New grads and ETT's

[pgg]

If morbidly obese up-size the ETT by 0.5.

Why?

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[deleted171991]

Why?

So he can deliver the same volume at a decent airway pressure in about the same time as in a thin individual.

The obese lung has lower volumes, plus the chest wall and diaphragm are less compliant. The airway resistance is also higher.

Altered respiratory physiology in obesity

Both respiratory resistance and airway resistance rose significantly with the level of obesity, which appeared to be inversely related to changes in functional residual capacity (FRC). These findings suggest that in addition to the elastic load, obese individuals must overcome increased airway resistance resulting from a reduction in lung volumes due to obesity.

 

[Noyac]

It's cheaper than your Porsche.

Boof!!!!!!!!

 

[Noyac]

I will use a 35F for a small woman under 5'2" or so. If the male is 6'4" I prefer a 41F but I've gotten a 39F to work a time or two buried to the hilt.

I place the largest DBL tube that I can get in comfortably (comfortably to me, not the pt).

 

[pgg]

So he can deliver the same volume at a decent airway pressure in about the same time as in a thin individual.

The obese lung has lower volumes, plus the chest wall and diaphragm are less compliant. The airway resistance is also higher.

Altered respiratory physiology in obesity

I know that; I was wondering if there was a better reason.

While changing the ETT diameter does change the tube resistance, that only changes the pressure the ventilator sees, not what the alveoli see. In other words, physiologically irrelevant.

 

[deleted171991]

I know that; I was wondering if there was a better reason.

While changing the ETT diameter does change the tube resistance, that only changes the pressure the ventilator sees, not what the alveoli see. In other words, physiologically irrelevant.

Now you have woken up my inner Mr. Feynman.

If the patient is breathing through a thinner straw, the gases exit the distal end of the ETT at a higher speed (i.e. much higher kinetic energy - proportional with the square of velocity) and will of course increase the pressures at the distal end.

Also, while the ventilator sees higher pressures, you cannot guarantee that the pressure at the distal end is in a safe zone, that you are not producing barotrauma. If a high velocity blood jet has shearing effects on the vascular wall, why would a high velocity air jet be benign?

When we go from a 7.5 ETT to a 6.5 ETT, the cross-sectional area decreases by (7.5^2-6.5^2)/7.5^2= 25%. Since area x velocity is a constant, gas velocity at the distal end of the tube will increase by a factor of 1/(1-0.25) = 1.33, kinetic energy by the square of it (1.78), and the distal tracheal pressure by the same factor as the kinetic energy. Now we can debate how much of the 1.78 factor will reach the alveoli.

 

[Arch Guillotti]

Now you have woken up my internal Mr. Feynman.

If the patient is breathing through a thinner straw, the gases exit the distal end of the ETT at a higher speed (i.e. much higher kinetic energy - proportional with the square of velocity) and will of course increase the pressures at the distal end.

Also, while the ventilator sees higher pressures, you cannot guarantee that the pressure at the distal end is in a safe zone, that you are not producing barotrauma. If a high velocity blood jet has shearing effects on the vascular wall, why would a high velocity air jet be benign?

When we go from a 7.5 ETT to a 6.5 ETT, the cross-sectional area decreases by (7.5^2-6.5^2)/7.5^2= 25%. Since area x velocity is a constant, gas velocity at the distal end of the tube will increase by a factor of 1/(1-0.25) = 1.33, kinetic energy by the square of it (1.78), and the distal pressure probably somewhere in between.

Whoa!

 

[deleted171991]

Whoa!

Please read the custom title under my avatar.

 

[pgg]

Now you have woken up my internal Mr. Feynman.

If the patient is breathing through a thinner straw, the gases exit the distal end of the ETT at a higher speed (i.e. much higher kinetic energy - proportional with the square of velocity) and will of course increase the pressures at the distal end.

As soon as the gases exit the tube (ETT), the diameter of the tube (trachea) dramatically increases, velocity decreases, and pressure (reduced intra-ETT) rises to a value very slightly less than pre-ETT. This is analagous to the concept of pressure recovery when comparing valve gradients measured by cath vs TEE.

