- CVP = filling pressure of the right heart
- Thus, = the pressure gradient which drives the flow, which drives the filling of the right heart end-diastolic volume.
- So, two degrees removed from right heart preload
- Recorded at the end of expiration
- Transducer zeroed at the right atrium: 4th intercostal space, midaxillary line
The waveform looks like this:
It is discussed in greater detail elsewhere.
- a wave: right atrial contraction
- c wave: tricuspid valve closure and intrusion into the right atrium
- x descent: downward movement of the contracting right ventricle, atrial relaxation
- v wave: Back-pressure from the rapid filling of the right atrium
- y descent: opening of the tricuspid valve
Factors which influence the accuracy of CVP measurement:
This came up in Question 10 from the second paper of 2004.
In brief, the following factors influence the accuracy of CVP measurement:
- Calibration of the transducer
- Selection of zero level
- Dynamic response of the circuit
- Transducer drift
- Infusions running through the monitored lumen
- Damping in the system (eg. the presence of air bubbles)
- CVC position (femoral vs. IJ, SVC)
- Tricuspid regurgitation