“I love sleep. My life has the tendency to fall apart when I’m awake, you know?” – Ernest Hemingway

How many times have you participated in this patient care scenario?

“My ICU patient on invasive mechanical ventilation is passing a spontaneous awakening and breathing trial, but isn’t waking up? I’m going to leave the patient intubated until he is more awake.”

I will be the first to admit that I have not only heard others say this but I have also said it out loud myself numerous times that I can remember just in the last few months. I think we have all added our own favorite “additional” criteria to the spontaneous awakening trial/spontaneous breathing trial (SAT/SBT) criteria (1) to assess the safety of extubation for our critically ill adults.  My patient is passing an SAT/SBT, but: they don’t have a strong cough when the in-line suction catheter is passed into the trachea, there are a lot of secretions in the endotracheal tube, they aren’t awake, they don’t follow commands, they look like they have a high work of breathing, etc. Remember, a comatose patient can still meet criteria for passing an SAT/SBT (stable coma is not a failure criteria for either SAT or SBT) (1). These reasons are why the respiratory therapist doesn’t just automatically extubate the patient who passes an SAT/SBT without asking the bedside physician. Again, I’m not criticizing any of these as I have said some of these myself and we can all think of patient scenarios where these sound like perfect logic, but we at least have to admit that with these statements we have gone over the edge of evidence. Until the study of this blog post’s interest (2), we had no evidence that these additional patient assessments made us any smarter about who would fail extubation.

Acutely brain-injured patients may be the best patient population to use to try to start adding evidence to the above patient care scenarios as they isolate the “not awake enough” issue. They are usually intubated for only mental status reasons, mental status is usually the only barrier to extubation once the acute injury is controlled, and they are usually free of the myriad of hemodynamic, metabolic, and infectious issues complicating other patients with respiratory failure. In other words, this may be the purest population to try to answer the question of whether our “not awake enough” criteria makes us any better at safely extubating patients. Give all the credit to the Canadian Critical Care Trials Group for identifying this common practice with a huge gap in knowledge surrounding it and designing the best quality study to date with acutely brain-injured adults.

This was an observational study of 192 acutely brain injured adults that were intubated in 2005, didn’t die on the vent, and didn’t self-extubate. About a third of patients had traumatic brain injury and almost all patients had blood somewhere where it shouldn’t be (subdural, subarachnoid, intracerebral). Of these 192 patients, 40 underwent tracheostomy prior to extubation and 152 underwent at least one extubation attempt. Expectedly, the 40 patients who went straight to trach had a GCS score of 6 and a higher severity of illness. Let’s ignore these 40 patients for now and focus on the 152 brain injured patients where at least one extubation attempt occurred. When these 152 patients passed an SBT, 45 (30%) were still not extubated that same day for reasons of low GCS, no cuff leak, or high PaCO2. Extubation failure rates were similar between these patients where it was delayed (27% failure rate) compared with those who were promptly extubated the same day (19% failure rate, p = 0.27). Delaying extubation was associated with longer ICU LOS, longer hospital LOS, and higher ICU mortality. There was a non-significant increase in the associated risk of pneumonia when extubation was delayed.

Now to the meat of the issue. Of all 152 patients where their doctors tried extubation, 32 (21%) required reintubation in the 72 hours after extubation due to upper airway obstruction, secretions, or low GCS. After adjustment for multiple potential confounders, only three variables assessed at the time of passing the SAT/SBT were associated with future extubation failure: older age, no spontaneous or provoked cough, and an increase in fluid balance. A patient’s GCS at the time of passing an SAT/SBT or at any other time was not associated with extubation failure.

In summary, a strategy of delaying extubation in acutely brain injured patients passing an SAT/SBT is associated with worse clinical outcomes and a patient’s GCS at the time of consideration for extubation is not predictive of future extubation failure. If you are currently saying to yourself that selection bias is the enemy of observational studies, you are warming my heart and are correct. The delayed extubation patients could have been selected for delayed extubation by the bedside doctor as they were sicker in some unmeasured way that the bedside doctors picked up on but the observational study didn’t. So it remains that the delayed versus prompt analysis could also be a sick versus less sick analysis. Additionally, the analysis showing GCS was not predictive of extubation failure included patients with a median GCS of 9, whereas the early tracheostomy patients took out the patients with a GCS of 7. Therefore, it would be difficult to say that GCS is never predictive of extubation failure as the GCS in the less than 7 range (lower end of the IQR included) was underrepresented in this analysis. In other words, if someone now tells me that the patient’s GCS is 3, I still won’t cite this study to support the idea that GCS doesn’t matter regarding extubation failure.

Is this the definitive evidence that we should drop the “not awake enough” criteria lots of us use for extubation decisions in the ICU? Certainly not and this is prime material for a randomized trial to give us a more definitive answer. But I do believe these are the best existing data on this issue and will likely move the needle for me towards extubating more patients passing a SAT/SBT with a cough who remain sleepy but not comatose. The provocative question here is what is the domain, as discussed in Semler’s previous post (Semler’s Domain Discussion), of this study? Do these data apply to the medical patient with respiratory failure? And what about the front end of critical illness: does intubation for “altered mental status”, which is the reason for one third of ICU intubations (3, 4), make much sense with these data?

 

References

  1. Girard TD, Kress JP, Fuchs BD, Thomason JWW, Schweickert WD, Pun BT, Taichman DB, Dunn JG, Pohlman AS, Kinniry PA, Jackson JC, Canonico AE, Light RW, Shintani AK, Thompson JL, Gordon SM, Hall JB, Dittus RS, Bernard GR, Ely EW. Efficacy and safety of a paired sedation and ventilator weaning protocol for mechanically ventilated patients in intensive care (Awakening and Breathing Controlled trial): a randomised controlled trial. Lancet 2008;371:126–134.

 

  1. McCredie VA, Ferguson ND, Pinto RL, Adhikari NK, Fowler RA, Chapman MG, Burrell A, Baker AJ, Cook DJ, Meade MO, Scales DC, Canadian Critical Care Trials Group. Airway Management Strategies for Brain-injured Patients Meeting Standard Criteria to Consider Extubation: A Prospective Cohort Study. Ann Am Thorac Soc 2016;doi:10.1513/AnnalsATS.201608-620OC.

 

  1. Janz DR, Semler MW, Lentz RJ, Matthews DT, Assad TR, Norman BC, Keriwala RD, Ferrell BA, Noto MJ, Shaver CM, Richmond BW, Zinggeler Berg J, Rice TW, Facilitating EndotracheaL intubation by Laryngoscopy technique and apneic Oxygenation Within the ICU Investigators and the Pragmatic Critical Care Research Group. Randomized Trial of Video Laryngoscopy for Endotracheal Intubation of Critically Ill Adults. Crit Care Med 2016;44:1980–1987.

 

  1. Semler MW, Janz DR, Lentz RJ, Matthews DT, Norman BC, Assad TR, Keriwala RD, Ferrell BA, Noto MJ, McKown AC, Kocurek EG, Warren MA, Huerta LE, Rice TW, FELLOW Investigators and the Pragmatic Critical Care Research Group. Randomized Trial of Apneic Oxygenation during Endotracheal Intubation of the Critically Ill. Am J Respir Crit Care Med 2016;193:273–280.

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