How to Zero a Pressure Monitoring Line

So you're new to the ICU and are working with your first arterial or CVP (central venous pressure) line.  How do you "zero" the line and what does that mean?

Why Do You Zero An Arterial or CVP Line?

Zeroing any kind of line that is monitoring pressure helps to give you the most accurate reading possible. You are closing off the line to the patient (so that no air goes inside of them while zeroing) and then opening the line up to air.  This allows the pressure reading to be set at atmospheric pressure as your reference point for monitoring blood pressure or central venous pressure.  Having an accurate atmospheric pressure helps to ensure the accuracy of your reading.

Steps for Zeroing

You can zero a pressure line in five easy steps.  We're going to refer to the following picture to help us with learning how to zero a pressure line:

1.  The spot where the zeroing takes place is at the transducer (shown by the above image). Start by turning the stopcock (white part of the transducer) off to the patient. In the picture, this would be turning the stop cock 90 degrees to the left.  This blocks air from getting into the patient while zeroing.

2.  Next, take off the cap on the transducer (the clear cap behind the stop cock). Some of these already have holes in them which would mean that you don't have to take it off.  In the kits at my hospital, the transducer comes with extra caps that do not have holes in them. I replace the hole caps with the solid caps because I feel like it's safer for the patients. Also, make sure that you keep the cap end sterile.  You don't want to introduce any kind of bacteria into the pressure line.

3.  Press the "zero" button on your monitor.  Wait for it to zero the line.  On our monitors it takes about five seconds or so.

4.  Place the clear cap back on the transducer.  

5.  Turn the stop cock back upwards (in the picture above, it would be turning it 90 degrees to the right). This allows the pressure line to actually monitor the pressure (BP or CVP)...and you're done!