Sunday, July 21, 2019

Move Over Feckless Extubation, Make Room For Reckless Extubation

Following the theme of some recent posts on Status Iatrogenicus (here and here) about testing and treatment thresholds, one of our stellar fellows Meghan Cirulis MD and I wrote a letter to the editor of JAMA about the recent article by Subira et al comparing shorter duration Pressure Support Ventilation to longer duration T-piece trials.  Despite adhering to my well hewn formula for letters to the editor, it was not accepted, so as is my custom, I will publish it here.

Spoiler alert - when the patients you enroll in your weaning trial have a base rate of extubation success of 93%, you should not be doing an SBT - you should be extubating them all, and figuring out why your enrollment criteria are too stringent and how many extubatable patients your enrollment criteria are missing because of low sensitivity and high specificity.

The excellent trial by Subira et al1 provides pivotal guidance for clinicians liberating patients from mechanical ventilation.  Good research often raises more questions than it answers, and this trial is no exception.  92.5% of patients passed a spontaneous breathing trial (SBT) in the pressure support ventilation group.  This percentage is so high that a rational clinician using the threshold approach to decision making2 may forego SBT altogether and extubate all patients meeting inclusion criteria.  Even if the failed extubation rate in the 7.5% of patients who were not extubated after the SBT were fivefold higher than those who passed had they been extubated (i.e., 55% rather than 11%), the overall failed extubation rate would rise to just 14.4% (83/575), lower than the average rate reported in most studies3.  This situation calls for attention to be refocused on the inclusion criteria which determined the pre-test probability of passing the SBT.  In this study they were stringent and, as has been customary for many decades, have an inherent omission bias4.  If we would not intubate a patient for a systolic blood pressure of 180 mmHg, or an FiO2 >0.4, why would we fail to consider them for extubation on that basis alone?  While stringent criteria increase the probability of successful performance during an SBT, they also increase the probability that patients will remain on mechanical ventilation who could breathe on their own were they allowed to do so.  The nearly identical rates of failed extubation in the two study groups suggests that when the pre-test probability of successful extubation is very high, increasing the severity of the SBT test merely serves to misclassify patients as being incapable of unassisted ventilation.  Given this, it is natural to ask whether the SBT itself, rather than aiding in the prediction of successful spontaneous ventilation, only reduces the number of patients who are given the opportunity. Thus one thing the trial of Subira et al teaches us is that the SBT may be among those tests that is not always indicated because clinical pre-test probability assessment alone leads to decision thresholds being crossed5.  More work is needed to evaluate the screening criteria used to determine eligibility for performance of an SBT, and what is the true ability to breathe spontaneously among patients who fail an SBT and are denied the chance to prove the result wrong.

1. Subirà C, Hernández G, Vázquez A, et al. Effect of Pressure Support vs T-Piece Ventilation Strategies During Spontaneous Breathing Trials on Successful Extubation Among Patients Receiving Mechanical Ventilation: A Randomized Clinical TrialEffect of Pressure Support vs T-Piece Ventilation on Successful Extubation of Mechanical VentilationEffect of Pressure Support vs T-Piece Ventilation on Successful Extubation of Mechanical Ventilation. JAMA 2019;321(22):2175-82. doi: 10.1001/jama.2019.7234
2. Pauker SG, Kassirer JP. The threshold approach to clinical decision making. N Engl J Med 1980;302(20):1109-17. doi: 10.1056/nejm198005153022003 [published Online First: 1980/05/15]
3. Krinsley JS, Reddy PK, Iqbal A. What is the optimal rate of failed extubation? Crit Care 2012;16(1):111-11. doi: 10.1186/cc11185
4. Aberegg SK, Haponik EF, Terry PB. Omission bias and decision making in pulmonary and critical care medicine. Chest 2005;128(3):1497-505. doi: 10.1378/chest.128.3.1497 [published Online First: 2005/09/16]
5. Pauker SG, Kassirer JP. Therapeutic Decision Making: A Cost-Benefit Analysis. N Engl J Med 1975;293(5):229-34. doi: 10.1056/nejm197507312930505
Scott K Aberegg, MD, MPH
Meghan Cirulis, MD
The University of Utah School of Medicine

Alas, the title of this post is partly a facetious pun - while it may superficially appear to be reckless to extubate a patient without performing an SBT, it is far from it.  It is a rational approach to the decision if the base rate is high enough.  True recklessness is leaving patients intubated longer than necessary as a result of omission bias and fecklessness.

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