Critical Care Mailbag - Induced Hypothermia - Airway Intubation Ventilation

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Chris C., M.D. -

Hi guys.
I think this piece should have been re done or at least an addendum added post the TTM trial. You are going to have a lot of people confused re how they should be managing post arrest patients: "But Scott Weingart said on EMRAP this month ..."

EMCrit -

EMRAP pieces are done a couple of months in advance; that is just the nature of the beast. Mel put out a weekly update talking about TTM. If you are not subscribing to those, you should. That's where all cutting edge stuff goes out and they are great. Luckily all TTM changes is what you set your machine to. Rob and I of course recorded another one of these addressing TTM, which you will have beamed to you v. soon.

Christopher R., M.D. -

I don't understand EVERY time we hear about vent settings you hear 6-8 ml/kg. BUT it isn't really their actual weight it is their ideal weight based on height. Wouldn't it be MUCH easier to just cut out the middle man and dose ventilator volume based on height?? I think that we have to blame the metric system for this complication. US physicians are comfortable using kg for weight (mass) but not cm for height. Someone needs to make this easier then "well they are about 5'6" give them 450"

EMCrit -

It may be if that was the only reason you would want an IBW, but so much of critical care is predicated on it that you may as well figure it out up front. Essentially, you want three weights in critical care:
Their premorbod actual weight
Their current weight
In the ED, the 1st and 3rd are usually the same, in the ICU they diverge.

not sure how it could be easier, then he is an average height man, use 70 kg, average size woman, give 60 kg. Shift from that based on unique body makeup.

Trent W. -

Great segment. Much appreciated.

This might be somewhat of a belated point with the TTM trial now out and some institutions changing their goal temperature. Still, quite a few centers are staying with 33 degrees as a goal temp (there are some decent arguments on both sides of that), so it probably does still matter; so, I’ll just toss this out there (note: it’s somewhat off-hand).

If you’re in an isolated setting and you are transferring a post-arrest patient, it is presumably to a place that should start TTM. Is there any evidence that initiating hypothermia prior to getting them there will be helpful (provided you can get them there within 4 hours or so of ROSC)?

I ask because, from what I can tell, it looks like earlier initiation is probably better in very controlled environments NOT similar to the ones discussed in the segment (animal studies, cooled only by an endovascular device in Germany, etc), but it hasn't panned out in more practical settings (ex. prehospital, Italian ICE study, etc), which might show a trend toward harm. The HACA and TTM trials had a goal induction of within 4 hours (I think the mean time to target temp in the HACA trial was like 8 hours or something).
I do worry that we'll end up starting cooling that isn’t well-controlled. Wide temperature swings (in the form of cooling, accidentally rewarming, then trying to cool again) might be bad for what is essentially a brain-injured patient, and might be harmful from a hemodynamic/metabolic standpoint as well.

No proof, here, but this does seem more likely to happen if patients are handed across multiple care environments and multiple providers. There are other parameters that might benefit form closer monitoring during hypothermia too, and some can’t be watched in transport.

I wonder if we could just say that, in regards to temperature control in isolated settings, even if you’re transferring to a place that will cool them to 33 degrees, you don’t have to start the hypothermia in your ED. As long as you can get them to that center within 4 hours, just make sure they don’t have a fever and defer any induced hypothermia until it can be started in a more controlled fashion. If you do this, you are practicing according to the evidence we have, and you might be avoiding harm.

I have zero expertise here. Any disagreement is very welcome.

EMCrit -

Here's what we know--super early cooling added no benefit
In animals waiting too long is bad
36 looks to be as good as 33
So for an outside hospital transferring, I think it is a brilliant strategy to do mild cooling to 36 (maybe 1 liter cold saline) and then let the receiving center choose to keep them there or take them down to 33 when they arrive

Trent W. -

excellent, Sir, thanks!

I will note that most post-arrest pts do come in between 35-36 (I think that might have been part of the rationale for the TTM trial's target), but will probably drift up as perfusion improves and they start to shiver.

I figure most folks won't require IV cooling initially - just exposure, shiver control (would paralyze most), + ice packs? probably decent to have cold saline on stand by just in case.

Makes TTM in isolated areas very workable.

much appreciated!

Andrew B., MD -

Sorry I'm a month behind the times, but I had a thought while listening to the segment on ventilator vs. BVM during CPR. While I'm pretty darn sure there're no data on this, what do you think about setting the ventilator to something like 10 or 20 cmH2O of CPAP (ie, no set tidal volume or respiratory rate at all) during CPR? The chest compressions would provide ventilatory tidal volume with chest recoil perhaps augmented a bit by the positive airway pressure.

I suppose the concern would be that constant positive intrathoracic pressure would impair venous return (especially in the hypovolemic patient), but rattling around in my inexpert mind, the concept seems to have some merit. Might I be on to something, or am I in the classic resident position of knowing just enough to be really dangerous?

EMCrit -

For exactly the reason you mention, probably not a great way to go. We want no pressure (and perhaps negative pressure NEEP) in between ventilations rather than PEEP. This is to augment return to the heart during the off phase of compressions.

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