12 Monitoring Invasive Pressure
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occludes the artery allowing the monitor to record changes in the intrathoracic pressures that occur
throughout the respiration cycle. The pulmonary wedge pressure is the left ventricular end diastolic
pressure (preload).
The most accurate PAWP values are obtained at the end of the respiration cycle when the intrathoracic
pressure is fairly constant. You can use the respiration waveform as a reference when assessing the
PAWP waveform, to ensure constant measurement timing relative to the respiratory cycle. The
monitor displays the PAWP value for up to 24 hours or until you admit a new patient.
WARNING
The pressure receptor in the catheter records pressure changes that occur only in front of the
occlusion. Even though the catheter tip is in the pulmonary artery, the receptor records pressure
changes transmitted back through the pulmonary circulation from the left side of the heart.
While performing the wedge procedure, the monitor switches off the pressure alarms for pulmonary
artery pressure (PAP).
Due to a slight measurement delay, you should not use sidestream CO
2
as a direct reference for
determining the end expiratory point in the pressure curve.
To start the Wedge procedure,
1 In the Main Setup menu, select Wedge to display the wedge procedure window.
2 Prepare and check the pressure line according to your hospital policy.
3 Use the Refernce Wave 1 and Refernce Wave 2 pop-up keys to select any ECG or respiratory
wave as reference waves.
4 Select Change Speed if you want to change the speed of the displayed wave. The speed can also
be changed in the screen for editing the wedge.
5 Select Change Scale to change the wave scale of the PAP. The same scale will be used in the
screen for editing the wedge. If the setting
Optimum Scale is used, the wave scale will be
optimized when a wedging waveform is recognized and will revert to the previous scale when the
wedge procedure window is closed.
6 Inflate the balloon when the monitor prompts you: Ready for balloon inflation. The waveform
changes from the PAP to the PAWP wave. The measurement takes approximately 12 seconds. On
completion, the monitor stores the PAWP waveform display and prompts you to deflate the
balloon. If the monitor cannot detect a wedging waveform you must use
Store Trace to store the
wedge and two reference waves manually.
7 Deflate the balloon when the monitor prompts you: Ready for balloon deflation and verify that
the waveform returns to pulmonary artery shape.
8 If you need to start a new measurement, select Restart Wedge.
Editing the Wedge
1 Select the Edit Wedge pop-up key to see the stored waveforms.
2 The monitor displays a cursor in the waveform at the PAWP mean value. It also displays any
previously stored value and the time it was stored.
3 Select Change Speed if you want to change the speed (resolution) of the displayed wave.
4 Move the cursors up, down, right and left to set them on the correct wedge position.
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