If you step on a hose in the middle, you don't get high velocities and high pressure at the far (open) end. You high velocities and low pressure at the exact point where your foot is, and you get reduced velocities and pressure just distal to the open end because (1) it's open and (2) there was some small amount of energy loss where your foot was.

Using a small endotracheal tube is like putting your foot on the trachea. It will require higher pressure from the ventilator, but the pressure distal to the tube is still less than the pressure proximal to the tube (as measured by the vent).

Also, while the ventilator sees higher pressures, you cannot guarantee that the pressure at the distal end is in a safe zone, that you are not producing barotrauma.

What are you arguing here? That because you cannot guarantee safe pressures distal to a tube of size X, you should use a tube of size X+0.5?

In any case, the pressure of physiologic interest is the plateau pressure, not the PIP.

The math (Pouiselle, r^4) tells us that a tube that is 0.5 mm larger has about 75-80% of the resistance of the smaller tube (given adult-size tubes), which I'll grant you isn't trivial. But this resistance will be reflected in the peak pressure, not the plateau pressure.

You can test this easily in the OR, without swapping tubes mid-case , by adding an inspiratory pause of 20% or more to get an accurate plateau pressure measurement, then slightly pinching or kinking whatever ETT you've got in place. The increase in PIP is substantially more than the increase in plateau pressure. If plateau pressure changes at all.

Plateau pressure, being measured at a time of no flow, isn't affected by the size or resistance of the tube, trachea, bronchi, or bronchioles.

The answer to your "cannot guarantee" question is that if you are seeing peak pressures that are uncomfortably high - regardless of the tube size in place - you're required to think, adjust the ventilator parameters, choose an appropriate tidal volume, I:E ratio, optimize PEEP, and take steps to measure plateau pressure in order to reassure yourself that the alveoli aren't being abused. The answer is not to arbitrarily increase your ETT size by 0.5 mm in obese people and call it good.

If a high velocity blood jet has shearing effects on the vascular wall, why would a high velocity air jet be benign?

High velocity air jet? Now you're really reaching.

1) This isn't a jet ventilator @ 50 psi through a 14g angiocath up against the trachea wall, we're talking about a 7.0 vs a 7.5 mm ETT at ~0.5 psi (40 cmH2O), perfectly centered by an inflated cuff.

2) Mass and viscosity of blood vs air

Of course the "jet" of air coming out of a 7.0 ETT is benign.


God that's a lot of words to argue that it doesn't make a ****'s difference what size tube you use.

 

[deleted171991]

As soon as the gases exit the tube (ETT), the diameter of the tube (trachea) dramatically increases, velocity decreases, and pressure (reduced intra-ETT) rises to a value very slightly less than pre-ETT. This is analagous to the concept of pressure recovery when comparing valve gradients measured by cath vs TEE.

If you step on a hose in the middle, you don't get high velocities and high pressure at the far (open) end. You high velocities and low pressure at the exact point where your foot is, and you get reduced velocities and pressure just distal to the open end because (1) it's open and (2) there was some small amount of energy loss where your foot was.

We were talking about the hypothesis in which you deliver the same flow at the distal end, meaning that you have to increase the proximal pressures.

Using a small endotracheal tube is like putting your foot on the trachea. It will require higher pressure from the ventilator, but the pressure distal to the tube is still less than the pressure proximal to the tube (as measured by the vent).

But much higher when compared to using a bigger tube while maintaining the same flow.

What are you arguing here? That because you cannot guarantee safe pressures distal to a tube of size X, you should use a tube of size X+0.5?

I am arguing that increasing the size of a tube improves ventilation, at least by decreasing distal turbulence, hence dead space, and possibly decreasing barotrauma. It's definitely more relevant in the ICU, once the tube diameter decreases even more because of the secretions.

In any case, the pressure of physiologic interest is the plateau pressure, not the PIP.

It's both, not just the PIP or, to be more precise, the peak transpleural pressure.

The math (Pouiselle, r^4) tells us that a tube that is 0.5 mm larger has about 75-80% of the resistance of the smaller tube (given adult-size tubes), which I'll grant you isn't trivial. But this resistance will be reflected in the peak pressure, not the plateau pressure.

See above.

