[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Nursing](https://durgical.com/en/nursing/) › [Critical care](https://durgical.com/en/nursing/areas/critical-care/) › Measuring central venous pressure: transducer and water manometer, the phlebostatic axis and reading trends # Measuring central venous pressure: transducer and water manometer, the phlebostatic axis and reading trends - Assessment Central venous pressure is read from a central line at the level of the heart, at the end of expiration; its trend means more than any single number. Updated Nov 13, 2026 ## Key points - Level and zero the transducer at the phlebostatic axis (4th intercostal space, mid-axillary line). - Measure with the patient supine or with the head raised up to 30°, the same way every time. - Read at end-expiration, when pressure inside the chest is lowest; PEEP and forceful breathing change the value. - CVP alone does not predict the response to fluid: follow the trend with blood pressure, perfusion and urine output. - A CVP that rises during fluid without any improvement in the patient can mean congestion: report it. ## What it is Central venous pressure (CVP) is the pressure in the superior vena cava, measured through the distal lumen of a central venous catheter. It stands in for right atrial pressure and reflects how cardiac function and venous return interact. In most ICUs it is read with a pressure transducer and shown as a waveform in mmHg; older units may still use a water manometer, which reads in a different unit. The nurse's job is an accurate, repeatable reading: the same position, the transducer levelled and zeroed, a clean waveform, and the value taken at end-expiration. CVP alone does not predict whether a patient will respond to fluid; a rising CVP without clinical benefit can be a warning of congestion. Central line care is on its own page. ## Reference values - Reference ranges differ between sources, roughly 0 to 8 mmHg in a person breathing spontaneously; follow the targets the team sets for each patient. - Positive pressure ventilation and PEEP raise the CVP; spontaneous breathing lowers it. - A water manometer reads in cm H₂O, not mmHg: never mix the two units in the same trend. ## What you need - A central venous catheter with a known tip position, its distal lumen connected to a transducer set. - Pressure transducer, flush system and monitor module, or the unit's water manometer set. - A way to mark the phlebostatic axis on the patient so that every shift uses the same point. ## How to measure it (and why) - Check the central line and use the lumen the protocol assigns to pressure monitoring — the protocol says which lumen and what may run in it. - Place the patient supine or with the head up to 30°, and note the position — readings are comparable only in the same position. - Find the phlebostatic axis, mark it and level the transducer there — a wrong height over- or under-reads. - Zero to atmosphere as the protocol says — this removes atmospheric pressure and drift. - Look at the waveform: clear a, c and v waves, no damping from air or clot — a damped trace gives a false number. - Read at end-expiration, on the waveform or with the monitor, and record value, position and ventilator settings — the trend needs context. - With a water manometer, follow the protocol for zero point and reading — its unit (cm H₂O) differs from the transducer's (mmHg). - Compare with the previous readings and the bedside picture — CVP is interpreted as a trend, never alone. ## How to read it - A low or falling CVP with signs of poor perfusion fits low preload, but it does not prove that fluid will help. - A high or rising CVP may reflect congestion, right ventricular strain, tricuspid regurgitation, tamponade or high pressure in the chest; it does not simply mean too much fluid. - A high CVP is associated with kidney injury, because it lowers the pressure gradient that drives blood through the organs. - Changes in the shape of the waveform can point to arrhythmias, tricuspid regurgitation or tamponade: describe what you see to the team. ## Next step: when to call for help - Report a sudden change in CVP after you have checked the position, the level, the zero and the waveform. - Report a CVP that keeps rising during fluid without better pressure, perfusion or urine output. - Call at once if a rising CVP comes with a falling blood pressure: the team must rule out tamponade and other causes. - Report a damped waveform, no blood return or signs of infection at the central line. ## Test yourself Think of the answer, then tap the question to see it. ## At what moment of the breathing cycle is CVP read? At end-expiration, when the pressure inside the chest is lowest and changes least. ## Why must the patient's position be recorded with each CVP reading? Because readings are comparable only in the same position, with the transducer levelled at the same point. ## Does a low CVP prove that the patient will respond to fluid? No. CVP alone does not predict fluid responsiveness; it is read as a trend with blood pressure, perfusion and dynamic tests. ## Can water-manometer and transducer readings be mixed in one trend? No. The manometer reads in cm H₂O and the transducer in mmHg, so the numbers are not the same scale. [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/nursing/measuring-central-venous-pressure-transducer-and-water-manometer-the-phlebostati/) ## Elsewhere in DurgiPedia - [Central venous pressure and the jugular pulse](https://durgical.com/en/physiology/central-venous-pressure-and-the-jugular-pulse/) - [Jugular venous pressure and the venous pulse](https://durgical.com/en/clinical-exam/jugular-venous-pressure-and-the-venous-pulse/) ## Connections ## Related 2 - [Central venous catheter care](https://durgical.com/en/nursing/central-venous-catheter-care/) - [Haemodynamic monitoring in general terms: MAP, CVP, cardiac output, preload, afterload and perfusion signs](https://durgical.com/en/nursing/haemodynamic-monitoring-in-general-terms-map-cvp-cardiac-output-preload-afterloa/) [← All of nursing](https://durgical.com/en/nursing/) Educational content for students; it does not replace your institution's protocols, supervised clinical training or a prescriber's order. Dose-calculation examples use made-up numbers: they are educational, not a clinical order. Sources: [Central venous pressure: current uses and prospects for an old parameter (Caplan M, Chew MS, Hamzaoui O, Intensive Care Med 2025;51(7):1363-1366)](https://pmc.ncbi.nlm.nih.gov/articles/PMC12283750/) (Intensive Care Medicine, open access in PubMed Central, 2025); [Central Venous Pressure Revisited: Physiology, Pitfalls, Misconceptions, and Modern Clinical Interpretation in Critical Care (Biuzzi C et al., J Clin Med 2026;15(11):4227)](https://pmc.ncbi.nlm.nih.gov/articles/PMC13258183/) (Journal of Clinical Medicine, open access in PubMed Central, 2026); [Hemodynamic monitoring: basic principles in operation room and intensive care unit (Mirus M, Saugel B, Spieth PM, J Clin Monit Comput 2026;40(2):375-389)](https://pmc.ncbi.nlm.nih.gov/articles/PMC13053478/) (Journal of Clinical Monitoring and Computing, open access in PubMed Central, 2026). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/nursing/measuring-central-venous-pressure-transducer-and-water-manometer-the-phlebostati/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/nursing/measuring-central-venous-pressure-transducer-and-water-manometer-the-phlebostati/