Double Triggering and Ventilator Asynchrony/Dyssynchrony

Let’s start off by defining double triggering. No, it’s not saying two things interpreted as inflammatory to someone back to back while they lose their minds. These are strange times we live in. I digress. Double triggering is something that occurs to patients who are mechanical ventilation. The lay person would interpret this as the patient fighting the vent. It’s a type of dyssynchrony after all. Many of us have seen plenty of this during the pandemic. I must disclose that their post is not going to be a nitty-gritty evaluation on how to fix these problems. There are better definitions out there than the one I have provided.

Double triggering is what we see when a patient takes a breath on the ventilator, they get their set I-time breath, and as that breath finishes, the patient takes another breath. Then the pressure alarms lose their minds and everyone does as well. There is either a very short or even no expiratory time. Why is double triggering a problem? Well, the pressure alarms are causing us to lose our minds because the patient just got a bunch of tidal volume force into their lungs. When they double trigger, another x amount of tidal volumes gets forced into their lungs on top of what was already there. Not good. Breath stacking is another term you may have heard. Here is a great resource much better than what I will provide: Deranged Physiology.

When this happens, the typical workup includes checking a blood gas to make sure that we are meeting the ventilatory demands of the patient. People often overlook the titration of the I:E ratio to where we need to provide the correct amount of ventilation to our patients. I am not going to dive into vent modes here because that is a completely different can of worms but an assist-control/volume control where the patient does not have to tug, so-to-speak, on the ventilator. We are all (mostly) using lung-protective strategies to avoid barotrauma so the set tidal volumes are reflective of their ideal body weight.

The respiratory rate is something else that can be tinkered with. But even after the best tinkering we can do, there are still issues with double triggering. This is where our nursing staff comes in an increases the sedation to a RASS of -4 or -5 and, at times, begrudgingly, we reach for paralytics. Sigh. Reaching for paralytics means we lost in my book because of all the associated consequences.

But what are the consequences of double triggering to our patients? What are they trying to tell us? How do we fix it? Yesterday, there was a paper published in Critical Care Medicine out of Brazil titled “Clusters of Double Triggering Impact Clinical Outcomes: Insights From the EPIdemiology of Patient-Ventilator aSYNChrony (EPISYNC) Cohort Study”. Unfortunately, this paper is hiding behind a paywall so you cannot read it for yourself and may have to trust me. Since that is the case, rather than go through the details which you can follow along on, I will just tell you what we initially suspected about double triggering but now know. It is bad and leads to serious consequences.

Yeah, we see double triggering quite often. But there’s a difference between occasional double triggering and a significant amount of double triggering as defined in this paper. In those patients who had a “high cumulative duration of clusters” they found:

  • Longer duration of mechanical ventilation (all-comers, p<0.01)
  • Longer duration of mechanical ventilation (in survivors, p<0.01)
  • Fewer ventilator free days (p<0.01)
  • Longer ICU length of stay (p=0.02)
  • Higher ICU Mortality; 28% vs 67% (p<0.01)
  • High Hospital Mortality; 39% vs 73% (p<0.01)

Here comes the chicken or the egg part, though. It was really disappointing that this part was in the supplement rather than the actual article. This included the fact that in the baseline characteristics those patients who had more issues with double triggering had a baseline arterial pH of 7.16 vs 7.36 in those who had fewer episodes of double triggering (p=0.02). In addition, although not statistically significant (p=0.065), the PF ratios were 213 vs 150. The baseline pCO2 was also almost different from the get-go as well (p=0.052) at 42 and 49 in the low cumulative and high cumulative duration cluster groups respectively. Again, I wish they didn’t bury this in the supplemental table. This is important to know up front because we all know that sicker patients, as noted here, have worse outcomes.

When I read papers like this I wonder how is this going to change my practice. In this case, I do not think this paper offers very much. I could be wrong, after all this is my blog post and I can write what I want since none of this is medical advice. If they were able to tease out a particular vent setting, sedation strategy, or management pearl to help us avoid double triggering would be great. Instead, and again I am not trying to be too harsh on these folks because it is a very cool article. We have learned that sicker patients have worse outcomes. Or perhaps I missed something. Fix the underlying problem and fast. I obviously cannot dissect every nuance of the study. I still tip my hat to the authors for their fantastic efforts in trying to tease out data regarding double triggering.

Here’s what we grossly need to do to fix double triggering: correct the underlying problem, be very diligent and methodical with our ventilator settings, and sedate the patients accordingly. Here are some additional blog post that I have created about mechanical ventilation.

Sousa MLEA, Magrans R, Hayashi FK, Blanch L, Kacmarek RM, Ferreira JC. Clusters of Double Triggering Impact Clinical Outcomes: Insights From the EPIdemiology of Patient-Ventilator aSYNChrony (EPISYNC) Cohort Study. Crit Care Med. 2021 Sep 1;49(9):1460-1469. doi: 10.1097/CCM.0000000000005029. PMID: 33883458.
Link to (NOT FREE) Article

Vitrag H Shah, Arijit Samanta, Sumit Ray. Patient-Ventilator Asynchrony: Etiology and Solutions. Indian Journal of Clinical Practice, Vol. 31, No. 8, January 2021.
Link to Article

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double triggering