It's silly but there's something called SILI , and some studies show it may be more about the transpulmonary pressures, not the airway driving pressure, that seems to contribute to lung injury. That along with PEEP and respiratory rate, but probably to a lesser degree.
I think there is some possibility / element of self-injury with excessive volumes coupled with high rates, although the evidence is in animal models. That being said, there is generally a reason why a patient is sucking a liter per breath, and many times it needs to be addressed. So, here is my stepwise algorithm for the OP, and it has served me pretty well so far:
1) Does the patient have a pathological reason to need a massive minute ventilation? The most common example would be severe metabolic acidosis that needs respiratory compensation. If yes, then I generally use PSV and let the patient have high tidal volumes and rates. Trying to control tidal volumes in these people may give you a dead patient since you can rarely match their minute ventilation with rate during ACV or SIMV, and there is very little pH room in patients who already have alien blood. Those high tidal volumes for a few hours while you address the acidosis are a necessary evil. If the RASS is creeping above 1, then I use ketamine or non-bolus dexmedetomidine to provide mild anxiolysis and analgesia without depressing their respiratory status. However, a pH of 6.8 is often more than enough sedation. You can proceed to steps 2 and 3 below if they don’t improve once the pH is above 7.2.
2) Is there a painful process that needs to be address? Sometimes it’s obvious like the linebacker orthopedist tugging on a fracture; other times much less so. For example, a massively swollen tongue pictured above being pinched by an ET tube against teeth probably hurts like a motherf**er. Thus, I generally start with a “opiate-first” strategy in all these patients even if I don’t see an obvious source for severe pain. It doesn’t need to be fancy but it needs to be meaningful, so I use a real dose of fentanyl (1-2 mcg/kg), morphine (0.1 mg/kg), or dilaudid (1-2 mg) and see how they respond.
3) Is there an agitation or anxiety issue that needs to be addressed? Is this large tidal volume associated with a high RASS? My “go to” these days is dexmedetomidine (yes, I’m aware of SPICE 3) without a bolus, but I’m not opposed to Propofol, ketamine, haldol, etc. Having said that, if we are getting to the 5 and 6 hour point on real doses of dex plus an opiate and the patient is taking massive volumes at a high rate, then I generally switch over to propofol at high doses and put the patient on PRVC or ACV. This is so I can gather my thoughts on what I might be missing and start slowly weaning the sedation to see if the patient wakes up without those massive volumes. Going back to the angioedema tongue guy above, put him down deep with propofol and ACV for for 24-48 hours while the swelling improves, then wake him up and extubate - far preferable to chasing your tail with PSV if he is not tolerating it. Having said that, the vast majority can be addressed at step 1, 2, or early 3.
I hope this helps and Happy New Year everyone.
