Here is the link to Dr. Weingart’s site EMCrit.
These are notes that I made of Dr. Weingart’s outstanding podcast, EMCrit Podcast 19 – Non-Invasive Ventilation February 5, 2010 , so I could quickly review it when I wanted to[this link is to the podcast and show notes]. 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.
And here are my notes of Dr. Weingart’s remarks:
There is much confusion about the terms used for noninvasive ventilation.
This is a therapy that can stave off intubation and that can turn patients around in front of your eyes.
Therefore, it’s really important to have a great understanding of this therapy.
The terminology out there makes the subject more confusing than it needs to be.
People talk about CPAP versus BiPAP and they talk about IPAP and EPAP.
Here’s what comes down to:
If you have a machine and you’re interfacing with the patient through a mask then you’re using noninvasive ventilation.
If you’re interfacing with the patient with an ET tube then you are using invasive ventilation.
The reason to use noninvasive ventilation as the term is because it embraces all the different settings that we can use with this technology.
And you pick your patient’s settings on the noninvasive ventilator based on the patient’s needs just as you would if the patient was invasive ventilation.
Each patients can have different settings and there is really no radical difference between BiPAP and CPAP.
Those terms are really antiquated.
So let’s start off with the most basic mode and that is essentially PEEP. It is positive end expiratory pressure.
If that’s the only thing you’re doing then by rights this is called CPAP which is continuous positive airway pressure.
And the above just means that there is one setting for the entire respiratory cycle whether they’re breathing in or whether They are breathing out, they see the same pressure.
Now if you have two settings on your ventilator and every time patient takes a breath in the ventilator switches to a higher pressure, well that’s BiPAP.
Because what BiPAP is is a continuous pressure at one level when the patient is not breathing in. And when they breathe in the machine senses that and switches to a higher pressure level.
And you set both of those levels.
So that’s what BiPAP is.
How you set the machine depends on the patient’s needs.
There are two kinds of respiratory failure.
Type I failure is a failure of oxygenation.
And type II failure is a failure of ventilation or too much CO2 [and hypoxia if present in type II ventilation is due to inadequate ventilation].
So, depending on what kind of respiratory failure they have,that is what determines the kind of noninvasive ventilation that they need.
And sometimes they’ll have both types of failure and we can treat that also.
If you patient has oxygenation issues, then they need PEEP. They need CPAP (which is the same thing by a different name).
CPAP (PEEP) fixes oxygenation failure. It recruits alveoli. It increases the matching between ventilation and perfusion. And if you have a pulmonary edema patient it decreases preload and after load.
Basically it does very good things for the patient with oxygenation failure. And you’ll see these good things almost immediately.
And over the course of the next half hour or so they’ll keep getting better as alveoli pop open.
So CPAP or peep is for oxygenation failure. Generally we start the setting at five and we can take it up to 15 if we need to.
Now if you’re using a standalone machine then they’re going to call it EPAP which is the same thing as CPAP or PEEP. All those terms are synonymous.
If the patient doesn’t have a ventilation issue, then they don’t need anything more than that expiratory pressure. Just CPAP is all that they need. So don’t bother adding on inspiratory pressure. They don’t need it. If they have purely and oxygenation problem then it is just CPAP.
Now what kind of patients have just oxygenation problems?
Well, your acute pulmonary edema patients: These patients have no ventilatory problems [as long as they are not tiring out. They have no problem getting air in or out. They just have a problem oxygenating.
Also your pneumonia patients and your atelectasis patients. These are also not ventilatory problems and you don’t need to muddy the water by giving them inspiratory pressure [again assuming that they are not getting respiratory fatigue].
The patients with type II respiratory failure [meaning inadequate ventilation], they are the patients who have problems with ventilation; like your asthma patients, and generally your COPD patients as well.
What these patients really need is inspiratory pressure support. They don’t really need expiratory pressure.
They already have auto peep Because they can’t get air out.
So what these patients need help getting air in.
Now you might saying to yourself that we’ve always learned that asthma is a disease where you have trouble getting air out.
Now it is true that asthma is a disease where you can’t get air out until the point where the patient starts looking like crap [meaning the patients have severe respiratory fatigue] and you think they’re going to need invasive ventilation.
And the problem that those patients have is that they’re so fatigued, their respiratory muscles have done so much work, there’s so much acidosis building up from CO2 increases, that they can’t even get air in. They don’t have the strength.
And when they get to that point that’s when their 02 saturation starts dropping. It’s not hypoxemia respiratory failure. It’s that at that point they’re not even getting in enough air to allow any oxygenation.
If you take these patients and put them on inspiratory pressure support, then they’ll start exchanging gas again. All of a sudden there oxygen saturation is back to hundred percent if you have them on supplemental FI02.
And now the patient is getting their respiratory effort augmented by the machine. They still tell the machine when they need to breathe but the machine helps them get the air in. And they start looking good again.
Same thing for your COPD patients.
So these type II guys just need inspiratory pressure. And that is going to be IPAP on a standalone machine and it’s going to be be pressure support on a ventilator.
Generally I’ll also start that around five and work my way up to 15.
Now most of these machines need just a little bit of Expiratory setting to keep the the masks open. So I’ll put that on two or three and not beyond that.
[So again these asthma and COPD patients just need inspiratory support for their oxygen saturations to improve.]
Now Dr. Weingart discusses some very important but confusing terminology.
On the standalone machines, generally they have an IPAP and an EPAP Setting. And those settings are absolute. They are not in relation to each other. So if you set the IPAP at 10 and the EPAP and five, then that’s exactly what you get. [The IPAP (breathing in pressure of the machine) will be 10 cm of water and EPAP (breathing out pressure of the machine will be 5 cm of water]
When they breathe in they get 10 cm of water and during the rest of the respiratory cycle they’re going to get five cm of water pressure.
Most ventilators do it a little differently. They have pressure support and PEEP. But those settings are additive. The pressure support is actually in addition to the PEEP.
So here’s what that means.
If you put the patient on the ventilator and you set their pressure supportive at five and you put there peep at five here is what happens:
As soon as they take a breath in, they are getting five of pressure support in addition to the five of of PEEP. So what they’re really getting is 10 cm of water when they breathe in and five during the rest of the cycle.
So on a ventilator a pressure support five and a PEEP of five is the same as a standalone machine set at 10 cm over 5 cm.
How To Make Noninvasive Ventilation Work For Your Patient
You need to be able to size the noninvasive mask and fit the noninvasive mask on the patient and you need to be able to set up the ventilator or the standalone machine and initiate the treatment all on your own.
This is because you can’t afford to wait 10 min until the respiratory therapist gets down to the ER [or heaven forbid comes in from home at night].
So the complete technique from start to finish of noninvasive ventilation should be a skill that you as a physician have.
Your respiratory therapists and YouTube videos can help you gain and keep competence in these skills.
And all the different sized masks need to be stocked in your immediate vicinity and again not brought down from somewhere else.
And the ventilator or standalone machine needs to be waiting for you in the emergency depart and not brought down from some where else.
And you personally need to be able to set up the bronchodilator inhalations medicines for your patient. Again your respiratory therapist and YouTube videos can help you gain and keep this skill.
[And finally noninvasive ventilation is for the patient who is alert and able to protect his airway and to breathe on his own. There are rare circumstances where you might use sedation or analgesia in noninvasive ventilation. And Dr. Weingart discusses these rare situations in his podcast.]