These are notes that I made of Dr. Weingart’s outstanding podcast just so I could quickly review it when I needed to. I’ve done my best to make sure it accurately reflects what Dr. Weingart said.
But for safety, you need to carefully listen to Dr. Weingart’s podcast at least once (I think it is really worth listening [like all his podcasts] several times). And you need to review the Shownotes for his podcast and be sure to read all the thoughtful reader comments and Dr. Weingart’s responses to the reader comments.
So here is the podcast:
And here are my notes of Dr. Weingart’s remarks:
This is the EMCrit podcast number three.
Today we talk about a question raised by one of my residents: Which is – how to go about intubating a patient with a severe metabolic acidosis.
And he actually sent me a case.
The patient has a case of severe metabolic acidosis [from diabetic ketoacidosis].
The patient is obtunded patient [and is getting respiratory fatigue]
He has an ABG pH of 6.65 (wow!), a PCO2 of 18, and a bicarb of 5.
The patient’s mental status is worsening and [his physicians] made the decision to intubate the patient.
And the question was how to go about doing this in the safest way possible because if you screw this one up and they get a little more acidotic because they lose their respiratory compensation they’re going to have severe cardiac dysrhythmias.
So the first question that comes up is should you give sodium bicarb to try to alkalinize the patient’s blood prior to the intubation.
I don’t have a problem with administering it but it’s probably not going to help that much because the way bicarb works is it takes hydrogen and metabolizes it to CO2.
And these patients are already trying to blow off all all the CO2 they can and unless they blow off the additional CO2 generated from the bicarb they’re not really changing their pH.
Now what bicarb will allow to happen is some of that intravascular acidosis will transferred intracellularly and that might buy you a little time and it might buffer your plasma somewhat.
So if you want to give it great but I wouldn’t look to it towards a real solution to the problem.
So let me tell you how I go about intubating these patients.
First let’s talk about what you need.
You need a noninvasive mask, a BiPAP mask.
You need a ventilator, not a noninvasive ventilatory machine (not a BiPAP machine) you need a real ventilator brought to the bedside.
You need someone who knows how to work that ventilator.
That person might be you; it might be a respiratory therapist but it needs to be someone who is familiar with the dials and can change them in real time.
You need all your normal intubation stuff and the meds to go along with it and if available you can really benefit from having waveform CO2 monitoring available [this was said back in 2009 – – now there’s no excuse not to have it]
The first thing you’re going to do is place the patient on pseudo-noninvasive ventilation.
I say pseudo- because you’re doing it with a ventilator.
The ventilator might not be specifically set up for noninvasive ventilation but it’ll be just fine for what you’re doing here
So you take your normal ventilator and you put it on SIMV mode, a mode we’re not usually using in emergency medicine.
SIMV mode just means the patient can take spontaneous breaths that are not going to be machine controlled; so essentially it’s going to allow you to simulate noninvasive ventilation
You place the machine on a title volume of 550 and FI 02 of 100% and you to change the flow rate to 30 L per minute.
Now we don’t talk about flow rate much in emergency medicine.
What flow rate is – is it determines how quickly the breath is delivered.
And you want nice slow breaths because you to be using these breaths on a patient was not yet intubated and it’s going to be going through that noninvasives mask.
And you do not want to insuflate the stomach so you want a nice slow breath.
And 30 breaths a minute will put a breath in over the course of about a second.
Normally we’d be putting breaths in over less than half a second so these are nice slow breaths.
You to put the peep to five and the pressure support between five and 10
[Altho I don’t think Dr. Weingart mentions this in the podcast, I believe that you will want to change the flow rate to at least 60 liters per minute once the patient has been intubated to allow for adequate expiratory times when you change the ventilator rate.]
Then here’s the most important part at this point [of setting the mode to SIMV].
You can to change the respiratory rate while on [SIMV] to zero or as low as your ventilator will allow you to take it.
Now you put on that noninvasive mask and you attach an end-tidal CO2 quantitative waveform device and you attach the ventilator
Now they are breathing on noninvasive ventilation.
