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Wednesday, December 16, 2009

Is BiPAP good for CHF?

As always I've been thinking too much lately. This time about BiPAP and CHF. The goal here is to make sure we are dealing with facts and not thinking BiPAP is doing something it's not.

So, that in mind, I created this Q&A. I did the research and then had a discussion with myself.

My Question: BiPAP is ordered for a patient who is labored, has a low PO2 despite 75% non-rebreather, and increased excessory muscle fatigue. Why does it work?

My humble answer: It works because the IPAP helps the patient take in a breath without having to use his excessory muscles. In this way it decreases muscle fatigue by decreasing work of breathing. The EPAP helps increase the patients FRC and thus increases oxygen delivery to the blood and to the tissues.

My Question: I understand that, but why is it every time I ask a doctor why he ordered BiPAP on a patient who shows signs of pulmonary edema yet has no signs of muscle fatigue and normal blood gases, he always says, "Because it pushes fluid out of the lungs?"

My humble answer: The idea that the BiPAP pushes fluid out of the lungs is a fallacy. It does nothing of the sort. I contemplated this and did some research. The best answer I could find came from Jeffrey Sankoff, MD, from Emergency Physicians. I will post what he wrote about his topic below and the next time you have a doctor say that you can show him this report:
Contrary to popular belief, NIMV does NOT push edema fluid out of the lungs. Patients with acute CHF have an imbalance in the CO (cardiac output) of the right and left sides of the heart. With the inciting event (detailed above) the left ventricle becomes compromised but the right ventricle usually does not. So the right ventricle continues to pump forward a normal volume of blood but the left ventricle becomes unable to keep pace. Fluid backs up into the lungs resulting in capillary leak and pulmonary edema. With NIMV, the resultant positive intra-thoracic pressure decreases venous return (blood flowing back to the heart). This reduces right-sided CO to a level that the left heart can equal or even exceed. Fluid ceases to back up and will even begin to be reabsorbed as left ventricular CO improves. Pulmonary edema ceases to worsen and may even diminish, often rapidly.

My Question: So does this explain why patients are still on BiPAP hours after their episode has been resolved and they are awake, alert, orientated, breathing normal, and irritated that they are still have the BiPAP mask strapped to their face?

My humble answer: I can't answer that for sure, but it's possible.

My Question: See, I have listened to doctors and nurses discuss how, "the BiPAP saved that patient's life." Yet I often wonder if it was the BiPAP at all but the medicine we use to fix the patient. What are your thoughts on this.

My humble answer: I think you guys are all right. I agree with you in that I have always thought of BiPAP as the machine version of Ventolin, that it does not cure, it treats the symptoms. A Ventolin treatment does not resolve the asthma episode, it merely treats the symptom of bronchospasm, thus buying time for other medicines (corticosteroids or antibiotics) to take effect. BiPAP is a treatment to relieve work of breathing and thus buy the patient some time while the medicines the doctor orders and the nurses give make the pump work better (Dopamine) and get the fluid out of the lungs (Lasix).

However, as you can see from the discussion we had above, BiPAP can also help decrease the amount of fluid in the lungs. Yet, still, it is just treating the symptoms while other therapies treat the CHF. Usually about 2-3 hours after treatment is started the patient feels great and the BiPAP is given credit for curing the patient. In this way, it is just like Ventolin.

Question: So, technically speaking, once the patients heart is stronger, the cardiac output improved, the fluid is off the lungs, and the patient is breathing better, the BiPAP can be discharged from the patient. Right?

My humble answer: Absolutely. When I was a student working at a larger hospital, back when these type of patients were put on Ventilators instead trialed on BiPAP, once the patient was better he was extubated. I work at a smaller hospital and the doctor won't extubate CHF patients who are intubated, and won't discharge the BiPAP now that this is the therapy of choice. That's just the way doctors work. It made the patient better and now they are afraid to take it off the patient.

Question: So are they being lazy, or is it because they think the BiPAP is keeping the fluid out of the lungs?

My humble answer: Your guess is as good as mine on that one.

So, while the main goal of BiPAP with CHF is to decrease work of breathing, it can also help increase cardiac output and decrease the amount of fluid in the lungs. It does not, however, push fluid out of the lungs. So we have once again debunked another RT fallacy.


Anonymous said...

Well written.

CountyRat said...

Excellent commentary. However, I think that you may be understating the value of the therapy you provide to patients with low O2 sat and low cardiac output. Yes, as you correctly indicate, the low sat and pulminary edema are just symptoms (actually signs, if you will forgive my compulsivity)and not the underlying pathology. However, while only results, and not causes of the patient's problems, they are also able to kill the patient, and often would without your respiratory therapy. Treating the underlying cause is, of course, the holy grail of all medicine. But it is not very satisfactory if the patient dies in the process, even if he or she only died as a result f "symptoms." You and your colleagues are much more valuable than you may appreciate. The fact that we work as a team rather than the solitary miricle workers depicted on TV medical melodramas does not deminish the fact that respiratory therapists lives.

Best wishes and happy holodays.

TOTWTYTR said...

Very well, written. In EMS, we are the ultimate temporizers. Just about everything we do is temporizing. In our case, we use CPAP, but the rationale and effect are the same. We are buying the patient time until the ED can fix them. Well, as much as anyone can fix CHF.

And yes, we tell the patients that CPAP pushes the fluid out of their lungs because it's the most simple answer.

FIN said...

I think your missing some pertinent bits and pieces. There is an affect on lympatic redistribution and directly impacted by afterload reduction as well as preload management. Have a read at this excellent article:

Rick Frea said...

Thanks for the comments and information and links. Will update the above as new wisdom is accrued.