Central venous pressure measurement
- 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.
In brief:
- 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:
Device factors
- Zeroing
- Calibration of the transducer
- Selection of zero level
- Dynamic response of the circuit
Artifact
- Transducer drift
- Infusions running through the monitored lumen
- Damping in the system (eg. the presence of air bubbles)
Patient factors
- CVC position (femoral vs. IJ, SVC)
- Tricuspid regurgitation
References
Most of this material can be found in Bersten and Soni’s” Oh's Intensive Care Manual”, 6th Edition, as well as the CVC section from The ICU Book by Paul L Merino (3rd edition, 2007)
Additionally, I have made use of the amazing Essentials of Critical Care, 8th ed.(ch.3 - Monitoring in the ICU).
For those willing to pay for it, there is a good UpToDate article on this.
For those unwilling to pay, Stanford University have this free article:
Pittman, James AL, John Sum Ping, and Jonathan B. Mark. "Arterial and central venous pressure monitoring." International anesthesiology clinics 42.1 (2004): 13-30.
Alzeer A et al. Central venous pressure from common iliac vein reflects right atrial pressure. Can J Anaesth 1998 Aug 45 798-801.
Most of this material can be found in From and Soni’s” Oh's Intensive Care Manual”, 6th Edition, as well as the CVC section from The ICU Book by Paul L Merino (3rd edition, 2007)
Additionally, I have made use of the amazing Essentials of Critical Care, 8th ed.(ch.3 - Monitoring in the ICU)
Marik, Paul E., and Rodrigo Cavallazzi. "Does the central venous pressure predict fluid responsiveness? An updated meta-analysis and a plea for some common sense*." Critical care medicine 41.7 (2013): 1774-1781.