You can test this easily in the OR, without swapping tubes mid-case , by adding an inspiratory pause of 20% or more to get an accurate plateau pressure measurement, then slightly pinching or kinking whatever ETT you've got in place. The increase in PIP is substantially more than the increase in plateau pressure. If plateau pressure changes at all.

See above.

Plateau pressure, being measured at a time of no flow, isn't affected by the size or resistance of the tube, trachea, bronchi, or bronchioles.

The answer to your "cannot guarantee" question is that if you are seeing peak pressures that are uncomfortably high - regardless of the tube size in place - you're required to think, adjust the ventilator parameters, choose an appropriate tidal volume, I:E ratio, optimize PEEP, and take steps to measure plateau pressure in order to reassure yourself that the alveoli aren't being abused. The answer is not to arbitrarily increase your ETT size by 0.5 mm in obese people and call it good.

Agree.

High velocity air jet? Now you're really reaching.

1) This isn't a jet ventilator @ 50 psi through a 14g angiocath up against the trachea wall, we're talking about a 7.0 vs a 7.5 mm ETT at ~0.5 psi (40 cmH2O), perfectly centered by an inflated cuff.

2) Mass and viscosity of blood vs air

Of course the "jet" of air coming out of a 7.0 ETT is benign.

Agree.

God that's a lot of words to argue that it doesn't make a ****'s difference what size tube you use.

The fun is in the debate. Especially with smarter people.

It's all just brain masturbation. In the end, we all know that bigger tubes are better, except when too large for the glottic opening.

 

[deleted162650]

I am arguing that increasing the size of a tube improves ventilation, at least by decreasing dead space

Pretty sure a larger tube actually increases dead space (by an admittedly insignificant amount).

Bottom line: Larger tubes in ICU = good
Larger tubes in OR = silly

 

[Laryngophed]

If this isn't the kind of discussion that gets you going, I don't know how to resuscitate you.


And I'm not joking.

 

[nimbus]

I've never encountered a ventilation problem that was caused by using a 7.0 tube instead of an 8.0. I suspect if I swapped out a 7.0 for an 8.0 midcase, I would see no difference in peak or plateau pressure. They are both big enough.

 

[deleted162650]

There's a good graph in one of Benumof's old airway books that plots resistance against tube diameter. There's essentially no meaningful difference until you get down to 6.0 and below.

 

[BLADEMDA]

I've never encountered a ventilation problem that was caused by using a 7.0 tube instead of an 8.0. I suspect if I swapped out a 7.0 for an 8.0 midcase, I would see no difference in peak or plateau pressure. They are both big enough.

Ok. Let's get real here. I've seen dozens and dozens of patients struggle to breathe spontaneously through a small ETT. This occurs during the wake up phase when there can be copious secretions and spontaneous respirations. While the slightly larger ETT doesn't solve all these wake up issues it does help with reducing the work of breathing through the straw in their mouth. Second, I prefer suctioning through the bigger ETT.

Many times I've encountered patients with low saturations unable to spontaneously breath through an ETT prior to extubation. Immediately after pulling the ETT and placing a face mask the work of breathing decreases and the saturation climbs into the high 90s.

So, I'm not a fan of small ETT in obese or sicker patients. If you prefer them then so be it but my anecdotal experience over 2.5 decades tells me not to place 6.0 or 6.5 ETTs in these patients.

I've always thought time and experience are great teachers to those who will listen. If your practice is primarily ASA1 and 2 patients then this discussion is moot. But. If your average patient is similar to mine the discussion has value.

 

[pgg]

Ok. Let's get real here. I've seen dozens and dozens of patients struggle to breathe spontaneously through a small ETT. This occurs during the wake up phase when there can be copious secretions and spontaneous respirations. While the slightly larger ETT doesn't solve all these wake up issues it does help with reducing the work of breathing through the straw in their mouth.

Totally agree that breathing through a straw is more difficult ... but this is what pressure support is for.

I think regardless of tube size, even if it’s an 8, if you let them breathe spontaneously through it for more than a couple minutes, you’re needlessly causing atelectasis. Probably not clinically significant in most patients, but why cause any?

For awake extubation, I turn the vent off when they open their eyes.

Second, I prefer suctioning through the bigger ETT.

That’s fair. I don’t find I need to suction most tubes prior to extubation though.

