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Wednesday, October 2, 2013

Myth buster: Ventilator weaning should be done on minimal settings (no t-piece)

There's truth to the saying: You do the best you can with what you know today, and when you learn better you do better."  No greater place is this more true than in the medical profession.  For, as I once wrote a post "t-peace no more," I must now, based on updated wisdom, reconsider.

Folks, we in the medical profession must always be humble; always open minded.  I say this because a majority of my fellow RTs I have interviewed rarely, if ever, wean by means of a t-piece.  The method of choice is minimal ventilator settings, such as a Peep of 5 and a Pressure Support (PS) of 10.

However, when fellow respiratory therapist K. Scott Richey recently suggested to me that it might be time to bring back the t-piece, I cringed. My initial reaction was, "Are you kidding?" Dogma aside, I read the articles he sent to me.  I am now convinced he is right, or at the least I'm willing to reconsider.  Read on, as I will provide the evidence

The man who posed the idea that a t-piece should be reconsidered is among the most respected physicians as far as mechanical ventilation is concerned.  As a matter of fact, he is the physician who wrote the book on mechanical ventilation. His name is Dr. Martin Tobin.  An editorial written by him was published in the American Journal of Respiratory and Critical Care Medicine in 2012 titled, "Extubation and the myth of minimal ventilator settings."

Dr. Tobin makes the following notes regarding this subject:
  1. The addition of a small amount of pressure support produces surprisingly large reductions in inspiratory work in ventilated patients: 5 cm H2O decreases inspiratory work by 31 to 38%, and 10 cm H2O decreases work by 46 to 60% (8, 9). Nonetheless, most—but not all—patients can tolerate a 30 to 60% increase in inspiratory load at the point of extubation
  2. Some clinicians believe that insertion of an endotracheal tube leads to the loss of “physiologic PEEP,” which is thought to result from intermittent narrowing of the vocal cords. The concept of physiologic PEEP, however, is a myth. Lung volume at end expiration generally approximates the relaxation volume of the respiratory system, which is determined by the static balance between the opposing elastic recoil of the lung and chest wall. Accordingly, static recoil pressure of the respiratory system is zero at end-expiration in a healthy adult. The addition of 5 cm H2O of PEEP can decrease work of breathing by as much as 40% in ventilated patients.
  3. PEEP also produces a substantial increase in cardiac output in patients with left-ventricular failure (13). In patients with heart or lung disease, the elimination of PEEP at the moment of extubation can lead to rapid cardiopulmonary decompensation. As when assessing patients on low levels of pressure support, observing a patient breathe on CPAP 5 cm H2O hampers the ability of a physician to predict the patient’s capacity to handle an increase in cardiorespiratory load following extubation.
  4. The expression “minimal ventilator settings” has become a commonplace, suggesting that pressure support of 5 cm H2O or CPAP 5 cm H2O provides little assistance to a patient. This cliche´ is oxymoronic, analogous to saying that a woman can be minimally pregnant. The increase in cardiorespiratory load engendered by a switch from pressure support of 5 cm H2O or CPAP 5cm H2O to zero assistance at the point of extubation is enough to precipitate a lethal cataclysm in some patients. Because it is difficult to foretell which patients will be unable to cope with an increased cardiorespiratory load after extubation, I check that patients are able to breathe without respiratory distress for about thirty minutes on a T-piece without CPAP before removing an endotracheal tube . (Although less than ideal, an equivalent assessment can be performed through the use of Flow-by—provided that pressure support and CPAP are both set at zero.)
A senior respiratory therapist once told me that the entire goal of weaning a patient from a ventilator is to give them a chance to fail before they are removed from the ventilator. If you create a situation from them where they have to work a little (such as would be the case breathing through the ETT with no support from the ventilator), and they do not fail, then you can feel pretty safe that patient won't require re-intubation.  

Our current policy, based on studies from about ten years ago, suggests that minimal ventilator settings are ideal to make up for resistance of the tubing and physiologic PEEP. Our policy is this:
  • ETT 8.0 or greater = PS of 5 and PEEP 5
  • ETT 7.5 or less = PS 0 and PEEP 5
Dr. Tobiin says that for a majority of patients this would work just fine.  However, he adds: "But here’s the rub. The challenge of clinical medicine is not about taking care of the great majority of patients who do well irrespective of the methods employed by their physicians. Instead, the goal is to take feasible steps that have a high likelihood of circumventing a catastrophe in a small number of instances."

Accordingto  "Tobin argues for true T-piece spontaneous breathing trials on more patients being planned for extubation (and presumably for most or all of those considered to be at higher risk for extubation failure). In his opinion, this method will identify more patients unable to tolerate extubation, compared to SBTs on “minimal vent settings.” (He does acknowledge there’s a lack of evidence to prove this.)" 

Based on Dr. Tobin's editorial, perhaps it's time for the experts to perform more studies in this regard, and, perhaps, it's time for us to revisit our extubation protocols and polities. Personally, my gut feeling is that it would be best for all parties to keep the patient on a ventilator with a PS of 0 and a PEEP of 0, allowing the flowby form the ventilator to make up for any resistance from essentially breathing through a straw.

Or, better yet, let's note what Dr. Tobin says, and use common sense.

Note:  Please refer to the links below for further reading and, of course, follow the links within these links.  

  1. Tobin, Martin, "Extubation and the myth of minimal ventilator settings," American Journal of Respiratory and Critical Care Medicine, 2012, volume 185, issue number 4, pages 349-340
  2. "Tobin: 'Minimal' PEEP and Pressure Support during SBT kills some patients (AJRCCM),",, accessed 9/14/13
  3. Arnaude, Thille, et al, "Outcomes of Extubation Failure in medical intensive care unit patients," Critical Care Medicine, December, 2011, volume 39, issue 12, pages 2612-2618
  4. Tobin, Martin J., "'Minimal Ventilator Settings' and Extubation: Reply," American Journal of Respiratory and Critical Care Mediicne, 2012, volumen 186, number 2, pages 199-202
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K. Scott Richey said...


First, Thank you very much for the mention.

Second, I agree with you on not just throwing everyone on a 'T-Piece' when you can accomplish the same thing with a "ZEEP(Zero End-Expiratory Pressure)trial" with the ventilator.

Third, you mention there is lack of evidence in these trials, yes published evidence which is easy to obtain. Conversely, a abstract was presented this year at the ATS on this topic.

The University of Missouri (Columbia) Respiratory Department has been performing ZEEP trials for a number of years. At the ATS conference they presented 6 years of data, showing how ZEEP decreased their reintubation rates by 4% compared to a standard SBT with Pressure support & PEEP.

The ZEEP trial exposes the patients that are likely to be false positives (De-compensated CHF & severe COPD) on minimal ventilator settings.

troy whitacre. university of mo. healthcare said...

we had always preferred t-piece trials over low support trials for our SBT's. this was to identify a relatively small population of patients with cardiomyopathies and severe COPD that may do just fine with even small levels of peep. during a time of poor staffing we started doing our trials (zeep with no PS)through the ventilator in order to take advantage of the montioring and alarms available and reduce the time needed for setting up the equipment needed for a tpiece trial. zeep with no PS remains our standard for our daily SBT's although who would argue with tobin's preference for tpiece trials as they are most likely the best way to perform them. he is