Is CPAP the next 8-Track?

[jrm818]

I don’t know if there will be any interest in this sort of discussion, but with all the talk about evidence based medicine, hopefully someone will bite.

I stumbled over an interesting study that questions the use of CPAP in acute pulmonary edema in the prehospital setting. I'll give you my background thoughts then my expanded version of an abstract.

The background is really questions I have about your treatment of pulmonary edema. The reason I went searching is partially a discussion I had in class with one of our professors about the use of high-dose nitrates. It seems that despite evidence supporting the administration of high dosages, lasix is still the mainstay of treatment, at least around here, and I’m curious how things are run elsewhere.

This relates to CPAP in that the existing CPAP literature generally compares CPAP with “usual care” and is a bit inconsistent in its reporting of what “usual care” constitutes (the all include nitrates, but dosage and route is inconsistent and sometimes not reported). Generally, though, I do not think previous studies compared CPAP with "high dose" nitrate therapy.

High dose nitrates have been demonstrated in several studies to be pretty effective in resolving cardiogenic pulmonary edema. This study may present a new perspective in that it does include relatively high nitrate doses.
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The study:

“Continuous positive airway pressure for cardiogenic pulmonary edema: a randomized study.” Am J Emerg Med. 2010 Apr 30. [Epub ahead of print]
http://www.ncbi.nlm.nih.gov/pubmed/20825901

This study was conducted in France with physician ambulances and compares “standard protocol-driven therapy for severe ACPE” consisting of:

furosemide 1mg/kg
isosorbide dinitrate infusion 2mg/h PLUS 2mg bolus if SBP above 180mmHg
O2 15LPM by face mask

Against all of that PLUS 10 cm H2O CPAP

124 reasonably well matched patients suffering from severe acute cardiogenic pulmonary edema (ACPE) were enrolled and randomized to a treatment group, primary end point after one hour was:

Resp. Rate less than 25/min
SpO2 >90%

They also looked at: frequency of failure of care strategy, need for in-hospital intubation, and 30 day mortality.

Results, (quoted from the abstract, emphasis added):
, 22 (35.5%) of 62 patients were considered as experiencing a treatment success in the usual care group vs 19 (31.7%) of 60 in the CPAP group (P = .65).

Seven patients died within 30 days in the usual care group vs 6 in the CPAP group (P = .52). There were no statistically significant differences between the treatment groups for length of stay either in hospital or in the intensive care unit.

Conclusion: “In the prehospital setting, in spite of its potential advantages for patients in ACPE, CPAP may not be preferred to as strict optimal treatment including low-dose morphine, furosemide, oxygen, and high-dose boluses of isosorbide dinitrate unrestricted according to clinical response.”
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I know not everyone has access to the full text, but if you can read the study, its a fairly quick read, and pretty interesting.


Some questions to get it started:

1. What do you use in your system? Any consideration for high dose nitrates? What do you think about the use of nitrates here versus the use of nitrates in other CPAP studies you have looked at?
2. do you think the results of the study would be mimicked in a paramedic-driven system?
3. are there situations when high dose nitrates may be contraindicated but not CPAP? Vice versa?
4. What do you think of their use of respiratory rate as a primary endpoint?

Since not everyone can get the full text and dissect the numbers, I’ll add that in my view this study is not a slam dunk against CPAP. Statistics is not my strong suit, but the study was originally powered to detect a difference of about 25% between groups, i.e. the authors expected CPAP to be a success 40% of the time and usual care only 15% of the time and calculated the needed sample size on that large difference. Smaller differences need larger sample sizes to evaluate. With much less difference, the study is probably underpowered to detect more subtle differences. Also, the study is clearly not designed or powered to detect differences in intubation rate, and probably not mortality either (the authors acknowledge this outright).

Still, the study does demonstrate (surprisingly to me) that even if CPAP had a benefit, that benefit was small.

What say you?

 

[18G]

While looking at the study only a measly 124 patients were enrolled in the study. This is an extremely small number to draw any real conclusion.

CPAP has been used for many decades and just recently came to the pre-hospital arena. One of the reasons it did was because of its effectiveness. There is lots of research that shows the real benefits of pre-hospital CPAP. CPAP offers dramatic improvement in patients. I think this study is way too small to say CPAP has minimal effect.

CPAP has worked wonders to eliminate the number of intubations. I don't think CPAP will become the next 8-track but who knows.

Who would have ever thought oxygen would become an 8-track

 

[18G]

I forgot to mention that in PA and MD high dose nitro is in the protocols.

 

[firetender]

From a Lizard's POV

Who would have ever thought oxygen would become an 8-track

Let's put it this way, we are in the midst of a very inexact and dynamic, if not unstable science. Let me illustrate.

