Transpulmonary Pressure (Ptp)-Guided Ventilation: A Case. #FOAMed, #FOAMcc

So in my last post I quickly reviewed the basics of Ptp-guided ventilation. So here is a case. We had a woman in her 60’s admitted with bilateral pneumonia, intubated and ventilated. She is morbidly obese and diabetic. Despite antibiotics and usual care, she was getting progressively worse, and was labelled “ARDS.”  POCUS showed she was not in terrible venous congestion, and she had been digressed to a relatively normal IVC. Slowly her ventilator settings crept up to a PEEP of 14 and FiO2 of 100%. As the plateau pressures were approaching 35, we were getting a little antsy, so decided to put in the esophageal balloon and get a better grip as to what was going on.

Here are her original readings:


So here we can see that her Pes in expiration is around 23. With a PEEP at 15, that gives us a Pep (exp) of -8. That likely represents a fair bit of atelectasis/derecruitment. Here are some measurements:



Her dynamic compliance is 21, and static 24. Not too great. Her PV loops are interesting, certainly not showing any over distension (the penguin beak look), and, as Jon Emile Kenny (@heart_lung) cleverly explains about the Pop tracing:

“On this patient, the stress index appears to be low, which is somewhat consistent with your Ptp tracing. there is a terminal fall in the Ptp [wave looks like an upside down U] which suggests terminal airway recruitment; that is, during the terminal portion of the breath, the Ptp is falling with equivalent volume delivered [again only works with square-wave/constant flow]. in other words, if [at the end of the breath] less Ptp is needed to accommodate equivalent flow/volume, there is terminal increase in compliance/decrease in elastance – or lung units are recruitedSo these numbers suggest that there is extrinsic compression of the lung, due to chest wall weight and abdominal pressure. This makes the airway pressure (Paw) not representative of alveolar stretch, and hence not a good guide of ventilation. The PEEP, despite being fairly high, is below the level needed to prevent atelectasis.”

Indeed Jon, that appears to be the case.

So we started to raise the PEEP, trying to get the Ptp (exp) closer to zero:





So we can see that our Ptp (exp) is approaching zero, and the PV loops suggest there is still no over distension. In fact, the compliance, as Jon had predicted, improves slightly. The plateau pressures are up into the mid 40’s which, without a balloon, would be pretty concerning. But the Ptp (insp) is less worrisome, in the mid 20’s, about at the limit we’d like.

At this point, still seeing that increasing compliance, we continue raising the PEEP to 23, and actually see the plateau pressures start to drop, consistent with having recruited lung. Now the Ptp (insp) is 23, and the compliances have increased.




We thus leave things as is, and by the next morning, we are down to 30% FiO2. Here are the before and after CXRs:


So a fair bit of her “ARDS” was actually atelectasis related to obesity and increased intra-abdominal pressure, and that what seems like exceedingly high PEEP is actually just enough to prevent atelectasis.


Love to hear from others who use the technology, or just interested!





N=1 Principle in ARDS and esophageal pressure directed mechanical ventilation. #FOAMed, #FOAMcc

So i recently came across a review on esophageal pressure-guided ventilation in ARDS, which is in fact a technology I’ve had in my shop since 2008, but rarely use.

The truth is that I haven’t seen much “ARDS” in the last years, and I believe quite strongly that this reflects simply our hospital’s increased awareness of the nocive effects of over-zealous fluid resuscitation. Although in the ICU we still admit patients who, in our opinion, have received a bit more fluid than they should have, we have become more aggressive with diuresis “despite” the presence of shock, and usually see “ARDS” resolve. This is a direct consequence of actually “looking” at our patients’ volume status using ultrasound (for more see, well…most other posts on this blog!).

However, what seems like genuine ARDS does come around once in a while, and we recently had severe respiratory failure develop in a morbidly obese patient, and all of a sudden, in the presence of an FiO2 of 100%, a PEEP of 14, intra-abdominal pressures between 20 and 25, and on Flo-Lan, it seemed it might be a good idea to tailor ventilation.

Current Practice:

The most common practice currently is the ARDSnet type low volume (5-7ml/kg) lung protective ventilation, using a PEEP/FiO2 scale and aiming for plateau pressures (Pplat) below 30. Generally speaking a good idea, but one has to understand that this is, once again, a one-size-fits-all (except for the per kg) approach, which isn’t ideal if you try to follow  the N=1 Principle.

Why is this?  Because, due to physical characteristics (obesity, chest wall stiffness, etc,) and pathology (increased abdominal pressure, etc), the airway pressure reflects the respiratory system pressure (Prs) rather than the transpulmonary pressure (Ptp), which is the variable most related to volutrauma (which has eclipsed barotrauma as the mechanism for most ventilator-induced lung injury (VILI).  Ptp essentially relates to overdistension, which is what results in pneumothoraces. In terms of parenchymal micro-injury, it seems to be most related to atelectrauma, in essence the opening and closing of alveoli, with the resultant shear forces disrupting surfactant and cell surface. This type of injury relates best to finding optimal PEEP to both recruit and prevent de recruitment – in effect minimizing the amount of lung tissue collapsing and reopening.


Esophageal pressure (Pes)-guided Practice:

So Pes is used as a measure of pleural pleural pressure, and:

Ptp = Paw – Pes

That equation is the central tenet to this, and basically, you have to reset your goals to:

a. Ptp (exp) around zero – optimal PEEP – (meaning no over distension and no de-recruitment)

b. Ptp (insp) below 25 – though this is not really individualized as a hard data point, but has been shown to be a reasonable cutoff for volutrauma.


How do you do this?

By slipping in a special oro/naso-gastric tube with a balloon connected to the ventilator, one is able to simultaneously measure airway pressure (as is standardly done) and esophageal pressure. This is what it looks like:


Here we can see that this patient has a PEEP of 20 (top), a Pes of about the same, and thus a Ptp (bottom) near zero.

We’ll discuss this case hopefully tomorrow, but just to show the mechanics/technique of it.


Bottom Line:

So this involves tossing out the ARDSnet charts and trying to individualize and optimize Ptp (insp and exp) instead of plateau pressures and PEEP.  How may it be useful clinically? Well, you may be able to detect unsuspected states of de-recruitment/ateletasis due to excessive chest wall or abdominal pressure, and allow you to increase PEEP “safely.”

When should I use this?

I’m not sure what everyone else is doing, but we are in the process of setting up a protocol where esophageal balloons will be inserted for any patient whose ventilator settings are approaching or exceeding FiO2 70%/PEEP 15, indicative of sufficiently severe respiratory failure warranting this additional level of fine-tuning.

I tend to use it when ventilating two groups: those with (a) elevated intraabdominal pressure, and (b) the obese patients, as they often have elevated Pes (usually due to diaphragmatic displacement. Interestingly, the correlation between obesity and Pes is not very good, so one should not “blindly” feel they can crank up the PEEP to 25 and ignore plateau pressures, as some obese patients have normal Pes (likely due to compliant abdominal walls.

Would love to hear what others do.


Here are the relevant articles/references: