Published Sep 30, 2018
Student Here. I'm currently learning about the mechanisms of right heart catheterization. I know that PCWP is essentially an indirect measurement of LAP, but I cannot figure out why this is. Can someone shed some light on this? Thanks
LAP is the pressure that is transmitted back through the pulmonary vasculature that must be overcome by the R ventricle in order for blood to flow and arrive at the left atrium.
The PA catheter floats out an artery (via the balloon) and occludes pulsatile flow from behind it that is generated by the R ventricle. Thus it's wedged in there. So the only pressure left that it is seeing is the pressure infront of it, which is transmitted back through the pulmonary system by the left atrium.
There is a relationship between the PAWP(or PCWP, same thing) and the pulmonary artery diastolic pressure: A PAWP higher than the PADP indicates that the PAWP measurement may be erroneous. On the other hand, if the PADP exceeds the PAWP by 6.0 mm Hg or more, the patient has probably developed pulmonary hypertension.
That's all I got.
Pheebz777, BSN, RN
Just think of lighting a bright flashlight in a dark hallway, the flashlight being the inflated balloon of the swan wedged in the pulmonary artery. You can see everything in front of the light, and you can't see anything behind the flashlight. Now imagine seeing a yellow balloon at the end of the hallway, and a similar balloon near the flash light. You know they both are yellow balloons.
The yellow balloon closest to the flashlight is your PAP, and the yellow balloon distal to the flashlight is your wedge pressure. In a regular healthy person with no valve disease or pulmonary disease both pressures should be within 5mmhg of each other to truly represent a close to accurate reading. That's why when a swan is first floated into the pulmonary artery, it's very important to document your wedge pressure and your PAP to see any differences when trending your pressures.
I and many others have abandoned the practice of "wedging" the catheter because of the extremely rare yet lethal complication of pulmonary artery rupture. That number is mostly useless anyway and not worth the risks.
I had thought wedge pressure readings had pretty well gone the way of the Dodo bird. The last couple places I've worked prohibited wedge pressures outright, the places before that highly discouraged them. They don't really offer anything to decision making in a way that is likely to actually affect outcomes, and they are relatively dangerous.
The incidence of pulmonary artery rupture is reported as high as 1 in every 500 balloon inflations, and half of those patients will die before the rupture can be repaired. That's a lot of risk for something that provides relatively little treatment-guiding hemodynamic data.
Yes, wedging the swan is rarely even performed due to the risks which out weight its use in the clinical setting. That's why when the interventional cardiologist floats the SWAN, he/she notes both the wedge pressure and PAP to establish a baseline relationship. Once that is established, they would no longer need to perform any further wedge pressures and just rely on the PAP pressures to give an accurate "rough" estimate of your end diastolic pressures or wedge pressure.
The numbers don't mean anything unless they first establish a relationship between the PAP and Wedge pressures in cathlab.
Yes, wedging the swan is rarely even performed due to the risks which out weight its use in the clinical setting. That's why when the interventional cardiologist floats the SWAN, he/she notes both the wedge pressure and PAP to establish a baseline relationship. Once that is established, they would no longer need to perform any further wedge pressures and just rely on the PAP pressures to give an accurate "rough" estimate of your end diastolic pressures or wedge pressure. The numbers don't mean anything unless they first establish a relationship between the PAP and Wedge pressures in cathlab.
Especially now that a simple bedside echo gives far more relevant information than a PA catheter in the majority of cases. They're really not worth the trouble except in very specific circumstances.
murseman24, MSN, CRNA
something about an uninterrupted fluid column between the pulmonary artery and the left atrium during a portion of the cardiac cycle which allows for interpretation of the left atrial pressure. But it is only accurate when there is no cardiac/pulmonary disease that would distort the numbers. So why would you put in a PAC in a completely healthy person? It is mainly used in the OR during open hearts to guide fluid resuscitation and if there are any specific abnormalities the cardiologist/anesthesia can interpret it and provide an appropriate intervention. In our ICU we used them for severe PAH to guide treatment of very potent pulmonary vasodilators.