Most of the stuff in my drug box that I saved lives with in the 1970's and 1980's has been debunked if not banned! I learned that all here and as I was going over the litany of my rejects (essentially declaring my drug box EMPTY except for enough MS to kill myself and enough Narcan to bring me back) what do they do?

They even took "A" and "B" out of the ABC's of CPR!

This is very much like TV...stay tuned!

 

[usalsfyre]

124 patient study smacks of a "publish or die" situation that is frequently seen in acedimic medicine. The only thing such a small study is good for is to say we need more studies.

NPPV is a treatment modality that has far more utility than just cardiogenic pulmonary edema. Study the effect is has on gas exchange and reduction of airway injury. Unfortunately it's action is often simplified down to moving fluid, which is actually the smallest part of what it does. If you take the time to dig a little deeper,you'll see why it's a wonderful adjunct for all respirtory failure and not just heart failure.

 

[usalsfyre]

Another thought I just had was it would be interesting to see how many of those 124 ended up needing fluid resuscitation during their admission.

 

[TacoMEDIC]

High dose nitrates, Furosemide, and CPAP are included in my protocol for treatment of these patients. CPAP is a great tool and I couldn't imagine not having it for some patients. Especially with the long transports in my area.

 

[jrm818]

Thanks much for the responses. I do have some replies.

While looking at the study only a measly 124 patients were enrolled in the study. This is an extremely small number to draw any real conclusion.

124 patient study smacks of a "publish or die" situation that is frequently seen in acedimic medicine. The only thing such a small study is good for is to say we need more studies.

So I'll lump the "small sample size" comments into one. I don't really agree with this criticism. The sample sizes here are actually larger than most of the studies that people cite to support the use of CPAP.

Compare the sample size in this study with the sample sizes in all of the studies used in this meta-analysis (free access, table 2):

http://ccforum.com/content/10/2/R69

This new french study is the bigger than every evaluated study save one! Sure a thousand patient study would be preferable and more powerful, but that's a huge investment in time and money....and in french EMS I bet it would take quite a while to even treat that many eligible patients.

Additionally, the sample size selection was not arbitrary. The authors specifically chose a sample size that was slightly larger than the size needed to detect the treatment effect they predicted. As I mentioned, since the difference in the groups was much smaller than expected, the study does not have adequate power to claim that there was absolutely no difference between CPAP and no CPAP, but there certianly was no 25% difference, as expected. I think that that the study was large enough and well designed enough to say that there was very little, if any, difference in CPAP versus no CPAP as measured by RR and SpO2.

CPAP has been used for many decades and just recently came to the pre-hospital arena. One of the reasons it did was because of its effectiveness. There is lots of research that shows the real benefits of pre-hospital CPAP. CPAP offers dramatic improvement in patients. I think this study is way too small to say CPAP has minimal effect.

CPAP has worked wonders to eliminate the number of intubations. I don't think CPAP will become the next 8-track but who knows.

Who would have ever thought oxygen would become an 8-track

I agree that there is much research supporting the efficacy of CPAP in comparison with traditional treatment. The meta-analysis I posted above is very supportive of that.

I think its important to emphasize the idea that when we talk about CPAP being "beneficial," we mean that it is "beneficial compared to current conventional treatment."

The reason I was interested in this french paper is because it compared CPAP not to "current conventional treatment" but to a pharmacological treatment (high dose nitro) that was not considered "conventional" in previous studies. I know (now that some of you have told me) that high dose nitro has become conventional in many of your systems, but in many of the studies that initially supported CPAP that was not the case and CPAP was compared to lasix and lower doses of nitro ( at least as far as I can tell...some authors infuriatingly neglected to describe their "usual care" treatments in detail.....drives me up a wall!).

So the question is - does CPAP really cause improvement above and beyond the improvement brought about by high dose nitro? I think this study is one of the few that starts to address that question, and the answer is surprising to me (and to the authors, who expected to see a big benefit to CPAP).

I don't think CPAP will become the next 8-track either...that was really just a inflammatory attempt to get views and responses

 

[jrm818]

NPPV is a treatment modality that has far more utility than just cardiogenic pulmonary edema. Study the effect is has on gas exchange and reduction of airway injury. Unfortunately it's action is often simplified down to moving fluid, which is actually the smallest part of what it does. If you take the time to dig a little deeper,you'll see why it's a wonderful adjunct for all respiratory failure and not just heart failure.

I've done some of that reading...still learning and have more reading to do, but thus far I agree. I am especially interested in CPAP the setting of cardiogenic pulmonary edema,though....primarily because I'm also interested in the apparent reluctance to de-emphasize diuresis and emphasize of nitro in my area.

Another thought I just had was it would be interesting to see how many of those 124 ended up needing fluid resuscitation during their admission.

