CPAP in ASTHMA? Absolute contraindication?

[OzAmbo]

Bare in mind that merely saying COPD you're referencing two common and yet very different diseases: Emphysema and Chronic Bronchitis.

I intentionally stated COPD specifically because it is a disorder consisting of the two diseases listed.

 

[zmedic]

With COPD/Asthma, there is air trapping which translates to auto-peep. The auto-peep creates a positive pressure in the terminal airways at the end of expiration which makes it extremely hard for the patient to inhale (ie increased work of breathing). Normally at the end of exhalation in a normal patient the pressure should be equalized... hence no airflow?

So, the patient has to work extra hard to inhale since they have to overcome this auto-peep pressure to create the pressure gradient to allow airflow in.

For patients who are refractory to treatment or are already in extremis, application of CPAP works by creating a pressure that is higher than the intrinsic auto-peep pressure... thus creating a pressure gradient allowing better airflow and taking the workload off the patient. With the CPAP exerting the positive pressure, the patient no longer has to expend high levels of energy and experience muscle fatigue to generate this pressure on their own.

This isn't really right. Yes as airways narrow it is a little harder to breath in, but the problem with asthma is really the exhalation. The problem is that when you breath out, the pressure inside the chest (and outside the airways) is higher than the pressure in the airway. This is even worse in patients with destructive lung disease like COPD. So the CPAP helps COPD by helping splint these open. Now BiPAP works by assisting the patient taking the breath in, like using a BVM. There is also some PEEP which helps keeps the airways open, but you set it low in asthma as others have said. CPAP alone isn't really going to help people breath in much. Think about it, it's a constant pressure. If you are setting your pressure at 2mmg of Hg for CPAP (to keep PEEP low), the patient only gets 2mmg for inspiration. When you are doing BiPap, the inspiratory pressure is usually set around 10mmhg.

As others have said, Bipaps role in asthma is really to help the tiring patient, giving them more time for the meds to open them up and try to avoid intubation. But it isn't the end all be all.

This is very different from other conditions like CHF with pulmonary edema, or COPD exacerbation where BiPAP alone can really turn people around.

 

[18G]

This isn't really right. Yes as airways narrow it is a little harder to breath in, but the problem with asthma is really the exhalation. The problem is that when you breath out, the pressure inside the chest (and outside the airways) is higher than the pressure in the airway. This is even worse in patients with destructive lung disease like COPD. So the CPAP helps COPD by helping splint these open. Now BiPAP works by assisting the patient taking the breath in, like using a BVM. There is also some PEEP which helps keeps the airways open, but you set it low in asthma as others have said. CPAP alone isn't really going to help people breath in much. Think about it, it's a constant pressure. If you are setting your pressure at 2mmg of Hg for CPAP (to keep PEEP low), the patient only gets 2mmg for inspiration. When you are doing BiPap, the inspiratory pressure is usually set around 10mmhg.

As others have said, Bipaps role in asthma is really to help the tiring patient, giving them more time for the meds to open them up and try to avoid intubation. But it isn't the end all be all.

This is very different from other conditions like CHF with pulmonary edema, or COPD exacerbation where BiPAP alone can really turn people around.

Anyone else's thoughts?

An increase in airway resistance (ie bronchoconstriction, increased mucus production, inflammation, exudative junk) = increased work of breathing / atelectasis.

The patient must expend extra energy and utilize accessory muscles to generate a pressure high enough to overcome the pressure present inside the chest to allow airflow to take place. This needs to happen for inspiration or expiration to occur. For example, in order to drop the pressure inside the lungs, the auto-peep pressure must be overcome so air can leave the chest and become more negative. CPAP can overcome this auto-peep pressure in some cases.

With Asthma, there is bronchoconstriction, inflammation, increased mucus, etc. so there is a component of difficulty inhaling with the increased airway resistance which needs to be addressed as well.

With CPAP, alveolar recruitment takes places and more alveoli are able to participate in gas exchange and they aren't as prone to collapse.

It seems counter intuitive that CPAP would work in asthma and does get kinda confusing.

