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Thursday, October 3, 2013

What are the advantages of BiPAP?

I had a doctor today order BiPAP on a patient who was suffering from heart failure.  I walked into the patient's room and saw that the blood pressure was 65/20.  Based on my knowledge of BiPAP, I felt that it was contraindicated for this patient. 

So I sat down with the doctor.  I said, "The patient has a low blood pressure. Do you still want to use BiPAP." 

He said, "Yes!  He's a very calm patient, and if you irritate him with that mask it may help get his blood pressure up." 

After taking a couple deep breaths, I said, "Can you explain to me what BiPAP does for CHF patients?"

He said, "Yes.  It increases the pressure in the lungs so that it forces fluid out.  It helps decrease the pulmonary edema."

I said, "What I learned about BiPAP is that it decreases preload to the heart, thereby decreasing cardiac output, and thereby decreasing blood pressure.  In this way, it helps to decrease the patients work of heart.  That is how it helps with heart failure.  It does not force fluid out of the lungs."

"Well, put it on him anyway," he said, and stormed out of the room.

That occurred in the emergency room.  Up on the floor, a doctor ordered BiPAP on a patient who was septic, suffering from kidney failure, and in metabolic acidosis.  The patient likewise had a low blood pressure, but it was being somewhat controlled by dopamine. 

I asked the doctor why he was ordering BiPAP.  He said, "Because it will decrease the work of heart.  The patient is a DNR and I understand she's going to crash at some point anyway, but this will help delay the inevitable."

I asked, "So, how do you think the BiPAP will decrease work of heart?"

He answered me:  "Becaues it will force fluid out of the lungs and make it so the heart doesn't have to work as hard to breathe."

I took a deep breath, and said, "BiPAP will decrease the work of heart, but it does it by decreasing preload. This in turn decreases after load, and therefore decreases cardiac output.  This is what decreases work of heart.  Since blood pressure is an indicator of cardiac output, I'm concerned BiPAP will comlicate your efforts to control her blood pressure."
"So what do you suggest?" he asked. 

Impressed that he asked me, I said, "She's breathing normal.  So how about we don't use BiPAP."

"Welp!" he said.  He hymned and hawed a few minutes, then he said, "EEEEEEeeeeee, let's just put it on and see what happens."

Well, at least I tried. 

So, what are the advantages of BiPAP?
  1. IPAP increases ventilation and helps to blow off CO2
  2. CPAP increases FRC and therefore keeps the lungs open so the next breath comes in easier
  3. Both IPAP and CPAP help to reduce work of breathing
  4. Both the IPAP and CPAP help reduce work of heart as explained above
Apperently this is not what's taught in med school.  I'll have to investigate to see if this topic was covered in the Real Physician's Creed.

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