 

[dhb]

I think regardless of tube size, even if it’s an 8, if you let them breathe spontaneously through it for more than a couple minutes, you’re needlessly causing atelectasis.

Probably no more than they will have 5min after extubation.

 

[Robotic Wis-Hipple]

Unless I think they are going to the unit or will be breathing thru it awake for awhile I size down.

I hear the whole peak pressures argument a lot, but why do I care about that if it’s from the tube? You aren’t causing a peak pressure >30 from a 6.5 or 7.0 and even if you did that’s not being transmitted to the alveolus so what’s the concern?

If I need a surgery I wouldn’t want an 8.0 or larger.

 

[nimbus]

Not long enough: when you have to hub it, they have a tendancy to move back out especially when moving to lateral.
I like 37 for women 39 for men 41 if really big.

I will use a 35F for a small woman under 5'2" or so. If the male is 6'4" I prefer a 41F but I've gotten a 39F to work a time or two buried to the hilt.

Since I've never encountered a problem with length, I did a little investigating. They're all the same length. Guess which one I used this morning

 

[Psai]

View attachment 223834



Since I've never encountered a problem with length, I did a little investigating. They're all the same length. Guess which one I used this morning

It's not just length, it is length times girth over yaw divided by mass over width

 

[Laryngophed]

It's not just length, it is length times girth over yaw divided by mass over width

We still talking about oETTs here?

 

[BLADEMDA]

View attachment 223834



Since I've never encountered a problem with length, I did a little investigating. They're all the same length. Guess which one I used this morning

https://digital.library.adelaide.edu.au/dspace/bitstream/2440/5893/1/hdl_5893.pdf

 

[BLADEMDA]

I typically use a 37F or 39F left sided double lumen ETT:

 

[BLADEMDA]

View attachment 223834



Since I've never encountered a problem with length, I did a little investigating. They're all the same length. Guess which one I used this morning

I always assumed the smaller double lumen ETT was more likely to become displaced from the Left main bronchus if it was undersized.

 

[BLADEMDA]

The margin of safety of a left double-lumen tracheobronchial tube depends on the length of the bronchial cuff and tip
Author(s): L. Partridge and W.J. Russell .
Source: Anaesthesia and Intensive Care.
Document Type: Article

Article Preview :

SUMMARY The left tracheobronchial double-lumen tube is the commonest device to separate the left and right lungs for differential ventilation. With the appropriate tube, the left bronchial cuff is positioned in the bronchus so that the cuff is beyond the carina but the tip of the tube does not occlude the aperture of the left upper lobe bronchus. The difference between the length of the left main bronchus and the length of the cuff and tip of the bronchial segment of the tube has been termed "the margin of safety" by Benumof. If the length of the cuff plus the tip exceeds that of the left main bronchus, there will be occlusion of the left upper lobe bronchus. The bronchial cuff and bronchial tip lengths were measured on two hundred and twenty left tracheobronchial (double-lumen) tubes from four manufacturers. The largest cuff-tip length was 40 mm with a Portex 41Fr tube but some 41Fr tubes from all manufacturers had cuff-tip lengths of 33 mm or greater which exceed the length of the shortest left main bronchus measured by Benumof. There was also a marked variation in cuff-tip lengths of the same size tube from the same manufacturer. The largest variation was 18 mm for the Portex 41 but substantial variation of 8 mm or more was found in at least one French size of all manufacturers. Users must be aware that significant cuff-tip length variation occurs and match the selected tube to the patient to ensure an adequate margin of safety. Key Words: double-lumen tube, lung isolation, equipment, margin of safety In 1987, Benumof wrote of the need to position the bronchial segment of a left double-lumen tracheobronchial tube so that it did not obstruct either the carina nor the left upper lobe bronchus origin (1). He measured patients, cadavers and cadaveric casts of the bronchi to find the length of the left main bronchus between the carina and the origin of the left upper lobe bronchus. The dimensions from all three groups were similar with a mean of about 48 mm and a standard deviation of 8 mm. Overall the shortest left...
Source Citation (MLA 8 th Edition)
Partridge, L., and W.J. Russell. "The margin of safety of a left double-lumen tracheobronchial tube depends on the length of the bronchial cuff and tip." Anaesthesia and Intensive Care, vol. 34, no. 5, 2006, p. 618+. Academic OneFile, Accessed 25 Sept. 2017.