To go along with my explanation I discovered this article which does a great job at explaining auto-peep with use of CPAP.

http://www.ccmtutorials.com/rs/peep/page7.htm

 

[Merck]

I'm not sure that I would use CPAP in an acute exacerbation of asthma. In my experience 95% of patients can be controlled with the usual nebulized meds. Those that are not usually respond admirably to judicious IV beta-lovin'. (i.e. epi). In the rare event that these are successful and/or things are trending poorly the best course of action is to intubate them anyway allow for very long expiratory phase, despite the hypercarbia that results.
There is a 2011 paper in CMAJ that outlines recommendations for NIPPV/CPAP and it does not state any recommendations for CPAP in asthma exacerbation as there is no evidence to support its use.
Just my 2 cents.

 

[Doczilla]

Again, the only use I've seen it in is in-line neubulizer. I wonder why it hasn't been brought up much?

 

[18G]

I'm not sure that I would use CPAP in an acute exacerbation of asthma. In my experience 95% of patients can be controlled with the usual nebulized meds. Those that are not usually respond admirably to judicious IV beta-lovin'. (i.e. epi). In the rare event that these are successful and/or things are trending poorly the best course of action is to intubate them anyway allow for very long expiratory phase, despite the hypercarbia that results.
There is a 2011 paper in CMAJ that outlines recommendations for NIPPV/CPAP and it does not state any recommendations for CPAP in asthma exacerbation as there is no evidence to support its use.
Just my 2 cents.

I've seen studies regarding use of CPAP in Asthma with favorable results.

 

[NomadicMedic]

I've seen studies regarding use of CPAP in Asthma with favorable results.

Post the citations.

 

[18G]

http://pats.atsjournals.org/content/6/4/367.full

 

[Smash]

http://pats.atsjournals.org/content/6/4/367.full

Garbage in, Garbage out. The quality of a review or a meta-analyses is only as good as the original studies that it looks at. And quite frankly, the studies they discuss in this paper are pretty useless. The vast majority of the studies look at BiPAP, not CPAP. The ones that do look at CPAP are so small as to be ridiculous (N=2!) The largest study that looks at CPAP as opposed to BiPAP is a retrospective review with N=22. Not exactly practice changing material.

The vast majority of literature I have come across deals with COPD, which has a different pathology to true asthma, as zmedic has pointed out.

The other issue I have when trying to interpret the (lack of) data is the terminology used. For most of us (certainly for me) CPAP means CPAP. I personally am limited to a fixed pressure of 10cmH20. I have no capacity to alter inspiratory support at all. I suspect that many of us in the pre-hospital field have the same limitations (ie we can't provide actual BiPAP)

However many studies use the terms CPAP, NIPPV, BiPAP and so on interchangeably. Whilst this may be technically correct, there is obviously a vast difference between slapping on 10cmH2O CPAP with 4/10 BiPAP (or whatever). So it makes interpreting the results of studies (such as they are) for use in the pre-hospital field problematic. Maybe some can provide actual BiPAP, but I know that this is limited for many.

 

[18G]

Garbage in, Garbage out. The quality of a review or a meta-analyses is only as good as the original studies that it looks at. And quite frankly, the studies they discuss in this paper are pretty useless. The vast majority of the studies look at BiPAP, not CPAP. The ones that do look at CPAP are so small as to be ridiculous (N=2!) The largest study that looks at CPAP as opposed to BiPAP is a retrospective review with N=22. Not exactly practice changing material.

The vast majority of literature I have come across deals with COPD, which has a different pathology to true asthma, as zmedic has pointed out.

The other issue I have when trying to interpret the (lack of) data is the terminology used. For most of us (certainly for me) CPAP means CPAP. I personally am limited to a fixed pressure of 10cmH20. I have no capacity to alter inspiratory support at all. I suspect that many of us in the pre-hospital field have the same limitations (ie we can't provide actual BiPAP)

However many studies use the terms CPAP, NIPPV, BiPAP and so on interchangeably. Whilst this may be technically correct, there is obviously a vast difference between slapping on 10cmH2O CPAP with 4/10 BiPAP (or whatever). So it makes interpreting the results of studies (such as they are) for use in the pre-hospital field problematic. Maybe some can provide actual BiPAP, but I know that this is limited for many.

There is limited data from evaluating CPAP in asthma. But there is some which shows benefit. Yes, COPD and asthma are different but they also share a lot of the same components as well. I never claimed these were groundbreaking or ne thing but do lend support for benefit.

 

[MSDeltaFlt]

An absolute contraindication of CPAP is the acute asthmatic would be a total loss of alveolar plateau as observe on the ETCO2 waveform. That's what Bob Page told us at the "Slap the Cap" lecture, anyway.