I agree. These patients were all diuresed at signifigant levels (furosemide 1mg/kg). I'm willing to bet that a lot were not fluid overloaded, and that the diuresis was inappropriate. I acutally found this study because I had a feeling that the idea of "pee the water out of your lungs" was missing a bit in its theory and I started to discover that just vasodialating the buggers probably worked better.

Unless you mean a fluid bolus to correct nitrate induced hypotension? Either way I do wish the authors had included a bit more data...

 

[jrm818]

High dose nitrates, Furosemide, and CPAP are included in my protocol for treatment of these patients. CPAP is a great tool and I couldn't imagine not having it for some patients. Especially with the long transports in my area.

Transport time is often cited as a possible drawback of CPAP because of the huge volumes of O2 that many systems consume. In your view, what makes it especially beneficial in the settings of long transport times? Do you find pharmacology is adequate only initially, and CPAP is necessary for maintenance?



For everyone: if you were convinced that the data in this study was good (and that the sample sizes were large enough), would you be tempted to alter your clinical approach to cardiogenic pulmonary edema patients? Would you still see a need for CPAP if nitro turns out to work just as well?

Also, I would especially like people to weigh in on the choice of resp. rate and SpO2 as determinants of "treatment success." I don't think I have enough clinical experience to be sure if these are good indicators of pathology resolution, and was hoping to get some thoughts.

 

[MrBrown]

What in the bloody hell is an 8 track?

 

[usalsfyre]

I agree. These patients were all diuresed at signifigant levels (furosemide 1mg/kg). I'm willing to bet that a lot were not fluid overloaded, and that the diuresis was inappropriate. I acutally found this study because I had a feeling that the idea of "pee the water out of your lungs" was missing a bit in its theory and I started to discover that just vasodialating the buggers probably worked better.

Unless you mean a fluid bolus to correct nitrate induced hypotension? Either way I do wish the authors had included a bit more data...

I did mean because if the diuesis. A good chunk (it's late and I can't think of the exact percentage, 46% maybe?) of acute decompensated heart failure (ADHF) patients are dehydrated at time if admission.

Heart failure is a complicated animal that has many forms. Heart failure as EMS likes to think of it (i.e. cardiogenic pulmonary edema) is usually a left sided systolic failure. This is really an afterload problem. High dose NTG works by increasing venous pooling and decreasing preload, which indirectly reduces afterload in addition to reducing MVO2. The true "bee's knees" and in my oppinon the next big thing coming down the pike is prehospital use of ACE inhibitors to have a direct affect on afterload. We've started using enaliprat and have had great success with it so far. I've yet to have to tube a HF pt this year between CPAP, high dose SL and IV NTG and enaliprat. We've come a long way from 15l via NRB, 1 NTG and 80 of lasix...

 

[FrostbiteMedic]

What in the bloody hell is an 8 track?

An 8-track is the BIG cassette tape, Mr. Brown......I actually have an 8 track player in my wonderful '78 Dodge Magnum.....and I still listen to it.....

 

[TacoMEDIC]

Transport time is often cited as a possible drawback of CPAP because of the huge volumes of O2 that many systems consume. In your view, what makes it especially beneficial in the settings of long transport times? Do you find pharmacology is adequate only initially, and CPAP is necessary for maintenance?

We are aware of the large volume of O2 consumed by the CPAP. Due to the distances to ERs in out area, we use "H" tanks instead of the "M" tanks found on most units.

In all honesty, I do not have specific info regarding your question. I have run many calls on patients that present with severe SOB and basilar rales. Almost 100% of the time our treatments begin with O2 15lpm by NRB and NTG at the appropriate dose based on SBP. I would estimate that approximately 50% of the time this initial treatment helps but does not significantly alleviate symptoms. In cases where the pt is still experiences moderate or severe SOB we have the option to administer Furosemide.

CPAP is a treatment that may be considered at any point during our treatment of these patients. In the area that I work in, it is not uncommon to have 30-60 minute response times. Generally speaking, pts with these conditions will compensate for a long time before they make a decision to call 911. If it takes us an hour to get to the pt after this point, the pt is likely very tired. It is in these cases where I think that it is extremely beneficial to initiate CPAP. I have noticed that pharmacological intervention alone is not effective enough for pts who are too tired to continue working as hard to breathe as they may have been able to had we gotten to the 30-60 minutes quicker. The assistance provided by CPAP seems to significantly decrease the pts difficulty of breathing in almost every case that I have seen. Keeping in mind that our hospitals are as far away as 2 hours by ground in remote areas of our district, I believe that the use of CPAP is the ideal treatment for this type of pt.

We also have the option of Naso Tracheal Intubation for these patients. In very severe cases i have gone to this treatment before CPAP. We have also utilized airships in cases where it was felt that quicker transport was necessary.