressure cuffs, the cuff will not make too much high pressure to the trachea, but...if the cuff diameter is too small to seal the trachea and we need to overinflate (hence, intracuff pressure is increased) to seal the trachea...don't you think that now it will behave like the high pressure cuff?
i think of it just like this: the overinflated cuff will only touch a small area of the tracheal wall and now, its high intracuff pressure will focus its force to that small area. Won't the pressure from that cuff pressing against the trachea will now be very high?

please help me to understand all of these.. thank you...
best regards, Ketap

 

[deleted162650]

hi,guys thank you so much for all the replies and discussions..i really appreciate it..however i need to ask again:
1. i found the definition from another dorsch's book:
"residual volume is the amount of air that can be withdrawn from the cuff after it has been allowed to assume its shape with the inflation tube exposed to atmospheric pressure"
i don't really get it.. what does this complicated sentence mean?




2. @nimbus and saltydog : i understand that with low pressure cuffs, the cuff will not make too much high pressure to the trachea, but...if the cuff diameter is too small to seal the trachea and we need to overinflate (hence, intracuff pressure is increased) to seal the trachea...don't you think that now it will behave like the high pressure cuff?
i think of it just like this: the overinflated cuff will only touch a small area of the tracheal wall and now, its high intracuff pressure will focus its force to that small area. Won't the pressure from that cuff pressing against the trachea will now be very high?

please help me to understand all of these.. thank you...
best regards, Ketap

On your first question: I think they are referring to the amount of air that comes in the cuff of a brand new ETT when you take it out of the wrapper. At least that's all I can think they could possibly be trying to say. Bottom line is you need to let it go and stop reading these texts. It has no relevance to patient care.

On your second question: Please refer to post #13

 

[propadope]

Never heard of residual volume but I did the following experiment. I took a 6.5 ETT. Inflated the cuff. I attached a syringe with the plunger removed so the cuff is exposed to the atmosphere. Once equilibrium is reached, I checked the volume left in the cuff which was 4ml. This is the residual volume and ideally the cuff should touch the tracheal wall with this volume.

 

[Noyac]

Noyac, how do you keep someone from coughing?

Again -telling my student today (after a patient...for whatever reason...was coughing non-stop for 15 minutes after the tube was pulled) "think about when you get just a teeny tiny bit of spit in your trachea - you cough up a storm for a very long time...and we are sticking a huge piece of foreign material down there likely irritating the crap out of all that cilia."

Anyway, I'd love to hear how you prevent it. It's a mystery to me - other than lots of opioids, or propofol from the OR to the PACU.

Coughing is caused by different things, in my mind. If the pt is coughing for 15 min post-op then I'm thinking things like rough ETT placement, asthma, smoker or some other irritant. Not DES.
I prevent coughing a few ways. Not 100% successful but damn close.
1- good LTA topicalization.
2- IV lidocaince 60-100mg just prior to extubation if case >1hr.
3- narcotics to RR 12ish.
4- peaceful wake up ( usually that means 20mg propofol prior to extubation).

If I really really don't want them to cough, deep extubation on occasion.

 

[sevoflurane]

Not a bad thread for a bunch of nurses...

In all seriuosness, I do feel that deep extubation adds a lot to a smooth wake up and significantly decreases coughing. I am a minimalist when it comes to narcotics so that may play a role.
To this day, most of my patients get extubated deep. The only time I don't extubate deep is the difficult airway or the patient that has a reason to aspirate at the end of the case (traumas, emergent cases, Diabetic with gastroperesis that has had some narcs the DOS, SBO that may not have been completely decompressed by either the surgeon or my NG tube, etc.).