 

[dhb]

Well i checked today and was very surprised that the lenght of the tubes as well as the lenght of the bronchial stem were identical for all tubes.
I really believed that the larger tubes where also longer.

 

[Psai]

We still talking about oETTs here?

Depends on how well they tolerate po

 

[BLADEMDA]

Well i checked today and was very surprised that the lenght of the tubes as well as the lenght of the bronchial stem were identical for all tubes.
I really believed that the larger tubes where also longer.

So, the question is does the increase in diameter of the double lumen tube result in fewer dislodgements? Or, is a 37F the new "standard" for all adult males?

 

[Ronin786]

Yup, DLTs are all the same length. The diameter is what changes and you'd be surprised to know that the outer diameter actually is very similar to an 8.0 ETT.

That said, there's good studies out there to show that tracheal diameter on CXR is what should choose your double-lumen tube size.
http://ether.stanford.edu/library/t...ntilation/Selection of Double-lumen Tubes.pdf

 

[BLADEMDA]

No single predictor can tell what size tube should be used. A large tube has less chance of being dislodged or producing significant resistance to gas flow. However, the placement of a larger tube should never be a goal of its own and the tube should never be advanced against resistance.

A study by Seymour et al showed that the mean diameter of cricoid ring is similar to main stem bronchus. [9] Therefore, if the tube cannot be advanced easily through that part of airway, it is probably too large and should be changed for a smaller one. Good preparation is important for a smooth and uneventful intubation process. Therefore, it is important that tubes of one size smaller and larger are readily available during the procedure.

Double-Lumen Endotracheal Tube Placement: Overview, Periprocedural Care, Technique

 

[BLADEMDA]

Anesth Analg. 2008 Feb;106(2):379-83, table of contents. doi: 10.1213/ane.0b013e3181602e41.
Practice patterns in choice of left double-lumen tube size for thoracic surgery.
Amar D1, Desiderio DP, Heerdt PM, Kolker AC, Zhang H, Thaler HT.
Author information

Abstract
BACKGROUND:
Some anesthesiologists choose smaller than body size-appropriate left sided double-lumen tubes (DLTs) ("down-size") for lung isolation in an attempt to limit the risk of airway trauma. There are few data on the effects of DLT size on intraoperative outcome measures.

METHODS:
In 300 adults undergoing thoracic surgery requiring lung isolation, we conducted a prospective pilot study to evaluate whether the use of 35 FR DLT, regardless of gender and/or height (care standard of two investigators), was associated with a similar incidence of intraoperative hypoxemia, lung isolation failure, or need for DLT repositioning during surgery (noninferiority) than with the conventional goal of inserting the largest possible DLT (care standard of two other investigators). DLT insertion position was immediately confirmed with fiberoptic bronchoscopy after direct laryngoscopic placement and after lateral positioning.

RESULTS:
The combined incidence of transient hypoxemia, inadequate lung isolation, or need for DLT repositioning during surgery did not differ among patients receiving 35, 37, or 39 FR DLT, regardless of gender or height. Despite the high frequency of 35 FR DLT use, 2% of patients required further down-sizing due to the inability to introduce the DLT into the left mainstem bronchus or when no inflation of the bronchial cuff was needed for lung isolation.

CONCLUSIONS:
Under the conditions of this pilot study, the use of smaller than conventionally sized DLT was not associated with any differences in clinical intraoperative outcomes.

 

[BLADEMDA]