More clinically relevant for an absolute contraindication Got CPAP would be respiratory failure: acute hypoxia with severe hypercapnia, fatigue, and/or a 2-3 point drop in GCS in your presence. Oh yeah, one more absolute contraindication: apnea.

Not just one item on a machine taught by someone with no pulmonary background. I like Bob's classes. I learn a lot from him. But if you want to learn respiratory components learn from RT's and pulmonologists. Just my humble two cents.

 

[ZootownMedic]

More clinically relevant for an absolute contraindication Got CPAP would be respiratory failure: acute hypoxia with severe hypercapnia, fatigue, and/or a 2-3 point drop in GCS in your presence. Oh yeah, one more absolute contraindication: apnea.

Not just one item on a machine taught by someone with no pulmonary background. I like Bob's classes. I learn a lot from him. But if you want to learn respiratory components learn from RT's and pulmonologists. Just my humble two cents.

Yeah I would hope nobody would try to CPAP a apneic patient.....guess it needs to be said or else someone willl do it though. Probably some dumb Paramedic intern :rofl:

 

[TYMEDIC]

The last couple of CPAP administrations ive did really didnt work well and just had to discontinue them on status ashmatics. The patient just didnt tolerate the mask, and ended up just using peep attachment via BVM and bagging albuterol+atrovent in. To me, its still the same. The real question is, not everybody has the ability to use bronchodilators via neb attachments to CPAP. It just ends up being inneffective. Why waste your time trying to hook all that crap up when you can just as easily bag a neb into someone. Ive been studying this method of treatment for a while now with CPAP. Those patient's are auto-peeping and can seriously cause damage.

 

[Aidey]

Ive been studying this method of treatment for a while now with CPAP. Those patient's are auto-peeping and can seriously cause damage.

Citation?

 

[WTEngel]

I have seen success with BiPAP and in line nebs. It wasn't all that uncommon to do this with acute exacerbation patients.

The real question is, when do they cross the threshold of acute exacerbation into full on status asthmaticus.

It has been my experience, and I have see a LOT of asthmatics, that once they are status, they need IV meds, bottom line. No matter what type of respiratory set up you want to use, CPAP, BiPAP, ET intubation with specific vent settings, etc. there comes a point where you need to pull the trigger and give mag, terb, theophylline, or aminophyilline as appropriate.

So there in lies the crux of the matter.

For the patients who are simply "tired" and just need a little adjunctive therapy to bridge that gap and stave off intubation, I think BiPAP with inline duoneb and IV solumedrol does the trick.

For the status patients, mag, solumedrol, BiPAP with inline duoneb.

I have seen status patients pushed to the verge of respiratory arrest with poorly applied CPAP or BiPAP used in without in line nebs and/or IV med therapy.

The real trick is having the experience to recognize when enough is enough and pull the trigger on mag, terb, theophylline, or aminophylline, depending on the patient presentation.

 

[zmedic]

The last couple of CPAP administrations ive did really didnt work well and just had to discontinue them on status ashmatics. The patient just didnt tolerate the mask,

I've found that when people are clawing away the mask (NRB or BiPap), that's the signal to intubate them. They are usually starting to get altered from hypoxia/hypercapnea at that point. Those patients either crash or get intubated. But sick asthmatics+pushing away mask=bad new bears.

 

[Christopher]

I've found that when people are clawing away the mask (NRB or BiPap), that's the signal to intubate them. They are usually starting to get altered from hypoxia/hypercapnea at that point. Those patients either crash or get intubated. But sick asthmatics+pushing away mask=bad new bears.

Ativan has helped in some of these situations, but this is where Ketamine would really shine!

 

[Doczilla]

+ over 9000.

Plus, ketamine is the induction agent of choice for status asthmaticus

 

[JakeEMTP]

I have seen success with BiPAP and in line nebs. It wasn't all that uncommon to do this with acute exacerbation patients.

What device are you using for BiPAP in prehospital?

We have the LTV 1200 on CCT but none of the other trucks carry it.

 

[WTEngel]

We used the LTV 1000.

BiPAP can be a pain in the rear on the LTV if you don't use it often. It is a little more complicated to set the vent up (as far as pushing buttons and getting to the right menus) but if you run it enough, like anything, you get the hang of it.