What this allows you to do is to preoxygenation them.
It is a fantastic preoxygenation device.
I use it for a lot of my patients who are already hypoxic before intubation but what you’re also getting is ventilatory support
Usually the reason you’re intubating these patients as opposed to letting them breathe on their own is that their flagging; that is, they’re getting tired.
They can’t really maintain anymore so this is going to allow you to have a buffer.
[This will] allow you to knock down that CO2 before you even intubate them by placing them on noninvasive ventilation
What you want to do is see what kind of end-tidal CO2 is your baseline.
And that’s the value that you try to keep them below at all times.
Now end-tidal CO2 is not a perfect surrogate for PaCO2 so it’s not been a be perfectly accurate but it’ll give you something to work with to make sure that end-tidal CO2 does not rise.
So generallyI’ll leave them on this noninvasive set up for a few minutes as I get my stuff together and now I’m actually ready to innovate the patient
So will push our RSI meds will give it 10 seconds or so for the patient to start getting the beginnings of sedation going
And at this point I have my respiratory therapist (or I do it myself) I turn the respiratory rate to 12 and I perform a jaw thrust.
[The reason that] this is good to do is [that] your patient will continue ventilating during their apneic period.
Now this is not classic RSI.
RSI would have you giving no ventilation’s during this apneic.
We’re not interested in just oxygenation in these patients.
In these patients we’re [also] interested in ventilation.
Now the beauty of using the ventilator rather than a BVM is that these are nice slow controlled breaths
They’re not epinephrine motivated squeezing the bag really rapidly and hard and now the patient’s stomach is insuflated.
We’re giving the patient the best chance of not having any gastric insufflation these are nice slow controlled breaths
You are perform a jaw thrust your to maintain that patent posterior passage of air
So I just thrust a jaw into my BiPAP mask and this takes the posterior for Angels ruptures off of the posterior aspect of the throat and allows passage for their
I’ll wait a total of 45 seconds for succinylcholine to make sure that we have full paralysis.
If using rocuronium, wait a full minute.
Now the person who should intubate this patient is the most experienced operator available.
This is not the time to allow an inexperienced resident to intubate this patient because you want first pass success.
You don’t want this patient to spend any time more than necessary at these lower respiratory rates.
So for first pass success you want a quick rapid intubation
At this point you attach the ventilator
You confirmed to placement by checking end-tidal CO2 and you would immediately increase the respiratory rate to 30.
[And I believe that you will change the mode from SIMV to A/C and change the flow rate to 60 liter/min. Again, I don’t think Dr. Weingart speaks to this in the podcast. In all cases of this sort I would be reviewing the ventilator settings with the intensivist who will ultimately be caring for this patient.]
And then change the title volume to 8 mL per KG of predicted ideal body weight. Ideal body weight just that means you look at the patient type and you guess what their ideal should be regardless of their actual weight
Now why 30 breaths per minute.
To maintain eucapnia, to maintain normocapniayou need 60 mL per KG per minute
As soon as you intubate the patient because of the additional dead space that number changes to 120 mL per KG per minute
That’s just a stayed PCO2 of 40.
We want to knock this patient down to at least 20
You have to double that again to 240 mL per kilogram per minute
Now if you’re giving the patient 8 mL per kilogram per breath that leaves 240 divided by eight or 30 breaths per minute to get the title volume you need.
So if you have an average 70 K patient place them on about 550 title volume
30 breaths a minute and you’ll get that magic 240 mLper KG per minute to maintain a half thing of their normal CO2 PCO2 of 20 which is where we want this patient to wind up.
Now look up at your monitor and check your end-tidal CO2.
You’ll want to make sure it’s at least as low as when you started.
If it’s not, increase that respiratory rate even more.
And you might want to verge up a little more on your title volume if necessary
Even if the end-tidal CO2 is less we told you that the end-tidal CO2 is not a perfect surrogate
So you need to check an ABG to make sure the pH is not dropped and that the CO2 has not risen
And at this point you can pat yourself on the back; you saved the patient’s life.