This is relevant to Question 10 from the second paper of 2004, "Outline the factors associated with the accuracy of central venous pressure measurement by a central venous catheter"A more extensive exploration is carried out in the core chapter on central venous pressure 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
- Patient movements
- Erratic respiration
The college answer is as follows:
"Accuracy of central venous pressure measurements depend on a number of factors. These include placement of device (tip in RA, RV, femoral vein etc), levelling (usually to phlebostatic axis), zeroing (zero means atmospheric pressure), calibration (measurement above zero is accurate when compared with gold standard [was mercury sphygmomanometer]), damping (not over or under, assessed by square wave or balloon bursting, prefer coefficient approximately 0.7). Frequency response of the system (intrinsic plus additional tubing) may significantly impact on damping (prefer shorter and stiffer tubing). Running averages also significantly alter ability to interpret spontaneous readings or variability associated with intra-thoracic pressure (better with printed waveform). Water column measurement is rarely done."