4 minutes ago, murseman24 said: It is mainly used in the OR during open hearts to guide fluid resuscitation and if there are any specific abnormalities the cardiologist/anesthesia can interpret it and provide an appropriate intervention.
It is mainly used in the OR during open hearts to guide fluid resuscitation and if there are any specific abnormalities the cardiologist/anesthesia can interpret it and provide an appropriate intervention.
We don't even do that anymore...it's all echo now...if the surgeon asks for a PA catheter anymore it's for ICU management.
6 minutes ago, offlabel said:We don't even do that anymore...it's all echo now...if the surgeon asks for a PA catheter anymore it's for ICU management.
cool. We use a TEE during the procedure but they still put the PAC in. I've heard a lot of places don't though.
BeatsPerMinute, BSN, RN
Thinking of it as a "window" to "try to see and guess" the LAP is a good way to start thinking about it.
Taking a stab at trying to explain it... A swan ganz catheter measures pressure inside of the heart. The Swan's other name is "PA catheter" for Pulmonary Artery Catheter. It is a long, thin, yellow colored catheter, flexible/floppy, and can be threaded into the body via a vein, through the superior vena cava, into the RA, then RV, past the RV and up into the pulmonary artery, where it can go no further, because the artery splits off into a bunch of smaller arteries that are too small for this catheter to go further.
So, your Swan cath can get through the right side of the heart, and get the RAP and RVP numbers, which is exciting and awesome, but then it gets stuck on the "bridge", the Pulmonary Artery, and cannot get to the left side for the LAPs and LVPs numbers, because the "roads" (arteries) ahead are too small, busy and messy for the pulmonary artery catheter and the catheter is distracted by the blood flow and pressure coming in its way from the right side. The Pulmonary Artery Catheter wants to know whats going on "the other side of this bridge" (past the pulmonary artery) or at least try to "see" the LAPs/LVPs since that can be ( in some cases ) very useful information patient diagnoses and treatment.
When you cannot physically take the measuring tool to the destination to obtain the measurement / numbers wanted, you have to get the next best thing, which is the best guess. Sometimes a wedge pressure number can provide you with a best guess of what is going on in the "left side of the heart"
So, the Pulmonary Artery Catheter is hanging out in the Pulmonary Artery, the "bridge", and is stuck there, and from that spot, it can inflate its tiny balloon, and completely block off blood flow, and "wedge itself" into the pulmonary artery, taking up the whole diameter of that pulmonary artery. In doing this, it cuts off the blood flow that is supposed to flow from the right side of the heart to the lungs and into the left side of the heart. You can imagine that leaving it like this for very long can be dangerous. The purpose though is that when you "wedge" your Pulmonary Artery Catheter you obtain a measurement/ pressure number called the "wedge" pressure, because as its sitting there completely cutting off blood flow from the direction that blood is supposed to flow, the catheter senses that there's blood flow and pressure from somewhere else - maybe from the LAP. While the cath is not physically and directly in the LAP, its there cutting off the flow from one direction, and it can "take a peak and guess" at the pressures from another area. The pulmonary artery catheter goes "hey, we just cut off blood flow from heart to lungs, best not do this for long, maybe just a few seconds ... but hey, I think I hear something over there, or see something? Theres blood flow and pressure over in that direction! I did not notice before I cut off this blood flow coming in from the right side!"
There is a relationship between wedge and LAP in healthy humans. It can be difficult to explain from the nurse perspective because in practice we have patients with a bad "right heart, a bad left heart, a bad pulmonary artery, or all of the above" and "literally just need a new heart" (and they wait with us until a new heart arrives for them to receive). It's an important concept to understand - otherwise it won't make much sense when you start talking about disease states that break the rules of the relationship.
Its complex and will take a few tries to understand the concept. Watching youtube videos and drawing it out really helped me to understand it.
Attached is a pic with healthy human / "normal" pressure numbers
Great explanation! Using this in nursing school now ?.
If you're not a teacher, I hope you become one. You're description is incredibly straightforward and easy to understand. This is super challenging in the medworld but you nailed it. ?
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