Abstract
Drs. Lohser and Brodsky1 raise the measurement of left mainstem bronchial diameter as an indicator of proper sizing for left-sided double-lumen tubes (DLT), and suggest that use of this technique in our recent study may have yielded different results. While we don't question the mathematical formulas, none of the clinicians involved in the study practice this method despite over 80 years of cumulative experience successfully placing DLT in an institution where >2000 thoracic procedures are performed each year. Accordingly, our work addressed the prevalent practice at our institution of sizing DLT by height and/or gender. Although the participating anesthesiologists were all initially trained to use conventional methods at a time when fiberoptic bronchoscopy was not readily available, the strength of our study design is that we compared outcomes in a single clinical setting between anesthesiologists whose practice now differs.2 Our data showed that in regard to intraoperative end-points reflecting the adequacy of lung collapse and preservation of oxygenation, both our “conventional” approach and intentional downsizing are comparable. While we appreciate the interpretation by Drs. Lohser and Brodsky that our observed “failure to isolate” temporarily may well have been due to undersized DLT, we maintain our stated conclusion that malposition was responsible.2
With respect to the rare event of DLT causing airway damage, the authors cite their own early data indicating that rupture in particular is most frequently associated with small DLT,3 perhaps due to the need for relative cuff hyperinflation. While we included this citation in our manuscript, we also included references indicating the possibility of trauma from either small or large DLT,4–6 a risk also previously noted by Brodsky and Lemmens7 and cited in our paper. Furthermore, despite use of down-sized DLT we rarely found that more than 3 mL was required to provide an adequate seal. The authors further point to the theoretical increase in auto-PEEP due to downsizing of DLT. While experimental studies have clearly shown differences in the gas flow characteristics between large and small DLT, neither results of the our study nor our extensive clinical experience have given any indication that the 0.6 mm difference between a 35 and 39 FR internal diameter has had any deleterious effects in our patient population. Indeed, our reported incidence of intraoperative hypoxemia and recently published incidence of acute lung injury in 1,428 patients undergoing lung resection are low and consistent with the literature.

In Response:
Anesthesia & Analgesia. 107(3):1082, SEP 2008

David Amar; Paul M. Heerdt; and 2 more

DOI: 10.1213/ANE.0b013e3181865e5c

 

[BLADEMDA]

View attachment 223834



Since I've never encountered a problem with length, I did a little investigating. They're all the same length. Guess which one I used this morning

So, my literature review along with your factual statement (much appreciated) seems to strongly suggest a 35F for typical Females and a 37F for most males should be the "go to" sizes for our cases.

I appreciate the discussion because from now on I'm likely to use a 35F or 37F left sided double lumen tube with only extremely tall males over 6'3" getting a 39F. I doubt I'll ever use a 41F again except if they play in the NBA.

 

[nimbus]

So, my literature review along with your factual statement (much appreciated) seems to strongly suggest a 35F for typical Females and a 37F for most males should be the "go to" sizes for our cases.

I appreciate the discussion because from now on I'm likely to use a 35F or 37F left sided double lumen tube with only extremely tall males over 6'3" getting a 39F. I doubt I'll ever use a 41F again except if they play in the NBA.

Appreciate the sentiment and the review. I do lung isolation on a regular basis, typically 3-5x/week and I wouldn't use 37L DLTs on everyone if it didn't work. I don't like the 35 because it's a very tight fit for our pediatric bronchoscope.

On a related note, I do tend to go a little larger with nasal RAE tubes because I have encountered length issues when I downsize those. I'll use a 7.5 or 8.0 for most men and a 7.0 or 7.5 for most women depending on height/face size/neck length.

 

[fakin' the funk]

Yup, DLTs are all the same length. The diameter is what changes and you'd be surprised to know that the outer diameter actually is very similar to an 8.0 ETT.

That said, there's good studies out there to show that tracheal diameter on CXR is what should choose your double-lumen tube size.
http://ether.stanford.edu/library/thoracic_anesthesia/One-Lung Ventilation/Selection of Double-lumen Tubes.pdf

You beat me to it. There are tables out there (this is just one) of tracheal diameter at thoracic inlet vs appropriate DLT size. These days, everyone coming for an OLV type case will have a chest CT -- that much easier.

 

[MaximusD]

Mental masturbation at its finest. 7 for females and 8 for males. >7.5 for ICU bound pts. Simple.

 

[Noyac]

Appreciate the sentiment and the review. I do lung isolation on a regular basis, typically 3-5x/week and I wouldn't use 37L DLTs on everyone if it didn't work. I don't like the 35 because it's a very tight fit for our pediatric bronchoscope.

On a related note, I do tend to go a little larger with nasal RAE tubes because I have encountered length issues when I downsize those. I'll use a 7.5 or 8.0 for most men and a 7.0 or 7.5 for most women depending on height/face size/neck length.

The best indication I know of for anything we do is experience.