Low Tidal Volume Strategy: Why You Can’t “Set it and Forget It”
In recent years, some studies have shown that higher tidal volumes for mechanically ventilated patients can be detrimental to their health, and possibly cause lung injury. It’s become standard practice to implement a low tidal volume strategy for all patients requiring ventilation, specifically 6 mL/kg of predicted body weight.
Pulmonologists from the University of Rochester Medical Center and Strong Memorial Hospital understand the importance of protecting the lungs. They also note that strict, unquestioning adherence to low tidal volume strategies may be a hindrance to practicing good medicine. Critical care specialists Caroline Quill, MD, and Anthony Pietropaoli, MD, advocate for making evidence-based decisions in individual patient care.
Why shouldn’t there be strict adherence to a low tidal volume ventilation protocol?
Quill: It has really become gospel, 6ml/kg. I think it is easy to lose track of normal physiology and what the evidence base really is. Most people believe that it was less that 6ml/kg helped people; it was 12 that hurt. There is absolutely a time for low tidal volume ventilation but there are also times where you should be a bit more liberal with tidal volumes. We can’t get stuck into thinking that there’s only one way of doing things.
Pietropaoli: You have to carefully assess your patient at the bedside and make adjustments for that individual patient. That’s where protocol gets us in trouble. Every patient is different, so the “right way” is different for every patient. The more unsure providers are, the more they rely on protocol. The problem is, that falls apart when you go to an individual’s bedside.
Where do you start with your own patients?
Quill: Targeting low plateau pressure for all patients is a good starting point, but if you have to do a lot in terms of sedation, neuromuscular blockade, etc., to get a patient to that point, you need to do a gut check about whether that patient is going to hurt themselves on the ventilator if you don’t do these interventions. Low tidal volume is a smart place to start, but it can’t be the end of your thought process, particularly if your patient does not have ARDS.
Pietropaoli: I would argue that it was a false dichotomy when it came to 6 versus 12 mL/kg. These two widely disparate tidal volumes may have been chosen by ARDSnet investigators because they wanted to scientifically prove that tidal volume mattered. They did prove that, but in a way that picked two extremes of tidal volume, especially the 12 ml/kg tidal volume, that weren’t really practical. We need to recognize that it’s a continuum of lung stretch that’s manifested by tidal volume combined with airway pressure. We need to be sure, like Dr. Quill said, and do a gut check. It shouldn’t be 12, but it doesn’t have to be 6; it’s a continuous, not a dichotomous, problem.
Did you have a specific case that made you feel strongly about this?
Quill: I had a patient with really severe ARDS from diffuse alveolar hemorrhage and a new diagnosis of lupus. He had been on low tidal ventilation, targeting a plateau pressure of less than 30. He was on high doses of sedation and neuromuscular blockade in order to achieve this. When he was weaning off mechanical ventilation, I took over his care. In the days leading up to this, as his sedation weaned and his ventilator settings decreased, he was taking larger tidal volumes, like 8 to 10 mL/kg, and his mechanics were great. When he would pull these volumes, his previous physicians kept sedating him to prevent him from pulling larger volumes even though his lung mechanics were fine. They had great intentions and thought they were doing the right thing, but I think this is an example of adhering to low tidal volume ventilation when it is no longer strictly indicated.
How do you approach this topic with residents, fellows, and APPs?
Quill: Our focus during the pandemic was to teach them lung-protective ventilation. I try to instill in them that it’s more nuanced than that, it’s more than “set it and forget it.”
Pietropaoli: I teach them that it’s day by day and you need to be by the bedside to assess. Low tidal volume makes sense in most cases and saves lives, there’s no question, but you have to talk about why a patient is on continuous sedation? Why are they still paralyzed? These downsides may outweigh low tidal volume, especially once the respiratory failure is resolving. It has to be a discussion. I hope we’re teaching them the nuances.