Wedge readings in PS, CPAP, PC, and APRV ventilation

Surgical Hrt RN · Jul 17, 2005

(also posted in the MICU/SICU forum):
Yesterday at work, two of the attendings were trying to figure out/remember where you read a wedge when the patient is on PC ventilation. They even asked our head nurse's opinion, but she wasn't sure either. I recently had the same confusion about patients on CPAP and PS ventilation, but they all said that you read the wedge at the "peak" of the waveform. I understand the thinking with CMV/AC ventilation versus spontaneous breathing off the vent, but I'm still a little confused about the rationale with CPAP, PS, and PC ventilation. I was also wondering about APRV. Does anyone here know the answer? Thanks!
Hillary

I have worked as a Clinician in an ICU for over a year now. For all my new nurses I put together a hemodynamic packet and part of that included this info along with the waveforms. Hope this helps! They loved this info so much that I laminated pages and kept it as a reference book on my unit.

Respiratory Effects

PAC's measure pressures in the heart. In addition to intrinsic pressure changes, the heart and vessels are subject to changes in the surrounding pleural(extrinsic)pressures caused by breathing.

Changes in the intrathoracic (pleural) pressure during inhalation and exhalation can cause pressures in the heart and large vessels to vary. Here are a few tips to remember:

- Hemodynamic pressures fall during spontaneous

inhalation, and then rise during exhalation.

- Hemodynamic pressures rise during mechanical

inhalation and then fall during exhalation

- Always measure all hemodynamic waveforms at

END EXPIRATION!!!!! (pleural pressure is near 0 at this time.)

How to Measure End Expiratory Pressures

- Locate End Expiration

- With spontaneous breathing locate waveform just

before pressures decline with inhalation.

- With mechanical breathing, locate waveform just

before the pressures rise with inhalation.

TSwindle, RN ICU Clinician 2004

Phishininau · Jul 28, 2005

HD's are measured at end-expiration. Pressure in the lungs is the closest to the pressure in the atmosphere at that point.

Also, dont forget that HD #'s can be a little skewed when you add PEEP to the picture.

Surgical Hrt RN · Jul 29, 2005

HD's are measured at end-expiration. Pressure in the lungs is the closest to the pressure in the atmosphere at that point.
Also, dont forget that HD #'s can be a little skewed when you add PEEP to the picture.

Absolutely.............peep affects HD's thanks for adding that!

benildaicu · Aug 5, 2005

also remember VENT VALLEY, when they're on vents doesn't matter what modes they're in, always measure mean at the peak of waveform. On the other hand, when they have spontaneous breathing, remember NEGATIVE pressure vs. POSITIVE pressure. With spontaneous breathing we use negative pressure so we take the mean of the lowest in the waveform (Negative=low). Hope this helps!

papawjohn · Aug 6, 2005

Hey Y'all

I live on TampaBay. Have a sailboat. Bear with me a minute and I'll tell you how this helps me 'splain to my Newbie Nurses how to look at a pressure wave form on the monitor.

The point of finding the 'mean' is to find where on the wave is one half of the volume of the fluid. So if we're down on the beach and the waves are rolling in and I say to you, how high up the face of that wave is the line that divides the AMOUNT OF WATER IN THE WAVE IN HALF?--then I am asking for the "MEAN" of the wave.

(I had lots of trouble getting wave form calculations though my thick red-neck head. Then one day Tinkerbell scattered magic dust on me or something and I realized--it's one half the VOLUME. Which turns out to be one third the height of the wave.)

So you can look at the wave forms (on the monitor, on the beach, in your beer mug--a wave is a wave) and find the "mean" now. It's the measurement one third the way up the height of the wave from the bottom.

Lets go back to the beach. Now the tide has come in. We're standing much farther up the beach. The 'MEAN' is the same--but there's lots more ocean there--yes?

The tide coming in is analogious to adding PEEP. Any increase in pressure increases the size of the air passages and increases the pressure on the heart and the PulmArtery.

Hope this helps de-mystify the P-A Catheter.

(Hint: Don't de-mystify these things completely. When you're master of the Swan-Ganz on your team, you can stand in front of some newbie nurses' monitor and intone "looks a little higher since they put her on pressure control, don't ya think?" And walk away feeling very very wise. ;->_)

Yer Papaw John

big sweet life · Aug 8, 2005

I like simple as possible. To assure I have end expiration I place my hand on the patient's chest, feel for exhalation fall of chest, I then give a quick flick on the catheter that shows on the waveform and take my wedge. This shows up on the strip that includes a corresponidng EKG waveform as well, so I know where I took my wedge. Hope it helps. the AACN website has a good link to this for study purposes for the Cardiac Surgery cert.(CSC)/ cardiac medicine cert.(CMC) tests. It is a webcast put on by Thomas Ahrens, DNSc who is a waveform guru. It is very informative and presented in an easy manner. At the website click on the certification area for CSC/CMC, then on left there is a Products/Courses- click that, then a menu showing :

AACN Study Resources for Subspecialty Exams (CMC and CSC) , and under that go to: Hemodynamic Competency-Reading Waveforms Accurately - Webcast.

benildaicu · Aug 8, 2005

Another website I could recommend is PACEP.ORG