When doing cardiac output for the wedge where are you setting the cursor for a non ventolated patient? And the ventolated patient? We have been having difficulty with this as we have recieved conflicting information and it does make a difference in the reading.
Mar 13, '99
The PCWP should be measured at end expiration and end diastole. The wave form differs between a ventilator breath and a spontaneous breath. Watching the ECG and listening to or watching the ventilator will give you the proper placement of the visual cursor. This should be at the top of the wave during end expiration and end diastole.
The variations in information you are receiving are probably because on a ventilated patient with a PEEP greater than 5 to 8 increases the intrapleural pressure (and the intracardial pressure in response) and therefore the pressure gradient between the left atrium and the atmospheric pressure.
This artifactually increases the PCWP. Using formulas to estimate the difference are usless as they do not accurately estimate the fraction of the PEEP that is transmitted to the heart.
I hope this helps to answer your question.
Apr 10, '99
If there is any question to where to read your wedge pressure, use a paper print out for the most accurate reading. It is best to correlate it with the cardiac cycle, i.e. do a two channel print out of the EKG and PCWP. If you have the capability, you could print out the resp waveform and the PCWP. Taking the wedge pressure off the paper print out will help you identify where end expiration is.